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Decimo Vatman 120D Calc
Mini Instruments Mini-Assay 6-20, 1974
As you may know to some extent virtually everything is radioactive, and that includes you and me. But how radioactive is a human, compared with a bunch of bananas, or a Uranium fuel rod? No doubt someone somewhere would like to know, though usually such questions are of a more serious nature, like measuring the amount of radioactivity in what we eat and drink, and the materials and chemicals we come into contact with. Needless to say the people who really need to know stuff like that generally wear white coats, work in laboratories, and when answering those kinds of questions, reach for instruments that can detect and identify very small amounts of radioactivity.
Back in the seventies and eighties that would probably be something like this Mini-Assay 6-20. It was made in 1974 by our old friends Mini Instruments, who at the time were churning out all sorts of radioactivity measuring and monitoring devices in Burnham on Crouch in Essex. Such was the quality of their wares that many vintage Mini Instruments products are in use to this day, and that includes the Mini Assay 6-20 featured here, which is still capable of doing a useful job.
Appearances can be deceptive and whilst it looks a tad complicated, what it does and how it does it, is actually straightforward. The main unit or ‘scaler’ contains three circuit modules. The first one is a mains power supply, which lives in the rear of the case. The second one is a PCB that generates a high voltage supply for the external probe. This board also has a simple timer circuit that counts the pulses coming from the probe for intervals of between 1 and 1000 seconds. Module number three contains the circuitry and components for counting and displaying the number of pulses generated by the probe.
The idea is you pop a sample (of known weight or volume) of the material that you want to test or assay, into a small cylindrical container or ‘well’ inside the top of a Type 43 Assay probe. (This is a modifid version of the Mini Instruments Type 42B scintillation probe). The next step is to set the time interval with the large rotary switch, then press the illuminated green start button. When the count comes to an end, shown by the illuminated red Stop button, the display freezes and you jot down the time interval and reading on the display. You now have a measurement that shoes, quantitatively, how much radioactivity a material sample produces.This can then be compared against a set standard, a calibrated radioactive ‘check source‘ or other samples, to see if it is more or less radioactive.
The Type 43 assay probe is one of the most interesting parts of this setup. The sample well at the top is set in the middle of a metal cylinder. In the space between the well and the cylinder’s inner wall there’s a transparent organic crystal, made of Sodium Iodide (Nal), mixed with a little Thallium (Tl). This chemical concoction has strange and useful property. When radioactive gamma particles pass out of the sample and strike molecules in the crystal surrounding it they produce photons, resulting in a very faint flash of light. The base of the Nal crystal is in contact with a device called a photomultiplier tube or PMT. This amplifies flashes in the crystal, which become distinct pulses. These are fed to the counter via the connecting cable (which also carries the PMTs high-voltage power supply). Incidentally, the top part of the probe, containing the crystal and sample well, is surrounded by a thin lead shield. This is meant to prevent readings being skewed by naturally occurring and man-made background radiation coming from outside of the probe.
There are a couple of interesting features in the main unit. The first is the 5-digit display on the front panel. It looks like an ordinary LED array but it’s actually a hybrid device, based on the ‘Nixie’ tube. These are glass cylinders -- they look like valves -- but they are filled with neon gas. Inside the tube there is a set of thin wires, formed into the shape of the digits 0 to 9 and stacked behind one another. The individual numbers glow with a red discharge when a voltage is applied to the appropriate pins on the base of the tube. The J102501 display modules used in the Mini Assay 6-20 use a similar red neon discharge, but instead of pre-formed digits, numbers are made using the same 7-segment layout as an LED or LCD numeric display.
There’s another reminder of the olden days, spread across the two circuit boards inside the case. It’s row upon row of microchips – 21 in all – and they are responsible for counting the seconds, counting the pulses and driving the displays. Such was the pace of development in the seventies and eighties that shortly after the 6-20 first appeared iit was possible to replace more than 80 percent of the components and devices inside case with a couple of chips and an LCD module. In just a few years they would cost a fraction of the price, be more accurate and capable of many additional functions. It’s easy to scoff, but you have to wonder how much of today’s microelectronic wizardry will still be working in 50 years time? That’s not to say old instruments like the 6-20 were any more reliable; they weren’t, but if they did develop a fault any reasonably competent electronics engineer could fix them.
The Mini Assay 6-20 shown here came from ebay. It was sold as ‘for parts or not working’ and cost £20.00 as a Buy It Now lot. I had been vaguely aware of its existence and the Mini Instruments name was familiar so I guessed, rightly as it turned out, that it might contain a number of difficult to obtain parts, common to their range of Geiger counters. As luck would have it the instrument was in excellent condition and full working order, thus avoiding a sad end as a scavenged donor device. The same could not be said of the Type 43 probe that came with it, which had already been butchered, leaving behind hardly anything of use or value or use. This wasn’t a problem, though as I had a Mini Instruments 42B probe to hand. The only significant difference is the layout of the top part, which on the Type 43 has the sunken well and hollow crystal. For the purposes of testing they work in exactly the same way and check samples can be simply placed on the top of the probe. I plan to restore the original probe at some point. Suitable crystal assemblies are available online from time to time, so there’s a good chance that one day I will actually get around to it. The overall condition was exactly as you see it now. It is in astonishingly good shape for its age, inside and out, and apparently little used so there is no reason to suppose it won’t still be working in another 50 years.
What Happened To It?
Highly specialised radioactivity assay instruments are still with us but the trend has been towards specialised and sophisticated devices that do more than just count radioactive particles over pre-set periods. This is made possible by another very useful property of scintillation crystals like sodium iodide and solid-state detection devices developed in recent years. In a regular Geiger Counter the detection device is usually Geiger Müller tube. This produces uniform pulses or clicks in response to all types of radioactivity (Alpha, Beta, Gamma etc). However, the flashes of light in a scintillation crystal are proportionate to the energy of the radioactive particle, so with a bit of digital jiggery-pokery it is possible to identify the radioactive isotope that produced it, displaying the results in graphical form, with the peaks indicating individual elements. Thanks to digital electronics radioactive spectroscopy has become the most accurate and widely used method of measuring and quantifying radioactivity. Spectral analysers can be small enough to fit into a pocket and effectively consigned old dinosaurs like this 6-20 to the scrap heap. Nevertheless, it is entirely probable that a few are still in use as it remains a quick and simple way to check and compare materials.
Even though the 6-20 was once an impressively expensive and exotic piece of laboratory equipment, and in spite of it still being in mostly good working order (assuming the original probe gets fixed) and it being rare and unusual, it is pretty much worthless to anyone in the nuclear biz. I suspect a few vintage rad-tech nuts (like me) who would be happy to give it house room, but even the most radiation-minded enthusiasts probably wouldn’t want to shell out more than the twenty quid I paid for this one, so it’s not something that’s going to go up in value any time soon. But as is often the case that’s good news for my fellow collectors, and me, and anyone inclined (or mad enough) to join in and try and save these wonderful old instruments for posterity.
First Seen: 1974
Original Price: £?
Value Today: £20.00 (0321)
Features: 5-digit ‘Nixie’ display, 1 – 1000 seconds interval timer, variable HT (0 – 1700 volts), display check function, Type 43 Gamma-sensitive well probe, PET probe connectors, tilt stand, carry handle
Power req. 110-115/220-250 VAC mains
Dimensions: 2115 x 145 x 140mm
Made (assembled) in: England
Hen's Teeth (10 rarest) 8
DP-75 Cold War Geiger Counter, 1980
Anyone interested in vintage Geiger counters will probably be aware of the hugely popular and very capable DP-66, manufactured in Poland and issued to Polish military during the 1970s. Like the iconic US Civil Defense CDV-700 series, British PDRM-82 and Contamination Meter No 1 it was a product of the Cold War and made in large numbers. In the early noughties the DP-66 was decommissioned and good many of them found their way onto ebay. Thanks to their sensitivity, versatility and very attractive price they sold in their thousands. Nowadays they're getting harder to come by and prices have soared. Clearly that's not the end of the story, though, and since 2018 stocks of the DP-75, the DP-66's replacement, have been coming onto the market, and by all accounts, selling well.
Outwardly the DP-66 and DP-75 appear similar; even the probes look alike but these are two very different animals. The more obvious parallels include heavy-duty brown thermo-setting plastic cases - the DP-75's is slightly larger -- with top-mounted controls and backlit, luminous analogue meters. They both have on-board chargers for DKP-50 pen dosimeters, and the multi-purpose probes have opening metal shields - to discriminate between beta and gamma radiation -- plus the option to attach it to a long telescopic handle. That's for getting the probe close to the ground -- like a metal detector -- and to help keep users a little further away from dangerously 'lively' sources of radioactivity.
The 75 has the same 6-step sensitivity control but the maximum reading is two and a half times higher that of the 66; we'll come back to that shortly. Both models are powered by three ordinary 1.5-volt D cells that can last for months, even with regular use. Thankfully the DP-75 does not come with the 66's near lethal mains adaptor, instead there's a pair of sockets for an external DC supply. As this unit operates over a range of 10 to 27 volts, it could be a handy post-apocalypse bonus ensuring that it can be powered, from a wide variety of sources, when eventually the supply of D cells runs out.
However, under the bonnet there are considerable differences between the two and the 75 is effectively a new design. The circuit boards retain a few elements of the older model but it uses hardy silicon transistors, instead of the more delicate germanium types found in the 66. Other components have also been upgraded with newer and more reliable types, not that the DP-66 had a poor record in this respect. The 75's probe has two instead of three Geiger Müller (GM) detection tubes and an alarm feature. This sounds an audible warning in the supplied earpiece and illuminates the meter face if the radiation level rises above one of the 5 pre-set levels. Most of the changes sound like improvements, and they might well have been, in the aftermath of a nuclear war, but it has meant that several features, which made the DP-66 so attractive to enthusiasts and urban prospectors, have been sacrificed.
The smaller of the two GM tubes (DO-180) used in the 75's probe is designed for significantly high levels of radiation (0.5 to 500 Roentgen/hr), up to and well past lethal levels. This compares with the 66, which had an upper limit of 200R/h. What makes the DP-66 so useful in Civvy Street is that one of its three GM tubes is a Russian SBM-20, which does all of the hard work on the highest sensitivity setting. In the 75 just one tube, a DO-130, covers the low level ranges. It is around half the size of the SBM-20, and they are both beta and gamma sensitive. The DO-130 even looks a bit like a miniature SBM-20, which it actually is. However, in the business of detecting radioactivity size can be very important - the bigger the surface of a detector the more radioactive particles it will interact with. So it follows that the 75's 'low range' tube is not as sensitive as its predecessor. Put simply the DP-66 and DP-75's abilities have been reversed. The DP-75 is measurably better at detecting moderate to deadly fry-your-bits levels of Gamma radiation. On the downside it is only around a third to a half as sensitive to low levels of both naturally occurring and man-made Beta and Gamma radiation. This also happens to be the main area of interest to antique collectors, rock hounds, experimenters, environmentalists, nuclear enthusiasts and urban prospectors.
It gets worse. The audio port on the DP-66 produced a healthy 'click', which could be heard through a supplied earphone or, using a simple adaptor, connected to conventional headphones, a 'sounder' module or a PC running logging or counter software. The DP-75 has the same 2-pin audio port but it has been repurposed. It's primarily there for the new alarm feature, which sounds a loud tone in the earphone whenever the radioactivity level exceeds one of the six pre-set thresholds. Faint clicks are just about audible in the background, but only on the very highest sensitivity settings, and only if there's little or no ambient noise. My theory is the designers took a decision to simplify operation for troops, not well versed in the subtleties of radioactivity detection and measurement, and to avoid potentially deadly misunderstandings. They're almost inevitable with personnel taking readings on a difficult to interpret meter. This would be in a high pressure and potentially extremely dangerous situation, dressed in full combat gear or a restrictive NBC (nuclear, biological chemical) protection suit. Giving the instrument a simple and unambiguous alarm function that leaves nothing to chance now makes a lot of sense. Audible clicks may have been considered distracting as well, so the big reduction in volume probably wasn't a concern.
Together, the changes to the probe and the alarm function make the DP-75 a less attractive proposition for some users. To be fair it is still tough and reliable, and very easy to use, with just a small handful of controls. That's just as well as they're labelled in Polish, but it doesn't take long to figure out that the two control knobs on the left are for selecting the meter/sensitivity range, and setting the alarm level (and battery check). There are two buttons, for zeroing the meter and operating the meter's backlight. The small knob on the right is for zeroing the reading on a pen dosimeter.
The DP-75 you see here came from ebay's leading seller of Polish radiation meters (and lots of other interesting ex-military stuff besides). After a good clean up it proved to be in tip-top condition and everything works, as it should. Apart from filling a gap in my collection of vintage Cold War Geiger Counters it also served as a test bed for a plug-in sounder module that I have been developing. I hoped it would overcome the earphone volume problem; it was originally developed for the speakerless CDV-700 Geiger counters and successfully adapted for the DP-66 (shameless plug, they're both available for sale on our sister site, anythingradioactive.com). Sadly it couldn't be persuaded to work on the 75, at least not economically or without modifying the Geiger Counter's internal circuitry. This would have required the user to take their DP-75 apart and solder components and connections in some very confined spaces.
What Happened To It?
The Cold War never really ended, nor has the real or perceived threat from thermo-nuclear weapons and 'dirty' bombs disappeared so there will always be a steady supply of decommissioned and ex-military radioactivity measuring and monitoring instruments. The problem with that is as they become more sophisticated, and targeted at detecting the very high levels they become less useful to amateurs, enthusiasts and experimenters. Many of them are actually completely useless without the highly specialised data readers, cables and software needed to use them. Between the late 60s and the mid 80s was a golden age for genuinely useful old-school Geiger Counters that could be bought cheaply and easily maintained and repaired, without specialist knowledge or (probably classified) test equipment. The DP-75 was one of the last of that generation of instruments and although it wasn't a classic, and a step backwards from its predecessor - in a civilian role - it is still a lot of Geiger Counter for your money. I wouldn't discount the possibility of significantly increasing its sensitivity with a simple GM tube swap, though this is on the rainy day to-do list. Even in its unmodified state it might also make a modestly successful investment -- if the current price of DP-66's is anything to go by. Worst case, it's still a handy survival took, at least for as long as nuclear warfare and terrorism remain a potential threat, which looks like being a very long time...
First Seen: 1980
Original Price: £?
Value Today: £150.00 (1120)
Features: 2-tube Geiger counter (D01-30 & D01-80), Beta & Gamma sensitivity 0.5 mR/h - 500R/hr (6 ranges) rotating Beta shield, audible alarm function (5-preset levels), built-in charger for DKP-50 type pen dosimeter, luminous & backlit meter scale, meter/reading zero, magnetic earphone output, external DC supply sockets (10 - 27 volts)
Power req. 3 x 1.5 volt D cells
Dimensions: 205 x 110 x 100mm
Made (assembled) in: Poland
Hen's Teeth (10 rarest) 4
Nuclear Enterprises Ratemeter RM5/1, 1980
It is tempting, but technically incorrect, to call this Nuclear Enterprises RM5/1 a Geiger Counter. It’s not but confusingly, that is what the one in the photo has become because it is connected to a probe (similar vintage to the RM5/1) that uses a Geiger Müller tube to detect radioactivity. Don’t worry it’s just another one of the many quirks and foibles of the nuclear radiation business. The RM5/1 is actually a Ratemeter and what makes it that, rather than a plain old Geiger Counter, is down to several useful features.
The first one is the socket on the front of the case. It’s for the a probe, which can be one of several types, including the Geiger probe shown – as well as other types, which we will come to in a moment. The next most important features are the preset control, marked ‘SET EHT’ (Extra High Tension or just HT) to the right of the main function knob on the top of the case. This adjusts the high voltage supply, to the probe, which significantly varies from one type to another. The useful voltage range is between 300 and around 1400 volts, which covers the vast majority of probes. Variable HT is actually a fairly common feature on Geiger counters and ratemeters but usually its hidden away, inside the case or only adjustable in software. Either way this usually means having to connect the instrument concerned up to a specialised voltmeter or a computer, which is a bit of a faff. Which brings us to another pair of handy features, and they are the EHT position on the main function control knob and the big meter. When the switch is in that mode the voltage output can be set using the meter’s inner red scale. It’s a bit rough and ready but accurate enough for most probes, which generally operate over a comparatively wide voltage range.
This combination of features makes probe switching a really quick and simple operation. It greatly increases the instruments flexibility, especially in the field, which helped to make the RM5/1 a popular choice in research, industry and medicine throughout the 80s and 90s. Radiation probes are typically designed to be responsive to one particular or a range of different types of ionising radiation. The three basic flavours are Alpha, Beta and Gamma and X-Ray (the last two are closely related) – there are other varieties but they are beyond the scope of the RM5/1.
Time for quick and dirty guide to common probe types. On paper Alpha radiation appears to be quite weak as it doesn’t travel more than a few centimetres through the air and can be blocked by a thin sheet of paper. This makes it quite difficult to detect, especially if you are not looking for it, or unaware that it is there. Although Alpha radiation cannot penetrate skin to any significant depth, it can do terrible damage to cells and organs if it gets inside the body, as the Litvinenko Polonium poisoning case in 2006 tragically proved. The most common type of Alpha sensitive probe is a modified Geiger Müller tube, sometimes called a ‘pancake’ (they tend to be flat and round), with a thin ‘window’ at one end made of the mineral Mica. This allows the Alpha particles to pass through, but prevents gasses inside from leaking out. General-purpose probes – like the 1257 C in the photo, have Geiger Müller tubes made of glass or metal. They cannot detect Alpha radiation but they are sensitive to Beta, Gamma and X-Ray radiation. This particular probe also has a sliding metal shield that covers the tube. The idea is it blocks Beta radiation so it can discriminate between the two types. The third class of probe is a Scintillation detector. Inside the probe there’s a detector ‘crystal’ (made of organic compounds or a special plastic). It emits weak flashes of light when exposed to Gamma radiation. The crystal is mounted on the face of a photomultiplier tube, which amplifies the flashes to produce the pulses that a ratemeter like the RM5/1 can measures or display on its meter. Incidentally, Scintillation probes can also be used to identify radioactive isotopes from the brightness and duration of the flashes, though this requires rather more sophisticated equipment.
Back now to a roundup of the rest of the RM5/1’s more notable features, starting with the meter. It is in unusual in that the moving pointer or needle travels through 270 degrees, which means the scale is significantly longer than most ordinary panel meters, which typically have 90-degree scales. The numbers on the scale, showing counts per second (CPS), increase logarithmically. This eliminates the need for a range switch and it can show readings, with reasonable accuracy, from just a few CPS right up to a rather scary sounding 5000 CPS. The upper end of the scale is mainly for the benefit of pancake and scintillation probes, which can be super-sensitive and might easily wrap the meter pointer around the end stop on instruments without a range switch or log-scale. It has a built-in ‘clicker’, heard through a small loudspeaker mounted on the front of the case. This can be muted from a switch to the left of the main function knob. It is powered by a pair of 1.5-volt D cells that should last weeks or months, even with regular use, and these live under the carry handle, which is held in place by four screws.
I have had this RM5/1 for several years, a swapsie for another instrument with a fellow rad enthusiast. At the time they were regarded as quite exotic and rarely seen outside of the usual industrial and scientific settings. It was in pretty good shape, in good working order and all it needed to make it presentable for this piece was a circuit check and quick wipe over. The RM5/1 first appeared in the early 1980s and even back then it was a fairly basic design. It uses only discrete components, there are no microchips and the large circuit board has wire-wrapped connections and a super neat, laced wiring loom. It is the kind of hand-assembled construction that harks back to an earlier age where money was no object and ruggedness and reliability were the prime considerations. And that is how it should be, considering that it was designed to be used in safety critical applications. The lower part of the case is the RM5/1’s only weakness. The plastic is a bit thin around the corners, which makes it prone to cracking if it is dropped or roughly handled roughly.
What Happened To It?
There’s a potted history of Nuclear Enterprises in the write up for one of its close cousins, the PDM1 Doserate meter. Suffice it to say that after numerous takeovers and mergers the brand is no more. At the time this instrument first appeared NE was doing well as a major supplier of radioactivity monitoring and measuring equipment to government and the nuclear industry. But even in its heyday, in the eighties and early nineties, the RM5/1 was starting to look a tad dated, compared with what was coming onto the market from other companies around the world. Nevertheless, because they were so reliable and simple to use many of them continued to earn their keep well into the noughties and were only replaced when they became uneconomic to maintain and cheaper and more sophisticated instruments became available. In the past couple of years hundreds of them have been decommissioned and inevitably a fair few ended up on ebay.
At the time of writing (Autumn 2020) there were a dozen or more for sale, ranging in price from £10 to £50. Buying one not listed as working could be a gamble, however. Most are labelled as untested and sold without probes but if you are feeling lucky, have a spare probe handy, a good working knowledge of electronics, a circuit diagram and some basic test equipment you should be able to track down most faults. Most parts are readily available, and even tricky items, like the bespoke meter and transformers, might be salvaged from cheap basket cases.
First Seen: 1980
Original Price: £?
Value Today: £25 (1020)
Features: Variable HT (0 - 1.4kV. voltage scale on meter), logarithmically scaled meter (CPS), GM tube and Scintillation inputs, battery check (on meter), built in ‘click’ sounder with mute, PET probe connector, built in carry handle
Power req. 2 x 1.5 volt D cells
Dimensions: 240 x 115 x 120mm
Made (assembled) in: Britain
Hen's Teeth (10 rarest) 5
Dosimeter Corp. MiniRad II Rad Monitor, 1977
Almost everyone coming into contact with radioactivity on a day-to-day basis can usually spot a radiation detection or monitoring instrument at 50 paces. Typically it’s the distinctive shape, size, colour, or the fact that it’s dotted with radioactivity symbols, ticks or beeps, that gives the game away. But every so often one comes along that could be almost anything. At first glance the MiniRad II Radiation Monitor looks like a simple electrical test meter, maybe a guitar tuner or even some sort of photographic gadget. The name should be a clue but even that is quite discrete, and you would have to be very close to read what the meter is measuring, which for the record is counts per minute and mR/h (millirems per hour).
This is a compact instrument, designed to be clipped to the user’s belt or worn around the neck on a lanyard, and whilst ‘dosimeter’ is printed on the front panel (actually the US manufacturer’s logo – Dosimeter Corporation) it’s basically a simple Geiger counter. The meter needle moves and it ticks in the presence of radioactivity, giving the user an approximate indication of the strength of the radiation field they are being exposed to. More up to date dosimeters generally record radiation dose. In other words they keep a record of how much radioactivity the wearer has been, or is being exposed to, over a preset period – 12 or 24 hours say. More advanced models may also sound an alarm when what is deemed to be a safe dose is at or close to being exceeded.
Inside the MiniRad’s metal case is a tiny DCA 5310 Geiger Müller (GM) tube, situated just behind the meter. This is the widget that detects radioactivity and white crosses on the outside of the case helpfully indicate its position and orientation, for making close-up measurements of radioactive sources. This GM tube is configured to be sensitive only to Gamma and X-Ray radiation, which, in sufficiently strong doses, are amongst the most penetrative and hazardous types of radioactivity, able to pass through most materials, including flesh and bones, and on the way through crashing into living cells, potentially doing serious damage. They are only stopped or impeded by really solid, dense and heavy stuff like metal, rock and concrete. All types of radioactivity have problems with lead and the tube in this instrument is wrapped in a thin layer of lead foil. This technique, known in the trade as energy compensation, is designed to shield the tube from other, lower energy types of radioactivity, which can skew readings as dose measurement is normally mostly concerned with heavy-hitting Gamma and X-Ray radiation.
So much for the theory. Thankfully operating of the MiniRad II is very straightforward. There are two rocker switches. The one on the left is for selecting high or low range, and if you see the needle move on the high range, you need to step away from the source, quickly! The right hand switch is for battery test and switching the unit on. On the top panel there’s a hole for the sounder or ‘clicker’ and a socket for a set of headphones (which mutes the sounder). On the right side of the case there are two presets for calibrating the dual meter scales. The lower part of the case is the battery compartment. This houses a 9-volt PP3 type battery that with normal use will last for several days. Around the back there’s a spring metal belt clip and a loop for a lanyard. The all-metal case is around the size of a pack of 20 cigarettes and really tough, suggesting it’s was designed to be used in harsh environments, such as mines, building sites and so on.
This MiniRad was part of a job lot of Geiger Counters bought a while ago on ebay. It’s hard to say how much it cost me but since it was the oldest and least sophisticated part of the package I estimate it accounted for around £10 of the overall price. I hadn’t seen one of these before and it was only when I tried to find out more about it that it became apparent just how old and unusual it was; more on that shortly.
It was sold as working and outwardly the condition was surprisingly good with only a few very minor scuff marks on the case. Inside was no different and it did indeed work, but sensitivity was quite poor. The reason for that turned out to be the energy-compensating shielding around the tube and as an experiment I carefully removed it. The increase in sensitivity was dramatic, up by around 50 to 60 percent, making it a useable little instrument, responsive to normal background radiation – clicking once or twice a second -- and genuinely handy for basic detection, prospecting and monitoring. Unfortunately removing the shield means the meter scales are all wrong. Not that it matters much for everyday use, but in any case mR/hr readings are pretty much obsolete these days, having been replaced by more meaningful microsieverts per hour (mSv/hr) SI units. It wouldn’t be too difficult to re-scale the meter to show true counts per minute or second but it’s always preferable to preserve vintage instruments in their original condition, so the lead foil will eventually be replaced.
What Happened To It?
There’s very little on the web about the Dosimeter Corporation of Cincinnati, Ohio apart from some patents filed in the mid to late 1980s and references to the company’s apparent disappearance at some point in the nineties. By the way, the date of 1977 for this MiniRad II is based on markings on the PC board, and that’s backed up by the use of mainly discrete components on the circuit board, which are typical of the time. During what appears to have been a fairly short period of operation the Dosimeter Corporation made a variety of instruments, including a version of the classic US Civil Defense CDV-700 and passive pen-type dosimeters. It seems likely that the company was merged or taken over in the early to mid 90s, possibly by the Bendix Corporation’s, which had busy military and instrumentation divisions. But this is all guesswork so as usual feel free to put me right on the origins and history of this enigmatic company. Incidentally, the MiniRad name seems to have been appropriated by several companies, none of whom, as far as I can see, have any connection with the Dosimeter Corporation.
Geiger Counters and dosimeters are still with us and thanks to digital chippery and solid-state displays, are a good deal smaller, smarter and cheaper these days. I wouldn’t mind betting this one cost several hundred dollars when new but if the number of appearances of this model in Google Images is anything to go by (precisely none…) comparatively few were sold, or survived. Indeed this may be the only one. Clearly that makes it very rare and extremely valuable, at least it should. In the real world relatively few vintage gadgets become sought after collectibles, and it is even more unusual for specialised devices like this to make the cut, at least not ones made as recently the late seventies. Whilst collecting old Geiger counters is never going to make anyone wealthy it is -- at the moment -- a relatively cheap way to get into an interesting hobby. What’s more, those of us who do get involved may have the last laugh come the next nuclear conflict or radioactive incident, assuming of course we keep our collections, and ourselves, in bombproof shelters…
First Seen: 1977?
Original Price: £?
Value Today: £30.00 (1219)
Features: Geiger Müller tube sensor, Gamma & X-Ray sensitivity, Hi/Lo range, moving coil meter display, scale 0 – 5mR/hr & 0 – 500 cpm, independent scale calibration presets, battery check function, built-in sounder, headphone socket, belt and lanyard clip
Power req: 1 x 9 volt PP3
Dimensions: 120 x 66 x 28mm
Made (assembled) in: USA
Hen's Teeth (10 rarest): 9
Recent research (carried out by some bloke down the pub) suggests that people spend more time thinking about which brand of cat food they’ll buy, rather than choosing the best Geiger Counter to have at their side for the next apocalypse or nuclear meltdown. Yes, it’s crazy, and a real concern. Leaving this crucial decision until the last minute could seriously affect your chances of survival, so for all of you fence sitters and shilly-shallies out there I have just one word for you, and it’s Ludlum.
Needless to say the perfect Geiger counter doesn’t exist but the Ludlum Measurements Model 2 featured here (and not forgetting models 1 and 3) comes pretty damn close. It’s a classic general-purpose design and the Model 2’s predecessor, the Model 1, dates from the early sixties. Model 2 appeared in the late seventies and the current version, the Model 3, hails from 2006. But the point is all three generations look substantially the same with a near identical set of features though, to be fair the electronic gubbins inside have become a bit more sophisticated over the years. Ludlum obviously got the basics just about right more than 50 years ago. They are a legend in the nuclear biz and it’s one of the go-to brands for discerning medical and environmental physicists, emergency personnel, industrial users, scientists, first responders, researchers, educators, enthusiasts and the list of satisfied goes on and on.
Back to this Model 2 though, and the standout features are the compact size, rugged all-metal construction, a clear and easy to read meter scaled in counts per minute (CPM) and milli roentgens per hour (mR/Hr), three detection ranges (x0.1, x1 & x10). It has ultra simple controls, a built-in sounder, long battery life and the icing on the cake, and externally adjustable probe supply, from 400 to 1500 volts. Basically this means it can be used with almost any type of radioactivity detector, from a basic Geiger Müller tube, to a supersensitive scintillation probe. That gives it the kind of flexibility needed to detect all of the main types of ionising radiation, from big fat Alpha particles that travel just a few centimetres through air, to Gamma and X-Rays that punch easily through most materials.
It’s also the little things that make this a truly versatile workhorse. They include individual calibration pots on the top panel, next to the range selector switch, and a battery check facility on the meter. The socket on the top panel makes probe swapping an absolute doddle. Factory fresh it’s fitted with an Amphenol C type connector or you could specify BNC or MHV type sockets when ordering. The sharp eyed amongst you may have spotted this one sports a TNC connector (threaded variant of BNC), which is my connector of choice. It took only a few minutes to fit, but it could be almost anything, they are so easy to work on. The audio – good loud blips – can be muted by a miniature toggle switch below the handle.
Next to that is another small switch for controlling the meter response. It's handy in a changing radiation field. In Slow mode it damps the meter's needle so a full scale reading takes around 11, seconds (in Fast mode full scale takes 3 seconds). The only other controls are a recessed preset for the variable HT probe supply and a reset button, for zeroing the meter when in ‘slow’ mode. The handle also deserves a mention; the cradle on top can accommodate a very wide range of probe types, from pancakes and ‘friskers’ with big handles, to slim tube-based models. Power comes from two standard 1.5-volt D cells, which last for around 600 hours and live in a compartment accessed by a hinged cover immediately behind the range selector knob. For the record this Model 2, one of two in my collection, is currently connected to a custom B/SBT-ll pancake probe; it’s a good all-rounder and sensitive to Alpha, Beta, Gamma and X-Ray radiation. Many other probes, from Ludlum and others are also available, to suit just about any application.
For once this Model 2 wasn’t a lucky find at a car boot sale, but a very deliberate purchase around 10 years ago from a contact in the nuclear business. As I recall I paid £50 for it, and it came with a factory fitted 44-7 end window probe; it was a real bargain then, and now. The main unit has a just a few signs of wear on the outer case, from very frequent use, but inside it’s in as-new condition. That’s not surprising as I have only ever opened it up a few times, mostly out of curiosity, to swap the probe socket and more recently to take the photos you see here. It works perfectly too and I have no doubt that it will continue to do so for another 40 plus years.
What Happened To It?
Don Ludlum established Ludlum Instruments Inc, based in Sweetwater Texas, in1962. He was an engineer with a lot of experience in radiation detection, having worked for five years for Eberline, another big name in the industry. He hit the ground running and the Model 1 was launched a few months after the company was founded, whilst working from the kitchen of his home. Don remained hands-on with the rapidly expanding company until his death in 2015. Ludlum is still very much a family concern, with 8 divisions dealing with almost all areas of radiation detection and measurement, employing nearly 500 people.
Ludlum Geiger Counters are available new in the UK dealers but very few ever make it onto the second user market for the simple reason that they are rugged, reliable and remain genuinely useful, even when several decades old. The odd one from a UK seller appears on ebay from time to time, usually for a stupid amount of money, but there’s no shortage of quite reasonably priced Model 2s on ebay US selling for between £150 and £300, usually with a decent probe. The problem though, is shipping and import taxes, which can easily add more than £100 to the final price. Of course it’s possible that one day one might turn up at a car boot sale or a vintage tech fair for a fiver but I really wouldn’t hold your breath. If you want one – and you would be mad not to – and you are thinking of planning a holiday to the US sometime soon here’s a hypothetical scenario. Forget bringing back the usual tourist tat. Track down a couple of cheap Model 2s while you are there and stuff them your luggage. Flog the spare when you get back and you could be part way to paying for your trip. Don’t say I suggested it though -- I didn’t, it was that research bloke down the pub -- and be aware you might have some explaining to do at UK customs…
First Seen: 1979
Original Price: £1000.00
Value Today: £250.00 (0419)
Features: moving coil meter display, range 0 – 5k CPM & 0 – 50mR/Hr, 3 switchable scales x .1, x1 & x10 with individual calibration pots, externally adjustable probe HT supply (400 - 1500 volts), multiple probe type compatibility, built-in speaker with switchable mute, switchable response (3/11 secs), integral carry handle/probe cradle, TNC probe connector (originally BNC, MHV or C-type)
Power req. 2 x 1.5 volt D cells
Dimensions: 200 x 175 x 85mm
Weight: 1.4kg (ex probe & batteries)
Made (assembled) in: USA
Hen's Teeth (10 rarest): 5
Victoreen 471 Wide Range Survey Meter, 1981
Should you get the urge to put the fear of God into someone, or even a lot of people, just put on your yellow Hazmat suit and wave one of these fearsome looking instruments in their direction. Nothing says radioactivity, and lots of it, like a humungous survey meter. Even if you’ve never seen one of these beasts before – and you had better hope that you never see one in action – it’s pretty clear what it does (though wearing a Hazmat suits definitely helps…). This is one of the all time classics, the Victoreen 741 Wide-Range survey Meter, designed to measure high and potentially harmful levels of radioactivity. It detects the four main classes of ionising radiation (not to be confused with electromagnetic radiation, the sort that comes from electrical and electronic appliances), known as Alpha, Beta, Gamma and X-Ray.
Gamma and X-Ray radiation are closely related and penetrate solid (and soft fleshy) materials with relative ease. This makes them both very useful, and dangerous, as high and lasting exposure can damage or destroy living cells. Beta radiation has much less penetrating power. It’s stopped in its tracks by a thin sheet of metal but can still be harmful, especially if it gets up close and personal with cells and organs. On paper Alpha radiation looks like the runt of the nuclear litter; the particles are enormous -- compared with the others – and have trouble passing through a thin sheet of paper or travelling more than a few centimetres in air, but again, get enough of it inside your body and you might not even live long enough to regret it.
The 471’s ability to detect all of the most common types of ionising radiation makes it really useful in medicine, science, the nuclear industry, emergency services and of course the military. This model first appeared in the early 1980s. It was a development of the 740 ‘Cutie Pie’ Survey meter, another icon in the nuclear biz as it looked like a giant ray gun. Although the 741 was discontinued some time ago many of them are still in regular use. That’s thanks to its robust construction and reliability but the big round thingy at the front is the star of the show. It’s an Ion Chamber, otherwise known as the 741’s business end, as it is the part that detects radioactivity. Unlike most other radiation detectors it is relatively simple, just an open ended metal cylinder with a fat electrode in the middle that carries an electrical charge. The front of the detector is covered with a thin film of Mylar plastic, mostly it’s there to keep out moisture and dust, but it has to allow radioactivity to pass through, including those big, poorly penetrating Alpha particles. When radioactivity enters the cylinder it ionises air molecules inside. This allows a tiny current to flow between the electrode and the metal sides of the cylinder. These currents are unimaginably small so in order to detect and measure them they have to be processed by a highly sensitive amplifier, and some sophisticated circuitry that turns signals from the ion chamber into a reading on the meter on the top of the case.
The robust metal case provides much more than physical protection for the delicate electronics. It also acts as a shield for pesky RF radiation, which if allowed to get in, would overwhelm the super-sensitive pre-amp module, mounted immediately behind the ion chamber. The only apparent point of entry is through the meter face but they’ve taken care of that as well, by mounting it inside its own metal box. There are only three controls; the knob in the bottom left hand corner is for setting the meter to zero. This is necessary due to the highly sensitive and unstable circuitry that responds to even small changes in ambient temperature, operating mode, range settings and so on. The left hand knob, just below the meter is for selecting the function, for continuous real-time measurement in Roentgen’s per hour (R/hr) or milli Roentgens per hour (mR/hr), or for taking cumulative or ‘Integrated’ readings over a set period of time. The right hand knob checks the condition of the 741’s two low voltage batteries and sets the range or sensitivity in 6 steps. So far it all sounds fairly straightforward, but the one thing that might put you off buying one is the batteries that it uses.
The main circuit board runs on two common or garden 1.5 volt D cells, so no problem there. However, it also requires four 22.5-volt A221/505A batteries for generating the high voltage charge for the Ion Chamber. The good news is they last for years. The bad news they are now effectively obsolete and very difficult to obtain. It proved to be quite an obstacle when it came to testing the 741. The best deal I could find in the UK was just under £10 each, and I wasn’t about to spend the thick end of forty quid on batteries for something that might not even work. There are ways to make up a 90-volt battery; ten 9-volt PP3s wired in series is reasonably easy to arrange, for example, but it’s already pretty crowded inside the case so they would have to be mounted externally, in a shielded case. There are also electronic circuits that boost a low DC voltage supply to 90 volts or more but they tend to create a lot of noise or ‘ripple’ on the supply line, which would undoubtedly cause problems for the sensitive pre-amp and measuring circuits.
This 471 came to me courtesy of fellow Geiger Counter enthusiast Carl Schieferstein in exchange for some related bits and pieces. It had recently been decommissioned by a Government agency, apparently because it was faulty. In spite of being the best part of 40 years old it appeared to be in excellent condition, inside and out. The first challenge was to find some way of powering it but using any sort of electronic power supply simply pegged the meter, undoubtedly because of the noise issue. The next attempt involved assembling a ‘brick’ of PP3s, a tricky customer, as it would almost certainly deliver an unwelcome shock if handled carelessly. This yielded some possibly encouraging results with the unit responding to a low level source, suggesting there still some life in it. There were small movements of the meter when the source was moved in front of the Ion Chamber window but I suspect that it is still faulty in several respects and almost certainly needs calibration, but due to more pressing matters that was about as far as I took it. It is something I will return to, but it will have to wait until I have figured out a cheaper and/or easier way to power it up.
What Happened To It?
Ion Chamber based survey meters are still in widespread use but modern units tend to be a lot smaller and more specialised, lacking the versatility of the 471. Other even more effective means of detecting and measuring high levels of radioactivity have also been developed over the past 40 years, some of them providing more detailed information about the nature of the source and its potential for harm.
The US based Victoreen Instrument Company should be familiar to those interested in vintage Geiger Counters being one the most innovative and prolific manufacturers of radiation detecting and measuring instruments. They’re also one of the companies responsible for the famous and still quite numerous CDV range of Geiger Counters, Survey meters and so on, for the US Civil Defense corps, during the Cold War years. Self-taught engineer and inventor John A Victoreen founded the company in the 1920s. His long-standing interest in radiation measurement resulted in a vast range of instruments over the years and Victoreen was also heavily involved in the Manhattan Project and the subsequent nuclear weapons testing programme after WW2. The Victoreen Company passed through several hands during the past 40 years, most recently by the Sheller-Globe Corporation. However, the name has recently disappeared from view following a merger with Radiation Medical -- a leading light in medical instruments and X-Ray equipment -- shortly after it was also acquired by Sheller-Globe.
Collecting radiation detecting and measuring instruments is very much a niche hobby, though there is still plenty of interest in the US. Americans have the advantage of a long and unique nuclear history, and a lot of naturally occurring sources of radioactivity to detect. The 714 is just about old enough to qualify as vintage but being somewhat specialist in nature relatively few of them come on to the open market. When they do asking prices on ebay can range from a few pounds to several hundred for examples in pristine condition and full working order, though I doubt that many, if any have actually sold for that much. If this one ever achieves full working order it might make up to £50 or so. However, if the fault turns out to involve the pre-amp module, or one of the custom components it will probably be almost impossible or uneconomical to source parts but it will still make an impressive doorstop and scary Halloween prop.
First Seen: 1981
Original Price: £1000?
Value Today: £10 - 50 (0319)
Features Ionisation Chamber type high radiation dose meter, sensitive to Alpha (above 3.4MeV), Beta (above 70keV) & Gamma & X-Rays (above 6keV), RF shielded moving coil meter & electronics, Rate measurement: 0-1, 3, 10, 30, 100 and 300 mR/h and R/hr; Integration measurement: 0-1, 3, 10, 30, 100, and 300 mR, response time: < 8 secs on 1mR/hr, 3 secs 3 on 3mR.hr range, < 1sec on other ranges
Power req. 2 x 1.5v D cells, 4 x 22.5v 505 batteries
Dimensions: 290 x 195 x 120mm
Made (assembled) in: USA
Hen's Teeth (10 rarest) 7
The Snooper Model108 Geiger Counter, 1952
In spite of what it says on the box The Snooper Geiger Counter, Made by Precision Radiation Instruments of Los Angeles -- is not a Geiger Counter. That’s simply because it doesn’t count anything, it merely indicates the presence of radioactivity. Apart from that it is a pretty amazing little gadget, spawned during one of the more bizarre episodes of the Cold War.
It all began in the late 1940s, when the Second World War was over the US and the Soviet Union became locked into a seemingly suicidal race to see who could amass the largest stockpile of nuclear weapons. One of the key ingredients in any half decent atom bomb is the comparatively rare radioactive element Uranium. The real problem is that vast quantities of it are needed to produce the relatively small amounts of highly-enriched fissile material needed for a useful bomb. The US’s solution was to encourage geologists and Joe Public to go prospecting. Large ore deposits were believed to exist in Arizona, Colorado, Oregon, New Mexico and Nevada, and to make it worth their while, they offered substantial bounties of up to $10,000. Unfortunately, to the untrained eye Uranium bearing rocks do not look significantly different to most other rocks, but they do have one very particular property; they are radioactive. To find them all you need is a Geiger Counter or similar radioactivity-detecting device. Within months of the US Atomic Energy Commission making its announcement -- triggering the so-called Uranium Rush -- dozens of American companies started churning out cheap instruments like Snoopers and Pioneers.
The Model 108 featured here has the distinction of being one of the smallest, cheapest and simplest of those designs. It has just seven components: two resistors, two capacitors, a transformer, an IU5 valve and a Geiger Müller tube. This is the detection device, sensitive to the Beta and Gamma radiation emitted by unprocessed Uranium ores. It is housed in a small, pocket-sized plastic box, and when exposed to radioactivity users hear the characteristic ‘clicks’ in the earphone. The valve circuitry it uses needs low and high(er) voltage power sources, so called ‘A’ and ‘B’ batteries. The A battery is an ordinary 1.5-volt D cell – the sort still used in large torches, whilst the B battery is a miniature 22.5 volt battery (type 505), commonly used in hearing aids of the day. The latter is now obsolete though there are modern replacements, however, there is a cheap DIY option. More about that shortly.
It is virtually idiot proof with just two controls, a slide on/off switch and an ‘operate' button. After switching it on the operate button has to be pressed two or three times. This sends pluses from the 1.5-volt cell into a transformer. When the magnetic field the coil creates collapses around 300 volts appears on the output winding and this is fed to a capacitor, which acts like a battery, holding a high voltage charge that powers the Geiger tube for several minutes. When radioactive particles enter the tube they ionise the gases inside, causing tiny currents to flow. These are amplified by the valve (powered by the 22.5 volt battery), generating clicks in the high-impedance earphone. Eventually the charge in the capacitor dissipates and every so often it is necessary to press the Operate button a few times to re-charge it. There's a circuit diagram in the manual for those who may be interested. Everything is neatly mounted on a simple metal chassis so it’s really robust and well suited to a spot of prospecting in the great outdoors.
A Snooper has been on my wish list for some time. When they occasionally appear on ebay in the US, even in poor condition, they tend to sell quickly for upwards of £100, so I wasn’t counting on seeing one in my price range anytime soon. As is so often the case this one was a chance find whilst trawling ebay early one morning. The listing was only a few minutes old and it was being sold as a Buy It Now lot for just $40.00. It seemed too good to be true and apart from appearing to be in great condition, it came in its original box, complete with the headphone, radioactive check source and one of the three manuals that it came with when new. It was listed as untested so I had no doubt that the chances of it working were small, plus there was another £25 to pay in shipping and import changes. Nevertheless the decision process to click the Buy button lasted around one tenth of a second. Bargains like this are rare, any delay runs the risk of it being snapped up, by US collectors, who would be waking up in the next few hours.
It was in even better condition than the description suggested and after a quick wipe over, it looked as though it had hardly been used. The only thing that showed any signs of old age was the plastic cased check source button, which had warped slightly. A thin layer of ancient varnish over the source material was also stating to flake, but this was easily fixed using modern epoxy resin, to seal the source and prevent shedding. Since the Snooper looked so clean I couldn’t wait to try it out, so after some basic continuity checks on the transformer and capacitor (both of which are prone to fail as they age), and a quick test of the headphone, I inserted a D cell and connected the B battery prongs to a desktop PSU. Unbelievably it worked straight away, registering the original, and as it turned out, still quite lively check source.
The ultimate goal was to power it entirely from batteries. Modern replacements are a touch pricey at £10.00 a pop so I decided to have a go at making one. A couple of 9-volt PP3 type batteries in series probably would have worked but there’s not enough space inside the case. I ended up making a stack of eight 3-volt CR2032 lithium button cells, which are cheap and widely available (thank you Poundland). To keep the cells together and insulated from the bare metalwork I encased them in heat-shrink tubing and made up the difference in length with a small piece of metal tube (from the stalk of a LED solar powered garden light; another pound shop bargain). Everything fits snugly in the case and its quite useable as a portable instrument. Sensitivity isn’t that great and I suspect some way below what it was originally capable of due to the ageing GM tube; even so it should still be able to detect a sizeable ore deposit, though you would need to be pretty close to it…
What happened To It?
It’s difficult to say how popular Uranium prospecting actually was. It seems the 'Rush' didn’t last very long and as it later turned out, some of those involved met a nasty end, due to exposure and inhalation of radioactive dust. However, judging by the number of adverts in 1950s editions of magazines like Popular Mechanics (see above) there was no shortage of reasonably priced equipment on offer. The budget Geiger Counters of the day would have been fairly fragile and some of them appeared to be quite poorly made so the survival rate is low. The fact that this one made it, and in such good condition, is unusual. I doubt that more than a handful of them come on to the market every year, and I have yet to see another complete outfit so cheap. The chances of any of them turning up in the UK is very small. Uranium prospecting is not and has never been a popular pastime on this side of the pond, even though there are significant deposits and mines in Cornwall and a lot of ‘hot’ rocks in Scotland. Collecting vintage Geiger Counters is never going excite much interest in the UK but for a few of us old instruments like this are really quite exciting – and yes, you are probably right, we don’t get out very often…
First Seen: 1952 (Manual)
Original Price: $24.95
Value Today: £100.00 (0119)
Features Pump type HV circuitry, type 1B86 glass encapsulated Geiger Müller detection tube, 1 x Sylvania IU5 diode-pentode valve, high impedance headphones
Power req. 1 x 1.5v D cell, 1 x 22.5v M505 ‘hearing aid’ battery
Dimensions (ex strap): 135 x 80 x 44mm
Made (assembled) in: USA
Hen's Teeth (10 rarest) 8
Thorn Radiacmeter NATO 6665-99-119-8766, 1975
Here’s another one of those radioactivity detection instruments that you never want to see reading anything other than zero. It should be said that we are all being exposed to radiation, all of the time, from both natural and man made sources. That’s perfectly normal, in fact minerals like granite with traces of uranium ores are called NORM or naturally occurring nuclear materials, and it has been that way since the planet was formed. What you don’t want, or need, is too much of the stuff, and that’s what instruments like this Thorn Radiacmeter were designed to alert the user to. In this instance the user would be a member of the Royal Observer Corps and military personnel, to help protect them in the aftermath of a nuclear war. It detects the very high and potentially lethal levels of radioactivity that almost everyone was expecting to sweep across the UK during the Cold War period, from the mid 1950s right up until the late 80s.
This is one of several portable radiation dose meters developed in the UK during that period and the immediate predecessor of the Plessey PDRM82. Thorn Automation made around 2,500 of them, which is a surprisingly small number, given the number of civilian and military personnel who might need one. Production runs of the previous and subsequent instruments ran into the hundreds of thousands. One suggestion is that this model was awkward to set up and, as an added complication, it needed a small radioactive source inside the device for calibration.
The detection device was quite unusual too. It’s an Ion Chamber, similar to the detectors used in the classic US Civil Defense CDV-715 & 717 Survey Meters, and a distant relative of the sensors found in most domestic smoke detectors.
Ion Chambers are surprisingly simple. Mostly they are just metal canisters with an insulated central electrode that carries a high voltage charge. When radioactive particles penetrate the metal skin they ionise the gas or air molecules inside, causing a tiny current to flow through the electrode. An electronic circuit amplifies the current and uses it to move the needle on a meter or drive a digital display The Ion Chamber in the CDV-715 is a ‘free air’ type filled, as the name suggests, with ordinary air. It’s only sensitive to alarmingly high levels of Gamma radiation, but since this is the stuff you really want to avoid in the short term, it’s perfect for the job. The Ion Chamber in the Thorn Radiacmeter is a more exotic sealed low-pressure type, filled with a gas mixture that’s more reactive to radiation than plain old air. It’s also more sensitive and can detect Beta particles, which can be a dangerous, especially when Beta contaminated fallout gets into food and water.
The Thorn Radiacmeter’s display is calibrated in ‘Rads’, which are fairly substantial quantities. For example a dose of 100 Rads over the course of a day is enough to cause significant changes to blood. 200 Rads can lead to a nasty case of Acute Radiation Syndrome or ARS, which probably won’t kill you outright but you will be very sick. A dose of 500 or more Rads in the course of a few hours can be enough to do very serious long-term damage and it’s probably game over if the meter on the Radiacmeter ever reaches the maximum reading of 1000 Rads/Hr.
It’s easy to use with just three main controls. The large knob operates a rotating Beta shield. This is a metal cylinder surrounding the cylindrical Ion Chamber with a 'window'. Gamma radiation easily penetrates the Radiacmeter’s outer case and the metal cylinder but together they block Beta particles. They can only pass though to the Ion Chamber when the window in the cylinder lines up with the foil capped holes on the front of the casing. The rotary shield also has role in calibrating the device.
When the Beta Shield selector knob is turned to the ‘Cal’ position the window aligns with small radioactive Beta ‘check source’. The reading on the meter can be adjusted to a nominal setting using the Calibration knob. Next to that is the rotary on/off and battery test switch. The silver nut-shaped object between the two switches is a moisture indicator. The white pad in the middle changes colour if the unit’s innards become damp. On the underside there’s a screw cover for the battery compartment. It takes one 6-volt lithium battery (V28PXL) and one 1.3 volt button cell (V625PX). There’s also a mounting point for a wrist strap, which also helps remove the unit from its tight-fitting padded carry case.
Military kit is generally designed to be able to withstand a lot of abuse. This is no exception, and probably cost the British taxpayer a small fortune. The thick steel case certainly gives the impression of being able to withstand a moderate nuclear explosion and it also helps protect the works from the effect of an Electromagnetic Pulse (EMP). It’s one of the side effects of an atomic explosion and can easily fry most electronic components. This also means it is quite heavy, a little over a kilogram in fact, which is more than enough to smash a PC keyboard, as I discovered to my cost whilst writing this… By the way, the only thing missing from this, and most other portable and personal radiation monitors of the time is any sort of audible or visual warning. Without one users had to constantly check the display and run the risk of straying into heavily contaminated areas.
I detected this one ebay whilst doing one of my occasional trawls for vintage Geiger Counters. It was a Buy It Now sale (£35, including postage) and honestly described – and as I had never seen one in the flesh before I felt it my duty to snap it up. It was, as promised, in excellent condition but untested and sold as seen, for parts or repairs. I wasn’t too surprised to discover that it wasn’t working. The lack of a circuit diagram has been a problem but after some poking around the innards with a multimeter I am fairly certain that the problem lies with the Ion chamber. So far I have been unable to find a suitable replacement and being a specialist component it is unlikely that I ever will but I live in hope. My guess is the gas in the chamber has leaked; data on the device is non-existent and I can’t even tell who made it. It’s theoretically possible that a determined experimenter could get it going again but even if it could be made to work, finding a legal radioactive source ‘lively’ enough to test it could prove challenging…
What Happened To It?
Back in their heyday Thorn Electronics (later Thorn EMI) were best known for making more consumer friendly products like TVs and radios under brand names that included Ferguson, Ultra, HMV, Radio Rentals and so on. Devices like the Radiacmeter were built in relative secrecy in small isolated units often located within larger TV manufacturing plants.
Throughout its production run, from 1975 to 1980 Thorn was a large and powerful company and as well as a wide variety of electronic widgets it also made such diverse things as gas cookers and lighting products. However, piece by piece its many divisions were either crippled by overseas competition, sold off or quietly folded. Today there little left; Thorn Automation, responsible for the Radiacmeter and various other items of military hardware, was dissolved in 2009.
The demand for personal and portable radiation monitors hasn’t gone away, though and in 1982 Plessey took over the government contracts to manufacture and supply the UK’s Civil Defence and armed forces with devices like the PDRM-82. It was simpler and cheaper than the Radiacmeter to make, and a lot lighter. More than 80,000 of them were made in the 80s and 90s, until it too was replaced by small, lighter and cheaper kit.
Collecting vintage military hardware has always been popular but items like this, which don’t go bang, look cool or dangerous or do weird things are often overlooked, That’s due in part to their somewhat specialist nature, and the simple fact that not many of them were made, or have escaped into the consumer marketplace. The few references I have found suggest that it is quite rare but, as is often the case, rarity doesn’t always translate into riches. The £35.00 I paid for it was about right; maybe on a good day another vintage Geiger Counter enthusiast – itself a very rare persuasion -- might be part with £50.00 for it, but that’s about it. It has future potential, though. Cold War memorabilia is gaining in popularity so if you ever come across one these little green boxes don’t pass it by, especially if reasonably priced and in good shape. One last thing, if anyone out there has a spare Ion Chamber, NATO Part No. 6665-99-119-6936, that they don’t need, please get in touch.
First Seen: 1975
Original Price: £?
Value Today: £35.00 (1218)
Features Low pressure sealed Ion Chamber detection device (Beta & Gamma sensitive), moving coil meter display (logarithmic scale, 0 – 1000 rad/hour), rotating Gamma shield, built-in check source, battery test function, calibration control, humidity detector, wrist strap, protective carry bag
Power req. 1 x V28PXL 6-volt battery, 1 x V625PX 1.3-volt button cell
Dimensions: 165 x 117 x 55mm
Made (assembled) in: UK
Hen's Teeth (10 rarest) 9
There is much wisdom in the old adage, ‘if it ain’t broke, don’t fix it’ and that’s something Mini Instruments Ltd clearly believes in. Here we have the Mini Instruments Scintillation Meter Type 5.40, which was made in 1982.
Most people would call it a Geiger Counter, though technically it’s known as a Rate Meter. By definition Geiger Counters detect radioactivity using a device called a Geiger Müller (GM) tube. However, one of the Type 5.40’s most interesting features is that it has the facility to use a wide range of detectors, including both GM tubes and Scintillation probes, of which more in a moment.
Although this one is more than 40 years old, on the outside it’s not significantly different to the current models in the Mini Monitor range. Then as now it is housed in a sturdy metal box – these days they’re coloured yellow – with a large and easy to read front panel meter and on the top of the case, there’s a carry handle and a clip for the detector probe. The modern instruments, in common with this vintage Type 4.50, are easy to use and very reliable; and that’s just some of the reasons they are still widely used in education, medicine, manufacturing and the nuclear industry.
Speaking of which. The UK’s Atomic Weapons Establishment (AWE) previously owned this Type 5.40. When new it was almost certainly equipped with a Scintillation type probe. These are based around a large crystal of sodium iodide. It has the useful property of emitting a brief but very weak flash of light (a scintillation) when struck by radioactive particles. The light flashes are captured and amplified by a device called a photo multiplier (or solid-state detector, also built into the probe body), and the output is displayed on the meter as counts per second (CPS). Incidentally Geiger Müller tubes detect radioactive particles when they interact with charged particles of pressurised gas inside a sealed glass or metal tube. Although they work in very different ways both types generally require a high voltage (HV or HT) supply, typically between 300 and 1200 volts. At some point the AWE carried out some modifications to this instrument, which included installing a power adaptor circuit to replace the internal batteries, so that it could run from an external 24-volt supply. Additionally the preset potentiometer, which adjusts the HT voltage applied to the detector, was moved from the circuit board to the outside of the case. Presumably this was to make it more accessible, and therefore easier to switch between different types of probe.
Professional radioactivity detectors can be fiendishly complicated but this one – like its modern Mini Monitor counterparts – couldn’t be simpler. On the original unit there were just two controls: a three-position switch for power off, battery check and power on, and below that a rocker switch to turn the internal speaker on and off. The real star of the show, though, is the meter. The really clever part is the logarithmic scale. Essentially this means there is no need for a range switch; it can clearly and accurately display both very low levels of radioactivity, from a few counts per second, on the first half of the scale, to high and lethal amounts shown on the other half of the scale. A built-in speaker that reproduces the distinctive ‘clicks’ is mounted on the underside. The re-positioned variable output voltage adjustment and external power connector are on the right side of the case and on the left there’s a socket for the probe connector. This one is a slightly unusual type, known as a PTE 100 or BNC 1.6/5.6 (nerdy factoid: nowadays most professional instruments of this type use industry-standard BNC or TNC type connectors. And for the ultra nerdy, the B and T in BNC and TNC respectively denote a Bayonet or Threaded fitting and the NC part comes from the names of the connector’s inventors, Paul Neill and Carl Concelman. So now you know…).
Inside the case the main circuit board is a model of simplicity and solidity. There are no microchips or digital trickery, just an assortment of mostly standard analogue electronic components that generate the high voltages, process the signal coming from the probe, and present the results on the meter (and through the speaker). There are a couple of custom inductors but overall it is all very straightforward, which means there is little to go wrong. If it does it is very easy to get at and repair. The meter is a high quality item made in the UK by Sifam. As a matter of interest they are also still in business and amongst other things, still making old school analogue meters for Mini Instruments, high-end audio and products for the recording industry.
This Type 5.40 came from ebay and was one of a batch of decommissioned units being sold for just £20.00. Normally working instruments of this type would sell for several hundred pounds but the price reflected the fact that that the expensive probes (and probe holders) were not included in the sale and to get it going again on battery power the AWE modifications would have to be removed. It was also sold without a guarantee and cosmetically it was in a bit of a state, to put it mildly... It was a gamble but it turned out to be an interesting, and successful restoration project, so much so that I later purchased the rest of the batch.
With so much work needing to be done the only way to proceed was to strip it down to its bare bones, though the first job was to check to see if it was working. Luckily it was, first time and I tested it using a number of GM tubes and a scintillation probe operating at between 450 and 900-volts. With everything removed from the case it was rubbed down, primed and resprayed with the same grey-black metal hammer finish paint that it came with. Case fittings were cleaned and replaced and the add-on adaptor board removed. The wiring also had to be returned to its original state and the now virtually obsolete BNC probe socket was replaced with a modern TNC socket. A red LED that had been added to show the power adaptor was working was replaced with a lower power type and repurposed as an ‘event’ flasher, to coincide with the clicks; this can be useful when the speaker is muted. A new switchable power socket was fitted, so it could be powered by battery or an external adaptor, and a battery holder (for 8x AA cells) was fitted to the back panel.
The biggest challenge was finding a replacement probe and probe holder. Fortunately I had a suitable Russian Geiger tube to hand and it fitted nicely into an aluminium housing, fitted with a TNC socket. The probe holder was much harder to replace though I eventually found that microphone holders (used on mike stands) made a pretty good substitute. I was able to reproduce the side panel labelling by scanning the originals (which were in very poor condition), touching up the images on the PC before printing them out on transparent OHP film and spraying the back with silvery grey car paint. After so much time and TLC it is now as good as new. Better in fact, thanks to the more accessible AWE voltage adjustment mod, which I retained, and it should be good for another 40 years at least
What Happened To It?
Mini Instruments was founded in the early 1960s, in the Essex town of Burnham-On-Crouch. There is surprisingly little about the company’s early days on the web but from the get-go it appears they made Geiger Counters, originally in plain grey-black metal boxes like the Type 5.40. In the late 80s they switched to the custom yellow metal cases that they use to this day. Although the innards of modern Mini Monitors are a bit more sophisticated the basic design attributes of accuracy and simplicity of use are still clearly in evidence. The company was bought out by the US-based Thermo Fisher Scientific Corporation, a world leader in scientific instrumentation, healthcare and research. Although the Mini Monitor range is now only a tiny part of a global operation there remains a steady demand for these rock-solid instruments, which are now assembled in Germany.
For some reason collecting vintage radiation monitors has yet to take off. Whilst this is good news for me and the small handful of fellow aficionados, being such a specialised field, with relatively few products making it onto the second-hand market, bargains tend to be few and far between. It also has to be said that even if when work they’re of little interest to most people, at the moment. Everything changes when there’s a serious nuclear accident or some rogue state proves it is capable of building atomic weapons. Even though most people have little idea of how to use a Geiger Counter, let alone how to interpret readings, prices – even for old instruments – tend to rise quite quickly. A few weeks later, when the fuss has died down, prices fall back to where they were, or less, if the event produced a glut of instruments. In short unless you can accurately predict when the next spike will occur they’re not much of an investment. On the other hand if you are interested in a much overlooked and little understood branch of science and technology, and want to learn more about your environment (and you might be surprised how many everyday objects are radioactive – including you…) then it’s a fascinating subject that’s well worth exploring.
First seen: 1980
Original Price: £900
Value Today: £350 - £500, depending on probe type (0817)
Features: Variable HT (350 1500 volts DC), logarithmic meter display (CPS), internal speaker, sound mute, interchangeable probes, battery check, probe cradle, carry handle
Power req. 8 x 1.5 volt AA cells, 12 – 18 volts DC via AC adaptor
Dimensions: 165 x 115 x 155mm
Made (assembled) in: Burnham On Crouch, England
Hen's Teeth (10 rarest): 8
SCG0012 Contamination Meter No. 1 Mk 2, 1955
Say what you like about successive British Government’s attitudes to Defence spending but back in the early 1950s no expense was spared. The spectre of the Second World War was still fresh in everyone’s minds, and the threat of nuclear proliferation and the beginning of the Cold War was a growing concern so somewhere deep in the Ministry of Defence a decision was taken to equip British forces with what was clearly reckoned to be the best radiation detection equipment that money could buy, and here it is. Meet the SCG0012, known to its friends and admirers as Contamination Meter No 1.
It was either very good, or it cost so much that the MOD couldn’t afford to replace it completely because it remained in service for around 30 years, until the early 1980s. To say it was over-engineered would be an understatement. At around 5.5kg in its canvas haversack it must have been a nightmare to cart around, especially if the user was also wearing a full NBC (nuclear, biological, chemical) protection suit. On the plus side, if the balloon went up the user could be fairly certain that when they flicked the On switch, even if they were being bombarded, nuked, soaked, frozen, or baked, there was a fair chance that it would work..
We’ll start with the case, which is in two parts and made from cast alloy. It’s incredibly tough and thanks to some heavy-duty rubber gaskets and washers, is entirely waterproof. So much so that the case is fitted with two humidity indicators that change colour should so much as a drip of moisture find its way inside. The all-metal case also provides screening against interference from other nearby electrical devices, and protection against the Electromagnetic Pulse or EMP that accompanies nuclear detonations. This is a powerful pulse of electrical energy that can fry delicate electronic components, though in this case it wasn’t a great concern because the internal circuitry was entirely valve-based (though transistors were later used, as we’ll see in a moment).
Controls are few and far between, which was important, as it had to be really easy to use, and understand the readings. On the top panel there are just two switches for power on/off and battery check. The latter is shown on the meter in the middle, which displays radioactivity levels in milli Roentgens per hour, but helpfully includes a colour coded scale that roughly translates as green = safe, yellow = caution and red = get the hell out of it! There are a couple of covered selector switches for changing the HT voltage, to suit different types of probe, and a 2-pin socket for a set of headphones.
Nerdy Fact: the meter featured here is the Mk 2 version; you can tell that because it has rubber covered sockets for the cable connecting the main unit to the probe. The Mk 1 had screw-fit connectors, which turned out to be a bit unreliable. Otherwise the Mk1 and Mk 2 designs are virtually identical.
The probe is a truly weird and unwieldy-looking shape, presumably designed to make it easier to hold when wearing thick protective gloves. It is connected to the main unit by a hefty rubber coated cable but strangely the delicate Geiger tube – the long black cylinder, has almost no protection, other than a thin rubber sheath. This is in stark contrast to the rest of the unit and accidental drops and knocks must have damaged a great many tubes. Odder still is the rectifier valve, which lives under the metal cap next to the probe handle. There must be a good technical reason why it, and its associated circuitry has to be on the probe handle, rather than safely inside the main unit, but it’s not immediately obvious from looking at the circuit diagram. Maybe someone more familiar with the workings of these devices can enlighten me?
Whilst it is a valve-based design, it uses what were then state of the art components. Unlike most run of the mill valves these are cold cathode tubes, which do not have power hungry heater elements. This was a smart move that dramatically reduced battery consumption. That was just as well because initially the main unit relied on a pair of 150-volt batteries, which must have been horribly expensive. Needless to say they stopped making them years ago and it seems this was a major concern fairly on in the meter’s career. At some point in the late 50s a transistorised ‘Vibrator’ power unit was developed that ran on 4 x 1.5volt AA type cells, which fitted snugly into the unit’s battery compartment. (Vibrator power units use a mechanical buzzer type device to generate an AC output, which drives a step-up transformer to boost the voltage to around 300 volts that is rectified and smoothed to a DC output).
In the 1970s and 80s ads for decommissioned Contamination Meters appeared regularly in the Exchange and Mart and classified sections of electronic magazines. Prices were typically in the £20 to £50 range, which was quite a lot back then, well out of my reach but it went on my wish list. Forty odd years later and I’ve managed to cross it off with this one, which turned up on ebay. They can sell for anything between £10 and £100, depending on condition and whether or not they work (few do) and I often have a punt on ones with low starting prices. I placed my customary £10 bid with no great expectations. The email informing me that I had won was a surprise, and a very pleasant one at that because I was the only bidder. More good luck, because of the weight the meter was collection only; the seller lived just 10 miles away so no expensive shipping charges.
It got even better. It hadn’t been fiddled with and the condition, inside and out was excellent. It came with the Vibrator Power Module (many have just the 150 volt battery holder), a set of instructions and the original canvas haversack. The power unit works but unfortunately the rest of it is as dead as a doornail. Normally this can be a problem for me. I dislike working on anything using valves as they always seem to give me shocks and burns, but the design and layout of this device makes everything really easy to get at. There’s also a wealth of information on the web, including repair manuals, which should all help to make it a fairly straightforward job. However, all of the advice starts by suggesting that the many waxed paper capacitors it uses should be replaced. That makes sense because after 40 plus years most will have failed. The few I have tested so far were all way out of spec. As soon as that’s done I can see what else needs to be changed. Fortunately I was able to check the GM tube, which can be difficult to replace, and that’s in good order but sadly the complete overhaul it probably needs will have to take its turn on the rainy day to-do list.
What Happened To It?
Although Contamination Meter No.1 was in service for several decades -- until well past its sensible use-by date -- since the 1970s the MOD and Civil Defence has been steadily updating their inventories of radiation monitors with smaller, lighter and even more reliable instruments. The Plessey PDRM-82 from the early 1980s is a good example of the newer semiconductor based devices that replaced it. Whilst they may be more functional there is no denying the Meter No. 1 was a class act, and really looked the part.
Collecting vintage Geiger counters is a fairly specialist hobby so if you fancy having a crack at it you are not going to encounter much in the way of competition. The downside is that the really interesting items, that are worth collecting, tend to be few and far between. There’s no marketplace as such, but ebay is an obvious place to look and you can sometimes get lucky when, thanks to the seller’s lack of knowledge, they are wrongly or inaccurately described. Antique markets are another occasional source and again, stall holders often have little idea of what they are selling and prices can be very reasonable. Contamination Meter No. 1 is an exception, though and there’s little doubt what it does and rock-bottom prices are rare. On the other hand the chances of finding an original one in working order is next to zero, which always helps when negotiating a price. It’s not a big deal, though, even in non-operational condition they’re a sight to behold and if the worst comes to the worst they make great doorstops and exercise weights…
First seen: 1953
Original Price: £?
Value Today: £50.00 (0617)
Features: Gamma detection range 0 – 10 mR/hr, variable HT, remote hand-held probe with 2M waterproof connecting cable, 50mm meter display, headphone socket, CV2247 GM detection tube, 5 x cold cathode valves (CV575 in probe, main unit: CV509, CV138, CV286 & CV284), battery test function, colour change humidity sensors, folding carry handles
Power req. 2 x 150 volt batteries, 4 x AA cells using Power Unit Vibrator module (6665-11029) or mains power unit (6665-110028)
Dimensions: 260 x 248 x 117mm
Made (assembled) in: England
Hen's Teeth (10 rarest): 7
DP-66M Cold War Geiger Counter, 1970
Even those who weren’t around during the Cold War will know that the US and much of Western Europe spent the best part of three decades living in dread of being blown to smithereens. What’s rarely mentioned is the fact that populations in the former USSR and Eastern Block countries had similar fears, possibly more so, thanks to tightly controlled media and even more pervasive propaganda. Precautions were taken on both sides to prepare for the aftermath of a nuclear exchange and this included manufacturing large quantities of Geiger Counters and radiation monitoring equipment for use by the military and Civil Defence services.
We’ve already covered several Western instruments, like the iconic American CDV-700 and the British PDRM-82, so it’s about time we had a look at what they were using (or rather, hoping never to use...) on the other side of the Iron Curtain. This is a DP-66, a Polish made derivative of the Russian DP-5V, and widely used in Warsaw Pact countries. In many ways the DP-5V was the Soviet equivalent of the CDV-700, however, it was nowhere near as good and nowadays is only of interest to collectors of Cold War memorabilia but the DP-66 is another kettle of fish and a vast improvement on the DP-5V. It was very well made with modern – for the time -- electronic components and unlike its predecessor, used readily obtainable batteries. Even though it dates from the late sixties they are still very useable and sensitive enough to detect low levels of natural and man-made radioactivity. Many were made and stockpiled and a lot of them have survived. What’s more, compared with Western instruments of the same period, they’re relatively inexpensive.
Although it’s similar in size to the CDV-700 there are a couple of very obvious differences. The first one is the brown Bakelite-type thermoplastic case; the other is the probe, which is a good deal larger than the one on its US contemporary. It is clear that the designers were keen for users to keep potentially dangerous sources of radiation at arm’s length, and preferably even further away, using the supplied half-metre long telescopic extension pole.
The other reason for the size of the probe that it contains not one, but three Geiger Müller detector tubes. These vary in sensitivity and the types of radiation they can detect, from low level Beta up to lethal, kill you dead Gamma. As an added bonus the DP-66 outfit comes with a DKP-50 quartz fibre pen dosimeter and there’s a charger built into the case. This is worn on the user’s clothing, to monitor long-term exposure to high levels of Gamma radioactivity. All of this means that the DP-66 outfit can function in a very wide range of post-apocalypse situations; the US approach was to use at least three separate instruments (CDV-700, CDV-715/7 & CDV-742), which was clearly less convenient than this one box solution.
The unit is powered by two standard 1.5-volt D cell torch batteries that can keep it running for 60 hours or more (most CDV-700’s used four D cells) and these fit into a cylindrical holder with a screw cover in the end of the case. The large moving coil meter in the middle of the top panel has several very useful features and as well as scales showing counts per minute and milli-Roentgen/Roentgen per hour (when measuring Gamma radiation), there’s battery test indication. It’s also backlit, by pressing the button marked ‘OSW’ to the right of the meter and it’s also luminous, so it’s easy to use at night or in darkened conditions. In addition to the backlight button there are three other controls. A second button, marked ‘KAS’ zeros the meter (enabling a new reading to be taken quickly as the needle moves quite slowly when taking continuous readings). A rotary control to the left of the meter (marked DKP-50) is used to zero the needle (quartz filament) inside the pen dosimeter during charging, which takes place when it is inserted into the capped tube in the bottom left hand corner of the top panel. Finally there’s the 8-position rotary switch on the right hand side. The Off position is marked ‘W’. The next position ‘K’ is for battery test and the remaining six positions set range and sensitivity. Positions 3, 4 and 5 are for detecting high to medium levels of Gamma radiation and relate to the Roentgens per hour part of the meter scale (0 – 200, 0 – 5 & 0 – 0.5); positions 6, 7 & 8 are for low-level Gamma and Beta radiation, as milli Roentgens/hr (0 – 50, 0-5 and 0 - 0.5) and counts per minute or cpm (0 – 1M, 0 – 100k & 0 – 10k cpm). In the middle of the top panel there’s a capped cover protecting the meter pointer’s zero adjustment. The thick cable for the external probe emerges from the right end of the case and on the other end of the case there are two small sockets for the proprietary two-pin connector used by the magnetic earpiece, which is also included with the outfit.
Before we move on a quick mention for the probe’s rotating metal shield, for discriminating between Beta and Gamma radiation. It has three positions: Bx1 has series of horizontal slots that exposes a thin internal aluminium foil window, allowing the weakest Beta particles to pass through to the detection tubes. The second Bx10 position has a single small hole, which decreases Beta sensitivity by a factor of 10, and the third position, marked ‘G’ shields the aluminium window so only gamma radiation can enter the probe.
Inside the case the electronic components are mounted on two superbly well-made printed circuit boards. It’s proper old-school construction with a neat, laced loom connecting the circuits boards and internal components. Both boards are protected from damp by effective case seals and a thick coating of waterproof or conformal paint.
A complete DP-66 outfit includes a heavy-duty leather carry case with shoulder and waist straps a rather dodgy looking mains adaptor that fits into the battery compartment, the previously mentioned probe extension pole, a DKP-50 pen dosimeter, a small screwdriver, a pack of protective covers for the probe and the instruction book and equipment log book (both in Polish – fortunately there are good English translations on the web). Everything is securely contained in a tough wooden case. It’s a bit rough and ready and typical of boxes used to transport military hardware, but stripped, sanded and varnished, it can look quite presentable. Normally the DP-66 comes with a radioactive check source, to verify that it is working and check calibration however, these were all stripped out following removal from storage.
This DP-66 is date-stamped 1970 and I acquired it some time ago, shortly after they were released from storage and found their way into the civilian market. It had been little used and was very well preserved. There was dirt and tarnish on exposed metal surfaces but it scrubbed up really well with liberal applications of household cleaner and Brasso. I suspect that the case had never been opened – the seals on the bolts holding it together hadn’t been touched – and inside it was as clean and dry as the day it was made. Since then it has only been opened a couple of times, but only to take photographs as it was working faultlessly when I got it, and has continued to do so ever since.
With a set of fresh batteries installed it gives good readings on the low ranges (with shield in Bx1 position) from watches and clocks with luminous radium painted dial and hands. There also healthy clicks from the earpiece. It sounds like an attractive alternative to the increasingly expensive American CDV instruments, and in many ways it is but there are a few minor drawbacks. To begin with it is around 20 percent less sensitive to Beta radiation than a CDV-700 so it takes a slightly more ‘lively’ source to really get the meter moving. The probe is a bit of a handful and not well suited to a spot of undercover detection – it’s pretty clear what you are up to if you’re out hunting for radioactive antiques, glass or ceramics, waving that big black and shiny probe around. Lastly, the electronics are more complicated than its US rival. There are 8 transistors, three Geiger tubes and a few components that could prove tricky to find should it go wrong. On the plus side they have proved to be more rugged and reliable than their American counterparts, and the manual includes a good circuit diagram, but if a fault does develop it could prove challenging to fix.
What Happened To It?
Production of the DP-66M continued until the early eighties and it remained in service until the late 1990s when it was presumably replaced by smaller, lighter and doubtless cheaper and more sophisticated instruments that would be easier to maintain and store. Even though most DP-66’s are now over 40 years old, in good working order they’re still practical instruments for detecting and measuring radioactivity. Clearly they’re a bit too bulky for discreet urban prospecting -- there are plenty of pocket-sized instruments better suited to that sort of application -- but they still have a lot to offer to experimenters, hobbyists, amateur scientists, environmentalists, rock hounds and not forgetting Doomsday Preppers. They’re affordable too, with prices for complete boxed outfits starting at around £60; these probably work but may need a good clean and some TLC. £100 or so should buy a more presentable example, but if that’s above your pay grade there’s always the bargain basement option. If you know your way around simple electronic circuits, dead ones can sometimes turn up on ebay selling for £30 or less, but be warned, you could be lumbered with a doorstep if the fault is due to a hard or impossible to obtain part.
First seen: 1969
Original Price: N/A
Value Today: £60 (0117)
Features: 3-tube Geiger counter (STS-5, DOB-50 & DOB-80), Beta & Gamma sensitivity 0.5 mR/h – 200R/hr (6 ranges) rotating Beta shield, built in charger for DKP-50 type pen dosimeter, luminous & backlit meter scale, meter/reading zero, magnetic earphone output. Accessories: earphone, mains adaptor, leather case with neck & waist straps, probe extension handle, manual & calibration logbook, wooden storage/carry case
Power req. 2 x 1.5v D cells
Dimensions: Main Unit: 173 x 115 x 100mmm, Probe: 290 x 49 (max)
Weight: 2.1kg (main unit & probe)
Made (assembled) in: Poland
Hen's Teeth (10 rarest) 4
Nuclear Enterprises PDM1 Doserate Meter, 1983
Although nuclear or 'ionising' radiation is invisible, has no taste or smell and is beyond the normal range of our senses, it is not too difficult to detect. There are several ways, like rampant zombieism,
or growing an extra head, but the best known is the ubiquitous Geiger Counter. Other method include things like Cloud Chambers and scintillation detectors, which contain exotic crystals that produce brief flashes of light when struck by radioactive particles. However, one of the simplest type of detector is the Ionisation Chamber. You probably have several of them in your home in the form of 'free air' ionisation chambers. These are the small metal or plastic devices found in most types of domestic smoke detector. They are open to the atmosphere and inside there's a tiny radioactive source. This emits a stream of particles and if it senses that the flow has been interrupted, by passing clouds of smoke or noxious gasses, an electronic circuit sets off the alarm.
Another type of ionisation chamber can be found inside this Nuclear Enterprises PDM1 Portable Doserate Meter, it’s around 50 times larger than the ones in most smoke detectors, and this time it is sealed and filled with a gas at low pressure. It works the other way around to a smoke alarm and is designed to detect radiation, rather than smoke, and instruments like this are used throughout the nuclear power industry, in research laboratories, hospital nuclear medicine and radiography departments and for environmental monitoring. If fact you’ll find them wherever there’s a possibility of encountering potentially harmful levels of X-Rays, Gamma rays and Beta particles, which are the main types of radioactivity proven to cause long-term damage to human tissue, with prolonged or uncontrolled exposure.
Inside the PDM1’s ionisation chamber there is a pair of electrodes carrying an electric charge. When a radioactive particle enters the chamber it interacts with or ‘ionises’ gas molecules, releasing electrons that head towards the electrodes – attracted by the electric field – and from there the tiny charges can be measured using relatively straightforward electronic circuits. This type of Ionisation chamber is not especially sensitive and it doesn’t respond to low-level sources or Alpha radiation but it is very good at detecting and accurately measuring radiation in terms of exposure or dosage.
It looks quite complicated but it is actually very easy to use and everything the user needs to know is shown on that large analogue meter. The rotary switch on left is responsible for switching it on, checking the batteries, zeroing the meter and putting it into measuring mode. There’s a small knob in the middle for the meter’s zero adjustment and the switch on the right sets the type of measurement (dose or doserate) and the measuring range.
Broadly speaking dose is an indication of how much radioactivity you are being exposed to at any one time. Nowadays dose is measured in Sieverts but a Sievert is a helluva lot of radioactivity and in practice it is more convenient to express it in terms of microsieverts (uSv). Doserate is a measure of radioactive exposure over time, in micro or milliSieverts per hour (uSv/hr). The Dose ranges on the PDM1 are 30 and 300 uSv, and for Doserate it’s 30 and 300uSv/hr and 3, 30 and 300 mSv/hr. What the readings mean, and when it’s time to run is another matter, but be assured that if ever your job entails using an instrument like this, you’ll know exactly what to do when you see that needle move…
There’s only one other item of interest on the outside and that’s a sliding panel on the base. When open this exposes a sheet of thin metalised plastic film, and behind that is another metal film covering one end of the ionisation chamber. The purpose of the panel is to block Beta particles, which the instrument will detect, but they skew readings of X-Rays and Gamma rays, which is what the device is calibrated to measure.
The PDM1 was made in the UK (Scotland) in the early 1980s by Nuclear Industries, then a division of Thorn EMI. It’s a little larger than a standard house brick and probably cost hundreds of pounds when new. Precisely how much it cost is difficult to say, it’s not the sort of thing you'd have found in an 80's Argos catalogue… Around a third of the case is taken up by the ionisation chamber, which is mounted underneath the meter. There’s a large compartment, beneath the carry handle, for the batteries; it takes five, four 9 volt PP3s, used to generate the high voltage field for the ionising chamber, and a 9 volt PP9, which drives the electronics. The sealed module beneath the battery compartment is a high-gain, low noise amplifier that’s connected directly to the Ionisation chamber. It is very sensitive and the designers have gone to a lot of trouble to shield it against interference from other electrical and electronic devices, which could cause spurious readings. No expense was spared in its design and construction, so you can take it as read that it’s rugged and capable of withstanding a lot of harsh treatment. The only really fragile components are those thin metalised plastic membranes covering the ionisation chamber and if the inner one is punctured it’s basically kaput.
According to the stallholder at the Surrey antiques fair where I bought this PDM1 (one of a pair of meters he had – the other, a simple PDR1 rate meter will appear here soon) it was part of a lot of instruments sold off by a company involved in the digging of the Channel Tunnel. It sounds quite plausible and there’s no doubt that the extracted materials would have been routinely monitored. However this one appears to have been removed from service quite early on in its career, judging by its unusually clean appearance and a ‘Not to be used sticker’ on the meter. In other circumstances it might have been a risky purchase but since the two meters only cost me £20, and the film covering the ionising chamber seemed to be intact, it wasn’t a huge gamble. The meters alone were worth the asking price. It turned out that the PDM1 had been decommissioned for good reason, someone forgot to change the batteries and there was a rather nasty mess inside the battery compartment. Fortunately the damage was minimal and mostly confined to the battery terminals, which had to be replaced. The corrosive fluid that leaked from the batteries had dried out and cleaned up quite easily. It didn’t even stain the thick layer of powder coat protecting the alloy case and apart from the battery terminals the only other casualty was a foam insert meant to stop the batteries rattling around.
There was a minor problem testing the unit as PP9 batteries are now obsolete. They are still available but very expensive and typically sell online for over £7.00, far too much to spend on what may have turned out to be a doorstop. Luckily they’re really easy to replicate with a cheap 6 x AA cell battery holder costing £1.50. I still wasn’t holding my breath; this particular instrument is well over 30 years old but I needn’t have worried and it fired up first time, responding well to a particularly ‘lively’ travel alarm clock with radium-painted luminous hands and face. The readings may not be that meaningful as by now it is well out of calibration but it definitely detects radioactivity, and long-term readings suggest that it may even be sensitive enough to respond to normal background radiation, and over time, could let you know if there’s an unexpected increase.
What Happened To It?
The roots of Nuclear Enterprises dates back to the 1950s as Netsensors, a company making instruments for the aerospace industry but after a number of takeovers and mergers it was sold to EMI in the mid 1960s, and became part of the Thorn EMI group in the late 70s. By then Nuclear Enterprises was heavily involved in radioactive measurement and instrumentation, and doing quite well by all accounts, but the division was sold off in 1987 in a management buyout. I worked for the consumer side of Thorns in the late 70s and I was aware that the company was having a tough time. By the mid 80s they were selling off a lot of their smaller subsidiaries, so it may have been a bit of a fire sale. Anyway, Nuclear Enterprises continued in the field of nuclear detection and instrumentation and in 2002 it was acquired by the French company FGP Sensors, at which point the NE brand and identity seems to have disappeared from view.
Back to the here and now and technology has moved on. Modern instruments are smaller, more responsive, have many more features and almost certainly cheaper than this old beast so it’s probably outlived its usefulness. Nevertheless, it is entirely possible that there are still a few PDM1s of a similar vintage still in service and provided they’re regularly calibrated and well looked after they can go on for a very long time. Outside of their natural homes, in the lab or in the field, they’re not a lot of use to the average citizen and the enthusiast and collector’s market is quite small, so don’t expect to turn a quick profit if you ever find one going cheap at your local car boot sale. On the other hand, if you’re of a cautious disposition, concerned about the next (and probably last, world war…) or living next door to a flaky nuclear power station or weapons facility, it might be worth having a working one tucked away, just in case the balloon goes up. It might be a long wait, though, so don’t forget to remove the batteries…
First seen 1983
Original Price £?
Value Today £10 (1116)
Features Down-pointing ionisation chamber with sliding beta shield, (100sq cm detection area), skin & depth dose/doserate measurement, (30 – 300 uSv, 30 – 300uSv/h & 3 – 300mSv/h, 9cm analogue meter display, battery condition indication, set zero adjustment
Power req. 1 x 9v PP9 & 4 x 9v PP3
Dimensions: 245 x 125 x 170mm
Made (assembled) in: UK
Hen's Teeth (10 rarest): 8
Most of us are familiar with tales of grizzled prospectors, staking claims, panning and digging for gold during the mid-nineteenth century Californian Gold Rush. What you may not be aware of was a later and even bigger hunt for mineral riches in the US. During the late 1940s and 50s’ tens of thousands of prospectors scoured the South-western states (mostly Arizona, Colorado, Oregon, New Mexico and Nevada) for buried ‘A-Metal’ or Atomic Metal, better known to us now as Uranium.
In the years following the Second World War and at the start of the Cold War, America was in the grip of a desperate arms race, to develop ever larger and more powerful nuclear bombs. This created a huge demand for Uranium for refining and processing, mostly into the isotope Uranium 238 for use in weapons and reactors.
The US Atomic Energy Commission actively encouraged both amateur and professional prospectors to locate deposits of Uranium ore, offering bounties of $10,000 for big finds. Gold is shiny and relatively easy to spot, when you know where to look, but to the untrained eye Uranium ore looks pretty much like any other rock. However, it does have one rather useful property, it’s radioactive. Companies manufacturing Geiger Counters, and scores of new ones, which appeared out of the woodwork, raced to sell their instruments to the hoards of hopeful prospectors, often making fanciful claims about vast fortunes to be made. The reality was somewhat different. Substantial finds were few and far between and those that found and mined deposits sometimes received dangerous and often lethal radiation doses whilst others tried to increase the value of the ore they found by refining it using suspect DIY methods, leading to large numbers of casualties and deaths.
But back to the business of prospecting and this little gadget dating from the mid 1950s. It’s a Pioneer G-5B Geiger Counter, manufactured by The Gaertner Company, located at the intriguingly numbered 812½ - 814 La Brea Avenue in Hollywood California. It was small, relatively affordable (it sold for under $60), sensitive and very easy to use. No arguments there and it’s a textbook example of just how simple a radiation detector can be.
Incidentally, strictly speaking the G-B5 is not a proper Geiger ‘Counter’ as it has no display or means of measuring the level of radioactivity, but we'll let that pass for now. It uses just a small handful of electronic components, and bizarrely, a Champion spark plug, but the key to its brief success, and short life, is a pair of Victoreen IB85 Geiger Müller detection tubes. These are genuinely sensitive devices, able to detect relatively low levels of the Beta and Gamma radiation emitted by Uranium ore but they have two very particular drawbacks. Firstly they require a 900-volt supply, and second, the outer casing is a very thin aluminium tube.
The power supply problem was solved using what may be described as a 'pump' circuit. Geiger tubes generally consume very little power, and once charged up to their working voltage, they need only occasional topping up as the charge dissipates, as and when radioactivity is detected. The Pioneer circuit uses a simple step-up transformer circuit to boost the voltage from one of the unit’s two batteries to the required 900 volts, by pressing a button on the top of the case every so often. It’s very similar to the way the ignition circuit works on older cars. This relies on a switch – the contact breaker -- that is mechanically coupled to the engine. When the engine turns over it opens and closes the contact breaker to produce a rapid series of low voltage pulses that are fed to the ignition coil and this generates the high voltages that create the sparks inside the cylinders. The spark plug in the Pioneer G-5B provides isolation and rectification in the high voltage (HV) circuit*. The real problem, though, was the fragility of the IB85 tubes. They are acutely sensitive to sudden changes in air pressure and you may be able see in the photograph above that both tubes in this G-5B have been crushed. It turns out that this was very common and many of them came to grief when the Geiger Counter was put in the boot (trunk) of a car and the lid slammed shut. If they hadn’t been crushed it probably wouldn’t have made much difference, though, and by all accounts these tubes only lasted a few years.
The rest of the circuit involves a single triode valve. When a radioactive particle enters the Geiger tube it produce the characteristic click and this is amplified by the valve and fed to a headset that plugs into a pair of sockets on the top of the case. And that’s pretty much all there is to it. Power comes from a pair of batteries; one is a low voltage ‘A’ type battery (typically 1.5 volts), for the valve’s heater filament. The other is a HT (high tension) ‘B’ type battery (45 volts), which powers the valve and provides the drive voltage for the transformer that feeds the Geiger tube.
The sort of compact high voltage B battery the G-5B uses would have been quite common and widely available back in the mid 50s as they were used in valve-based portable radios. They stopped making them years ago but it is possible get modern repros or replicate them by connecting 9-volt transistor radio batteries in series. However, it’s going to take a fair bit of work to get this particular unit working again. Intact IB85 Geiger tube are virtually unobtainable; modern 900 volt tubes might be persuaded to work, but there are serious question marks over the valve -- not helped by the number having rubbed off -- and the high voltage transformer. These are a common failure point as the insulation on the windings degrades over time, especially if the unit has been stored in a humid atmosphere for any length of time. Even a tiny pinhole rupture in the insulation can be enough to produce a high voltage arc that will destroy it.
Otherwise it is in extraordinarily good condition for its age. The metal case is very clean, free of any serious scratches or corrosion and the green plastic protective shields for the Geiger tubes – on the underside of the case – are uncracked. All of the switches work; the only other components (two very large resistors, which can just be seen in the photo above) check out as okay, and there’s really not much to go wrong with the spark plug. The bottom line is that it could be restored but for the moment it’s going to have to wait its turn on my long (and rapidly growing) list of rainy day jobs.
For the record I found this one on the US ebay site some time ago and fully expected it to be snapped up by collectors. It was accurately titled and described, with a low starting price of $25 and free shipping (within the US) so I was surprised to discover, just two hours before the auction was due to end that it hadn’t attracted a single bid. I still had no doubt that it would fetch a decent price but just in case I put on a speculative bid of $30 and went to bed. There were no other bids and two weeks and $45 later (shipping was another $20) it was in my very grateful hands.
What Happened To It?
The Uranium ‘Rush’ only lasted a few years and it appears that relatively few Pioneer G-5Bs, or the many other basic prospecting detectors from the same period, have survived so by rights it should be quite collectible. However, it was part of a fairly obscure slice of US history and the market for this kind of Atomic Age curio is currently quite small. They do turn up on ebay every so often and occasionally, when a couple of bidders get stuck in, they can top £50. Like prospecting for Uranium it’s not going to make you rich but relics like this can suddenly take off, and are definitely worth grabbing, if you ever come across one for a sensible price.
* Update. I am obliged to members of the excellent Geiger Counter Enthusiasts forum on Yahoo for additional information and corrections to my assumption that the spark plug was for voltage regulation, and that the B battery was 45 volts, not 67.5 volts.
DUSTY DATA (Manual)
First seen 1955
Original Price $59.95
Value Today £50.00 (0116)
Features 2 x IB85 Geiger Müller detection tubes, ‘pump’ type tube power supply (900-volt nominal), headset output, headset and check source included with outfit
Power req. 1 x 67.5 volt Eveready 467, 1 x 1.5 volt filament battery
Dimensions: 155 x 140 x 83mm (inc handle)
Made (assembled) in: USA
Hen's Teeth (10 rarest): 8
General Radiological Ltd Type NE 029-02, 1957
Firemen often seem to have the best toys, which of course are entirely necessary in their clearly hazardous profession, but who amongst us wouldn’t want to have a ride on a fire engine or have a go with one of those ‘Jaws of Death’ car peelers? Fire station poles also look like a lot of fun and how about a quick squirt with one of those high-power hoses? They’ve got loads of more exotic stuff as well, and tucked away inside their equipment lockers quite a few of them have Geiger Counters.
This is not a new development in response to any terrorist threats or atomic accidents, they’ve had access to them for decades, since before the Cold War and for at least as long as there have been nuclear weapons, power stations and radioactive waste being carted around the country. Here’s an example of one that apparently they used to have back in the fifties and sixties, at least that’s the story, which I have yet to corroborate, but it all looks and sounds very plausible.
The age of this instrument, a Type NE 029-02 made by General Radiological Ltd., is in little doubt though, and it proved fairly easy to date. On the circuit board inside the case there’s a pair of TJ1 point contact transistors and these were made by STC, but only for a brief period, starting in 1956. I have Andrew Wylie and his excellent Mister Transistor website to thank for that useful titbit and a wealth of other information about vintage semiconductors. It’s a surprisingly compact design, most other military and industrial Geiger Counters of the period tended to be large and bulky; this one fits snugly in the palm of a hand.
It is really rugged, which fits in with the Fire Brigade story; it’s almost certainly waterproof as well and easy to carry and operate, even when the user is wearing thick protective clothing and gloves. Inside the light but tough two-part cast alloy case there’s a Mullard MX129/01 Geiger Müller tube. This is mainly sensitive to Gamma Radiation, which can be nasty stuff and is the kind that does the most damage and poses the greatest threat to those unlucky enough to be close to an exposed source. On the top panel there’s a small meter showing a relative reading of radiation dose in milliroentgens per hour; the rotary switch below the meter has four positions: Off, Battery Test and Sensitivity (0-0.5 and 0-5 mR/hr). Incidentally, nowadays most instruments of this type measure gamma radiation dose in Sieverts and REMs (Roentgens Equivalent Man), rather than mR/hr but the basic principle is the same and if the needle moves, especially on the high range, you’ve found your source radioactivity and it’s time to back off! The NE 029-02 also has an audio output and comes supplied with a single headset, which plugs into a small two-pin socket on the top panel. This allows the user to hear the clicks coming from the detector tube, which can be helpful when trying to locate hazardous sources of radioactivity.
It is powered by three1.5 volt AA cells, which live in a sealed compartment on the top panel. The two previously mentioned transistors look as though they are used in a simple multivibrator circuit, which pumps pulses of electricity into a coil and multiplier that generates the 400 or so volts needed to power the Geiger tube. As you may be able to see from the photos it’s a real work of art, beautifully built, by hand, with all of the components neatly soldered to orderly rows of pins. Fragile components, like the point contact diodes have small coils wound into their leads to provide some cushioning against knocks and bumps. Rubber seals around all of the case and battery cover joints make sure water can’t get in.
I found this one hidden at the bottom of a pile of Fire Brigade related items at a large open-air antique fair in Surrey. The stallholder said the collection belonged to a retired fireman, and he believed everything was standard service issue. It appeared to be in very good condition and came with its original bright red carry case, shoulder strap and the high impedance headset. The seller didn’t know if it was working or not, hence the asking price of just £6, which I felt duty bound to haggle down to £4.00 – bargain of the day!
Unsurprisingly it was as dead as a doornail and the most serious fault wasn’t hard to find. A leaky set of cells had rotted away the spring steel contacts in the battery compartment. Fortunately there was no other damage and it cleaned up easily. Connecting a bench power supply to the unit indicated that the battery test function was okay, but the detector circuit remained stubbornly silent. The two transistors produced some slightly anomalous readings but there were no obvious faults. Replacing the transistors didn’t help so the suspicion has now shifted to the high voltage transformer, half a dozen or so long obsolete selenium rectifiers and the Geiger tube. The big problem, though, is the lack of a circuit diagram, so it will have to join the waiting list until I have time to re-trace the circuit, or track down a service manual. It almost certainly is repairable but it’s going to take time. On the plus side the condition, outside and in, is extraordinarily good; the circuit boards looks as though they was assembled yesterday, and the case shows only very light signs of use.
What Happened To It?
Up to date information on the sort of radiological monitoring equipment currently used by Fire Brigades in the UK is a bit thin on the ground but in 1995, in reply to a parliamentary question on the topic, it turned out that there were only 6 units to cover the whole of London. Seemingly radioactivity was not considered to be a huge priority back then. They’ve probably upped their game by now and it would be very surprising if a lot more instruments have not been issued, but it is highly unlikely that any of these old NE 029-02s are still in circulation.
General Radiological Ltd., was bought out by the Rank Organisation in the early sixties and since then seems to have vanished from sight. Although the NE 029-02 is well built it is no match for modern instruments, in terms of sensitivity and accuracy, and my guess is that they wouldn’t have remained in service for very long, probably less than 10 years. Maintenance would have been a problem; first generation semiconductors had a fairly short life expectancy Other components, like electrolytic pacitors and selenium rectifiers, degrade over time and the one thing you don’t want in a Geiger Counter, used in safety-critical applications, is unreliability.
I can find no information on how many NE 029-02s were built but I suspect it was probably in the low hundreds as the demand wouldn’t have been that great. That would make this one quite rare but sadly it doesn’t translate into big bucks; it’s a bit too weird to attract most collectors of vintage electronics, and unfortunately, in its present state it is of little practical use. Nevertheless, it’s an unusual and arguably historical example of early transistor technology and if anyone has any more information, or a circuit diagram I would be very interested to hear from them.
First seen 1957
Original Price £?
Value Today £25 (0715)
Features Mullard MX129/01 halogen-quenched gamma-sensitive Geiger Müller tube (0.0004 – 0.2R/hr), selectable range (0-5mR/hr & 0–0.5 mR/hr), 2 x transistor HV generator (2 x STC TJ1), battery test function, waterproof case, headphone output, carry case & strap supplied
Power req. 3 x 1.5 volt AA cells
Dimensions: 198 x 123 x 49mm
Made (assembled) in: England
Hen's Teeth (10 rarest): 9
CDV-700 Civil Defence Geiger Counter 1960 - 68
This is the classic Geiger Counter that has featured in countless movies and TV programs over the years. Although the design is more than 50 years old it is still seen from time to time in current productions, including recent episodes of NCIS. I always have a little chuckle when I see one on the screen as it is usually accompanied by a 'ticking' sound as our hero or heroine locates a radioactive source. In fact there is no built-in speaker, just a really weird and long obsolete socket for an equally obsolete headset. but the point is, it looks the part.
These instantly recognisable instruments were first produced in the early 1960s, at the height of the Cold War. Hundreds of thousands of them were made for the US Civil Defense Corps, to be kept in fallout shelters and issued in the aftermath of a nuclear attack. Several different models were made and the manufacturing was contracted out to specialist companies, including Electo-Neutronics Inc (ENI), Universal Atomics, Victoreen, Anton and Lionel, the latter being better known to many Americans as a maker of toy trains.
The CDV-700 (sometimes CD V-700) was the most sensitive model; it uses a Geiger Muller tube and can easily detect low levels of background radiation up to lethal doses. Other models, like the CDV-715 and 717 were only capable of sensing very high levels and if you ever saw the needle move on one of those you were probably going to die...
No expense was spared in their design and construction. They were built to last; those that survived mostly still work, or can be easily bought back to life as the electronic circuitry is very simple (most had just two or three transistors). They run off standard 'D', type torch batteries that last for several weeks in continuous use. The Geiger tube is housed in the detachable probe handle and it has a clever rotating shield that allows the user to discriminate between Beta (nasty but doesn't travel very far) and Gamma (really bad and gets through almost anything) radiation. It was meant to be easy to use and came with an instruction manual that could be understood by untrained personnel. Calibration was simple, on the side of the unit is a 'Check Source' label containing a small piece of radioactive material (Radium D/E or Lead 210) and when the probe is bought close to it, the meter on the top can be adjusted to give the correct reading. Over the years the radioactive material has decayed - the half-life of the source is around 22 years -- so they are no longer reliable but there's still enough activity enough to give a decent reading.
What Happened To It?
CDV Geiger Counters, Survey Meters and dosimeters were produced throughout the 1960s and the stocks were scrupulously maintained - regularly tested and recalibrated -- until the mid 1990s when they were gradually phased out. Local and Federal government bodies auctioned off stocks and many of them ended up in private hands, schools and colleges, which is where I come in. A few years a go I bought up a few CDV-700s, mostly 'as new' unissued stock, which I have been steadily selling off on my anythingradioactive web site. Sadly they are coming to an end now but you can still find them on ebay in the US. The only problem is they are quite heavy and the shipping costs can be prohibitive, moreover in some states the export is banned, probably due to the radioactive check source labels.
The great thing about CDV 700s is that they are a practical gadget and (mostly) still work. You would be surprised how much radioactivity there is out there, everything from the hands and dials on old watches and clocks with luminous hands (radium paint was used up until the 1950s), glassware and porcelain that uses uranium tints and glazing, old gas mantles (doped with thorium to increase brightness) and even granite kerbstones which can contain traces of naturally occurring uranium ore.
I doubt that you will see very many of them here in the UK but if you do, it's not a silly price and it still works grab yourself a little piece of Cold War history.
First seen: 1960
Original Price £ unknown
Value Today? £30 - 100, depending on condition
Features: Single switch off x100, x10 & x1 range, detachable probe with beta shield, carry strap, water-resistant case, three range settings, covering 0 - 0.5, 0 - 5 and 0 - 50 mR/h (millirontgens per hour), check source label, high impedance headphone
Power req. 2 or 4 D cells (depending on make)
Weight: 1.5kg ex batteries
Dimensions: 120 x 210 170
Made in: USA
Hen's Teeth (10 rarest): 7
Victoreen CDV-715 1B Survey Meter, 1965
This is arguably one of the most useless gadgets we have featured to date (but give it time…) and if you ever see the meter on a CDV-715 move of its own accord you have probably just survived a nuclear explosion and may shortly die a horrible death…
The Victoreen CDV-715 was produced at vast expense and in large numbers (almost 600,000 were made) throughout the mid to late 1960s, at the height of the Cold war. They were intended for use by US Civil Defense personnel in the aftermath of an attack, and designed to indicate if it was safe to leave your bomb shelter. It looks a lot like the classic Geiger Counters of the era and it does indeed measure radioactivity, but this is quite a different beast and technically known as a Survey Meter. It’s definitely not a Geiger Counter for the simple reason that the radiation detecting device inside the box is an Ionisation Chamber, rather than a Geiger Muller tube, and whereas Geiger Counters generally measure (and count) relatively low levels of radioactivity; Survey meters like this respond only to very high, and usually lethal doses, which is why you never want to see that needle move.
Following the end of the Cold war in the l990s the US Civil Defense scrapped most of these meters, tens of thousands of them were sent to landfill or sold as scrap but a lot found their way onto the market through government surplus sales. Unfortunately they are often mistakenly or misleadingly labelled as Geiger Counters and inadvertently bought by people who believe that they are going to protect or alert them to radioactive leaks, contaminated food and so on. This is something the CDV-715 definitely cannot do. There are usually quite a few of them on ebay (US) and I suspect that in a lot of cases they are innocently described because the seller simply doesn’t know much about it. However, there are plenty of examples of them being deliberately mis-sold, and this happened a lot in the aftermath of the Fukishima power plant accident in 2011; at one point they were being sold on Amazon, with optimists asking several hundred dollars for them.
Ion Chambers are one of the simplest types of radiation detector and you almost certainly have at least one of them in your own home, as they are a key component in most household smoke detectors. Essentially it’s a small, enclosed metal cylinder with an insulated electrode inside. A voltage is applied across the electrode and the body of the cylinder and when radioactive particles enter the can the gas inside (air in the case of the CDV-715) is ionised, generating a small current that is detected by a simple electronic circuit. If there are enough particles, a reading will be displayed on the meter. Basic ion chambers like this one are pretty insensitive and it takes a lot of radioactivity to produce a reading but is possible to increase their sensitivity by filling the chamber with specialised gasses at high pressures. Incidentally, the ion chambers in smoke detectors work in a slightly different way. They have a small radioactive source inside (normally a tiny pellet of Americium 241), which emits a constant stream of alpha particles – it’s okay, they are very weak and can’t get out. This produces a constant ionisation current, but if smoke enters the chamber the stream is interrupted and this triggers the alarm.
The 715 is actually very easy to use. It has only two controls, the knob in the middle has a spring-loaded circuit check position that tells the user that the battery is okay and it is working. The next position is for zeroing the meter using the small black knob beside the handle (ion chambers are very sensitive to humidity) and there are three range settings for gauging the level of radioactivity, calibrated in the now almost defunct Roentgen units. They were built to government specification by several companies, this one is made by scientific instrument manufacturers Victoreen, other makers include Lionel (a well known US toy maker) and Landers Frary & Clarke. At the time money was no object, reflected in the quality of the materials and the high build quality. There is little to go wrong – leaky batteries were the commonest cause of failure -- and during their service life they were regularly checked and maintained. Many of the ones that come on to the market are still in good condition, though they often show signs of wear and tear on the case.
What Happened To It?
Survey meters are still being made though most modern instruments are a lot more sensitive than the 715, designed for specialist applications within the nuclear power industry and rarely end up on the open market. This one is part of a batch of near-mint units that I purchased several years ago. I occasionally sell them to collectors of Cold War memorabilia and experimenters on the strict understanding that they are for decorative purposes, conversation pieces or doorstops…
The price and quality of the ones on the ebay in the US tends to be fairly variable but the real problem is that they are bulky and fairly heavy, and although they often sell for $20 - $50 the cost of shipping one to the UK can easily be as much, if not more than the purchase price. The current concern over all things nuclear also means they are sometimes intercepted and confiscated by UK Customs, even though they are most definitely not radioactive or in any way restricted for sale or use. Clearly it’s not something you will ever need and even one in working condition is no more than a novelty but you might find a use for one as a stage prop or part of a Halloween costume but be warned, it’s probably not the sort of thing you should wave around in public, unless you want to cause a panic or get arrested…
First seen 1965
Original Price £n/a
Value Today £25 – £50 depending on condition
Features High range ionisation chamber survey meter, 0 – 500 Roentgens/hr (4 ranges), batter test & zero set functions, high quality moving coil meter display, carry handle & strap
Power req. 1 x 1.5 volt D-Cell
Dimensions: 220 x 103 x 140mm
Made in: USA
Hen's Teeth (10 rarest): 4
Victoreen CDV-717 Radiological Survey Meter, 1965
It’s a well established fact that a whole body radiation dose of 500 rem (Roentgen Equivalent in Man) is enough to kill most people. That’s a helluva lot of radioactivity and what you might expect to receive in the aftermath and vicinity of a nuclear detonation, which is not a place you want to be, but if you were lucky enough to be in a bunker, you would probably be quite grateful to have one of these. It’s a Victoreen CDV-717 Radiological Survey Meter, thoughtfully calibrated to read up to, and including that lethal dose, but unlike most other survey meters, this one is designed to let you monitor radiation levels remotely, without necessarily exposing yourself to harmful doses.
The CDV-717 is based on the CDV-715 but with one important extra. The Ionisation Chamber, which detects the high levels of gamma radiation that survivors are keen to avoid, lives inside a detachable box. This can be connected to the main unit by a 6.5 metre (25 foot) long cable, so it can be dangled outside the shelter to take readings. This is clearly a major bonus and means you can stay reasonably safe whilst those outside are dying a horrible death, or turning into zombies – depending which experts you talk to.
Unfortunately, in the absence of a nuclear holocaust, that is just about all the CDV-717 and its ilk is good for. Almost all Survey Meters are designed to detect only extremely high levels of Gamma radiation. It’s also important to say that they are not to be confused with more sensitive instruments, like Geiger Counters, which is what they are often deliberately (and occasionally mistakenly) called on ebay, with prices to match!
A guided tour of the 717’s main features and controls doesn’t take long -- they were designed to be used by largely untrained personnel -- and there are only three items of interest on the top panel. The first is the large meter. This is a little unusual in that it’s ‘ruggedised’. Most of the meters fitted to US Civil Defence (Defense, if you’re on the other side of the pond) from the Cold War era are fairly cheap and cheerful types and do not take kindly to heavy knocks or vibration. This one is in an altogether different league. It’s housed in a metal, rather than plastic case, and the components inside are made of sterner stuff and less prone to failure and damage. It’s also waterproof and the metal case provides additional protection against the Electromagnetic Pulse (EMP) generated by nuclear weapons that can destroy electronic equipment. The controls are confined to a range switch, with positions for Circuit Check – to test the battery and electronics – and meter Zero, This is where the other control knob comes in and when the switch is in the Zero position the knob is used to set the meter to zero to ensure a (reasonably) accurate reading.
All of the electronics – an unholy mixture of technologies that includes a germanium transistor a tiny valve and some ultra high-value, high-tolerance glass encapsulated resistors – are inside the upper part of the case. To be fair it has been really well made, using top-grade parts and yes, it should survive a nuclear war. The bottom part of the case contains the ionisation chamber and a spool of coaxial connecting cable. The ionisation chamber is not as interesting as it sounds; basically it is a metal can -- around the size of a small tin of baked beans -- filled with air and a single, insulated disc-shaped electrode mounted in the centre of the container. The chamber is hermetically sealed to stop variations in atmospheric pressure, temperature and humidity affecting accuracy.
For anyone interested in how these things work here’s a quick and dirty explanation. A charge of around 50 volts, generated by the transistorised section of the circuit, is applied to the central electrode. Radioactive particles entering the chamber cause the air molecules inside to ionise, releasing charged particles or ions. Positive ions are attracted to the central electrode whilst negative ions go to the sides of the container. This creates a microscopic current that is proportional to the intensity of the radioactivity. It is amplified by the miniature valve (technically an electrometer) and the rest of the circuit is used to measure the output and display it on the meter. The really clever part is that a single 1.5-volt D cell torch battery powers everything and because the currents involved are so small, it can last for months.
Overall the standard of construction is extremely high. They must have cost the US Government a very pretty penny and upwards of 100,000 of them were made, almost all by the Victoreen Company of Cleveland Ohio. This particular one rolled off the production line in August 1965, according to a date stamp inside the case, and it probably spent most of its life in storage in Civil Defense depots or shelters. It is in virtually as new condition, still in its original box, and would only have been removed for periodic tests and calibration checks.
It came into my possession in the early 90s as part of a small consignment of CDV-700 Geiger Counters. The US seller included it as a free sample, to see if I would be interested in buying some more of them. He had several hundred up for grabs, with an asking price of just $5.00 each. In retrospect I foolishly declined the offer, mostly because they are really heavy so the cost of shipping them from the US would have been astronomical and, at the time, there was simply no market for them. Nowadays they are being sold on ebay (mostly misleadingly) as Geiger Counters for between £50 ands £150, but ignoring the fact that they are next to useless for anything radiological, the vintage parts inside the case are now worth more than a few bob to vintage tech enthusiasts. Hindsight is a wonderful thing…
What Happened To It?
When the Cold War was finally declared over, some time in the 80s, the US Civil Defense either destroyed or sold off its vast stockpiles of 60’s and 70s Geiger Counters and Survey Meters. Where necessary they were replaced by smaller and more accurate and reliable, modern instruments. (That’s open to debate and ironically, modern instruments, reliant on microchip technology, are much less likely to survive the EMP of a nuclear blast). However the iconic yellow CDV-700, 715 and 717 models live on and continue to be the go-to stereotypical Geiger Counters for Hollywood movies and TV series. I’m always amused when they ‘tick’ as none of them ever had any sort of built in speaker.
The CDV-700 model is a genuinely useful and surprisingly sensitive instrument but the best thing you can say about these old Survey Meters, from a practical point of view, is that they make half decent doorstops. Tragically they also end up butchered, as table lamps, or dissembled and used as dog bowls and ashtrays. Hopefully there will never be a time when they can be used in anger, but I’m hanging on to mine, just in case…
First seen 1965
Original Price £ a lot!
Value Today £50 (0116)
Features Detachable ionisation chamber radiation sensor, remote cable connection (6.5 metres/25 feet), 3 ranges (0-0.5, 0-5, 0-50 and 0-500 r/hr), ruggedised meter, battery/circuit check functions, meter zero & range set controls
Power req. 1 x 1.5 volt ‘D’ cell
Dimensions: 220 x 160 x 115mm
Made (assembled) in: USA
Hen's Teeth (10 rarest): 7
CD V-742 Pen Dosimeter & CD V-550 5b Charger, 1962
Here’s another relic from the Cold War era of the 50s, 60s and 70s and once again, it’s not the sort of thing you would ever want to see actually working because it would almost certainly mean that the balloon has gone up, and you are hunkering down in a fallout shelter…
The CD V-742 is one of a range of pen dosimeters, elegantly simple little devices that measure how much X-Ray and Gamma radiation the wearer has been exposed to. This particular model is a high range type with a range of 0 – 200 Roentgens; others, like the CD V-730 and 740 had ranges of 0 – 20 and 0 - 100 Roentgens respectively. These days the Roentgen has been largely replaced by the Sievert as a measurement of radioactive dose but to put that scale into perspective, exposure to 500 Roentgens over a period of several hours is usually lethal. In theory one of these could come in quite handy if you somehow managed so survive a nuclear attack but in practice if your CD V-742 ever showed any sort of reading you were probably a goner…
It is very easy to use and all you have to do is pop one in your top pocket and leave it there while you go about your radioactive business. Basically it’s a sealed metal tube with a transparent window at one end, with a central electrode, and an eyepiece lens at the other. Inside there is a fine quartz whisker, mounted above a small screen engraved with the aforementioned Roentgen scale. Before use the dosimeter has to be zeroed, and this is where the yellow CD V-750 charger unit comes in. The 742 is pressed down on a spring loaded button in the top left hand corner; this simultaneously lights up a small torch bulb inside the case and applies a 200 volt charge to the central electrode. The user peers down the tube to read the scale and by turning the knob on the top right of the case, the whisker can be moved to the zero position and it is ready to go.
Gamma radiation penetrating the tube has the effect of dissipating the charge, causing the whisker to move up the scale in direct proportion to the level of radioactivity. In normal use the dosimeter would be read at the end of the day or shift, to determine how much radiation the wearer has been exposed to, and if the reading was really high, it was time to start planning for an early retirement…
Hundreds of thousands of dosimeters and chargers were manufactured from the mid fifties to the mid sixties for the US Civil Defence corps and distributed to the nationwide network of shelters and control centres. Dosimeter pens and CD V-750’s were made by several companies on money no object contacts for the US Government, including Bendix, Jordan, Universal Atomics and in the case of this one, the International Electronic Hardware Corporation. The charger is sturdily made, strong enough to survive an atomic blast in fact. It is powered by a single standard D Cell and there’s even a spare torch bulb inside. Although they are more than 50 years old both devices appear to be in full working order, though in the absence of any highly radioactive sources to test it on, that has to be taken on trust…
What Happened To It?
The CD V-742 and 750 shown here are part of a batch I acquired a few years ago as part of a US Government clear out of old stock. Such is the simplicity and reliability of the design that pen dosiumeters are still being made to this day, for use in the nuclear industry and military applications. The basic design has hardly changed over the years, though there are many variations on the theme, including a wrist-worn version, which until recently was standard issued for NATO armed forces.
For years old pen dosimeters and chargers like these sold on ebay US for a few dollars and were mainly bought for their novelty value and by collectors of Cold War ephemera. They have little or no practical use but there was a huge spike in demand, and a tremendous price hike, following the Fukishima accident in 2011. Sad to say they were mostly misleadingly sold as personal radiation monitors, and purchased by people frightened by the scary news reports coming out of Japan but it’s doubtful that a 742 would have read anything, further than a few tens of metres away from a damaged reactor. Things have settled down and although prices haven’t fallen back to pre-Fukishima levels, you can find dosimeter and charger sets on ebay, often in ‘as-new’ condition for less than £30; pens on their own cost around £5.00. It’s probably not the sort of thing you would want to go out of your way to buy, but who knows? If they ever drop the big one prices are bound to go up and you would be glad to have a few of them handy, for throwing at zombies and the three-headed wolves roaming the post apocalypse wasteland…
First seen 1962
Original Price £n/a
Value Today £25
Features CD V-742 quartz fibre indicator, 0 – 200 Roentgens. Illuminated press to charge contact, zero set control, spare bulb
Weight: CD V-742 22g, CD V-750 420g
Power req. CD V-742 n/a, CD V-750 1 x D Cell
Dimensions: CD V-742 112 x 9mm, CD V-750 104 x 104 x 68mm
Made in: USA
Hen's Teeth (10 rarest): 6
Wallac Oy RD-5 Geiger Counter, 1963
For a country that’s practically next door to Russia and one of the planet’s largest stockpiles of atomic weaponry, not to mention a country with a patchy history for the safety and integrity of its nuclear power stations, it comes as a bit of a surprise to learn that Finland isn’t better known as a manufacturer of Geiger Counters.
In fact there appears to have been only one of them, a company called Wallac Oy, which is now part of US-owned PerkinElmer Lifesciences.
This RD-5 is one of what I believe to be a small range of radiation monitors, produced in the 1960’s at the height of the Cold War and judging by the almost complete lack of information regarding this, and other Wallac products from the sixties, it appears that not many of them were made or it wasn’t around for very long. Either way this seems to be one of the very few to have survived, or escaped into the public domain.
It deserves to be better known, though as it was a competent and rugged instrument, designed to cover a wide range of radiological measurements, from very low-level contamination to fry-your-brains, zombifying fallout and at its heart is a Geiger Müller detection tube called the MX-142. This was manufactured by Mullard (part of the Philips group), and it is quite unusual because it is sensitive to the three main types of radioactivity, known as Alpha, Beta and Gamma. The vast majority of Geiger Counters can detect Beta and Gamma radiation, because of the energy and penetrating power of the particles and waves, but Alpha radiation, by comparison, is extremely weak. So weak, in fact, that it cannot travel more than a few centimetres through the air, and it can be blocked by a thin sheet of paper. This makes it rather difficult to detect, as it would be blocked by the metal or glass enclosure of a Geiger tube, (they are sealed and contain an exotic mixture of gasses that react to the ionising properties of radioactive particles). The solution, used on the Mullard MX-142 and most other Alpha-sensitive GM tubes is to fit a very thin window to the end of the tube, made from the mineral Mica. This still blocks some Alpha radiation, but enough of it gets through to be measured. When not in use the GM tube, which is on the end of a curly cable, stows away in a compartment on the rear of the case.
It is possible that this model came equipped with one or two extra tubes. There is a tube-sized compartment on the rear of the case and if so they were likely to be high-range types, better able to cope with high levels of radioactivity, that would otherwise swamp or saturate a sensitive tube like the MX-142. One other item of interest is the hybrid electronic circuitry. There is a pair of transistors in the low voltage portion of an oscillator circuit, used to generate the 500 or so volts needed to power the GM tube; there’s also a DL-67 sub-miniature pentode valve for the audio and meter circuits and a bank of six XC-12 85 volt voltage regulator tubes. Valves and transistors usually make poor bedfellows as they operate over widely differing voltage and temperature ranges, but this sort of arrangement was not unusual back in the early 60s, when transistors were just starting to be reliable enough to be used in safety critical devices like this, but could not, as yet, replace valves in applications involving very high voltages or currents.
Operationally it is very easy to use; there are only two controls, a rotary on/off range switch and a toggle switch for selecting the internal speaker or external headphone sockets (banana type). There is also a pair of banana sockets for an external 3VDC power supply. The unit is powered by two 1.5 volt D cells, which fit into two tubular compartments on the front of the case. The speaker is mounted beneath the angled carry handle on the top of the case. Readings are displayed on an unusual analogue meter with a 270-degree movement. The dial is illuminated by a tiny and sadly, long-deceased bulb, a type that apparently hasn’t been made for more than 30 years. It is housed in a tough all-steel case and although it’s looking a bit battered now, with a few small patches of surface rust, there is no doubt that it could survive for another 50 years.
I stumbled across this one, at a large open air antiques fair in Surrey; it was in amongst a pile of what looked like scrap metal, in a pretty sorry state and the stall holder seemed quite happy with the £5.00 that I offered for it. It was a gamble and there is only so much you can check on a Geiger Counter that clearly hasn’t been used in decades, with an old, and leaky battery stuck in the holder tube. There was also no way to check the GM tube, apart from a visual inspection of the mica window and if that had been broken or cracked my offer price would have fallen to 50 pence as they are nigh-on irreplaceable.
It looked a lot worse than it actually was and once the battery had been extracted it was clear that there was only light corrosion on the battery contacts. I didn’t dare power it up, though. Any faults on the circuit board would, like as not, have blown the delicate germanium transistors and diodes, so – and this is now routine on any early 60s gadget passing through my hands – it was treated to a new set of electrolytic capacitors and a thorough circuit check, looking for obvious shorts, open circuits and dry soldered joints. I was a little disappointed that it didn’t fire up straight away but I hadn’t taken into account the valve circuitry, which takes a few moments to get going, after which some reassuring ticks came from the speaker. The meter remained stubbornly inert, though but a quick dab of the soldering iron on a dry joint on one of the meter wires got it moving again. Not surprisingly the GM tube seems to have lost some of its youthful vigour and alpha sensitivity is mediocre but it responds well to beta and gamma sources. It is by now far beyond accurate calibration, but it works, and that’s clearly a remarkable achievement for such an ancient instrument, so hats off to the designers and manufacturers.
It was just as well that it worked, troubleshooting such an idiosyncratic circuit would be a nightmare. Fortunately there was the majority of a circuit diagram folded in the bottom of the case, though the middle part had rotted away. It was actually for an RD-7, presumably a later model, though I was able to determine that the key parts of the two circuits are almost dentical, but the missing portion will have to remain a mystery unless someone out there has an intact copy.
What Happened To It?
I have been unable to find out anything about Wallac’s activities in the 60s or the RD-5, beyond a few citations in scientific publications where it had been used to take measurements. The simple controls and rugged construction suggest that it may have been designed for the military, which might also explain why there are so few of them around today -- in fact I have never seen another one -- so if anyone can fill in the gaps I would be very pleased to hear from them.
It’s present value is impossible to gauge; the market for vintage Geiger Counters is tiny, in fact there are probably only a couple of dozen weirdos, like me, in the world, who covet them and I doubt if any of them could be persuaded to pay more than £50 for one, even if it is in fairly good shape and semi-working order…
DUSTY DATA (Manual -- partial circuit diagram)
First seen 1963 (1014)
Original Price £?
Value Today £50
Features Alpha, Beta, Gamma-sensitive mica window Mullard MX-142 Geiger Müller tube, ranges 0 – 10 & 0 - 200mr/h, internal speaker with headphone output sockets, external power socket, 2 transistors (OC72 & OC74), 1 x DL-67 sub miniature pentode valve, 6 x XC12 voltage regulators
Power req. 2 x 1.5 volt D cells
Dimensions: 245 x 150 x 100mm
Made (assembled) in: Finland
Hen's Teeth (10 rarest): 8
I am grateful to Joel Mellin, from Finland, for the following background information about Wallac.
Wallac manufactured radiation meters from the late 1950s until the 2000s, and perhaps even after that. The name and ownership of the company has changed over the years, and manufactured radiation monitoring instruments under the Alnor OY and Rados brands.
RD5, RD6 and RD7 models were produced in large quantities, for various Finnish organisations including Defence, Civil Protection, Fire Brigades, the Radiation and Nuclear Safety Authority (aka ‘STUK’), hospitals and universities, for medical use.
Technically, they are all relatively similar, although minor improvements and changes have been made to each model. Unlike successor models (e.g. Wallac RD8, and Alnor RD10), they were never sold outside Finland, which partly explains their rarity and the paucity of data in the wider world.
They occasionally come up for sale in Finland as the various organisations auctioned old stocks, and they also turn up at flea markets and yard sales etc.
Joel also provided links to Finnish websites and YouTube with more information and videos featuring Wallac instruments.
Plessey PDRM-82 Portable Dose Rate Meter, 1982
The Plessey PDRM-82 was a standard issue radiation monitor for UK military, emergency and Civil Defence services in the 1980s; rumour has it that it may still be current for some NATO forces. In theory it could actually be quite useful, provided the user is one of the lucky(?) ones still alive after a nuclear detonation... Over the years a lot of these instruments have found their way into civilian hands but they are often misleadingly described as Geiger Counters, usually with the implication that they could somehow be used in health and safety applications, detecting low to moderate levels of radioactivity. Worse still, a great many of them were sold on that basis to concerned citizens following the Fukishima nuclear power station incident in 2011, often at vastly inflated prices. The fact is, unless the user was standing within a few metres of the damaged reactor it is highly unlikely that the display would register anything. That’s because the PDRM-82 is a very high range dose meter and only capable of reading near lethal levels of radioactivity, far above anything that any normal person, outside of the nuclear industry, would ever be likely to encounter.
That said, this is actually a rather interesting device and uncharacteristic of a lot of post WW 2 military hardware, which tended to be clunky, reliant on old technology and frequently unreliable. To begin with it is surprisingly small, and in stark contrast to the big, unwieldy radioactivity detecting devices issues to troops in many other countries. Most other instruments of that era, like the classic US CD V-700,relied on analogue moving coil meter displays to show radioactive levels; this one has a large 4-digit LCD display, and remember this was the early 1980s and LCDs had only been around for a relatively short time.
There are more surprises; it uses an early microcontroller chip, to operate the display, run a self-test routine at switch on, monitor the circuitry and battery level, and compensate for the characteristics of the Geiger Muller tube detection device. This was all pretty advanced stuff back then, especially on something that was (a) expected to survive a nuclear explosion and (b) used in what would undoubtedly be a hostile and challenging environment, by largely untrained personnel. The requirement to be rugged, in this case, goes far beyond being able to endure a bit of battlefield rough and tumble; it needs to be able to withstand an EMP or Electromagnetic Pulse. This is a high intensity burst of energy, generated by nuclear weapons, which can destroy some electronic components, tens of kilometres distant from the explosion. The PDRM-82 is apparently hardened against EMP – it’s not a claim that can be easily tested; what is more certain is that the plastic case, display and battery holder are well waterproofed and designed to be easily decontaminated. As an added bonus it requires no routine maintenance or calibration, runs for up to 400 hours on a set of 3 standard C cells, and was designed to have a 20-year operational life.
The only downside to the PDRM-82, apart from the fact that it is virtually useless, is that the readout is calibrated in units of radiation dose known as ‘Grays’ (Gy). It is borderline archaic and almost no one uses Grays anymore (for the record 1 Gray is equivalent to 100 Rads, which probably still doesn’t tell you very much…). The PDRM-82 has a working range of 0-300 centigrays (1 centigray equals 1 Rad, in case you were wondering), but without knowing about such sciency things as absorbed radiation dose, dose equivalents, and the ability to relate that to more widely used units of radioactive dose and contamination, the average squaddie or civil defence volunteer would probably have been hard pressed to say how many centigrays means get the hell out of there. In fact the only real indication that things are getting a bit hairy is the display, which flashes when it reaches 300 centigrays per hour. The lack of any audible or more attention grabbing warning indicator suggests that it could be possible for an unobservant user to wander into extremely dangerous, highly contaminated areas, without knowing a thing about it.
What Happened To It?
As the stockpiles of the PDRM-82 reached the end of their operational lives they were either scrapped or sold off, usually in Government military surplus auctions and for 10 years prior to the Fukishima accident you could pick them up for a few pounds, usually unused, as new and still in their original cardboard box, along with the accompanying strap, lanyard and instructions. I have bought and sold quite of few of them over the years and was always careful to point out that they were pretty much useless, though I did once manage to get one to read close to normal background levels of radioactivity by changing the Geiger tube to a more sensitive type. It wasn’t a practical mod, though, the microcontroller took exception to the alien tube and the LCD display was meaningless. Given sufficient time and expertise I suspect it may be possible to convert and reprogram it to do something useful, but quite honestly, unless you had access to large stocks of them it simply wouldn’t be worth the effort.
PDRM-82s continue to sell on ebay for stupid amounts. I would say £10 to £20 would be a fair price for someone collecting Cold War memorabilia to pay but I have seen them go for more than £150. This is almost always due to the seller suggesting it is a practical radiation measuring instrument. Sometimes it is a genuine mistake and due to lack of knowledge, but I suspect that more often than not the seller knows full well its capabilities and is just trying to make a fast and dishonest buck. This also suggests that there may be a lot of people out there checking the readouts on their PDRM-82s every time they hear of a nuclear accident or spill somewhere in the world. On the plus side, they are never going to be unduly alarmed as it is probably always going to read zero...
First seen 1982
Original Price £250
Value Today £20
Features High dose survey meter, halogen quenched Geiger Muller tube detector, 4-digit LCD display, detection range 0-300 centigrays/hour (cGy/h) in 0.1 cGylh increments, +/-20% accuracy display flash at 300 cGy/h, self test.
Power req. 3 x 1.5v C cells
Dimensions: 170 x 140 x 55mm
Made (assembled) in: England (Poole, Doset)
Hen's Teeth (10 rarest): 5
Kvarts DRSB-01 Radiation Monitor, 1988
Strictly speaking the manufacturing date for the Kvarts DRSB-01 pocket radiation monitor is mid 1992, however, this one is the later Mk 2 version, and the Mk1 (on the left in the picture below), was where it all began, a couple of years after the terrible Chernobyl nuclear reactor accident in April 1986. That’s enough of the history lesson, suffice it to say this is just one of several personal radiation monitors manufactured in the former USSR, in response to widespread public concern over radioactive contamination.
Technically it is fairly unsophisticated, basically just a ‘ticker’ -- as they came to be known -- and that’s pretty much all it does in response to a source of radioactivity. It is definitely not a Geiger Counter, as they were frequently and misleadingly described, for the simple reason that it doesn’t count anything. In fact there are no displays, just a pair of LEDs. The green one, marked ФОН indicates normal background radiation with the occasional flash (and accompanying tick), whilst the red one, labelled ВНИМАНИЕ means ‘Attention’ and when you see that light up, you know it’s time to get the hell away from whatever is making it flash and tick!
Radioactivity is detected by a Russian-made SBM20 Geiger Müller tube – they’re the brass-coloured cylinders in the photograph. In the world of radiation monitoring this is a bit of a classic, noted for being small, remarkably sensitive and, at one time, incredibly cheap. A lot of them have been made over the years and they are still being used in many modern radiation detecting instruments. The SBM20 is sensitive to the two most hazardous forms of radioactivity: Gamma, which is the nasty and most dangerous sort, and Beta, which is a lot less damaging, though you still wouldn’t want to keep a source of it in your underpants…
You may have noticed that the Mk1 version has two SBM-20 tubes, and this made it very sensitive, possibly to the point where it was producing too many false alerts, or it was just a cost-saving measure, either way the Mk 2 only has one tube and it is unlikely that most users would have noticed, but it was a great shame for the small band of Geiger Counter enthusiasts in the west.
During the mid 1990s a great many surplus DRSB-01’s were being sold across Europe and the US, often for just a few pounds; the first ones I bought cost less than £10 each. Most of those sold in the early days were the twin-tube Mk1 version and they were bought in considerable numbers, by experimenters and even some companies, essentially for the SBM-20 tubes. Apart from their high sensitivity and military grade build quality they cost a fraction of the price of Geiger tubes made in the west, which tended to be less sensitive, needed more elaborate circuitry and in many cases were encapsulated in glass, which made them extremely fragile.
Back now to the DRSB-01, and as you may be able to see from the internal photograph, there’s not much to see. The plastic case is simply and cheaply made and it is powered by a pair of AA cells, which can last for several weeks. The lower half of the circuit board is responsible for generating the 300 or so volts needed to power the GM tube (the black cylindrical component in the bottom right hand corner is a ‘toroidial’ high voltage transformer); the upper half is concerned with detecting pulses from the tube, driving the two LEDs and generating the ticks from a piezo sounder. It is a characteristically messy design, with loose wires and tacked on components – typical of state-owned Soviet factories in the 80s and 90s – but it works, and they were surprisingly reliable.
What Happened To It?
There’s not a lot of information available on the Kvarts factory, prior to the breakup of the Soviet Union, but I am fairly certain that they were involved in the manufacture of military equipment; later they went on to become a leading maker of scientific instruments; their present status is unknown. The DRSB-01 appears to have been in production until at least 1995, by which time it was it had become rather dated and despite a facelift, with those snazzy yellow and orange stripes on the front panel (the Mk1 has a very plain appearance) consumer demand had long since tailed off.
I bought a fair few DRSB-01s and other Russian made instruments, like the DRSB-88, DRSB-90 and Biri-1 during the late 90s and early noughties. Prices were incredibly low to begin with and I resold a few of them on ebay at a small profit for £20 to £25 but as stocks started to run out Russian suppliers put up their prices and they virtually disappeared from view, until the Fukishima accident. Quite a few turned up on ebay, presumably from old Soviet stockpiles, often for ridiculous amounts of money and I remember several being snapped up for more than £100 but supplies ran out very quickly and in the last few years they have become quite rare.
It is difficult to say what sort of money they might fetch nowadays, though one thing is certain, it is nothing like those mad post Fukishima prices. No one would seriously consider using one as a radiation monitor but they could have a certain novelty value and might appeal to collectors of Soviet era technology. If nothing else they are worth at least as much as the SBM-20 tubes they contain (currently around £10 - £15 apiece), so the Mk 1 version is the more desirable, and providing it is in good working order £10 - 30 might be a reasonable price
First seen 1988
Original Price £?
Value Today £10 - £100
Features Hard Beta/Gamma sensitive SBM-20 Geiger Müller detection, built in sounder. Dual LED display (‘Background’ and ‘Attention’), on/off switch
Power req. 2 x 1.5v AA cells
Dimensions: 150 x 65 x 23mm
Made (assembled) in: Former USSR
Hen's Teeth (10 rarest): 7
Kvarts DRSB-90 Geiger Counter, 1988
Following in the wake of the Chernobyl nuclear reactor accident in 1986 Soviet factories previously engaged in churning out military kit and scientific instruments quickly adapted to manufacturing vast numbers of cheap and simple to use radiation monitors. One of the most prolific was Kvarts, a Ukrainian enterprise the developed a series of innovative, sensitive and surprisingly robust personal Geiger Counters and dosimeters. Public concern eventually abated and large stocks of these instruments began to build up. After the collapse of the Soviet Union and growth in foreign trade, a small but steady stream of Russian Geiger Counters started to find their way to the west.
Most of these instruments were fairly basic and in truth only capable of alerting the user to dangerously high levels of radioactivity. This meant that that they were of little practical value though they had a certain novelty appeal and would occasionally click and tick in response to natural background radiation, but there were exceptions. This is one of them; it’s the DRSB-90 and it is a true Geiger Counter in that it uses a Geiger Müller tube for detecting beta and gamma radiation, and a circuit that ‘counts’ the clicks and displays the result on an analogue moving-coil meter.
Thanks to its SBM-20 Geiger tube it is actually quite sensitive and readily responds to low level sources, including naturally radioactive minerals like granite (you would be surprised how lively some roadside kerbstones can be…), as well as other everyday objects, like old (pre mid 50s) clocks, watches and compasses with luminous, radium-painted hands and dials, antique ceramics (Red Fiestaware) and glass (Vaseline, Depression, Uranium), doped with Uranium to give it a characteristic lustre in sunlight. It also surprises a lot of people that salt substitute (Lo-Salt, Nu Salt etc), contains small but detectable amounts of radioactive Potassium K40.
Operation is relatively straightforward, once you have figured out the control labelling, which is in Russian. One of the exporters supplied sticky labels, with the functions translated into English, but it was always a bit of a turn-off for some users. For the record there are three slide switches; the large one is for power on/off and battery check – shown on the meter. Next to that is a two position range switch (x1 or x10), and below that a slide switch for muting the built in piezo sounder, which ‘chirrups’ with each detected event, and emits a continuous tone when the alarm threshold is exceeded. There are also two buttons, one for a small light to illuminate the meter at night and the other is for ‘dumping’ or zeroing the meter. The latter is because it uses a simple ‘integrating’ counter circuit that displays an accumulated reading over a period of around one minute. If the source of radioactivity is removed the meter needle falls only very slowly, so it is necessary to press the dump button before a new reading can be taken. It is powered by three AA cells and these can last upwards of 200 hours with continuous use.
The meter is also labelled in Russian but it is reasonably easy to figure out. The top scale is in microsieverts per hour (0 – 3), whilst the lower one shows microroentgens per hour (0 – 300), both of which are widely used and readily understood international units of radioactivity and radiation dose. Comparisons with a modern instrument, using a calibrated check source, shows that the DRSB-90 remains reasonably accurate, and still perfectly capable of warning the user to step smartly away from whatever is making it chirp…
Build quality is unsophisticated but it is pretty robust and typical of what was coming out of Russian factories at the time. There are some nice old fashioned touches, like the neatly tie-bundled wiring loom, and moisture proofing around the high voltage components is taken care of by the old Russian trick of coating everything in a thick layer of goopy wax; don’t mock, it works! Over the years I have bought and sold several dozen DRSB-90s and still get the occasional enquiry but I will be hanging on to this, my last remaining sample, which still works perfectly.
What Happened To It?
When they first became available in the late eighties, the DRSB-90 was at the high end of the price range for Russian radiation monitors. They typically sold for £20 - £25, which wasn’t a lot, even then, for what is still a relatively sophisticated instrument. The problem was you could pick up cheap and cheerful ‘clickers’, like the DRSB-88 for around a fiver, and with no immediate threat from radioactive fallout, it was no contest. They probably didn’t sell in very large numbers and the Russian labelling on the controls and rather old-fashioned design didn’t help. As supplies dried up the prices rose a little but eventually they disappeared, apart from the occasional sighting on ebay during the nineties and early noughties, where they would typically go for £40 - £50. For the past few years, since the Fukishima accident in fact, prices have soared and the last time I saw one on ebay it fetched almost £200! It’s clearly not a frontline collectible but should one ever cross your path, it still works and the price is the right side of stupid, I would grab it, because you never know when another radioactive incident is going to send prices spiralling…
DUSTY DATA (Manual)
First seen 1989
Original Price £25
Value Today £80
Features SBM-20 GM tube (hard beta/gamma sensitive). 2 x LED display (orange ‘event’, red alarm), audible bleep/alarm, 12-transistors, 1 x colortron voltage regulator, moving coil meter, power on/off/batt test, range switch (x1/x10), meter backlight, audio mute, meter ‘dump’,
Power req. 3 x 1.5v AA cell
Dimensions: 147 x 70 x 30mm
Made (assembled) in: USSR
Hen's Teeth (10 rarest): 6
Kvarts DRSB-88 Radiation Monitor, 1989
This little device would have been familiar to anyone living in what used to be the Soviet Union towards the end of the 1980s and early 90s. It’s a pocket radiation monitor and hundreds of thousands, possibly millions of them, were produced, and sold or distributed to Russian citizens in the wake of the Chernobyl disaster in 1986.
The threat of radioactive fallout from Chernobyl accident produced considerable public alarm and it was hoped that cheap and simple instruments like this would give the public some reassurance that they weren’t about to be exposed to dangerous radioactive contamination. As it turned out it wouldn’t have done users much good, unless they were living uncomfortably close to the exclusion zone. This was due to it’s tiny Geiger Muller tube detector, which isn’t very sensitive and almost certainly incapable of detecting emissions from fallout further than a few tens of kilometres from the stricken nuclear plant.
Nevertheless, it was, and still is a working radiation monitor and will register relatively low-level sources when held against the detection window on the side of the case. These include things like old watches and clocks that have luminous radium painted hands and dials, ‘lively’ minerals and old thorium doped gas mantles.
It is very easy to use, just pop in a single AA cell, which can last anything up to two weeks, and switch it on. When the GM tube detects a source of ‘hard’ beta or gamma radiation the red light on the top flashes and a tiny built in speaker emits a characteristic click. The electronic circuit inside the case use a bizarre mixture of components and crude construction techniques, but that was hardly surprising with a selling price of only £5.00 or so. The circuit has just three transistors; one is used in conjunction with a toroidial transformer and a simple voltage multiplier (daisy-chained capacitors and diodes) to generate the 400 volts needed to power the tube, and the other two are responsible for amplifying the click and blinking the light on the top. The latter is an especially weird component, and as best I can make out, a cross between a neon bulb and a corona type voltage regulator tube. But it works, which is what matters, and that is in spite it apparently being assembled in a tractor factory – which it probably was -- with no detectable quality control procedures.
The DRSB-88 was one of several models produced by Kvarts, which, prior to Chernobyl was mostly involved in manufacturing scientific instruments and radiation monitors for the Soviet military It’s a very far cry from the standard of construction of products then coming out of Hong Kong and Japan. For example, the way the designers got around the problem of keeping moisture out of the way of high voltage components clearly betray it semi-agricultural Soviet origins. On a similar western or far eastern product the first line of defence against water getting into the works would be to put it inside a water resistant case. The Kvarts solution, which is elegantly simple and works brilliantly, is to coat the whole thing in goopy wax. It’s very effective, and only becomes a problem if anything goes wrong as the thick wax makes it nigh on impossible to repair.
What Happened To It?
Sadly the supply of ultra cheap DRSB-88s eventually dried up and by the early noughties the few that were still around were selling for between £30 and £50 on ebay. By the time of the Fukishima disaster, in 2011, the price of all radiation monitors had shot through the roof and on the odd occasion that a DRSB-88 appeared on ebay it would fetch £100 or more. Things have calmed down a lot since then and Geiger Counter prices have come down. Second hand DRSB-88s come up for sale every so often but they are almost always non-working. It’s not the sort of thing collectors of vintage electronics are likely ever to be interested in, nor does it stack up well against more recent radiation monitors, but it could be in great demand once again, if there is ever another nuclear accident, though if you do have one, I wouldn’t rely on it too heavily to keep you out of danger…
First seen 1989
Original Price £5
Value Today £30?
Features Hard Beta/Gamma sensitive SBM-10 Geiger tube,, audible and visual indicators, on/off switch
Power req. 1 x 1.5v AA cell
Dimensions: 133 x 36 x 28mm
Made (assembled) in: Former USSR
Hen's Teeth (10 rarest): 7
Biri-1 Keychain Radiation Monitor, 1987
On April 27th 1986, my wife Jane and I were in the USSR, as was, preparing to return to the UK from a short trip. It was an exciting time to be in the country and a real sense of change was in the air. Reforms made by Mikhail Gorbachev were starting to have an impact on the tightly controlled Soviet state and media, though to a visitor, it still felt very isolated. What news there was tended to be bland and highly filtered so we didn’t pay much attention to vague reports of an industrial accident the previous day, somewhere in the Ukraine. It wasn’t until we returned to Gatwick the following morning, and upon landing our plane was directed to a remote corner of the airport for quarantine and the possibility of radioactive decontamination, that we learned what had happened…
Everything changed following the Chernobyl disaster. Nuclear power’s mostly benign image was tarnished forever and the lack of information meant it was a fearful time for the Soviet people and those caught up in the accident, which brings us to the Biri-1 keychain dosimeter. It was one of a number of personal radiation detectors produced in the USSR in the wake of Chernobyl and sold to concerned citizens. They were made in large numbers, mostly by state-owned factories involved in manufacturing monitoring equipment for the military.
The Biri-1 is no larger than a slim box of matches and for its size it is surprisingly sensitive. The radiation sensor is a tiny SBM-10 Geiger Müller tube just 28mm long, able to detect both beta and gamma radioactivity. The tube is powered by a simple high voltage circuit that produces a charge of 400 volts; when a radioactive particle or ray enters the tube it ionises a mixture of gasses, generating a tiny pulse that is amplified and processed to flash a red LED on the top and a chirrup like sound that merges to a constant squeal when the radiation level rises to potentially hazardous levels. It is a really clever design; the high voltage circuit ‘pumps’ the Geiger tube to constantly top-up the charge, and this is used to create a regular low-level ‘tick’ that indicates that the device is working. The high voltage transformer doubles up as an audio transducer and a small metal plate, attached to it by a screw, acts as a baffle to amplify the sounds.
Build quality is a typical of Soviet era gadgets. Outwardly it appears fairly crude – compared with slick Japanese made devices of the period. The on-off switch on the rear is a particularly poor design and prone to failure, and the high voltage areas of the circuit board are coated in a wax-like substance, which provides protection against the ingress of moisture and stops the components moving around, but apart from the switch, it still works well after more than 30 years. The other shortcoming is the batteries; it comes with a pair of rechargeable button cells, which have a tendency to leak after a few years, but the biggest problem is the mains charger. This is a dreadful design and in addition to having a badly fitting battery cover and terminals that corrode easily, it gets really hot, falls apart easily and is potentially lethal. Fortunately there is a near equivalent alkaline cell (LR9) that fits snugly into the Biri’s battery holder and can keep it powered continuously for a week or more.
What Happened To It?
I first came across the Biri-1 in the late 1990s when surplus stocks were being sold by a Russian entrepreneur for around $20 each. Over the next few years I bought a number of them and they proved to be very reliable. Gradually the supply dried up and they disappeared from view, though recently a US company had a few NOS (new old stock) Biri-2s for around $40. These were basically the same as the Biri –1 but with modified case cosmetics, though sadly these now seem to have run out but they do still turn up occasionally on ebay.
Following in the wake of the Fukishima accident quite a few companies have been knocking out personal radiation detectors and it has to be said most of them are over-priced rubbish and virtually useless for meaningful monitoring of the very low levels of radiation they are supposed to warn against. This old Biri-1 wipes the floor with many of them and at close quarters responds to relatively weak sources, such as uranium doped Vaseline glass, the radium-pained luminous watch and clock hands and dials that were common before they were banned in the 1950s and even the naturally occurring uranium in granite kerbstones is enough to get a few chirrups.
As a radiation safety device it is of questionable value but it is certainly a conversation piece and a handy thing to have about your person if you are into urban prospecting, rock hunting or antique collecting. Just keep it well away from anyone undergoing radiotherapy investigation or treatment, it will scare the pants off you both…
DUSTY DATA (Manual)
First seen 1987
Original Price £?
Value Today £40
Features SBM-10 Geiger Müller tube, audible clicker/alarm, LED indicator
Power req. 2 x A-06A rechargeable cells (western alkaline equivalent LR9)
Dimensions: 65 x 35 x 12mm
Made in: USSR
Hen's Teeth (10 rarest): 7
Here’s a truly weird, wonderful and rather appropriate gadget from the late 1970s with some bizarre contemporary connections. It’s an anti-static brush, used to de-dustify things like vinyl records and photographic film.
So far so ordinary, but there’s a few things about the Staticmaster that makes it rather interesting. Firstly it’s radioactive, that’s right, if you look closely, just behind the bristles you can see a small grating with some brown material deposited on the surface.
This is the radioactive element and it creates a ‘field’ of ionised particles up to an inch or two ahead of the bristles and this has the effect of neutralising the static charge that makes dust stick to surfaces.
Here’s the second surprise, the radioactive material used in the brush is none other than Polonium 210, the same stuff used in the recent horrific poisoning incident that resulted in the death of the Russian ex-KGB agent Alexander Litvinenko.
Polonium 210 emits alpha particles. These are very weak and cannot penetrate skin so they are relatively ‘safe’ in the contained environment of the brush head. It is also significant that Polonium 210 has a half life of 139 days, which basically means that virtually all of the radioactivity disappears within a couple of years of manufacture, as the polonium turns into an inert isotope of lead, so these old brushes are now completely harmless.
The alpha particles emitted by Polonium 210 become dangerous when ingested into the body in liquid form or in very fine particles in quite significant qualities so before you ask, you would need a great many brushes, some pretty sophisticated equipment and very specialised knowledge to create anything dodgy from them.
What Happened to It?
Here’s another surprise, they’re still being made, and this is the only legal way you can obtain Polonium 210. The brush shown here was made in 1978 by a US company called Nuclear Products. Nowadays they are manufactured, along with a wide range of industrial and consumer anti-static products by Amstat Industries.
First seen: 1965
Original Price £8.00
Value Today? £2
Radioactive anti-static brush
Dimensions: 125 x 30 x 20 mm
Made in: USA
Hen’s Teeth (10 rarest): 1
P.H. Ltd Spinthariscope, 1970?
This rather disreputable looking object is definitely not something you see every day. It’s a Spinthariscope, and the idea is you look through the eyepiece and watch atoms splitting, really!
The Spinthariscope was invented back in 1903, by William Crookes and for most of the past 100 years they have been regarded as interesting novelties and educational toys. This one, which I believe dates from the late 60’s was designed for use in schools, which explains its rather battered appearance. The reason you don’t see them very often is because inside there’s a speck of radioactive material, 0.02 micrograms of Radium to be precise.
It all sounds a bit scary but the fact is, the Radium source is miniscule, less radioactive than the sensors in most household smoke detectors, and a magnitude less than old watches and clocks with luminous hands but anything labelled as radioactive these days worries a lot of people… See my anythingradioactive site for a basic guide to radioactivity and – shameless plug – lots of cheap Geiger counters and nuclear novelties.
The Radium source shoots out alpha particles, and if you know anything about radioactivity you’ll know these are the weakest sort, barely able to penetrate a sheet of paper (though you certainly wouldn't want a lof of them inside your body...), but the point is none can escape from the cannister.
Inside the tiny piece of Radium is mounted on a small spike in the middle and beneath it there’s a coating of a chemical that almost certainly includes Zinc Sulphide. This has a very interesting property. When it is struck by an alpha particle it emits a brief flash of light, and this is what you see when you look through the eyepiece.
You have to use it in total darkness, and you need to allow at least five minutes to let your eyes adjust, but it’s worth the wait and you’ll see hundreds of flashes each minute as atoms disintegrate and smash into each other.
What Happened To It?
Spintariscopes have rather gone out of fashion thanks largely to misinformed attitudes towards radioactivity and the inevitable health and safety concerns. Nevertheless, at least one company in the US is still making them, but does not export them outside the US (even though you would need tens of thousands of them to make a small 'dirty' bomb).
This one isn’t that special, it turned up in a box of lab equipment bought at a boot sale a couple of years ago and the whole lot only cost me £5.00. However, good ones are most defintiely collector's items. Original ornate wood and brass Crookes ‘pattern’ Spinthariscopes, dating from the 1920s and 30s, are worth a small fortune and I have seen them selling on ebay to collectors for several hundred pounds.
First seen: 1903
Original Price £?
Value Today? £25
Features: Eyepiece with magnifying lens, 0.02ug Radium source
Power req. n/a
Dimensions: 68 x 60mm
Made in: England
Hen’s Teeth (10 rarest): 8
Kodak Pony 135 Model C, 1958
You may be wondering what this rather ordinary-looking 1950’s 35mm film camera is doing here. It is not an especially interesting or unusual design and there are no obvious features that warrant more than a passing mention. It wasn’t ahead of its time in any particular respect and as far as I am aware the pictures it took were not that different in quality to those shot on scores of similarly specified models from the same era, but there is one thing that sets it apart, certainly from most other still cameras, and that’s the lens. This camera is fitted with a 3-element Kodak Anaston lens with a focal length of 44mm; so far so ordinary, but the key point is that it is made using Thoriated glass, which means that it is mildly radioactive. In fact it is actually quite ‘lively’ and the alpha, beta and gamma radioactivity it emits is easily detected, even by modestly specified radiation monitoring instruments, but more on that in a moment.
Kodak’s Pony range was mainly aimed at amateur photographers; it’s an intermediate model, sitting between basic point and shoot cameras, like the classic Kodak ‘Brownies’, and more advanced and capable pro and semi-pro designs. The first Pony’s appeared in the late 1940s but this one, the Model C dates from the mid to late 50s. It’s a tough little camera, with a brown Bakelite body, good quality mechanics and optics. It uses 135 film cassettes, which was the Kodak designation for 35mm film; this is loaded into a compartment on the rear of the camera and manually threaded onto a take-up reel. The film is advanced, one frame at a time by turning the large knob on the right side of the top panel (looking at it from the rear), and when the roll has been exposed, it is wound back into the cartridge by the big knob on the left.
There are no fancy-schmancy meters or automatic controls, just a decent assortment of manual exposure options. The flash synchronised shutter is manually cocked and the speed can be adjusted between 1/25th and 1/300th of a second in 4 steps. There is also a ‘B’ or Bulb setting, where the shutter stays open for as long as the shutter button is pressed. (Bulb is a reference to the early days of photography when camera shutters were operated pneumatically, by pressing a rubber bulb). The iris or aperture range is from f/3.5 to f/22, in 7 steps, and to make things really easy it can be set by the numbers, or according to the conditions (Bright, Hazy, Cloudy, Cloudy-Bright), calibrated for Kodak’s black and white (Ektachrome) and colour (Kodachrome) films. The focussing ring on the front of the lens barrel is calibrated for distances of between 25 feet to infinity. The shutter’s manual cocking lever is on the side of the lens barrel and just below that there’s a bayonet connector for a flashgun.
Back now to that scary-sounding lens, and the reason it is radioactive is simple. Mixing glass with the radioactive element Thorium (actually Thorium Oxide), up to 30 percent by weight, does several useful things, including increasing the glass’s refractive index. This means that lenses can be made thinner (which also helps reduces the cost). It also reduces chromatic aberrations in the glass, which causes objects to have coloured fringes, due to differences in the way glass focuses different colours. Over the years other radioactive elements have also been used in lenses, including Lanthanum, but it is not as cheap, effective (or radioactive).
In its pure state Thorium is only weakly radioactive and emits mostly Alpha particles, and on the scale of nastiness this is considered the least harmful type, outside of the body at any rate. Alpha radiation has very little penetrating power – particles can be stopped by a sheet of paper and do not pass through skin – so on the face of it, its inclusion in glass lenses doesn’t seem especially controversial. However, as Thorium decays it creates Beta and Gamma radiation (weirdly, the production of decay products means that the radioactivity increases over time, which is the opposite of what you would expect). Beta and Gamma has more penetrating power than Alpha radiation and it can cause problems, especially when there’s enough of it, in close proximity to living tissue. Fortunately the amounts of radioactivity given off by these and similar lenses is not generally regarded as hazardous, under normal circumstances and with normal use. However, radiation is tricky and highly contentious stuff so play safe and on no account put a bag full of Thorium-doped lenses in your trouser pockets… Joking aside, if this is something you are concerned about the clever thing to do is read up on the subject, and if you want to check if the cameras in your collection, or plan on buying, have radioactive lenses do your homework – there is plenty of information online -- and it could be worth your while getting hold of a Geiger Counter (sorry for the shameless plug).
My little Pony came from ebay a good few years ago and as far as I recall it cost a couple of pounds. It is still in great condition and I have no doubts that it is still capable of taking photographs. I actually sought this model out, as a radioactive test source, after acquiring one of my first Geiger Counters. It proved to be very effective, though it needs to be in close physical contact with most instruments to get any sort of reading, and it doesn’t register anything when held a few centimetres away.
What Happened To It?
Kodak’s Pony series ran from 1949 to around 1962 and throughout that period most models were fitted with either an Anaston or the higher quality 4-element Anastar lenses, and almost all of them used Thoriated glass. By the time it was being phased out Kodak had introduced the first of its pioneering Instamatic cameras, which at the time was arguably one of the biggest advances in photography for 50 years. Kodak obviously didn’t abandon the 35mm format but it gradually evolved into a serious amateur and semi pro format, with Instamatic and Instant cameras rapidly taking over the mass market. It is not known how many Pony cameras were made but you can take it as read that it was a heluva lot. They are really well made, and usually come with a protective leather case so there are still plenty of them around. They’re flea market and car boot sale regulars and because they look so ordinary, tend not to attract much attention and typically sell anywhere from 50 pence to £5.00, sometimes more if they’re in tip-top condition, boxed and come with instructions. Pony cameras are not yet serious collectibles but inevitably prices will only increase so now is as good a time as any to add one to your collection and whilst it is not much to look at, it does have an interesting story to tell. By the way, although there are no significant health hazards associated with this and other cameras with radioactive lenses if you have one then it is prudent not to let children play with it and it’s a good idea to store it safely, preferably in a metal box.
First seen 1955
Original Price £22 ($34)
Value Today £10 (0315)
Features 35mm format, Thorium doped Kodak Anaston lens: 44mm, shutter: B, 1/25, 1/50, 1/100, 1/300th sec, aperture: f/3.5, 4, 5.6, 8, 11, 16, 22, presets Ektachrome/Kodachrome Bright/Hazy/Cloudy/Cloudy Bright, shutter sync, optical viewfinder, film advance interlock (to prevent double exposures)
Power req. n/a
Dimensions: 140x 65 x 85mm
Made (assembled) in: Rochester, USA
Hen's Teeth (10 rarest): 5
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