DP-5V (ДП-5B) Soviet military roentgenometer   Leave a comment

I’m republishing this old post in English, thanks to the outstanding help of my friend Mary Jo Barber, who kindly translated it for me. She is a professional translator, so she can deal with all kind of texts from Spanish to English, even the freakiest ones as you can see 🙂 So if you need anything properly translated, don’t doubt it, you have the link above to contact her. Thanks a lot Mary Jo!!

> Original post in Spanish <

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The DP-5V may be considered the little brother of the DP-3, featured in the previous entry…

Unidad DP-5V

Roentgenometer DP-5V

… although only because both belong to the same family (DP) and because the 5V is not as old as the 3. Apart from that, they are quite different.

To begin with, the DP-5V is actually a Geiger counter: it uses two GM tubes to detect beta and gamma radiation. This makes it much more accurate and sensitive than the DP-3 with its ion chamber system. As it is much more sensitive, it can measure very faint levels of naturally-occurring environmental radioactivity. The probe on the 5V is shorter and more manageable and it features a glass window to allow beta radiation through to be measured. I understand that the DP-3 could not do this, as there is no opening on its metal cover and it seems solid and thick enough to stop beta particles (apart from the fact that it would have been installed inside a vehicle, so they would have been blocked by the bodywork anyway), although I can’t be totally sure.

Another major difference is that the DP-5V was conceived for personal use, not as part of the equipment of a vehicle. It is portable and runs on batteries, although these are a bit special, as we will see below. It is lighter and its casing is plastic, though it feels solid and resistant.

Apart from that, the 5V and other 5-series models appear to be relatively common and well known to Geiger counter enthusiasts and military collectors in general. There is far more information available about it on the internet than there is about the DP-3, there are units for sale on eBay and at military surplus shops, and there are all kinds of videos about it on YouTube.

These appliances were in use throughout the 1980s (mine is dated 1981), so they must have had plenty to do back in 1986. I found out about them from this entry on the fantastic La Pizarra de Yuri blog, which also contains information about how to get hold of one. I couldn’t resist the temptation and two or three weeks later I had one in my house, all the way from Ukraine. The complete kit comes in a wooden box with metal trim, painted army green, and contains everything (except the batteries) so you can start measuring the radioactivity behind the toilet or issuing from your WiFi router and put your mind to rest 🙂

Kit DP-5V completo

DP-5V full kit

  • The DP-5V unit, with probe, in an imitation-leather carrying case with adjustable straps.
  • An electricity adaptor with 10 metres of cable; this fits into the battery compartment, allowing the DP-5V to be connected to a 12 or 24 volt battery.
  • A telescopic metal rod, which fits over the probe for measuring at ground level or other hard-to-reach places (under vehicles, culverts, etc.).
  • Some really cool headphones 🙂 to listen to the clicks made when the counter detects radioactive particles. As well as being really cool, they are also very handy, as they allow the operator to detect sources of radiation without having to keep looking at the dial, which can be quite complicated when you are moving around.
  • A plastic bag containing a pair of lamps (used to light up the dial if necessary, activated by a switch) and a spare rubber seal.
  • A set of transparent plastic sleeves that can be slipped over the probe to protect it from dirt when in use.
  • A screwdriver.
  • A user’s manual, in perfect Russian.
  • A sheet used to log the use of the appliance. According to this, my unit was never in use in Pripyat. Damn 😛 Actually, it appears never to have been used, as the only entries refer to routine revisions and calibrations, performed every five years up to 1995. Ok, so this counter may not have led a very exciting life, but on the other hand it looks new and seems to work perfectly 😀
  • Three little fabric bags which at first I thought would contain spare parts, but which turn out to be the Soviet equivalent of the little silicon sachets used to absorb humidity and keep things dry.

And how do we know that it works and that it actually measures radioactivity? We’d need a strong source of radiation of known strength, but you can’t get cobalt 60 on eBay and it’s not a very good idea to have it in the house 😉 Luckily, one of the funny things about the DP-5 is that it comes with its own source of strontium yttrium radioactivity (pure beta, specifically), that we can use to check that it is at least measuring, instead of just clicking randomly and lighting up a couple of bulbs when the button is pressed.

This source of radiation is isolated underneath the metallic casing of the probe (being beta radiation, it cannot penetrate through this thickness of metal) and it is quite faint, so it wouldn’t be a danger even if it were exposed. However, the appliance is sensitive enough to measure it easily enough and transmit through the earphones the furious crackling that we could expect to hear if we ever found a bit of the one of the bombs that fell on Palomares 🙂 When the covering of the probe is turned to a certain position, the source lines up with the glass window, and the needle on the dial moves to 1.5, more or less, if the selector knob is turned to position x10.

Midiendo la radiación de la muestra incorporada

Measuring the radioactivity of the sample

But before doing all this, first we obviously have to connect the counter to some form of electricity supply. Globalisation hadn’t yet arrived and the Soviet engineers who designed the DP-5V never thought of letting it operate using AA batteries from a Walkman, so we need at least three A336 batteries, the type used by the Reds back then and now impossible to find.

One option is to use the 12V supply from a PC, like we did with the DP-3, using the built-in adaptor, but that won’t take you very far, no more than 10 metres to be precise – not much use when your intention is to travel the wide world looking for things to set it off 🙂

We’re in luck, however: A336 batteries are 1.5V, just like our normal batteries, so the only difference is in the size, and adapting AA batteries to the DP-5V is much easier than you could imagine. There are thousands of ways of doing it: I chose bits of hosepipe and tinfoil.

Adaptando pilas AA a tamaño A336

Adapting AA batteries to A336 size

Hosepipe gives us the right length to fit the batteries in lengthways as well as the right width to ensure that they stay in place and don’t roll around in the battery compartment. You need to ensure that the set-up isn’t too tight, so that the cover isn’t distorted when you screw it on. If this happens, it is easy enough to shave off some of the plastic using a box cutter.

I used tinfoil to fill the gap between the negative terminal and the corresponding contact. Not very pretty, I know, but it works. You could also melt some tin in a mould to the right shape and size.

Colocando las baterías

Fitting the batteries. 

So… ready to go! After checking the contacts and that the gauge turns on and does what it is supposed to do, lights checked, headphones one, pack on shoulder and probe in hand, it is now time to go outside and find an interesting exclusive or public health threat. Naturally, I thought of the CIEMAT and went down for a mosey around but, unfortunately :), it’s as clean as a whistle.

However, you might not be too happy about going around with a clunky Cold War device looking like an antisocial uber-nerd or loony conspiracy theorist missing his tinfoil hat, or both. People will probably think it’s a metal detector, but to avoid funny looks you could undertake this simple and very cool mod (warning, the “sound track” on the video is a bit high and, to my taste, horrible):

Adaptador de auriculares

Earphone adaptor

So now, instead of frightening people, you now look like a normal citizen listening to music. All you need is a cross strap and a simple adaptor to let you use plain ordinary earphones. I made one by taking the female connector from a broken pair of earphones with a volume control on the wire, and the metal terminals on the end that goes into the DP-5V are of the Molex type, taken from the internal connectors of a PC. If they are a bit loose (the diameter is smaller), you can get them to stay in place by bending the two small metal fins outwards using a small screwdriver or a toothpick.

DP-5V con auriculares

DP-5V with earphones

The following table shows the different sensitivity levels and their measuring ranges, chosen using the knob on the front of the appliance.

Level Knob position Dial scale Unit of measurement Range
1 200 0-200 R/h R/h 5 – 200 R/h
2 x1000 0 – 5 mR/h mR/h 500 – 5000 mR/h
3 x100 0 – 5 mR/h mR/h 50 – 500 mR/h
4 x10 0 – 5 mR/h mR/h 0.5 – 5 mR/h
5 x1 0 – 5 mR/h mR/h 0.5 – 5 mR/h
6 x0.1 0 – 5 mR/h mR/h 0.05 – 0.5 mR/h

The dial measures in two scales, roentgen per hour and miliroentgen perhour. Roentgens are used only Level 1; at all other levels the mR scale is used. The reading is then multiplied by the number indicated on the knob position.

A very attractive and totally functional device, and one we hope we never have to use except out of pure curiosity, amateur interest or as an excuse to visit interesting spots 🙂

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Publicado 20 junio, 2015 por bravido en Cold War, Collecting, Militaria, Nuclear, Uncategorized

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