Ok, this one was on my to-do list for a very long period of time. Today I’ll show you the most radioactive Geiger counter the world has ever seen. Let’s take a closer look at the DP-63-A.
The DP-63-A is a high range Geiger counter designed to detect contamination after a nuclear attack or an accident. It has two measuring ranges, 1.5 R/h and 50 R/h. The 1.5 R/h range uses the upper scale and 50 R/h range uses the bottom scale. In order to take a measurement, we must hold the 1.5 R/h or 50 R/h button that is located on the right side. Holding both buttons at the same time will result in a circuit test. This unit is equipped with 2x Geiger Muller tubes, one for the lower range and the other for the higher. DP-63-A also has a beta window which allows measuring beta+gamma or gamma only. Since these are high range Geiger counters, I don’t think there are very practical, unless you are planning on going inside of CNPP reactor 4.
These units were produced during the Cold war from 1958 until the 1970s. What makes them really interesting is the fact that the models produced from 1958 to 1966 used radium (Ra-226) paint on the scale. This was done in order to make the scale glow in the dark environment, however, it also resulted in the meter itself being extremely radioactive. Today the scale doesn’t glow at all even when light-up using a black light.
It seems that there are two versions of the radioactive DP-63-A. The early models had little bit more radium paint on them making them “hotter”. Few years after the production has started, the amount of radium paint was reduced in order to make the DP-63-As “safer” but they were still stupidly radioactive! These two versions can be easily told apart. The “hotter” units have a year of production written on the front panel, while the less radioactive ones have only the serial number. My unit is the “hotter” one.
Units produced after 1966 used luminance paint but it wasn’t radioactive like on early units. Unfortunately, units without radium scale look almost identical to the units with less radium paint. This makes finding a DP-63-A with radium scale more challenging.
My first shot at getting DP-63-A with radium scale was unfortunately unsuccessful. Luckily I managed to return it and I started looking for another unit but with radium scale.
After some time, I found an auction with DP-63-A from 1965. I reached out to the seller and ask him if the unit was factory sealed. Unfortunately, it was opened by someone else in the past but I still decided to pull the trigger after I got a really good deal on it.
When the packaged arrived I immediately knew that I got a unit with a radium scale since my Geiger counter was screaming when it was anywhere near the box.
After opening the box, I knew I had to remove the radium scale from the unit and put it into a lead pig for safety reasons before I could make a more detailed video on this Geiger counter.
Although I removed all radioactive source, the unit was still radioactive. That was because radium 226 decays into radon 222 which is a gas, meaning the inside of the unit was heavily contaminated. I used a water sprayer in order to wash out as much contamination as I could. Unfortunately, radon decay products tend to “stick” to different surfaces which meant that even after a lot of decontaminating, the unit was still radioactive but luckily nowhere near the levels when I first opened it.
Inside of the unit, there are two Geiger Muller tubes but what is interesting, is the use of B-8 Strontium 90 Source (click here). You may ask why is there a check source right under Geiger-Muller tubes. Well, this is a great example of soviet engineering. If you look at the front scale you can see that the upper scale (1.5 R/h) has 0 in a different place than the lower scale (50 R/h). In order to compensate the 0 position, a strontium 90 was used to raise the needle slightly when using 1.5 R/h scales. The B-8 strontium 90 source reads around 1 mSv/h (1026 uSv/h) on the Terra-P when measured right next to SBM-20 GMT.
Now, let’s talk about the other check source this unit has to offer, the DP-63-A’s legendary radium scale. On first glance, it doesn’t look like radium paint. It has a white, slightly creams colour while usually, radium paint has a brown/dark orange colour.
The layer of radium paint is very thick making the scale insanely radioactive. When measured with my Terra-P, the readings seemed to be around 3.5 mSv/h which is around 3500uSv/h of beta+gamma and gamma only was 420uSv/h! These are some very scary numbers. Just to give you some perspective, on average, a human receives 3-5 mSv/year from natural background radiation. Just for fun I also measured the scale with my Ludlum Model 3 with alpha/beta/gamma SBT-11A tube. Even though I was on the x100 scale, Ludlum got maxed out instantly at over 500 000 CPM.
In order to store this radium scale safely, I put it inside of a plastic bag which I then put inside of another plastic bag which I then put into a glass jar which I finally put inside of a lead pig container. The reason why I used a glass jar is to prevent radon 222 from leaking out. As the result, I managed to reduce gamma radiation from 420uSv/h to only around 8 uSv/h. I’ve also used the rule of inversed square law and placed the lead pig with radium scale as far away as possible. At a distance of one meter, the dose dropped to the normal background when measured with my RAYSID gamma scintillator/spectrometer (click here).
Overall, the only reason why I would recommend this Geiger counter to anyone is for its two, strong check sources. This being said, I highly discourage anyone from opening this unit or removing the radium scale since it is extremely dangerous!