30th Anniversary of the Chernobyl Tragedy – or – Building a PIN Diode Geiger Counter

Exactly 30 years ago a great disaster struck the region of Chernobyl: a nuclear accident occurred that released a large quantity of radioactive particles into the atmosphere. And it is only five years ago that, with the Fukushima Daiichi nuclear disaster, a second similar catastrophic event has taken place.

These anniversaries did not directly let me build a PIN Photodiode based Geiger Counter, it is more or less a coincidence. The main drive to build such a device was my curiosity and (please forgive me) a fascinating green glow I’ve seen on various fluorescent Uranium minerals under UV light. But in this context it should not be forgotten that at present there still is a significant increase in background radiation in some regions and some agricultural products due to these events.

There are lots of descriptions of how to build such a device; even cheap commercial products (e.g. the Smart Geiger) use such a design. Especially two sites caught my attention: OpenGeiger.de and Das Gammastrahlen-Mikrofon (German). The design I’ve chosen is based on these sources but I’ve begun to further modify it. In this post I’m showing the design I’ve started with. It mainly relies on two BPW34 (Vishay Datasheet) photodiodes connected in parallel, and two transistors to amplify the voltage fluctuations of beta and/or gamma rays striking the diodes. A 9 Volt battery was added to increase the pulse height.

The common approach to protect the photodiodes from light is to use one layer of tin foil and connect it to ground. This should also protect the circuit against electromagnetic radiation. I’ve started with something different and dipped the diodes three times into liquid rubber (Plasti Dip). My hope was to at least allow some beta particles to reach the semiconductor material.

Photodiode with Liquid Rubber Coating

So far I’ve tested the basic design shown above and had mostly noise on my microphone input. I’d say that sporadic crackling has more to do with the 1 hour hacked together design than beta or gamma rays. The liquid rubber seems to block of light, but the simple design is sensitive to electromagnetic radiation. Waving your hand or even movements in about 1 m distance is visible in the sound profile. An additional tin foil shield connected to ground did not change the noise profile, although the EMR influence was reduced. I’ve tested it with two different sound cards (microphone inputs).

I’m currently redesigning the whole approach and expect better results. So stay tuned…

14 Replies to “30th Anniversary of the Chernobyl Tragedy – or – Building a PIN Diode Geiger Counter”

  1. Hey Kai, You might find this project interesting…

    Peter put alot of work into it, and check out his schematics in the logs. Using similar setup piggy back and well wrapped in foil with his, although I did suggest to him to try the Plasti-Dip route. He actually may be interested in your results:

    HackaDay, Project Name: OpenCT2
    http://hackaday.io/project/5946/logs

    Just an FYI – might be helpful for you as well. I realize they are different directions but I just thought with a similar detection method.

    1. Hi Chris,
      I’ve taken a look at the OpenCT2 and the App Note 2236 by Maxim. I’m impressed by Peters work with the BPW34 in his CT scanner and got a few new ideas for my own project. Thanks for pointing me to this project! — Kai

  2. Hey guys, I’ve been trying to build one of these PIN diode detectors for months. I can’t get them to work. First I started with the one by Weinzel on techlib then I tried the one at http://www.b-kainka.de/bastel131.html.

    I am no electrical engineer but I have been connecting a piezo ear piece across the transistor in each case and when I test it by just touching the two pins of the PIN sensor together I get an audible click. And when I take a bare PIN sensor and run a light across it I get a very slight audible “woosh” as the light passes. But then I stick the diode into a lead pig with a piece of uranium and seal off the light and I get nodda.

    For the techlib wenzel one I followed the specs exactly up to the coupling capacitor for the blinker where I put my piezo ear piece instead. Nadda. Then with the second one I had to substitute the transistors with an MPSA18A and a 2907A because I don’t have the “BC” ones listed. Could that be the trouble? If so, why didn’t wenzel’s work when I follwed the specs exactly? I really would appreciate any help. I’d love to see these work. Thanks!

  3. Use two complementary darlington transistors and IT DOES WORK using a .1uF capacitor in series before the center pin output!

  4. Your PlastiDip was a mistake. It is black and that means carbon in the mix. While not necessarily “conductive” it falls under the same problems as black electrical tape, also an insulator and yet conductive enough to drain off much of the signal from any high impedance source. So you basically added a several hundred megohm resistor across your BPW34 and it’s probably grounding a bite out of your gamma signals. (in addition to a dozen other little errors that can crop up in these sensitive projects) You might look into the DIY ionization chamber projects for Alpha detection. To minimize drain on the gate of the transistor they don’t even let the gate touch the circuit board. And be sure to wash your gate area and BPW34 post-build with isopropyl or ethyl to get fingerprints and contaminants off. I have found signal much improved after cleaning.

    1. Hi Matt, yes this probably explains the leakage I’ve encountered with the design (i.e. with enclosing the BPW34 with plastidip). Also your tip of removing any residue from the sensors (with isopropanol) is important to point out.
      Another issue I’ve encountered in the mean time with using at least thin layers of plastidip is that it is not completely blocking off the full spectrum of sun light, i.e. using such a sensor at daytime outside may cause false signals.

      1. Using tin foil (like in most other projects) improved the design. But I have to come back and improve the overall design when I have time for it…

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