Use a Cheap PIN Diode as a Geiger Counter

After the Fukushima nuclear power plant disaster, radiation measurement became newly relevant for a lot of people. Geiger-Müller tubes, previously a curiosity, became simultaneously important and scarce. (English-language version here) has complete instructions for making a Geiger counter without a Geiger-Müller tube. Instead, this counter uses a PIN photodiode and some carefully chosen operational amplifiers. The total cost of such a device is significantly cheaper than the alternative: under $1 for the diode and around $5 for the rest. And since the PIN photodiode in question is used in many other devices, it’s not a niche component like a Geiger tube is.

The secret sauce is in component selection and tuning. Opengeiger uses the BPW34 diode because it is relatively common and has a large surface area, but also because it has a very low capacitance when reverse-biased. The first-stage opamp choice is also fairly critical. Considering that an average gamma radiation event produces only around 10 nanoamps for about 50 microseconds, a lot of amplification (100,000x), low noise, and high bandwidth are a must.

If you want to get started with this project, you could first browse through the explanation (PDF) to get an overview of the project’s goals, read up on all the technical considerations (PDF) or just head straight for the DIY instructions for the “Stuttgarter Geigerle” (PDF, schematic is on the last page). All of the documentation is chock-full of relevant references and totally worth the read.

44 thoughts on “Use a Cheap PIN Diode as a Geiger Counter

  1. Good, good, keep em’ coming, it’s about time we finally put the GM tube away in favor of silicon. The more these become widely known, the more cheap radiation detectors will become available.

    1. Silicon diodes can only pick up certain types of energy (mostly gamma). You’re never going to pick up alpha radiation with a PIN diode. You’ll have a very long wait if you want geiger tubes to go away. This Opengeiger device is mostly useless as a general purpose radation detection device.

      1. The problem is not the diode, but the case around it. If you can cut open the case, the diode can be used. The website has some pictures of a diode in a big metal can that’s cut open, and works as an alpha radiation detector.

        1. Simple: get a metal can high frequency transistor, decap it without damaging the chip inside, and you get a photodiode with built-in amplification with its base pin left floating when properly biased. When the particle strikes the B-E junction you get a big amplified spike.

  2. I would suggest that the moment someone integrates this kind of design in to a small (around the 20mm square marker) cheap (around $5) smd (for ease of mass production) ‘duino/pi compatible sensor board, they will fly off the shelves. Kickstarter anybody?

    1. Photodiodes are literally that, but not so excessively large. Solar cells average out collisions, whereas an array of photodiodes would give a detection grid. It’s a bit like having a touchscreen that only gives the average of the force on it, and no coordinates.

  3. I’ll be the pedant in the room. It’s not a Geiger counter. A GEIGER COUNTER is a Geiger-Muller tube opperated in the Geiger voltage region for the tube. You can also operate a Geiger-Muller tube at a lower voltage as a GAS PROPORTIONAL COUNTER. GM tubes are essentially capacitors with high breakdown voltage and a specific gas mixture for the dielectric composed of a noble gas to supply the electrons, and a quench gas, such as methane, to stop the discharge once it’s started.

    Silicon and Germanium detectors are a different type of detector geared towards gamma ray detection. (GM tubes don’t see many gammas, mostly beta and x-ray). Si and Ge detectors are reverse biased diodes.

    1. I disagree. Geiger tubes do detect gamma photons, and are likely much more sensitive to them than silicon, although high energy gamma rays can be an issue. If we take this to its logical conclusion, based on your comment, the only particles a Geiger tube would be beta particles, and possibly x-rays, which would not be particularly useful!

  4. Or perhaps just take your mobile phone, cover the camera’s lense, record the black video and count white flashes. Better resolution with a few mm2 CMOS sensor. Possibly can detect the 3D direction as well .. job done, no reason to reinvent the wheel again. Chinese 4 core Andrid phone with 3G, GPS, wifi, BT, 2 MPixel camera for $45 if you buy more than 10 …

        1. They will not let you anywhere near the interesting (“hot”) parts in Fukushima…
          As for Chernobyl – while not near the conflict zone, right now it is not advisable to travel to Ukraine as a tourist. With all the increased security and everything, they most likely will not let you roam around the zone like you sometimes can (some tours will not even let you into the grassy areas), so that you could try to find a fuel fragment (insanely radioactive, sand-grain sized pieces of actual reactor core lying around).

          If you want a powerful, yet more available source of ionizing radiation, a medical X-ray will do just fine if you stuff the device right in front of the X-ray head.
          Or if you’re in the US, you can rent (sadly not buy) fairly active test sources.

  5. THIS ISN’T A GEIGER COUNTER PERIOD. it detects gama rays for gods fucking sake but not the killer radiation from toxic nuclear sites that kills you.

    basic physics folks. geiger counters are for measuring radiation from transuranic elements and irradiated materials. not from detecting gamma rays from outer space.

    1. It will also be sensitive to alpha and beta radiation , which just about covers all radiation from the decay of radioisotopes. Alpha is less likely because these particles will be stopped by anything used tkeep light off the sensor, but cheap geiger tubes have a similar problem because of the way they are constructed (no window to let alpha particles in). The bigger issue , and possibly the one you so eloquently tried to describe, is the lack of sensitivity (10’s of counts over a minute vs 100’s or higher for a Geiger tube).

  6. I found a similar project, also with the BPW34 diode, at Elektor a while ago.
    The actual article is from 2011.

    I bought all the parts but didn’t assemble it yet, because I had problems compiling the software which is written in BASCOM. Is anyone capable of making a .hex for the ATmega88 out of it? Otherwise I would try to rewrite the software in C.

  7. Is there any advantage to using a Geiger-Muller tube over this type? I was of the understanding that part of the difference is that the tubes are calibrated where other solid state methods may not be. Is there an IC designed for this purpose that is available to hobbyists?

  8. I tried the techlib circuit up to the coupling capacitor and used a piezo ear piece instead of the LED circuit and I could not get this to work. I was able to effectively shielding the circuit from light/Electromagnetic Radiation, but it did not respond to radiation at all and I had a pretty powerful source.

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