Cheap spark detector for alpha particles

[JAC_101] wrote in to let us know that the Truely Mad Scientist’s LVL1 Splinter Group just built a simple Alpha Particle detector.  The detector is a high voltage DC spark gap that is triggered by ionizing radiation. Making one of these detectors involves gutting a cold cathode power supply for some high voltage AC, then bumping that source up to crazy high voltage DC with a Cockcroft-Walton generator.  Once the spark gap distance is carefully adjusted it will light up brilliantly with the introduction of a radioactive source, we are told. There are no videos, or even pictures of the thing running, but we found this one that is pretty darn cool. Maybe all that spark-gap related RF killed their camera or something, their page at least promises videos soon.

In the mean time check out Truely Mad Scientist’s LVL1 Splinter Group’s ionizing cloud chamber for more radioactive fun.


  1. John U says:

    Presumably one could make a low-voltage “sense” output by monitoring the current draw, or possibly by a small induction coil w/ smoothing circuit.

  2. macona says:

    Link is not good, should be:

    The voltage multiplier puts out maybe 8-10kv, not much, really.

    Detection can be accomplished just like a geiger tube, watch the voltage drop through a capacitor.

    • JAC_101 says:

      Thanks for noticing the link problem (the mods fixed it).

      The measured voltage out was almost 8kv. When testing the design I left off the current limiting resistor and hit the power. The arcing was great but not as I intended.

      Caution is necessary when dealing with high voltages. This may not seem high but it is dangerous. I need to emphasize safety more.

  3. Ren says:

    Do smoke detectors (non-IR sensor) emit alpha particles? If so, they could use one to test it.

    • Leithoa says:

      There are many that use a small(1 micro Curie) sample of americium in them.

    • fffffffff says:

      Please don’t take apart your smoke detector! You could accidentally break the source and contaminate your surroundings. These sources are not meant to be handled!

      If you’d like to to radiation experiments, invest in a safe sealed check source. These are usually discs of radioactive material potted in epoxy, with a plastic housing. They are OK to handle and won’t contaminate you or your surroundings.

      United Nuclear has them, but they are on the pricey side:

      Polonium 210 is a great source for alpha particles.

      check around for better deals online. There are plenty of forums and mailing lists that can help you find a good check source.

      • carlwillis says:

        Smoke detector Am-241 sources are sealed sources, built to a higher standard of ruggedness than many of the alpha check sources one can buy. They’re far less expensive, and eminently suitable for hobby use. In my mind, the only reasonable impediment to sacking a smoke detector for the source is the interpretation of the NRC’s administrative code regarding whether or not the smoke detector body, etc. are part of the “source.” One observes all manner of amateur lawyering and manufactured grief on this subject, but I’ve never seen any official communication from regulators enjoining the reuse of a smoke detector source.

  4. AussieTech says:

    A possible alternative to a Cold Cathode power supply might be the flashgun assembly from disposable cameras.

    • JAC_101 says:

      There are many alternatives to powering the device. I chose the CCFL because it was handy and already wired for a PC power supply. The basic idea was to create lab equipment to run off the PC supply.

      There are many examples of high voltage supplies on the net using ignition coils, flyback transformers and hand wound coils. For lab equipment, I chose reliability (consumer products).

  5. ginsublade says:

    I just got my cloud chamber working a day or two ago, now I gotta build this…I love this site!

    • JAC_101 says:

      After you finish this build, the Truly Mad Scientist’s LVL1 Splinter Group will be posting a geiger counter and laser build. Mixing the two will then follow (unless we get sharks with head gear).

  6. ginsublade says:

    The smoke detector sample is great and easy to acquire. It worked real well in my cloud chamber…

  7. JB says:

    Can’t build this. I’ve been drinking too many Nuka Colas :P

  8. WD says:

    Sorry if this is a dumb question but when would this be useful?

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