Start Detecting Radiation with This Minimalist Geiger Counter

Radiation comes in many forms, and it’s all around us at all times. Visible and non-visible light from the sun is, for example, radiation. So are the radio waves being transmitted by the wireless devices that surround us. But when most people hear the word “radiation,” they think of the ionizing radiation that is actually dangerous to humans. Ionizing radiation is a particle or wave capable of detaching electrons from atoms, which is a problem for anything living. Geiger counters are devices capable of detecting that ionizing radiation, and Hulkbuild has a tutorial that you can follow to build one with a minimal number of parts.

You can buy Geiger counter kits for less than $100, or you can make your own from scratching using a handful of common and affordable components. The key component of this build is an SMB-20 Geiger-Müller tube, which can be purchased for around $20. This tube is filled with an inert gas and contains two electrodes — one held at a high voltage potential and the other grounded. Normally, a connection between the electrodes is absent. But, when ionizing particles enter the tube, the inert gas becomes briefly ionized and that facilitates a connection between the electrodes that can be detected. You just need a high voltage for one electrode and some way to detect when the electrodes are connected.

To bring the voltage from a AA battery up to something useful, Hulkbuild used the DC step-up converter from a cheap electric flyswatter. Other than the Geiger-Müller tube and the step-up converter, all you’ll need are common components like Zener diodes, resistors, an NPN transistor, and a piezo speaker. The circuit is fairly simple, and uses the transistor to connect power to the piezo speaker whenever the electrodes in the Geiger-Müller tube become connected through ionization. The result is a chirp of the piezo speaker whenever ionization radiation particles pass through the tube. You can then test your new Geiger counter using the americium found inside of many residential smoke detectors!