What is it?

Like many other hobbyist I have always been fascinated by radioactivity and the sensors to detect it. Geiger-Müller tubes are a common and relatively inexpensive way to measure radiation. GRAD is a complete solution for beta and gamma radiation counting in an Arduino shield form factor. Its main features are dual tube support to increase sensitivity and very low power consumption

Tube options

The board is designed to work with 105mm Soviet SBM-20, STS-5 and the Chinese J305 or the 90mm J305 and M4011. Any other 400V tube will also work with some customized tube mounting. In case of custom mounting, to minimize parasitic capacitance, it is important to keep the positive wire as short as possible. For tubes requiring different voltages, the Zener diode(s) should be changed to obtain the required voltage. Any diode with 0.5uA or less of leakage should work.

Measuring Radiation

To verify the correct function of the Geiger counter a radiation source is required. These can be purchased online from specialty suppliers. Alternatively specific vintage items that were built using small quantities of radioactive materials can be purchased at a thrift store or ebay. Common radioactive items include: uranium glass items, thorium lantern mantles and selected colors of vintage fiestaware items. Lacking any of these another simple way is to check the decay product of Radon captured by the air filter from an air conditioner or an air purifier. These have a relatively short half life (in the order of tens of minutes) so make sure you run the AC for a couple of hours and then measure the filter immediately. If the filter is fine enough to it will emit radiations at a rate many time higher than background in your area. The chart below shows the count reaching almost ten times the background and then following the exponential curve typical of radioactive decay.