Multi Channel Analyzer for Gamma Spectroscopy With Arduino & Theremino

I’d like to show you my homemade multi-channel-analyzer for gamma spectroscopy using a.) the freeware theremino and b.) an arduino. First of all I have to say some words about gamma spectroscopy at all. To detect radioactive decays you need a detector like a geiger-Counter. For gamma-spectroscopy you have to take a photomultiplier combined with a scintillation crystal made of sodium Iodide. You can get both things on ebay for less than 100 USD. The gamma-rays from the radioactive source is going through the scintillation crystal and produce very faint light-flashes. Those light-flashes are recorded by the photomultiplier, who converts them is small voltage-pulses at the Output. For this the photomultiplier and the Crystal have to be in a absolutely light-tight housing. I use shrinkable tubing for that. The Job of the multi-channel-analyzer (MCA) is to measure the height of those pulses coming from the photomultiplier. This is because every gamma-photon produces a voltage-pulse with a height depending on it’s energy. The higher the energy of the gamma-photon, the higher the voltage pulse. When the pulse-height has been measured, the number pulses with this recorded amplitude can be increased by one. At the end you get a spectrum of number of pulses versus pulse-height, which is characteristic for each radioactive element. For example cesium-137 emits gama-rays with an energy of 662 keV. They will produce pulses with a certain pulse-height. With a MCA you’ll get a spectrum with a peak at a certain voltage corresponding to the pulse-height. Therefore you can identify radioactive sources with a MCA. You don’t get just the so called photo-peak, but also characteristic structures like the compton-edge, which is produced by the scattered electrons.”