Open-Source Gamma Spectrometer

By Rob Zwetsloot. Posted

Radiation detection is not something we often have to consider here at The MagPi – we’re not sure if that makes us lucky or boring – but the equipment is fascinating nonetheless. It’s also quite expensive. This is where, once again, Raspberry Pi Pico comes in to help reduce the cost and ease of access of this important kit, with thanks to Matthias Rosezky as well.

“This is a cheap, complete, and open-source gamma spectrometer that you can build for yourself and use without having to worry about expensive equipment or any hardware design,” Matthias tells us. “With it, you can easily detect even low levels of gamma radiation, and run spectrometry to determine the composition of a radioactive material. It’s highly modifiable, both in hardware and in software, due to different variable on-board parameters and custom pin headers.”

It uses a mixture of Arduino code and Pico hardware, with processing done entirely on Pico itself. It makes use of a silicon photomultiplier (SiPM) and scintillator crystal which interact with the detector board to manage this, whereas other solutions need USB sound cards and up to a kilovolt of power. This only needs 30 V.

Microcontroller for the job

“I tried many different microcontrollers before the Pico was released, but availability and cost were always a concern for me,” Matthias says, as he explains to us why he chose Pico. “That’s because a standard Arduino Uno isn’t nearly fast enough for the job and most of the other SAMD microcontrollers, for example, mostly lack excellent software support for the Arduino IDE. When Pico came out, I was amazed by the low cost and, at the same time, great performance and modifiability. You can do so many things with it, and the software support is great thanks to the Pico SDK and the awesome Arduino-Pico library. And last, but not least, you can get it almost everywhere [cheaply], even in the current state of the industry!”

With a microcontroller selected, Matthias started creating separate modules for his device and assembled them on a breadboard before designing PCBs for the final product.

“Loads of different PCBs actually,” Matthias mentions. “There have been so many revisions, I lost count of them. I still have a good amount of them here (the ones that worked). The last few board revisions, finally, were more like fine-tuning and creating a more user-friendly PCB so that everything’s in one piece and easier to build (this includes the Pico being SMD-mounted for example).”

Practical sensitivity

For the detection part, Matthias told us that, technically, Geiger counters can do a similar job, and are also pretty cheap.

“What’s really the one single benefit of having a gamma spectrometer is the energy spectrum with which you can guess what exact radioactive materials are in your sample,” Matthias explains. “Got radioactive ceramics? You can easily tell if it’s from after WW2, pre-WW2, and even from the beginning of industrial pottery in the 1800s, just looking at the spectrum. Ionization smoke detector? You can tell exactly what’s in there ionizing the air. You can identify natural occurring isotopes in rocks, measure the potassium content in food, check your soil or rainwater for contaminants, and so much more.”

Check out magpi.cc/opengamma for information on how you can make your own.

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