Building a Particle Playground

Compton scattering is a fundamental process in physics that occurs when a photon collides with a charged particle, typically an electron, and transfers some of its energy to the electron, causing it to recoil. As a result, the photon undergoes a change in wavelength and direction after interacting with the electron. This change is dependent on the energy and angle of the photon, as well as the mass of the electron.

This knowledge has enabled Compton scattering to be utilized in a number of technological innovations, in fields including astronomy, medical imaging, and materials science. In medical imaging, for example, this process has allowed detailed images of internal structures of the human body to be reconstructed. By emitting high-energy photons (such as gamma rays) into the body and measuring the scattered radiation, medical professionals can create precise images that aid in the diagnosis and treatment of various medical conditions, including cancer and bone fractures.

But surely outside of industry and research labs, Compton scattering is not something that anyone can experiment with, right? I mean, playing with gamma rays is not exactly a great idea, after all. Romanian hacker Mihai Cuciuc, who has a background in particle physics and embedded design, has no reservations about it, however. Cuciuc has built a device that allows him to experiment with Compton scattering and measure its effects. This project is definitely in the “do not try this at home” category though, as it requires the use of radioactive materials.

Cuciuc has been developing a low-cost gamma radiation detector called Pomelo for some time now, targeting hobbyists as the intended users. In his latest experiment, Cuciuc used two Pomelo modules to enable coincidence measurements. Coincidence measurements help distinguish between events of interest, like interactions between photons and electrons, and background noise.

Using the pair of Pomelo devices, which were wired together for a hardware handshake that enables coincidence measurements, as well as a lead brick with a hole in it that exposes the radioactive isotope cesium-137, Cuciuc had an experimental setup for detecting and measuring Compton scattering. As gamma rays exit the lead brick through the hole, they interact with the first Pomelo detector. Those that are scattered at just the right angle additionally interact with the second Pomelo detector. This is a rare event in contrast with all of the other gamma rays the detectors will see, so the coincidence triggering mechanism is crucial in order to pick them out.

As Cuciuc points out, the setup is not especially precise, so the results are not perfect, but nevertheless, the scattering events can be clearly seen in the data. At present, Cuciuc is working to improve the accuracy of the system with the hope of eventually being able to detect cosmic muons with it.

Detecting the scattering of colliding particles may not exactly be useful to many hobbyists, but it is undeniable that it is extremely cool that Cuciuc was able to get this working. And while handling radioactive elements is generally not a good idea, the Pomelo detector itself is only a spectrometer, so it can be safely used to detect natural phenomena. But if that is not your cup of tea either, you will still want to take a look at the project write-up to learn from Cuciuc’s experiences.