Robert Harts' Clever Kit Brings the Joy of Cosmic Ray Detection to All

Maker Robert Hart has released an open source kit designed to deliver a detector for cosmic rays — energetic particles created as material from supernovae and black holes hit the Earth's atmosphere at a decent fraction of the speed of light.

"I'm regularly approached by people wanting me to construct [cosmic ray detectors] or needing assistance. These include musicians, artists, educators, and enthusiasts," Hart explains. "However, juggling new projects with job and family life have posed some constraints. Consequently, I’ve recognized the need to develop a straightforward simplified kit that will empower anyone to construct and customize their own detector. For whatever their intentions or interest: education, for art, music or just wacky nonsense. My reasons are: I have a love for making things and a passion for science."

Hart's no stranger to cosmic rays, or muons: he's been building detectors since 2007. While previous efforts were one-offs, always seeking a new approach or optimizations, his latest is designed with longevity in mind — a kit that anyone can use to build their own detector in the comfort of their home, garage, school, lab, or almost anywhere else, complete with a relatively permissive license.

The kit is based around two Geiger–Müller tubes, most commonly associated with the Geiger counter — a tool typically used to find Earth-based radiation sources. While professional grade tools for spotting cosmic rays have since moved on to photomultipliers, Hart picked the classic Geiger–Müller tubes as being uniquely economical and accessible for building detectors at the do-it-yourself level. Other parts of the design include a power supply with an adjustable feedback circuit, a coincidence circuit — a design dating back to Bruno Rossi's work in the 1930s — and the all-important shielding, in the form of simple copper tubing with 3D-printed end-caps.

"Shielding is mainly used to increase the statistical difference of noise in the coincidence circuit," Hart explains. "With 2 main aims: 1) To differentiate the noise within each Geiger–Müller tube due to natural radioactive decay in matter e.g. gasses, glass and metals surrounding the detector and materials used to manufacture Geiger–Müller tube. 2) Cosmic Ray muons start with very high energy and speed, having the capacity to ionise many atoms before their energy is exhausted. Shielding in combination with the coincidence circuit helps to differentiate between slow moving particles from background radiation and muons which will pass through any shielding applied."

The kit is documented in full on Hart's website, where schematics, PCB production files, KiCad project files, and a bill of materials are available under the Creative Commons Attribution-NonCommercial license.