$100 pocket size muon detector

Cosmich Watch is simple, physics-motivated machine- and electronics-shop project for university students and schools. Our detector is a self-contained apparatus that employs plastic scintillator as a detection medium and a silicon photomultiplier for light collection. These detectors can be battery powered and used in conjunction with the provided software to make interesting physics measurements. The total cost of each counter is approximately $100.

Why is this better than conventional instructional muon detectors?

It is fully self-contained: you don’t need a HV power supply, NIM modules, oscilloscopes…
It is efficient. It draws less than 1 watt per detector.
It is USB powered. You can also use a 5V power connector on the barrel jack. We sometimes use a cell phone spare battery to run the detector.
It is light-weight. The current detector weighs 68 grams.
It is not expensive. Students can build the detectors for sub-100$/unit.
The software is simple. They save the data through the USB connection using the website or running a simple python program.
It is expandable. The Arduino allows students to implement their own hardware. We’ve had students add on bluetooth connectivity, SD card readers, and temperature sensors.
It’s a lot of fun. Try climbing a mountain with it.
It makes a photon measurement. We measure the pulse amplitude, and are able to see single photons with the upcoming device.
It’s a fantastic science toy.
The build time is short. First time students can typically build on in under 3 hours (with supervision). Later they can build one in under an hour.

Muons can usually pass through walls, but sometimes they collide instead, meaning that a detector will see fewer muons if there are walls or other objects in the way. By measuring how many muons pass through a certain area—like a building—they can figure out exactly how much of that area is solid and how much is empty space.

It’s a technique that’s being used right now to map the debris inside the collapsed reactors at the Fukushima nuclear plant in Japan, and it was also recently used to discover a previously unknown chamber in the Great Pyramid of Giza.

By calculating the difference between angles using several detectors, researchers can get an idea of the path the muon took through objects. And with enough muons, they can draw a pretty good picture of what’s going on inside.


Muon Radiography – muons coming from the sky are detected above and below a truck. Muons passing through high-atomic-number materials (like uranium and plutonium) are scattered more than those passing through other materials (like steel or water). (Photo credit: Wikipedia)

About 90% of cosmic rays are protons, 9% are helium nuclei, and the remaining 1% are heavier nuclei. When the cosmic rays hit the nuclei of the atmosphere, a shower of particles are produced including pions and kaons. These are the progenitors of the muons.

The muons that are ultimately produced in the shower are fundamental particles that carry electric charge of +1 or −1 and have mass that is about 200 times that of the electron.

Muons are unstable and will decay to an electron, a neutrino and an anti-neutrino. At rest, the lifetime of the muon is approximately 2.2 microseconds. Given that the muons are produced in the shower at more than 10 km above the Earth’s surface, Galilean relativity calculations will show a very small probability of survival to reach the desktop muon counter. However, because the muons are produced at high energies, relativistic time dilation extends their lifetime. As a result, muons can survive to be detected on Earth.

The muon flux at sea level is about one per square centimeter per minute for a horizontal detector.

Arxiv – The Desktop Muon Detector: A simple, physics-motivated
machine- and electronics-shop project for university students