Cosmic Rays for Fun and Profit.

I am a bit of an amateur/armchair particle physicist. I guess I am always drawn to the fundamentals, and there is nothing more fundamental then Nature. I spent a few years working on a neutrino physics experiments, but most of my effort was spent on FPGA and PCB work. I always wanted to make a particle physics measurement outside of work, and now thanks to a handful of cold war relics, I can. Geiger tube are among the oldest radiation detectors out there, and are still in use today. Old Soviet tubes in particular are easily acquired from your favorite online flea market. After a few decades of laying in a dusty civil defense warehouse, these devices are now trickling down to makers around the world.

As a cosmic ray interacts with the upper atmosphere, a muon is born. This muon will generally keep moving in the same direction as the cosmic ray, and travel deep into the earths crust, until they decay. As an old experimental physicist graybeard once told me muons are free. I did not fully appreciate this fact, until we were tasked with commissioning a small scintillator based neutrino detector. The first order calibration was not performed with a radioactive source, or a neutron generator, but with your friendly atmospheric muons.

Muons make up a large portion of background radiation at the earth surface. At sea level the rate is about \(1 \frac{cm^2}{min} \) Another curious fact is a muon angular distribution, which follows \(cos^2(\theta)\) with respect to zenith. Finally your average comic ray muon is very energetic, with plenty of energy to trigger multiple Geiger tubes if it happens to pass through them.

So here is the plan, I will build an array of Geiger tubes arranged kinda like this:
This will give it some angular resolution simply by looking at the pairs of tubes which triggered in a short window. What kind of measurements can I do with such a device? I could probably measure the angular distribution \(cos^2(\theta)\). With a little radioactive source I could try my hand at imaging, and tracking. Should be fun!