For the holidays this year, the girlfriend and I came up with the idea of celebrating Spacemas (unrelated to the Canada's Space Channel. We don't own TVs, nor do we speak Canadian). Spacemas is an ill-defined holiday, burdened by neither Capitalism nor religion, which exists solely as a periodic moral booster for the brave men and women living on the frontier of space. At least, that's what it will become, if we have our way. And what better way to commemorate the first Spacemas than with a Cosmic Ray detector?
What is a Cosmic Ray?
Here's a more authoritative source, but what it boils down to is this: high-energy particles (mostly protons) are spat out from explosions on our Sun, supernovas, even quasars and other phenomenon from outside our galaxy. These particles are constantly bombarding us from every direction, and although some are blocked by the solar wind and the Earth's magnetic field, many make their way through to our atmosphere, where some of them slam into air molecules, creating a cascade of secondary particles, such as neutrons, mesons, pions, and kaons. Some of these decay into Muons, which, because of their relatively long decay lifetime (and time dilation effects from going 0.98 times the speed of lite), are able to reach the surface.
And it turns out that Muons are actually fairly easy to detect. They readily ionize Geiger-Müller tubes, just like beta radiation . The first resource I came across was from Robert Hart, who has done some really cool stuff with Muon detectors. The secret sauce here is Coincidence Detection. When a Muon passes through, it will ionize one tube, and unlike beta or gamma radiation, it will keep on going, ionizing the next tube. The two pulses appear at nearly the same instant; you run two or more geiger counters into an AND gate, and there anything that hits multiple tubes at the same moment was probably a Muon. Easy peasy.
I ordered some tubes off of ebay, but after a bit more reading, realized that they might not work so good for this application. The larger a Geiger tube is, the more sensitive it is (larger volume for particles to hit). The tubes I ordered were very small, and by early December, it was much too late to order any tubes from Russia. Every tube you could dream of is available (and inexpensive) from the likes of SovTube and GSTube, if you're willing to wait a few weeks. I opted instead to order them from small online Swiss retailer Boxtec, who could overnight me some nice, sensitive SI-180G tubes.