I'm gonna build me a cloud chamber

20 Feb 2012

Sunday we all(1) went to the AAAS Family Science Day and ho boy, it was fun. The kids had fun, of course; the demos were aimed pretty much right at them, and there were stickers and lasers and more stickers and popcorn. Friends of ours showed up with their two kids in tow, and all the boys got to run around and shine lasers at each other's heads. My wife had fun cos hey! SkyTrain! that's fun. But also? I had fun. And by fun I mean ZOMG. Because among other things, the Physics Department(2) from UBC had a real, working cloud chamber. A CLOUD CHAMBER.

When I was a kid, I bought this book at a library book sale: a collection of Scientific American "Amateur Scientist" columns. There was all kinds of stuff in there, from how to build your own solid rocket motors to measuring the metabolism of rats (I think part of it was TAKING SAMPLES OF THEIR BLOOOOOOOD) to grinding your own telescope mirror. For a budding geek, this was simply endless entertainment.

But -- BUT -- there was also a column explaining how to build your own cloud chamber and watch cosmic rays decay before your eyes. There was also an offer to mail you a radioactive speck so that you'd see more exciting stuff, which I thought was possibly the coolest thing ever.

This may have been the beginning of my interest in particle physics, expressed in later years when I:

a) got a local welder to weld some copper pipe in a loop, in preparation for a sadly-never-completed circular particle accelerator (linear accelerators are for suckers and chumps);

b) sent a fan letter to Carlo Rubbia and was thrilled to get a personally-signed letter back;

c) went to university to take physics in preparation for a career at CERN (only to get distracted by the Internet and libraries that were open 'til midnight, and fail out two years later); and

d) was amazed that a coworker at my first sysadmin job was the son of the director of IT for CERN; I tried to get him to get me a job, and he said no, but he gave me a cool CERN swatch instead.

And in all that time, do you think I'd ever seen a real, live cloud chamber? Had I bollocks. I'd printed out pictures of bubble chamber tracks, read up on spark chambers, learned about emulsion tracks, but never actually seen a working cloud chamber.

This thing was cool. I had not realized how dynamic they were. They'd put in a radioactive source, of course -- maybe they had sent off for a radioactive speck back in the day -- but there were also cosmic rays and other natural sources of radiation leaving their marks. There were tracks appearing constantly, and then fading away; it was hypnotic to watch. This video shows exactly what I mean:

The woman giving the demo said that some of the tracks were muons. Dude! MUONS! I was seeing MUON TRACKS! And then I got embarassed 'cos I couldn't remember whether beta radiation was photons or helium nuclei (neither: they're electrons or positrons; gamma radiation is made of high-energy photons) and felt insecure about the whole prospect of being in the same room as all these scientists since I obviously needed a remedial course in shoelace tying if I couldn't remember what beta radiation was.

(My brain, it does not always make sense.)

And so but it turns out you can find a lot of instructions on how to build a cloud chamber (the Starbucks chamber gets big props for being a cool hack), forums, and even a company that will build one for you (starting price for museum-grade model: $48,000). Now I just gotta track down some dry ice.

---

(1) "my family"? "my wife and I and kids"? I think (by which I mean "worry", by which I mean "obsess") about these things.

(2) You damn betcha it's capitalized.