Peltier Cooler Based Cloud Chamber
Cloud chambers let you see paths left by radioactive particles as they pass through a supersaturation of alcohol vapor. Vapor trails are formed when the radiation ionizes the alcohol.
They need to be very cold (about -15f) - so most designs require dry ice.
Originally developed by Rich Olson - this design uses inexpensive electrical "Peltier" coolers instead. Unlike other peltier-based cloud chambers - it does not require ice water to operate.
See the Make a Cloud Chamber using Peltier Coolers (Instructable) for full details on making your own for about $100.
Reference information on the "product" version of the cloud chamber
is available here.
(Instructables.com has more detailed instructions than the video below)
Some footage from the for sale version of the chamber:
Links to related projects:
http://chambrebrouillard.wifeo.com - great info on various particle traces
http://wilsoncloud.wordpress.com- very impressive chamber builds