Never Seen A Cloud Chamber? Check This Out!

Cloud chambers show subatomic particle contrails which is short-hand for "condensation trails", usually associated with the condensation of water behind airplanes.  This video starts off with just background radiation and then an Am-241 source is introduced.  But the best is saved for last, Rn-220 (the video uploader says radium, but she meant radon).

Cloud chambers were used frequently in the early 20th century and this one in Berlin has WOW.