Cloud Chamber

The trajectories of individual charged particles leave behind cloudy trails as they ionize the cooled, supersaturated air-alcohol vapor inside this diffusion cloud chamber. Alpha particles from the radioactive decay of an inserted 2% thorium alloy rod form dense condensation trails nearby. Farther from the rod (beyond 10 cm or so) various types of charged particles leave evidence of their activity, including alpha particles (dense tracks, perhaps from the decay of radon isotopes), muons and energetic electr