7D30.60-Diffusion Cloud Chamber

Video: Harvard Demo Video

Description: This demonstration illustrates the behavior of radioactive decay.


  • Dry Ice
  • Minimum 91% Isopropyl Rubbing Alcohol
  • Nuclear Cloudmaster
  • Radioactive sources such as:
    • Gamma Particle emitter
    • Alpha Particle emitter
    • Beta Particle emitter
  • Insulating Gloves
  • Plastic tweezers
  • Torch Light


  1. Place dry ice on the tray and in the cavity under the tray.
  2. Soak the sponge with the alcohol.
  3. Place the radioactive sources inside the chamber and seal it with the lid.
  4. Dim the background light and point a torch towards the chamber.
  5. Observation: Alcohol condenses first and after a while you should able to see various foggy paths made by the particle.

Concept: When the alcohol soaked pad is enclosed in the chamber, the difference in temperature of the pad and the bottom of the chamber causes condensation of the alcohol. The radioactive particles, being emitted through the alcoholic rain, ionize the alcohol droplets along the path they travel showing a foggy streak of where it was.


  1. Make sure that the alcohol doesn’t drip from the sponge.
  2. Always handle the dry ice with gloves, and the radioactive sources with tweezer.
  3. To increase the temperature difference for a better result, try heating the lid with a lamp.