Purpose: To exhibit the tracks left by radiation from radioactive materials.

Place dry ice or liquid nitrogen between the insulating base and the cloud chamber. Pour about 1/3 the ethanol onto the felt pads on the top of the cloud chamber. Pour the remaining ethanol into the cloud chamber bottom.

Place the illumination light in the window at the back of the cloud chamber. A electric field can be set up to force the charged particles downward into the sensitive layer by rubbing the top glass with silk. A permanent magnet can be placed underneath the chamber to show the deflection of the charged particle by a magnetic field.

You can see the tracks left by the radiation from the sources and from cosmic rays by viewing the chamber from an angle of about 60 degrees from the horizontal. (Note: To make this demonstration useful for a large classroom a close-up camera should be used to view the chamber.)

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