This demonstration illustrates the effect of intense radiation on matter. More specifically, it shows color centers resulting from radiation damage and the release of light when the color centers are destroyed by heat.

Nuked Salt,i.e., sodium chloride irradiated in a nuclear reactor.
Hotplate
Spoon or spatula

This demonstration should accompany a discussion of the effects of radiation in nuclear chemistry. Explain to your students that the orange crystals are plain table salt that have been exposed to intense radiation (neutron flux) inside a nuclear reactor. The color is a visible effect of radiation damage (see discussion below) and is indicative of the energy stored in the salt crystals as a result of absorbing radiation. When heated strongly, the crystals release the stored energy in the form of visible light.

To demonstrate the phenomenon, darken the classroom and sprinkle about a teaspoon of the irradiated salt on the hot surface of the hotplate. The crystals will emit green light for several seconds. This is visible even in a large auditorium if the room is dark. When light is restored, the salt crystals will be their ordinary white color.

The only real hazard for the demonstrator is the slight danger of accidentally touching the surface of the hot plate while the room is dark. Be sure you know where things are located before you turn off the light! The salt is not radioactive and poses no hazard. Students often ask whether it would be safe to eat the irradiated salt. The salt is not radioactive, but its environmental history is uncertain. On the basis of common sense and good practice, the answer to this query is no.

This demonstration has been described in an article in Chem 13 News, November 1989.