Brian Kean, age 15, of Fairfield, Iowa, a reader of the Colorado Springs Sun, for his question:

WHAT IS NUCLEAR FISSION?

Nuclear fission is the only type of nuclear reaction that is controlled by man to produce energy. It happens when a nucleus of uranium or another heavy element is split in two nearly equal parts.

A fission reaction releases only part of the energy of the nucleus. Most of the energy that is released takes the form of heat. The rest takes the form of radiation.

Nuclear energy is measured in units called electron volts. The burning of one atom of carbon in coal or oil produces about three electron volts of energy. The fission of one uranium nucleus produces about 200 million electron volts.

Uranium makes a good reactor fuel because it can create a continuous series of fission reactions.