Nuclear fission

Lore & Background

Physicists Lise Meitner and her nephew Otto Robert Frisch explained it theoretically in January 1939. Frisch named the process "fission" by analogy with biological fission of living cells. In their second publication on nuclear fission in February 1939, Hahn and Strassmann predicted the existence and liberation of additional neutrons during the fission process, opening up the possibility of a nuclear chain reaction by assembling a critical mass of fissile material. Most fissions are binary fissions producing two charged fragments, but occasionally ternary fission produces three positively charged fragments.

Reader's Guide

Nuclear fission is significant because it provides a mechanism for both controlled energy release in nuclear power plants and uncontrolled energy release in nuclear weapons. Fission is a form of nuclear transmutation, producing daughter atoms of different elements than the parent. The energy from fission is produced by its fission products, with about 85 percent found in fragment kinetic energy. Natural nuclear fission reactors have formed under very rare conditions, though fission is considered negligible for the evolution of the universe compared to nuclear fusion.

Did You Know?

• The fission process often produces neutrons and gamma rays, and releases a very large amount of energy even by the energetic standards of radioactive decay.