Loyola University Medical Education Network

Byproducts of the fission reaction

The final group of interest includes Xe-133, Mo-99, and I-131, all of which are byproducts of the fission of U-235. Produced in great quantity in nuclear reactors, these isotopes are regarded by the nuclear power industry as waste products. Once they have been purified adequately, however, they are perfectly suitable for human use.

The process involves the fission of U-235 by bombardment with of neutrons. The result is formation of an unstable "compound nucleus" that fragments into two parts with molecular weights of approximately 100 and 135. As indicated by their atomic masses, Xe-133, Mo-99, and I-131 have molecular weights of 133, 99, and 131, respectively. Many other isotopes are produced which have commercial value.

The reaction may be represented by the following equation. Note that 2.3 neutrons are released for each one participating in the reaction. The reaction becomes self propagating and requires special care to prevent it from quickly running out of control.


Stephen Karesh, PhD.

Last Updated: August 14, 1996
Created: March 1, 1996