Has a half-life of 30.17 years and decays by beta and gamma radiation. Cs-137 is produced by nuclear fission for use in medical devices and gauges and is one of the byproducts of nuclear fission processes in nuclear reactors and nuclear weapons testing. Small quantities of cs-137 can be found in the environment from nuclear weapons tests that occurred in the 1950s and 1960s and from nuclear reactor accidents, such as the chernobyl power plant accident in 1986, which distributed cs-137 to many countries in europe.