Alkali metal from the Chernobyl accident. Caesium-137 undergoes high-energy beta decay and eventually becomes stable barium-137. It is a strong emitter of gamma radiation. Caesium-137 has a very low rate of neutron capture and cannot be feasibly disposed of in this way, but must be allowed to decay. Caesium-137 has been used as a tracer in hydrologic studies, analogous to the use of tritium. Small amounts of caesium-134 and caesium-137 were released into the environment during nearly all nuclear weapon tests and some nuclear accidents, most notably the Goiânia accident and the Chernobyl disaster. As of 2005, caesium-137 is the principal source
Isotopes of caesium only long after the nuclear explosion is over. The combined yield of Cs and Cs is given as 6.7896%. The proportion between the two will change with continued neutron irradiation. Cs also captures neutrons with a cross section of 140 barns, becoming long-lived radioactive Cs. Caesium-134 undergoes beta decay (β), producing Ba 134 directly and emitting on average 2.23 gamma ray photons (mean energy 0.698 MeV). Caesium-135 is a mildly radioactive isotope of caesium with a half-life of 2.3 million years, decaying, via emission of a low-energy beta particle, into the stable isotope barium-135. Caesium-135 is one of the 7