Caesium-137

Caesium-137 (¹³⁷
₅₅Cs
), cesium-137 (US),[7] or radiocaesium, is a radioactive isotope of caesium that is formed as one of the more common fission products by the nuclear fission of uranium-235 and other fissionable isotopes in nuclear reactors and nuclear weapons. Trace quantities also originate from spontaneous fission of uranium-238. It is among the most problematic of the short-to-medium-lifetime fission products. Caesium-137 has a relatively low boiling point of 671 °C (1,240 °F) and easily becomes volatile when released suddenly at high temperature, as in the case of the Chernobyl nuclear accident and with atomic explosions, and can travel very long distances in the air. After being deposited onto the soil as radioactive fallout, it moves and spreads easily in the environment because of the high water solubility of caesium's most common chemical compounds, which are salts. Caesium-137 was discovered by Glenn T. Seaborg and Margaret Melhase.

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Caesium-137, ¹³⁷Cs

A sealed caesium-137 radioactive source
General
Symbol	137Cs
Names	caesium-137, 137Cs, Cs-137
Protons (Z)	55
Neutrons (N)	82
Nuclide data
Natural abundance	0 (trace)
Half-life (t1/2)	30.05±0.08 years[1]
Isotope mass	136.907 Da
Spin	7⁄2+
Parent isotopes	137Xe (β−)
Decay products	137mBa 137Ba
Decay modes
Decay mode	Decay energy (MeV)
β- (beta decay)	0.5120[2]
γ (gamma-rays)	0.6617
Isotopes of caesium Complete table of nuclides