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
Radiation effects from the Fukushima Daiichi nuclear disaster put out a total of 85 PBq of caesium-137. However, later reporting on 12 April estimated total caesium releases at 6.1 PBq to 12 PBq, respectively by NISA and NSC – about 2–4 kg. On 23 April, NSC updated this number to 0.14 TBq per hour of caesium-137 on 5 April, but did not recalculate the entire release estimate. On 12 October 2011 a concentration of 195 becquerels/kilogram of Strontium-90 was found in the sediment on the roof of an apartment building in the city of Yokohama, south of Tokyo, some 250 km from the plant in Fukushima. This first