Caesium is one of the radioactive fission
products created within a nuclear reactor during its operation.
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Caesium-137 is one of the major radioactive
isotopes of caesium. It is a major
radioisotope in the radioactive waste
resulting from nuclear reactors.
Caesium-137 is radioactive for a long period of time (half-life is about 30
years) and can contaminate property, entailing extensive cleanup. It can also be
absorbed into the food chain.