Caesium-137 or approximately 44 μg/kg) of caesium-137 (and 950 to 1400 rads), they die within 33 days, while animals with half of that burden all survived for a year. Accidental ingestion of caesium-137 can be treated with Prussian blue, which binds to it chemically and reduces the biological half-life to 30 days. Caesium-134 and caesium-137 were released into the environment during nearly all nuclear weapon tests and some nuclear accidents, most notably the Chernobyl disaster and the Fukushima Daiichi disaster. As of 2005 and for the next few hundred years, caesium-137 is the principal source of radiation in the zone of
Isotopes of caesium into solution and is returned to the surface of the earth as a component of radioactive fallout. Once caesium enters the ground water, it is deposited on soil surfaces and removed from the landscape primarily by particle transport. As a result, the input function of these isotopes can be estimated as a function of time. Caesium-131, introduced in 2004 for brachytherapy, has a half-life of 9.7 days and 30.4 keV energy. Caesium-133 is the only stable isotope of caesium. The second is defined by a specific caesium-133 transition. Since 1967, the official definition of a second is 9,192,631,770 cycles of