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
Caesium-137 in flow meters, thickness gauges, moisture-density gauges (for density readings, with americium-241/beryllium providing the moisture reading), and in gamma ray well logging devices. Caesium-137 is not widely used for industrial radiography because it is quite chemically reactive, and hence difficult to handle. The salts of caesium are also soluble in water, and this complicates the safe handling of caesium. Cobalt-60, , is preferred for radiography, since it is chemically a rather nonreactive metal and produces higher energy gamma-ray photons. As a purely man-made isotope, caesium-137 has been used to date wine and detect counterfeits and as a relative-dating material for