Caesium-137

Caesium 137 is an isotope of caesium. It is radioactive. It is often a by-product of nuclear fission. It has a half life of about 30 years. Many areas where nuclear accidents have occurred, such as Chernobyl and Fukushima, are contaminated with caesium-137.

Caesium-137 Media

The ten highest deposits of caesium-137 from U.S. nuclear testing at the Nevada Test Site. Test explosions "Simon" and "Harry" were both from Operation Upshot–Knothole in 1953, while the test explosions "George" and "How" were from Operation Tumbler–Snapper in 1952.
Calculated caesium-137 concentration in the air after the Fukushima nuclear disaster, 25 March 2011.

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