Fukushima Daiichi nuclear disaster casualties of radioactivity released into the atmosphere was approximately one-tenth as much as was released during the Chernobyl disaster. Significant amounts of radioactive material have also been released into ground and ocean waters. Measurements taken by the Japanese government 30–50 km from the plant showed caesium-137 levels high enough to cause concern, leading the government to ban the sale of food grown in the area. Tokyo officials temporarily recommended that tap water should not be used to prepare food for infants. In May 2012, TEPCO reported that at least 900 PBq had been released "into the atmosphere in March, 2011 alone."
Caesium inside old stars and by the R-process in supernova explosions. The only stable caesium isotope is Cs, with 78 neutrons. Although it has a large nuclear spin (+), nuclear magnetic resonance studies can use this isotope at a resonating frequency of 11.7 MHz. The radioactive Cs has a very long half-life of about 2.3 million years, longest of all radioactive isotopes of caesium. Cs and Cs have half-lives of 30 and two years, respectively. Cs decomposes to a short-lived Ba by beta decay, and then to nonradioactive barium, while Cs transforms into Ba directly. The isotopes with mass numbers of