Chernobyl disaster substantial levels of caesium, which were believed to have been passed onto them during their consumption by wild boars, a significant number of which already contained radioactive particles above the allowed level. Like many other releases of radioactivity into the environment, the Chernobyl release was controlled by the physical and chemical properties of the radioactive elements in the core. Particularly dangerous are the highly radioactive fission products, those with high nuclear decay rates that accumulate in the food chain, such as some of the isotopes of iodine, caesium and strontium. Iodine-131 and caesium-137 are responsible for most of the radiation
Isotopes of caesium not produced by nuclear weapons because Cs is created by beta decay of original fission products only long after the nuclear explosion is over. Cs also captures neutrons with a cross section of 13.00 barns, becoming medium-lived radioactive Cs. Caesium-136 undergoes beta decay (β−), producing Ba-136 directly. Caesium-137, with a half-life of 30.17 years, is one of the two principal medium-lived fission products, along with Sr, which are responsible for most of the radioactivity of spent nuclear fuel after several years of cooling, up to several hundred years after use. It constitutes most of the radioactivity still left from the