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Caesium-137 (137 55 Cs ), cesium-137 (US), [ 7 ] or radiocaesium , is a radioactive isotope of caesium that is formed as one of the more common fission products by the nuclear fission of uranium-235 and other fissionable isotopes in nuclear reactors and nuclear weapons .
The low decay energy, lack of gamma radiation, and long half-life of 135 Cs make this isotope much less hazardous than 137 Cs or 134 Cs. Its precursor 135 Xe has a high fission product yield (e.g., 6.3333% for 235 U and thermal neutrons ) but also has the highest known thermal neutron capture cross section of any nuclide.
Caesium-137 is one such radionuclide. It has a half-life of 30 years, and decays by beta decay without gamma ray emission to a metastable state of barium-137 (137m Ba). Barium-137m has a half-life of a 2.6 minutes and is responsible for all of the gamma ray emission in this decay sequence. The ground state of barium-137 is stable.
Figure 1: Sodium iodide gamma spectrum of caesium-137 (137 Cs) An example of a NaI spectrum is the gamma spectrum of the caesium isotope 137 Cs —see Figure 1. 137 Cs emits a single gamma line of 662 keV. The 662 keV line shown is actually produced by 137m Ba, the decay product of 137 Cs, which is in secular equilibrium with 137 Cs.
The beta decay from 137 Cs to 137m Ba results in gamma radiation as the 137m Ba relaxes to ground state 137 Ba, with the emitted photons having an energy of 0.6617 MeV. [ 59 ] 137 Cs and 90 Sr are the principal medium-lived products of nuclear fission , and the prime sources of radioactivity from spent nuclear fuel after several years of ...
A mining company dropped a tiny capsule of caesium-137 somewhere along an 870-mile stretch of Western Australia’s Great Northern Highway. The plan is to find it before someone gets hurt, Liam ...
137 lead-196m3: 140 lead-190m1: 150 thallium-198m2: 150 americium-239m: 163 lead-192m1: ... caesium-137: 30.17 952 10 9 seconds (gigaseconds) isotope half-life years
A new sealed cesium-137 radiation source as it appears in its final state. A radioactive source is a known quantity of a radionuclide which emits ionizing radiation, typically one or more of the radiation types gamma rays, alpha particles, beta particles, and neutron radiation.