Caesium-135
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| Long-lived fission products |
||||
|---|---|---|---|---|
| Property: t½ Unit: (Ma) |
Yield (%) |
Q * (KeV) |
βγ * |
|
| 99Tc | .211 | 6.1385 | 294 | β |
| 126Sn | .230 | .1084 | 4050 | βγ |
| 79Se | .295 | .0447 | 151 | β |
| 93Zr | 1.53 | 5.4575 | 91 | βγ |
| 135Cs | 2.3 | 6.9110 | 269 | β |
| 107Pd | 6.5 | 1.2499 | 33 | β |
| 129I | 15.7 | .8410 | 194 | βγ |
Caesium-135 is a caesium radioisotope with a half-life of 2.3 million years, undergoing low-energy beta decay to barium-135. It is one of only 7 long-lived fission products, and one of the 3 abundant ones. 135Cs's low decay energy, lack of gamma radiation, and long half-life, make this isotope less hazardous than Cs-137 or Cs-134.
Its precursor Xenon-135 has a high fission yield of 6.3333%, but also has the highest known neutron capture cross section of any nuclide, so some of the Xe-135 produced in a nuclear reactor (as much as >90% at steady-state full power [1]) will be converted to stable Xenon-136 before it can decay to Cs-135. A much smaller amount of 135Cs will also be produced from nonradioactive fission product Caesium-133 by successive neutron capture to Cs-134 and then Cs-135.
135Cs's thermal neutron capture cross section and resonance integral are 8.3±0.3 and 38.1±2.6 barns respectively. [2] Disposal of Cs-135 by nuclear transmutation is difficult, because of the low cross section, because neutron irradiation of mixed-isotope fission caesium produces more Cs-135 from stable Cs-133, and because the intense medium-term radioactivity of Cs-137 makes handling difficult. [3]
