![]() ![]() ^ Per 65 thermal neutron fissions of 235U and 35 of 239Pu.^ Decay energy is split among β, neutrino, and γ if any.134Cs also captures neutrons with a cross section of 140 barns, becoming long-lived radioactive 135Cs.Ĭaesium-134 undergoes beta decay (β −), producing 134Ba directly and emitting on average 2.23 gamma ray photons (mean energy 0.698 MeV). The proportion between the two will change with continued neutron irradiation. The combined yield of 133Cs and 134Cs is given as 6.7896%. It is also not produced by nuclear weapons because 133Cs is created by beta decay of original fission products only long after the nuclear explosion is over. ![]() Caesium-134 is not produced via beta decay of other fission product nuclides of mass 134 since beta decay stops at stable 134Xe. It is produced both directly (at a very small yield because 134Xe is stable) as a fission product and via neutron capture from nonradioactive 133Cs (neutron capture cross section 29 barns), which is a common fission product. The second, symbol s, is defined by taking the fixed numerical value of the caesium frequency, Δ ν Cs, the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be 9 192 631 770 when expressed in the unit Hz, which is equal to s −1.Ĭaesium-134 has a half-life of 2.0652 years. Since 1967, the official definition of a second is: The SI base unit of time, the second, is defined by a specific caesium-133 transition.
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