The cross-section of the reaction 134Cs(nγ)135Cs and the half-life of 134Cs

The isotopic composition of caesium samples which had been subject to intense reactor neutron irradiation was measured with a 6 in. radius, 60° sector field, mass spectrometer fitted with a triple filament thermal ionization source. The cross-section of the reaction 134Cs(nγ)135Cs was calculated from the observed isotopic composition and found to be 134 ± 12 barns. By measuring the change with time of the 134Cs/(133Cs + 135Cs) ratio using the mass spectrometer the half life of 134Cs was found to be 2·15 ± 0.040.08 years. In a subsidiary experiment the cross-section of the reaction 133Cs(nγ)134Cs was found by activation to be 30·4 ± 1·7 barns.