Measurement of 137Cs(γ, n) cross section by nuclear recoil separation method

Abstract The average cross section of the 137 Cs(γ, n) reaction in the giant dipole resonance region was measured by using the nuclear recoil separation method. Thin 137 Cs targets on aluminum supports were prepared by evaporating a 137 CsCl solution which was diluted with certain amounts of natural 133 CsCl in a vacuum chamber. Six targets having different 137 Cs activities and 133 Cs carrier concentrations backed by aluminum catcher foils were irradiated in a vacuum cell with bremsstrahlung having a maximum energy of 60 MeV and 45 MeV. The 136 Cs and 132 Cs activities, recoiled from the target foil by the (γ, n) reaction, were measured with a pure Ge detector. The (γ, n) cross section ratios of 137 Cs(γ, n) 136 Cs and 133 Cs(γ, n) 132 Cs were 1.10 ± 0.05 and 1.22 ± 0.11 for 45 MeV and 60 MeV bremsstrahlung, respectively, by using the internal standard method. The average cross sections of the 137 Cs(γ, n) 136 Cs reaction could be estimated to be 135 ± 8 mb/eq.q. and 157 ± 15 mb/eq.q. for 45 MeV and 60 MeV bremsstrahling, respectively.