MEASUREMENT OF CS-137 (GAMMA, N) CROSS-SECTION BY NUCLEAR RECOIL SEPARATION METHOD

The average cross section of the Cs-137(gamma, n) reaction in the gian t dipole resonance region was measured by using the nuclear recoil sep aration method. Thin Cs-137 targets on aluminum supports were prepared by evaporating a (CsCl)-Cs-137 solution which was diluted with certai n amounts of natural (CsCl)-Cs-133 in a vacuum chamber. Six targets ha ving different Cs-137 activities and Cs-133 carrier concentrations bac ked by aluminum catcher foils were irradiated in a vacuum cell with br emsstrahlung having a maximum energy of 60 MeV and 45 MeV. The Cs-136 and Cs-132 activities, recoiled from the target foil by the (gamma, n) reaction, were measured with a pure Ge detector. The (gamma, n) cross section ratios of Cs-137(gamma, n) Cs-136 and Cs-133(gamma, n) Cs-132 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 cro ss sections of the Cs-137(gamma, n)Cs-136 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.