MEASUREMENT OF THERMAL-NEUTRON CROSS-SECTION AND RESONANCE INTEGRAL OF THE REACTION CS-135(N,GAMMA)CS-136

The thermal neutron (2,200 m/s neutron) capture cross section (sigma(0 )) and the resonance integral (I-0) of the reaction Cs-135(n, gamma)(C S)-C-136 were measured by means of an activation method to obtain fund amental data for research on the transmutation of nuclear waste. Targe ts of radioactive cesium, which include Cs-135 and Cs-137 as well as s table Cs-133, were irradiated with reactor neutrons within or without a Cd shield case. The Co/Al and Au/Al alloy wires as activation detect ors were irradiated together with cesium samples to monitor the neutro n flux and the fraction of the epithermal part (Westcott's index). A h igh purity Ge detector was used for the gamma-ray measurements. The Cs -137 nuclide was used as a tracer of Cs-135, since Cs-135 decays throu gh a beta-transition, but does not emit gamma-rays. The ratio of the n umber of nuclei of Cs-135 to that of Cs-137 in the target was measured with a quadrupole mass spectrometer. This ratio and the ratio of acti vity of Cs-136 to that of Cs-137 in the irradiated target were used fo r deduction of the sigma(0) and the I-0 of Cs-135. The sigma(0) and th e I-0 of the reaction Cs-135(n, gamma)Cs-136 Were 8.3+/-0.3 barn and 3 7.9+/-2.7 barn, respectively. The sigma(0) is in agreement with that r eported by Baerg et al. within the limits of error, while the I-0, is about 2/3 of that reported by Baerg et al.