Measurement of photo-neutron cross-sections in (208)Pb and (209)Bi with 50-70 MeV bremsstrahlung

Abstract

The photo-neutron cross-sections of Pb-208 and Bi-209 induced by 50-70 MeV bremsstrahlung have been measured by using the off-line gamma-ray spectrometric technique in the electron linac at the Pohang Accelerator Laboratory. The experimental Pb-208(gamma,xn) and the Bi-209(gamma,xn) reactions cross-sections at the bremsstrahlung energy region of 50-70 MeV, which are determined for the first time, are in general good agreement with the theoretical values based on the TALYS 1.0 code. We observed that the photo-neutron cross-sections for the (gamma,xn) reactions of Bi-209 and Pb-208 increase with increasing of bremsstrahlung energy from 50 to 70 MeV, which indicates the role of excitation energy. It was also observed that the (gamma,xn) reaction cross-sections of the doubly magic shell nuclei Pb-82(126) are always higher than those of the singly magic shell nuclei B-83(126) in the bremsstrahlung energy of 50-70 MeV. This may be due to the fact that either the shell effect are washed out at the higher excitation energy or due to the lower fission cross-section of Pb-208 compared to that of Bi-209. This observation indicates that there is a competition reaction between fission and neutron emission. (C) 2011 Elsevier B.V. All rights reserved.