Cross-section measurement and analysis for the {sup 149}Sm(n,alpha){sup 146}Nd reaction at 6.0 MeV

We have measured the {sup 149}Sm(n,alpha){sup 146}Nd cross section at 6.0 MeV to be 0.12+-0.018 mb. This is the first reported result for this cross section in the MeV region and so should be helpful for constraining nuclear data evaluations (which differ by a factor of 40 for this reaction at this energy) and for testing and improving nuclear models. The experiment was performed at the at the 4.5-MV Van de Graaff accelerator of Peking University. Neutrons were produced via the {sup 2}H(d,n){sup 3}He reaction using a deuterium gas target, and absolute neutron flux was determined with a small {sup 238}U fission chamber. Alpha particles were detected using a two-section gridded ionization chamber in which two large-area {sup 149}Sm{sub 2}O{sub 3} samples were placed back-to-back so that the cross section and forward/backward ratio were measured for nearly the entire 4pi solid angle. The data were compared to statistical-model predictions using the code talys. Good agreement between the measured and theoretical cross sections could be obtained with a small modification of the alpha-optical potential parameters from their default values in talys. However, we were not able to reproduce the measured forward/backward ratio. In addition, using the previously reported {sup 147}Sm(n,alpha){sup 144}Ndmore » cross section at 6.0 MeV together with our new result, good agreement was found between the measured and predicted cross-section ratio for these two isotopes. Finally, none of the existing evaluated data libraries are in agreement with our new data to within the experimental uncertainties.« less