Cross section measurement for the 231Pa(n, f) reaction

The cross sections for the 231Pa(n,f) reaction were measured at several neutron energy points from 2.12 MeV to 7.65 MeV with 2-MV and 5.5-MV Van de Graaff accelerators by making use of a chamber composed of a silicon detector and an electrodeposited film of 231Pa. The results from 2.12 MeV to 6.16 MeV are nearly constant and exist between 1.26 b and 1.49 b, and are around the previous data and Drake's curve within the experimental errors. The present value at the energy of 7.65 MeV gives 1.87+-0.14 b which is larger than those of lower energies. The sudden rise of the fission cross section at this energy may be derived from the (n,n'f) reaction. (auth.)