Level Densities in the actinide region and indirect n,y cross section measurements using the surrogate method

Abstract

Results from a program of measurements of level densities and gamma ray strength functions in the actinide region are presented. Experiments at the Oslo cyclotron involving the Cactus/Siri detectors and 232 Th(d,x) and 232 Th(3 He,x) reactions were carried out to help answer the question of which level density model is the most appropriate for actinide nuclei, since it will have an impact on cross section calculations important for reactor physics simulations. A new technique for extracting level densities and gamma ray strength functions from particle-gamma coincidence data is proposed and results from the development of this technique are presented.In addition, simultaneous measurements of compound nuclear gamma decay probabilities have been performed for the key thorium cycle nuclei 233 Th, 231 Th and 232 Pa up to around 1MeV above the neutron binding energy and have enabled extraction of indirect neutron induced capture cross sections for the 232 Th, 231 Pa and 230 Th nuclei using the surrogate reaction method. Since the neutron capture cross section for 232 Th is already well known from direct measurements a comparison provides a stringent test of the applicability of the surrogate technique in the actinide region.