Fission Physics and Cross Section Measurements with a Lead Slowing down Spectrometer

A Lead Slowing Down Spectrometer (LSDS) provides a high neutron flux environment that enables measurements of small samples (∼μg) or samples with small cross sections (tens of μb). The LSDS at Rensselaer Polytechnic Institute (RPI) was previously used for fission cross section measurements and for studies of methods for assay of used nuclear fuel. The effective energy range for the LSDS is 0.1 eV to 10 keV with energy resolution of about 35%. Two new LSDS applications were recently developed at RPI; the first enables simultaneous measurements of the fission cross section and fission fragment mass and energy distributions as a function of the incident neutron energy. The second enables measurements of the (n,α) and (n, p) cross sections for materials with a positive Q value for these reactions. Fission measurements of Cf, U, and Pu were completed and provide information on fission fragment and energy distributions in resonance clusters. Measurements of the (n,α) cross section for Sm were completed and compared to previously measured data. The new data indicate that the existing evaluations need to be adjusted.