Fast Neutron Capture Cross Section Measurements Evaluations And Model Calculations Of Fission Product Nuclei 0 5 To 4 0 Mev

The fast-neutron capture cross sections of elemental rhodium, palladium, neodymium, and samarium were measured in the energy range 0.5 to 4.0 MeV relative to the standard capture cross section of gold. A large liquid scintillator and the time-of-flight technique were used in these measurements. Experimental data are rare or non-existent in this energy range and evaluations differ substantially, with a factor of 5 being common. The present data were used together with other experimental data and nuclear model calculations in order to provide a consistent set of isotopic and elemental capture cross sections. 5 figures.

To satisfy nuclear data requirements for fission-product nuclei, Hauser-Feshbach statistical calculations with preequilibrium corrections for neutron-induced reactions on isotopes of Se, Kr, Sr, Zr, Mo, Sn, Xe, and Ba between 0.001 and 20 MeV. Spherical neutron optical parameters were determined by simultaneous fits to resonance data and total cross sections. Isospin coefficients appearing in the optical potentials were determined through analysis of the behavior of s- and p-wave strengths as a function of mass for a given Z. Gamma-ray strength functions, determined through fits to stable-isotope capture data, were used in the calculation of capture cross sections and gamma-ray competition to particle emission. The resulting (n, .gamma.), (n, n'), (n,2n), and (n,3n) cross sections, the secondary neutron emission spectra, and angular distributions calculated for 19 fission products will be averaged to provide a resulting ENDF-type fission-product neutronics file. 11 references.