http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
effects of flux anisotropy on thermal neutron flux perturbations
The effects of neutron flux anisotropy upon thermal neutron flux perturbations were found by experimentally determining the perturbations induced by foils placed in fluxes of known angular distributions. Anisotropies in the magnitude of the vector flux were introduced by placing a "black" cadmium absorber sheet in an isotropic flux produced by a uniform slowing down source in water. The resulting angular distribution of the thermal neutron flux was computed by using Yvon's method to solve the Boltzmann equation for an absorbing half space containing a uniform slowing down source. Using indium foils with thickness from 14 mg/cm² to 184.9 mg/cm², the flux perturbations were measured to within (plus or minus sign) 1% in regions which varied from a highly directional flux near the cadmium surface to essentially an isotropic distribution several mean free paths from the absorber. In addition, the dependence of flux perturbation on a neutron angular distribution was studied theoretically by investigating the change in the modified Skyrme theory due to the anisotropies present in the experimental test section. Furthermore, the effects of the neutron temperature change in the test section on the calculated flux perturbations were also investigated. The theoretical predictions that the flux depression would decrease in the region of a boundary were experimentally verified. The experimental data indicated that the flux perturbation remained constant at all distances greater than about five mean free paths from the non-re-entrant boundary, but decreased in the region near the boundary. It was concluded that this decrease was due to both neutron angular distribution and temperature changes. The temperature and anisotropy effects were separated, and it was observed that, with the temperature effect removed, the flux perturbation remained constant at all distances greater than about three mean free paths but decreased significantly near the boundary.
Ph. D. in Nuclear Engineering Texas A & M University