Thermal neutron distributions near material discontinuities

• Main Author: Fehlberg, William Thomas
• Format: Others
• Published: 1964
• Online Access: https://thesis.library.caltech.edu/3508/1/Fehlberg_w_1964.pdf; Fehlberg, William Thomas (1964) Thermal neutron distributions near material discontinuities. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/GSNH-HP15. https://resolver.caltech.edu/CaltechETD:etd-09132002-091916 <https://resolver.caltech.edu/CaltechETD:etd-09132002-091916>

A method is presented for the approximate calculation of the neutron flux near plane interfaces between different heavy monatomic gaseous media with absorption cross sections inversely proportional to the neutron velocity. Approximate analytic results are obtained for both the diffusion theory and transport theory models. It is found that the flux on each side of the interface can be approximated by the sum of two terms. One term has the same energy dependence that would exist in an infinite medium composed of the heavy monatomic gas that is on that side of the interface. The spatial dependence of this term is determined by diffusion theory. The other term, called a boundary layer correction, makes an appreciable contribution to the flux only near the interface. The procedure presented develops equations and boundary conditions which determine the different terms of the approximate flux. It is found that the approximate flux at the interface, for both diffusion and transport theory, is the average of the two infinite medium fluxes.