Neutron diffusion and thermalization parameters : measurements with graphite and theoretical review

Underlying theories of thermal neutron diffusion length and pulsed-neutron decay constant are introduced. Then follow reports on the measurements of these quantities which were carried out with graphite at Nuclear Engineering Department in 1971. This series of experiments produced nuclear reactor physics parameters (L, Σ ̅_a , D ̅∙v ̅ and C) of graphite in reasonable agreement with published values. The discrepancies in some of the parameters are discussed. After the report, the recent developments in neutron thermalization theory are reviewed. In particular, the minimum transverse size of a graphite prism required in diffusion length measurement is derived following William’s work. Then the mechanism of pseudo-discrete mode, which appears as a single exponential decay in pulsed-neutron experiment, is illustrated following Corngold and Durgun’s work. The present article is intended to present an introductory, simple review of the efforts in this field by these two examples. It is intended to make this field accessible to broad range of researchers in both within and outside this field. Possibilities of further investigation on neutron transport are discussed for thermal (0-0.l ev) and fast (0.1-15 Mev) neutron energy ranges.