Measurements of the Neutron Slowing Down Times in Finite Graphite Systems by the Resonance Filter Method

Abstract

To shed further light on the neutron slowing down process, slowing down times were measured in graphite systems by the resonance filter method. The distribution of the slowing down time from 14MeV to a few energy points from thermal equilibrium was obtained in the form of differences of time response between compensation-filter covered and resonance-filter covered BF3 counters. From the time distributions thus determined were derived the most probable slowing down time t max and the average slowing down time <t>, which were compared with the theoretical values calculated with the use of various scattering kernels. The effects of finite medium and space dependence were also evaluated. The values of t max obtained were 9.5±0.5, 10.5±0.5, 20±1, 55±4, 71±4 and 101±8μs for 5.2, 4.91, 1.46, 0.28, 0.2 and 0.11 eV, respectively. Of these values, those over 1.46 eV show good agreement with the theoretical values by 0°K free gas kernel, while those under 0.28 eV agree well with the values by Williams' model, in which the effects of chemical binding and thermal vibration are considered.