Time-Dependent Thermal-Neutron Energy Spectra in a Monoatomic Heavy Gas PDF Download

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The time-dependent thermal neutron energy spectra, for times greater thsn the slowing-down time, were generated in a monoatomic heavy gas using multigroup formalism. These spectra were obtained for infinite as well as finite media of Be and graphite. The behavior of asymptotic energy spectra during the last stage of neutron thermalization and diffusion periods was studied. The thermalization time constant for the establishment of the final Maxwellian velocity distribution of neutrons, in a monoatomic heavy gas, was estimated to be equal to (l.l74 xi SIGMA /sub so/v/sub o/)/sup -1/. Total thermalization times for neutrons in Be and graphite were found to be equal to 114 and 238 mu sec, respectively. Using the energy-dependent transport mean free path, the diffusion cooling coefficient for Be was calculated to be equal to 0.890 cm/sup 2/. For graphite, under the constant diffusion coefficient assumption, the diffusion cooling coefficient was determined to be equal to 1.922 cm/sup 2/. (auth).