ON THE SLOWING DOWN RELAXATION TIME FOR NEUTRONS IN MODERATORS
In a previous investigation it was shown that the slowing down properties of a moderator could be determined from the rate of decay of thermal neutrons from an instantaneous source of fast neutrons. The assumption was made that the transport mean free path of neutron in the moderator is independent of neutron energy and that the rate of slowing down of neutrons is exponential in time. It is shown that the first assumption may lead to lange errors and that the second assumption is not necessary. When a burst of fast neutrons is injected into a finite moderator, the neutrons rapidly slow down by elastic collision until they reach very nearly the binding energy of the atoms. This stage of slowing down can be treated classically except for complications arising from angular distribution of scattered neutrons and inelastic levels of moderator nuclei. For neutron energy less than the binding energy of the atoms, the classical treatment fails. since the neutrons no longer lose energy by elastic billiard-ball collisions. Equations are given for the decay rate of thermal neutrons and the diffusion coefficient for neutrons at equilibrium temperature. (A.C.)
- Research Organization:
- Atomic Energy Establishment, Trombay, India
- NSA Number:
- NSA-12-017674
- OSTI ID:
- 4286528
- Journal Information:
- J. Nuclear Energy, Journal Name: J. Nuclear Energy Vol. Vol: 7
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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