The probability and intensity of nuclear reactions involving neutrons are
characterized by the corresponding reaction cross-sections which are known to
depend strongly on the incident neutron energy. In real applications the
neutrons are seldom or never monoenergetic, and are usually characterized by
certain continuous energy spectrum. The detailed knowledge of the neutron
spectrum is crucial for numerous applications such as the nuclear reactor
operation, the traveling wave reactor (TWR) development, including the search
of the neutron energy ranges suitable for the wave nuclear burning, the search
and prediction of the so-called "blowup modes" in neutron-multiplying media,
the verification of neutron moderation theories and so on. In this paper we
describe a method of GEANT4-based Monte Carlo calculation of the neutron
spectrum evolution as well as the steady-state neutron spectrum in a system
containing a persistent neutron source.Comment: 18 pages, 10 figure