Geant4 simulation of the moderating neutrons spectrum

In this paper we deal with the problem of predicting a steady-state neutron spectrum in media arbitrary composition and geometry. The analytical calculations such are often too complex, if at all possible. We describe method Geant4-based Monte Carlo calculation medium containing fixed source. addition to spectrum, obtain snapshots evolution time, which may be thought as non-equilibrium spectra, their form is considerable interest for further studies.