Geant4 simulation of the moderating neutrons spectrum

In this paper we deal with the problem of predicting a steady-state neutron spectrum in media of arbitrary composition and geometry. The analytical calculations of such spectrum are often too complex, if at all possible. We describe a method of Geant4-based Monte Carlo calculation of the steady-state neutron spectrum in a medium containing a fixed neutron source. In addition to the steady-state spectrum, we obtain the snapshots of the neutron spectrum evolution in time, which may be thought of as the non-equilibrium neutron spectra, and their form is of considerable interest for further studies.
Comment: 18 pages, 10 figures; v2: Revised and extended, 23 pages, 13 figures; v3: more concise and focused revision, 22 pages, 13 figures; v4: revised text, new comparison added to Fig.13, 24 pages, 13 figures