  In this paper we present the analytical expression for the neutron scattering
law for an isotropic source of neutrons, obtained within the framework of the
gas model with the temperature of the moderating medium as a parameter. The
obtained scattering law is based on the solution of the kinematic problem of
elastic scattering of neutrons on nuclei in the L-system in the general case.
I.e. both the neutron and the nucleus possess the arbitrary velocity vectors in
the L-system. For the new scattering law the flux densities and neutron
moderation spectra depending on the temperature are obtained for the reactor
fissile medium. The expressions for the moderating neutrons spectra allow
reinterpreting the physical nature of the underlying processes in the thermal
region.
