Statistical description of radiation fields on the basis of the invariance principle. II. Mean number of scatterings in a medium containing energy sources

Under very general assumptions concerning the elementary scattering event, equations are obtained for determining the mean number of photon scatterings in a three-dimensional semi-infinite medium when the primary sources of the photons are within the medium. The numbers of scatterings of photons that perish in the medium and of photons that leave it are considered separately. The dependence of the number of scatterings on the initial characteristics of the photon is found. The case of scattering with complete frequency redistribution and with allowance for absorption and emission in the continuum is analyzed in more detail. Some new expressions are obtained for the mean number of photon scatterings in semiinfinite and infinite media