AbstractSome problems of the theoretical interpretation of pulsed neutron experiments are investigated in this paper, on the basis of the energy dependent Boltzmann equation. The relation of the infinite medium theory to the finite medium experiments is discussed in details. We perform a calculation inP1L1approximation in order to determine the form of neutron flux and the extrapolation length. It is demonstrated that the existence of an asymptotic region is not required to apply the infinite medium theory to the finite medium experiments.