On mathematical modeling of pulsed neutron-gamma log problems

The work is devoted to the direct and inverse problems of the transport equation, which are connected with a type of nuclear geophysical technologies, namely, the problems of the pulsed neutron-gamma inelastic log. In the first part we analyze the distribution of fast neutrons from a pulsed source of 14.1 MeV, and also we study the distribution of inelastic scattering gamma-quanta. The distributions of particles are computed by Monte Carlo methods. In the second part of the paper we consider the problem on evaluating the elemental composition of the formation based on measurement data. To solve it the method of "successive approximations by the characteristic interactions" is used which relates to the “prime” iteration type. At each iteration step the corresponding direct problem for the system of transport equations for neutrons and gamma quanta is solved. It is presented main points of the method and the results of numerical experiments confirming the convergence to the exact solution.