Inversion methods are very important components of nuclear-geophysical technologies. Their main aim is to evaluate the set of parameters of a formation, using measurements data. The parameters describe the properties and the elemental content of it, and they enter into coefficients of the transport equation. In this paper we develop and formalize an approach to problems on mathematical interpretation of the data, we state two inverse problems to the equation and construct successive approximations of the "prime" iteration type to solve a corresponding system of parameters evaluation. The approach is based on concepts defined of "characteristic" interactions, elements, and matrix, it uses the superposition principle for transport processes and linear a priori constraints for the unknowns. Earlier a few concrete problems were examined within this approach