A FORTRAN Facility to Compute Physical Parameters for Multigroup Gamma Ray-based Logs

Efficient numerical solutions of gamma ray transport equations in geological media normally require an additional process that includes a scheme of diffusion for multiple coupled energy groups. To predict adequately the values of the experimental and theoretical parameters in a such scheme it is necessary a new look that takes into account the wide variation of nuclear parameters with gamma ray energies. Unfortunately, many of these parameters cannot be determined directly from the tabulated data. To overcome this problem it is introduced FORTRAN algorithms to include these groups coupling and can at the same time be applied to a wide variety of lithologies with 1 ≤ Zeff ≤ 20. To perform this approach, many FORTRAN subroutines and functions are developed to compute diffusion coefficient and total and scattering cross-sections for a large number of discrete energy groups. It is found that any intervals of energy below 5 MeV can be simply implemented and have successful applications on the computation of these parameters in addition to the elements of a transition matrix that couples energy groups. As a help an useful and simple scheme for group selection is also proposed, which has improved the accuracy of the FORTRAN algorithms.