Spectral gamma-ray calculations with an efficient and accurate radiation transport model

This paper describes applications of a versatile computer model that simulates natural gamma-ray spectroscopy measurements. In the modeling procedure, gamma-ray fluxes are calculated throughout a rock formation, borehole, and logging tool with a fast and accurate discrete ordinates radiation transport code. Independently, a Monte Carlo code calculates the detector response functions. An enfolding code then combines the flux results with the response functions to generate a pulse height spectrum. Since the flux calculations are decoupled from the detector response calculations, detector responses need be calculated only once for a given detector. Subsequent investigations of detector sensitivity to alterations in the environment, such as changes in tool design parameters, require modifications in the discrete ordinates codes only. This modeling approach permits efficient modeling of tool responses for a variety of rock formations, gamma-ray sources, borehole conditions, and detector types. The accuracy of the model has been established by comparing calculated results with experimental borehole data. Calculated count rates agreed, in an absolute sense, with measurements to within 8 percent