I. Introduction
The detection of gamma rays emitted by 238U and its daughter nuclei is one of the reference methods for detecting uranium in borehole. One approach consists in inferring the uranium concentration in boreholes from the total count rate provided by scintillation counters such as NaI(Tl) detectors. This approach, known as gross count gamma-ray logging [1], [2], requires a calibration coefficient which is usually measured in the concrete blocks of well-defined composition with known uranium concentration. However, the measurement conditions of the calibration coefficient are not always representative of field conditions and corrections of the measured calibration coefficient are needed [1]. This paper reports numerical simulations performed with the Monte Carlo N-Particles (MCNP) code in view to improve the accuracy of uranium concentration determination in gross count gamma-ray logging.