Direct mathematical method for calculating the photofraction and intrinsic efficiency of 4πNaI(Tl) borehole cylindrical detectors

A direct mathematical method for calculating the photofraction and intrinsic efficiency of a borehole cylindrical detector is derived using a direct mathematical method. This method depends on the photon path length inside the detector active volume and the geometrical solid angle Ω subtended by the source to the detector. The comparisons with the experimental and Monte Carlo method data reported in the literature indicated that the present method is useful in the efficiency calibration of the borehole detector.