The solid angle subtended by a well-type detector and a cylindrical source.

A Monte Carlo approach, based on total variance reduction, was presented in order to evaluate the solid angle subtended between a well-type NaI detector and a cylindrical source within the well. The results obtained, in the form of the geometrical efficiency εg, were within 0.7% of those in the literature, for a point and a volumetric radioactive source within the well. The effect of self-absorption on the geometrical efficiency was investigated for different gamma-ray energies emitted by the volumetric source, different source matrices and radii. Self-absorption is found to be particularly significant for gamma-ray energies below 300keV regardless the source matrix and radius. Furthermore, self-absorption becomes significant, in the case of the larger radius volumetric source, for the gamma-ray energies up to 1MeV considered. Hence, the effect of self-absorption on the geometrical factor should be considered in the absolute quantification of radioactivity of volumetric sources.