A Monte Carlo method to calculate the average solid angle subtended by a right cylinder to a source that is circular or rectangular, plane or thick, at any position and orientation

This note describes the development of a short program for a personal computer to calculate the solid angle subtended by a right cylinder detector to a circular or rectangular, plane or thick source at any position and orientation to the cylinder. The program also calculates the number of hits on the cylinder side and on each end, and the average pathlength through the detector volume (assuming no scattering or absorption). The current performance of personal computers makes it realistic to model the order of 10(9) simulations of radiation emission and achieve accuracies of solid angle estimates typically better than 0.03%.