A Monte Carlo method to calculate the average solid angle subtended by a detector to an ellipsoidal surface or solid source at any position and orientation.

This note discusses and implements an algorithm for modelling a uniform distribution over a scalene ellipsoidal surface or in a solid so that a Monte Carlo method, suitable for a personal computer, can be used to calculate the average solid angle subtended by a right cylinder or rectangular cuboid detector to the ellipsoidal surface or solid at any position and orientation. The distributions over the surface include 2π and 4π surface sources. The algorithm is developed for truncated ellipsoidal solid and surface sources (where the planes of truncation are restricted to those normal to one of the semi-axes).

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.