Calculation of the average solid angle subtended by a circular disc detector to a circular disc source

The average solid angle subtended by a circular disc to a circular disc was calculated and tabulated for various radii of the circular discs. During the course of calculation, the circular discs were replaced by both circumscribed and inscribed polygons. The calculated values agreed within 0.02% with those suggested by Gardner and Verghese. The present method is simpler to formulate than the existing methods and can be used to evaluate the error involved in the calculation of the average solid angle. (author)