The Calculation of Gamma Ray Penetration of the Walls of Cylindrical and Conical Collimating Holes

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Abstract
The ratio f of quanta from a point source of gamma radiation which penetrate the side wall of a collimating hole to those which pass through the exit pupil of the hole is derived for the cases of a cylindrical and a conical hole. In the case of a cylindrical hole values of f are obtained as a function of [mu]H where [mu] is the linear absorption coefficient of the material of the collimator and H is the distance of the source from its lower plane. It is shown that for a constant value of H, the value of f is constant for all points lying within the projection of the collimating hole. The formulae given apply to any cylindrical hole within the limits of the approximations made in their derivation. The formulae for focusing collimators, where the holes are truncated cones, are derived for axial point sources only, and it is shown that the value of f is smaller in this case than for the equivalent situation with a cyclindrical hole.
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