Theoretical Study of Slit Scattering

Abstract

An expression is derived for the flux of multiply scattered charged particles emerging from a square‐edge collimating slit for a parallel beam at normal incidence. Full allowance is made for the continuous energy loss in the slit material, and the results are compared with those from Courant's theory. The effective increase in aperture is calculated for 50‐MeV protons on elements throughout the periodic table and the optimum materials for collimators are discussed. A computation of the origin on the collimator face of the slitscattered flux from 50‐MeV protons on copper shows that over 90% originate in the first 0.025 cm from the edge, when all energies are detected, and in less than 0.01 cm for energies above 37.5 MeV. The energy distribution is calculated as a function of the angular range accepted. The projected angle distribution, integrated over all energies, is found to have a maximum at about 1.5° for carbon, 4° for copper, and 7° for lead, with 50‐MeV incident protons. The higher energy slit‐scattered protons are shown to peak at smaller angles. Approximations in the theory are discussed and the results compared with those from Monte Carlo calculations by Becker and from the work of Överås.