GAMMA-RAY TRANSMISSION THROUGH FINITE SLABS

The quantity which is considered most important is the build-up factor for a monoenergetic, monoangular beam of photons incident on a slab of finite thickness but infinite extent. This quantity is obtained for a set of discrete values of slab thickness, in mean free paths, over the interval o,20 incident energy, in units of mc squared, over the interval 1,20 and incident angle, in degrees, over the interval 0,90. Pb and Fe are used for the slab. The processes used to obtain the set of build-up factors and to establish their accuracy within reasonable limits are such that a considerable amount of supplementary information is produced. This information is also presented. The supplementary results consist of the probabilities and expected energies corresponding to the transmission of photons with exactly 1, 2, of 3 scatterings distributions of the transmitted photons over energy and angle some results for slabs of air and of the pure Compton scatterer some build-up factors in an energy range just below that stated above photon and energy densities for 3 source configurations and other quantities which on occasion might prove interesting or useful. A discussion of the effect of variation of the total absorption coefficient on transmission probabilities is given which leads to estimates of build-up factors for a material of arbitary atomic number Z.