Experimental Differential Number, Energy and Exposure Albedos for Sem-finite Media, for Normally Incident Gamma Photons

Differential angular and energy distributions of backscattered gamma rays have been measured for photons normally incident on essentially semi-infinite scattering media of various atomic numbers. The measurements have been made by permitting a highly collimated 3- × 3-in. sodium-iodide (thallium-activated) scintillation crystal to view a sample area at the center of a scattering slab region irradiated by a broad beam of gamma radiation. The spectra have been recorded on a 400-channel pulse-height analyzer and reduced to detector incident flux by means of an IBM-7094 digital computer. The results have then been expressed graphically in terms of albedos and fitted to simple empirical expressions. In the case of high-atomic-number scatterers, K x-ray fluorescence has been separately evaluated.