Measurement of the spectra of multiply-scattered radiation in a medium irradiated with Co60 gamma rays

Abstract

A knowledge of the spectral distribution of scattered radiation at a point is of value in planning effective radiation therapy and adequate personnel protection. Some spectra have been calculated theoretically or measured experimentally for a few particular irradiation conditions. In this investigation, the spectral distributions of multiply-scattered Co60 radiation were measured at depths of 2 cm., 5 cm., 10 cm. and 15 cm. in tissue-equivalent material with beam areas of 25 cm.2 and 100 cm.2. Total-scatter spectra, including both singly- and multiply-scattered radiation, were measured at various angles. Then, upon subtraction of the single-scatter spectra contribution from the total-scatter spectra, multiple-scatter spectra were obtained. The integrated and corrected multiple-scatter spectra were compared to corresponding spectra derived from data calculated by Bruce using the Monte Carlo method. The shapes of the experimental multiple-scatter spectra show fair agreement with Bruce's theoretical spectra. The greatest discrepancy between the spectra occurs in the low-energy end of the spectra. For all measured depths and beam areas the theoretical low-energy peaks appear at an energy from 10 to 30 KeV higher than that of the experimental peaks.