Reflection and transmission of gamma radiation by barriers: Semianalytic Monte-Carlo calculation

Abstract

transport equation for photons which ~ave been Compton-scattered repeatedly with a specJfie~,sequence of energy. losses ~n.d deflectlOn.s was solved analytically, by an " orders of scattermg approach, to obtam cond itIOnal reflectIOn and tranS'11.ission probabilities. These p.roba?ilities were then averaged ~)Ver all possible intermediate angular and energy configura-tIOns m ~ Monte Carlo calculatIOn carne~ out o~ the NBS automatic COTP.puter (SEAC) . The effiCiency of the Monte Carlo calculatlOn was mcreased by taking advantage of the close correlation b.etween the t:ansm!ssio~ of radiation through thick barriers and the correspondmg penetratlOl1 problem III an mfilllte homogeneous medium for which a.n exact solution was avai la.ble .. The reflected and transmitted energy flux (integrated over all spectral energies and duectlOns) has been calculated for 0.66-, 1-and 4-Mev radiation incident on water barriers and 1-, 4-, and 10-Mev radiation incident on iron, tin, and lead barrier s. Angular and energy spectra were obtained for water at 0.66 Mev. The ratio of the scattered energy flux, transmitted through a barner to the scattered fiux at equal depth in an infinite medium was found to be constant for distances from the source greater than four mean fr ee paths df the source radiation.