Monte Carlo Calculation of Gamma-Ray Albedos of Concrete and Aluminum

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Abstract
Number and energy gamma-ray albedos have been calculated for a material of Zeff=13, corresponding to both concrete and aluminum. The Monte Carlo method was used, the calculations being performed on an IBM-701. The single- and multiple-scattered components were evaluated separately; the multiple-scattered component was considerably the larger of the two in most cases, being as much as three times as large as the single-scattered component. For moderately small incident angles, the emergent photons are distributed approximately proportional to the cosine of the normal angle of emergence. The spectra peak around 150–250 kev and in some cases have a second peak at higher energy; such secondary peaks move upward in energy and increase in importance as the angle of incidence increases. The average energy of the emergent photons varies from 0.33 to 1.4 moc2. For the multiple-scattered component the average energy varies from 0.30 to 0.93 moc2. Buildup factors have been calculated for 2 moc2 gammas normally incident on aluminum of 2 and 4 mean free paths thickness.

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