Calculation of the Long-Lived Induced Activity in Soil Produced by 200-MeV Protons

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Abstract
Calculations have been carried out to obtain the time and spatial dependence of the long-lived induced activity in soil produced by 200-MeV protons incident on a small cylinder of graphite buried in soil. Only radioactive nuclei with halflives greater than or equal to that of 7Be (0.147 year) were considered. Monte Carlo methods were applied to determine the induced neutron flux which was combined with both calculated and experimental radiochemical cross sections to determine the rate of residual-nuclei production. Through the use of the results of the calculations, a procedure has been established whereby the approximate contribution of each target nucleus to the production of a particular radioactive nucleus can be obtained. The results of the calculations are also used to approximate the long-lived induced activity in soil when the small cylinder of graphite is embedded first in another material, such as iron, which is in turn surrounded by soil.