The effect of volume- and surface-distributed activity sources on surface doses

The purpose of this study is to investigate and evaluate the effects of surface and volume activity distributions from spherical-shaped hot particles on surface doses at 4, 7 and 40 mg cm(-2) using the Monte Carlo neutron particle code. The work attempts to examine whether surface dose levels increase or decrease when activity, otherwise distributed throughout the sample volume, is all relocated to the sample surface. Apart from small diameter sources (<0.5 mm), the results clearly indicate that for all depths and source densities, calculated doses based on volume distributed activity are likely to be underestimated. The conversion factors vary depending on the source diameter, the source density and the thickness of the activity layer. To further enhance the study, a comparison between measurements and calculations was also made and discussed.