Abstract
Monte Carlo radiation transport modeling is an indispensable tool for understanding the fate of radionuclides released into the environment after a nuclear accident. Radiation transport modeling is used to derive conversion factors for in air detector responses to ground contamination levels, and thus for quantifying the activity and distribution of radionuclides released to the environment. In the converse scenario, radiation transport modeling is used to predict future air dose rates upon separate modeling results for radionuclide movements and decay within the environment. We have studied the effect of land topography on air radiation dose levels across a range of heights from ground level to 300m using the PHITS Monte Carlo particle transport code. The geometries considered were a simple conical geometry, where the angle was varied to simulate locations from hilltops to valley bottoms, and angled ground at the intersection of two planes, where the land surface gradient changes uniformly perpendicular to a horizontal axis. Relationships between the air dose rate and the activity of radiocesium on the ground were derived for these geometries. The results show that air dose rates at large heights above the land surface are more strongly affected by land topography than dose rates measured close to the ground.
