Abstract:
Alpha dose rate variation has been modelled using Monte Carlo techniques written in MATLAB, providing plausible simulation of alpha dose rate variation in real sediments. The results are particularly relevant when smaller grains must be used and etching to remove the external alpha dose is not feasible. ‘Typical’ sediment environments were created by randomly packing dosimeter and source grains. The alpha track dose rate to dosimeter grains was then calculated as the average of the track dose rate for a series of randomly selected points within each grain. For each such point the track dose was estimated in turn by averaging the track dose rate due to adjacent sources in a series of randomly selected directions. The effects of air or water in pore spaces between grains were included in the calculations. Dose rate distributions can usually be approximated by log-normal distributions, with significant high-dose-rate tails when source grains are sparsely distributed. The average alpha dose rate can differ strongly from uniform-matrix predictions. A bias in the usual “infinite matrix” alpha dose rate estimate is identified, which applies also to all fine grain dating.