Optimization of gross alpha measurements using Monte-Carlo simulations

As part of the French radioactivity monitoring of drinking water, the gross alpha measurement takes an important place for rapid screening of the indicative dose. The evaporation method is commonly used in France because it is easier to perform and cost-effective, but the reproducibility is very poor (i.e. up to 40%). For this purpose, the Institute for Radiation Protection and Nuclear Safety (IRSN) propose to study the gross alpha measurement using Monte Carlo N-Particles (MCNP) calculations. In addition, a method using autoradiography has been developed for modeling realistic salt deposit. The model is able to predict the total efficiency with uncertainty considering all sources of variability in the gross alpha measurement. The model has been validated experimentally with a mean relative error of 6% for simulated detector counting efficiency and self-absorption correction factors. Comparison between simulated self-absorption curves made up with different radionuclides has demonstrated the area density should be limited to 2.5 mg.cm
^-2
.