Study of coincidence summing effect using Monte Carlo simulation to improve large samples measurement for environmental applications.

A new measurement model composed of High Purity Germanium detector HPGe including Lead Shield with a mixed source of Am-241, Cd-109, …in a soil matrix packed in a cylindrical container was developed by Monte Carlo N-Particles code MCNP5. The Monte Carlo models being largely used for efficiencies calculations in routine environmental radioactivity measurements of high volume soil samples. In order to validate the simulation, a multi-radionuclides soil matrix source in a cylindrical container is prepared. Comparing the simulated results to the experimental ones, allows us to correct coincidence summing in the soil standard and study its effect in activity measurements where a good agreement is found between corrected activities and results found by another geometry and show how uncorrected efficiency curves lead to erroneous activity calculation. Finally, the developed model is applied to study the distribution of natural and artificial radioactivity in a forest site in Bainem, northern of Algeria, these results are invested for radiological impact and soil erosion studies in the study Area.

Monte Carlo calculations of the HPGe detector efficiency for radioactivity measurement of large volume environmental samples.

A fully detailed Monte Carlo geometrical model of a High Purity Germanium detector with a (152)Eu source, packed in Marinelli beaker, was developed for routine analysis of large volume environmental samples. Then, the model parameters, in particular, the dead layer thickness were adjusted thanks to a specific irradiation configuration together with a fine-tuning procedure. Thereafter, the calculated efficiencies were compared to the measured ones for standard samples containing (152)Eu source filled in both grass and resin matrices packed in Marinelli beaker. From this comparison, a good agreement between experiment and Monte Carlo calculation results was obtained highlighting thereby the consistency of the geometrical computational model proposed in this work. Finally, the computational model was applied successfully to determine the (137)Cs distribution in soil matrix. From this application, instructive results were achieved highlighting, in particular, the erosion and accumulation zone of the studied site.