Design by numerical simulation of an in situ alpha spectrometer operating at ambient air pressure
CEA, DEN, SEAD/LSTD
D. Degrelle, J. Venara, M. Cuozzo and C. Mahé are with the CEA, DEN, DE2D, SEAD, Dismantling Technics and Simulation Laboratory F-30207 Bagnols-sur-Cèze, France (email: email@example.com)
M. Ben Mosbah is with the CEA, DEN, DTN, SMTA, Nuclear Measurements Laboratory, F-13108 Saint-Paul-lez-Durance, France
R. Serrano is with the CEA, DEN, UADF, F-91191 Gif-sur-Yvette, France.
Published online: 20 January 2020
Alpha emitters are usually identified and quantified by alpha spectrometry measurements in a vacuum chamber performed in laboratory environments. This study shows that transuranic elements can be distinguished under ambient conditions using a grid collimator. The aim of this work was to use numerical simulations with the MCNP6 code to design a grid with a resolution high enough to differentiate the same radionuclide combinations as alpha spectrometry in a vacuum chamber, namely 239Pu + 240Pu, 241Am + 238Pu and 244Cm. Results show that a compromise is required to obtain the best performances in terms of energy resolution and detection efficiency, leading to the choice of two hexagonal grid collimators. The first has a collimation height of 0.5 cm and an apothem of 1 mm. Laboratory tests on electrodeposited sources show that the target radionuclides can be identified without prior deconvolution, with an energy resolution of about 70 keV and a detection efficiency of 0.74% at incident energies of 5–6 MeV. The second grid has the same collimation height but a coarser mesh with an apothem of 2 mm. In this case, the alpha peaks are still distinguishable, but with a lower resolution of 125 keV. The detection efficiency is three times higher however.
Key words: Ambient conditions / In situ alpha spectrometry / Monte-Carlo simulations / Nuclear waste / Radiological characterization
© The Authors, published by EDP Sciences, 2020
This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.