EPJ Web of Conferences 225, 06004 (2020)
https://doi.org/10.1051/epjconf/202022506004

Design by numerical simulation of an in situ alpha spectrometer operating at ambient air pressure

CEA, DEN, SEAD/LSTD

^* deborah.degrelle@safetechnologies.fr
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: julien.venara@cea.fr)
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

Abstract

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.