Design and development of a portable β-spectrometer for 90Sr activity measurements in contaminated matrices

Determining the nature and activity of radionuclides is an important task in the nuclear industry. Pure β-emitters are hard to characterize because the mean free path of electrons in dense matter is very short. Most measurement techniques are therefore based on destructive laboratory analyses. This article presents a non-destructive approach based on a portable β-spectrometer, designed to provide qualitative and quantitative information on pure β-emitters, notably 90Sr. Building on existing methods focused on the measurement of 90Sr activity in natural soil contaminated by the Chernobyl accident, the aim of this project is to develop a detector for the radiological characterization of different types of contaminated matrices, in particular the contaminated concrete structures typically found in nuclear facilities. A measurement device equipped with an EJ200 plastic scintillator was designed using Monte Carlo simulations with the MCNP6 and PENELOPE calculation codes. The energy calibration and the response of the detector were determined using experimental measurements and MCNP simulations of laboratory configurations of standard β-sources. These data were used to validate the model of the detector, as well as to determine calibration coefficients by numerical simulation for various on-site measurement configurations. The device was then used to characterize samples of sand from a decommissioning site in France (Fontenay-aux-Roses). The resulting 90Sr activities are within experimental uncertainties of those obtained using destructive measurements. These results are promising for wider applications on nuclear decommissioning sites.