Calibration of neutron dosimeters for radiation protection use at the ALBA synchrotron experimental hall

Abstract

Bright beams of synchrotron radiation are produced from a 3 GeV electron accelerator at the Spanish synchrotron facility ALBA. The electron acceleration and storage mechanisms lead to complex secondary radiation fields. These fields include electrons, photons and neutrons of a wide energy range, and have an important pulsed behaviour and very significant spatial variations. In order to perform correct dose assessments for radiation protection purposes, it is necessary to measure separately electrons, photons and neutrons. In the case of neutron dosimetry, given the strong dependence with energy of the radiation weighting factor and of the fluence to ambient dose equivalent conversion coefficient, it is necessary to have some spectrometric information to correctly assess dose. Neutron dosimeters designed at UAB, based on PADC (Poly Allyl Diglycol Carbonate) track detectors, were exposed in different places of the ALBA experimental hall and tunnel. As to date, no calibration facility provides neutron fields similar to those found at ALBA, ambient dose equivalent was originally evaluated with calibration coefficients obtained from calibration at an Am-Be neutron source. A procedure for calibrating the dosimeters based on the knowledge, either by simulation or experimental determination, of the neutron unit fluence distribution ϕE(E) at every specific point of measurement and of the dosimeter response function in terms of fluence Rφ(E) is stablished in this work. Specific values of the calibration coefficient Si, that allows determining the ambient dose equivalent value from trak density measurements, were calculated at different points of interest in ALBA and are in the range 35.8–258 cm-2mSv-1.