Discussion on sources of uncertainty for two TLD albedo dosimetry systems in a comparison of individual monitors in a reference 241Am–Be field

Abstract

Under standard conditions, several studies assess uncertainty values for individual dosimetry for photons, but seldom for neutrons. The Thermoluminescent Dosimetry Laboratory (LDT) of the Instituto de Radioproteção e Dosimetria (IRD), Brazil, has been running a neutron individual monitoring service using two different albedo monitors. This paper presents a study of the contribution of relevant sources of uncertainty for neutron dose evaluation, for both systems (called System 1 and System 2), using a reference 241Am–Be field, at normal incidence. The combined and expanded uncertainties were calculated using GUM methodology and follows RP160 from the European Commission. This methodology was applied to calculate the uncertainties associated with the LDT assessment of neutron doses in the First Brazilian National Comparison on Measurements for Neutron Individual Monitors. The LDT participated in this comparison with its two systems, both presenting satisfactory performance. For System 1, at low neutron doses, the reproducibility of the apparent neutron dose is the more relevant source of uncertainty. However, for higher doses, the neutron calibration factor, NCF, becomes more important. For System 2, NCF is the main source of uncertainty for low and high doses. For occupational doses, the uncertainty will be much higher due to the need of additional correction factors, which depend on stray neutron field.