engleski

Introduction of optically stimulated luminescence based postal audits for radiation protection level dosimetry at Secondary Standard Dosimetry Laboratories

The IAEA has introduced an Optically Stimulated Luminescence Dosimetry (OSLD) system to conduct postal audits to Secondary Standard Dosimetry Laboratories (SSDLs) for radiation protection level. The audit independently checks 137Cs radiation protection air kerma calibrations provided by the SSLDs. The OSLD system has replaced the previously used TLD based audit for radiation protection. The OSLD system used in the audit consists of nanoDot dosimeters and MicroSTARii reader (Landauer, IL, USA). Prior to introducing the audit service, an extensive commissioning process quantified the dosimeter reading reproducibility, signal depletion and fading, linearity of response to air kerma, individual sensitivities of OSLDs and optical annealing procedure for the dosimeters. In an audit run, the participating SSLDs are supplied with two dosimeter sets consisting of two lightweight holders each preloaded with two OSLDs. The participants are asked to irradiate them with 5 mGy air kerma free in air, following their standard laboratory procedures. The OSLDs returned to the IAEA are evaluated by the IAEA Dosimetry Laboratory. The OSLDs demonstrated acceptable reading reproducibility of 1.75% and a signal depletion of 0.25% per readout. The OSLDs signal fading resulted in a signal decrease of 2.1% in the period from eight days to over 160 days post irradiation. A relative expanded (k = 2) uncertainty of the OSLD determined air kerma was estimated to 3.08%. In two audit runs in 2015–2016, 29 SSDLs participated. The average ratio of the air kerma measured by the IAEA to the air kerma stated by the SSDL was 0.998 and the standard deviation of the distribution of results was 1.8%. All participants except one had results within the acceptance limits of ±7%. One laboratory with the result outside the acceptance limit was invited to a follow-up procedure with the aim to resolve the discrepancy.

optically stimulated luminescence dosimetry ; remote audit ; radiation protection ; air kerma

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