Study of dose rate profile at sample disks in a Risø OSL single-grain attachment system

Abstract

The spatial variation of dose rate from a 90Sr/ 90Y calibration source mounted on a Risø equipment TL-DA-15 was investigated. Six disks accommodating single grains of α - Al 2 O 3 :C were irradiated at the Secondary Standard Dosimetry Laboratory (SSDL) at GSF to a uniform photon radiation field. The corresponding single-grain OSL signals of each grain were then compared with those obtained after the irradiation of the disks with the built-in beta source of the equipment. Additionally, the irradiation system was modelled to perform a Monte Carlo calculation assuming a homogeneous source. A continuous drop of the beta dose rate with increasing radial distance from the centre of the disk was observed in the experiments, indicating that grains located in the central part of the disk absorbed a higher dose than those placed in the outer region of the hole matrix. This experimental dose profile pattern was also confirmed by the results of the Monte Carlo calculation. It can therefore be concluded that different calibration factors, depending on the grain location, should be applied in order to improve the reliability of equivalent dose assessment using single-grain OSL measurements.