Calculated energy response correction factors for LiF thermoluminescent dosemeters employed in the seventh EULEP dosimetry intercomparison

Abstract

Several dosimetry intercomparisons for whole body irradiation of mice have been organized by the European Late Effects Project Group (EULEP). These studies were performed employing a mouse phantom loaded with LiF thermoluminescent dosemeters (TLDs). In-phantom, the energy response of the LiF TLDs differs from free-in-air, due to spectral differences caused by attenuation and scatter of x-rays. From previous studies, energy response correction factors in-phantom relative to free-in-air were available for full scatter conditions. In the more recent intercomparisons, however, full scatter conditions were not always employed by the participants. Therefore, Monte Carlo calculations of radiation transport were performed to verify the LiF TLD energy response correction factors in-phantom relative to free-in-air for full scatter conditions and to obtain energy response correction factors for geometries where full scatter conditions are not met. For incident x-rays with HVLs in the 1 to 3.5 mm Cu range, the energy response correction factor in-phantom deviates by 2 to 4 per cent from that measured free-in-air. This is in reasonable agreement with previously published results. The energy response correction factors obtained from the present study refer to a calibration in terms of muscle tissue dose in-phantom using gamma rays. For geometries where full scatter conditions are not fulfilled, the energy response correction factors are different by up to about 3 per cent at maximum from that at full scatter conditions. The dependence of the energy response correction factor as a function of the position in-phantom is small, i.e. about 1 per cent at maximum between central and top or bottom positions.