A METHOD OF INDIVIDUAL CALIBRATION OF LIF OPTICAL-ABSORPTION DOSIMETERS

Optical grade crystals of lithium fluoride (LiF) have been developed f or high level (50 MGy) and high temperature (250-degrees-C) dosimetry at GSF, based on optical density (OD) measurements. The measuring accu racy however was limited by a relatively high coefficient of variation (20%) for the interspecimen scattering of response. A method is descr ibed to improve precision by individual probe calibration at a relativ ely low dose level (1 kGy) by using F-centres only. It is shown that t he calibration factors are applicable at high doses, where other centr es are involved. By this procedure, the coefficient of variation for i nterspecimen scattering can be reduced to less-than-or-equal-to 5%. Th ermoluminescence (TL) and trace element analysis was performed to find an explanation for the interspecimen scattering. While no correlation could be found between optical density and trace element content and between optical density and TL, a strong correlation was observed betw een optical density and fluorescence.