Long Term Recycling Characteristics of LiF (TLD-100) Dosimeter Material

Abstract

Changes in the sensitivity of LiF (TLD-100) dosimeters subject to standard 400°C annealing treatments for up to 100 cycles have been investigated. Results indicate that for extruded ribbon dosimeters cycled through a 1-hr, 400°C anneal, the resulting thermoluminescent sensitivity decreases as the number of cycles increases. The maximum effect is seen in samples exposed to 1R of 13'Cs irradiation between cycles, which for annealing in air causes a decrease of about 6% after 50 cycles, accelerating to nearly a 15% decrease in sensitivity after 100 cycles. Samples not exposed to irradiation between cycles show a smaller resultant sensitivity decrease. Comparison of the TL response of samples annealed at 400°C for 100 I-hr cycles to those annealed at 400°C for 2 SO-hr cycles shows a smaller decrease in sensitivity after the 2 50-hr anneals. This indicates that the cause for the observed behavior lies in the heating and cooling process itself, rather than in the time at temperature. Further comparisons between extruded ribbon and single crystal samples and between samples annealed in air, argon or vacuum are also presented. For routine dosimetric use with the standard 400°C anneal cycle, a maximum re-use of 50 times is recommended.