Effect of TLD-700H (LiF: Mg, Cu, P) sensitivity loss at multiple read-irradiation cycles on TLD reader calibration

We investigated the loss of sensitivity on Thermoluminescent Dosimeter (TLD)-700H(LiF: Mg, Cu, P) by Thermo Fisher Scientific at multiple read-irradiation cycles on two different TLD readers. Our test results suggest that the current Time Temperature Profile (UP) with a maximum temperature of 260 degrees C overheats DT-702/PD's thinnest chip 3 causing 29% +/- 7.4% loss in sensitivity over 1000 cycles. For the other three elements, it is significantly less. A possible cause of this effect is overheating of element 3. Our results indicate that one possible solution is to modify TTP for all chips and decouple the UP for chip 3. There is also significant variability ranging from 22% to 40% between different TLD's and 8%-22% for different readers. Calibration cards undergo the highest number of heats and irradiation cycles because they are used to calibrate TLD's and readers. The stability of calibration card's sensitivity is critical to provide accurate dose of record. Any change in the calibration card element correction coefficient (ecc) is reflected immediately in calibration of other TLD's and readers. A variety of processes have been implemented to control sensitivity of calibration cards. Proficiency and intercomparison results support the current operating policy and procedures to protect the accuracy and efficiency of our personnel dose program. Suggested TIP modification may reduce the loss of sensitivity for and may extend the life of calibration TLD's to over 1000 heat cycles. Published by Elsevier Ltd.