LOW PRE-IRRADIATION AND POSTIRRADIATION FADING OF LIF-MG,TI (TLD-100,TLD-600, TLD-700) USING A PREHEAT TECHNIQUE

High pre- and post-irradiation fading prevents the attainment of high accuracy in dosimetry measurements, especially in routine dosimetry wh en the exact duration and time of exposure are not known. An attempt w as made at the Soreq Dosimetry Centre to reduce the fading following o r preceding gamma radiation, by employing a high post-irradiation preh eat temperature of 150 degrees C. Measurements of TLD-100, TLD-600 and TLD-700 were conducted during mild and hot seasons, for fading period s that varied from 1 to 27 weeks. Findings showed relatively little fa ding for both pre- and post-irradiation, with a slightly higher fading during the hot and humid season. One-month fading varied between 7% f or TLD-100 and similar to 10% for TLD-600 and TLD-700. Somewhat higher losses occurred after 3 months: similar to 11% and similar to 14%, re spectively. The overall loss of the TL signal for the main type of dos emeter (TLD-100) issued for one month of use and 'in the field' for ap proximately two months, was 12 +/- 1% regardless of the actual time of exposure to gamma radiation during the issue period. A simultaneous c omparison study that was carried out with a lower preheat temperature of 100 degrees C showed a much higher post-irradiation fading. The los s of TL signal for TLD-100 due to storage following gamma irradiation was 19% and 22% for one and three months, respectively, thus lending s upport to the claim that the technique of high preheat temperature red uces the fading of LiF:Mg,Ti TL signal.