Low Pre- and Post-Irradiation Fading of LiF:Mg, Ti (TLD-100, TLD-600, TLD-700) Using a Preheat Technique

Abstract

High pre- and post-irradiation fading prevents the attainment of high accuracy in dosimetry measurements, especially in routine dosimetry when the exact duration and time of exposure are not known. An attempt was made at the Soreq Dosimetry Centre to reduce the fading following or preceding gamma radiation, by employing a high post-irradiation preheat temperature of 150°C. Measurements of TLD-100, TLD-600 and TLD-700 were conducted during mild and hot seasons, for fading periods that varied from 1 to 27 weeks. Findings showed relatively little fading for both pre- and post-irradiation, with a slightly higher fading during the hot and humid season. One-month fading varied between 7% for TLD-100 and ∼10% for TLD-600 and TLD-700. Somewhat higher losses occurred after 3 months: ∼11% and ∼14%, respectively. The overall loss of the TL signal for the main type of dosemeter (TLD-100) issued for one month of use and 'in the field' for approximately two months, was 12 ±1% regardless of the actual time of exposure to gamma radiation during the issue period. A simultaneous comparison study that was carried out with a lower preheat temperature of 100°C showed a much higher post-irradiation fading. The loss of TL signal for TLD-100 due to storage following gamma irradiation was 19% and 22% for one and three months, respectively, thus lending support to the claim that the technique of high preheat temperature reduces the fading of LiF:Mg,Ti TL signal.