Reproducibility of glow peak fading characteristics of thermoluminescent dosimeters

This study examines the reproducibility of LiF:Mg,Ti pre-irradiation and post-irradiation fading rates. To test post-irradiation fading, 99 calibrated 3.2 × 3.2 × 0.9 mm3 LiF:Mg,Ti thermoluminescent dosimeters (TLDs) of dimensions were first annealed. The set was then irradiated to an average of 4.4 mGy using a 3.2 × 1011 Bq 137Cs source. The irradiated TLDs were allowed to fade at room temperature for 0.5, 1, 2, 3, 4, 8, or 17 d. The TLDs were then read out over a 3.5 h time period using a standard commercial hot planchet TLD reader with nitrogen gas to prevent chemiluminescence. The experiment was then repeated for the other fading times. To test pre-irradiation fading, the TLDs were annealed, then placed in storage for 0.5, 1.6, 3, 4, 8, 18, 27, or 43 d. After that time, the TLDs were irradiated and read out. A computerized glow curve deconvolution program was used to fit the glow curve data to a four-peak first-order Gaussian kinetics model. The areas of peaks 2, 3, 4, and 5 were retrieved in order to be studied alone, as well as normalized to other peaks. The peak areas and peak area ratios were then fit to two or three term exponential decay equations that allowed the determination of the fading rate by calculating their parameters. These parameters were then compared for different TLDs in order to determine if their values followed a Gaussian distribution. Then, a group mean and standard deviation could be used for each value for all TLDs for later use instead of calculating an individual mean for each TLD.