Effects of Heating Rate and Dose on Trapping Parameters of TLD-100 Crystals

Abstract

The characteristics of the thermoluminescence glow curve and dosimetric peak of LiF:Mg,Ti (TLD-100) crystals are studied, with emphasis on the evaluation of the influence of the irradiation dose and heating rate on the dosimetric peak (peak 5) trapping parameters. These parameters were obtained using a computerized deconvolution routine that assumed first-order kinetics for each peak composing the glow curve. This routine was able to fit accurately (1.2% < FOM < 3.4%) all measured glow curves. It was found that for the evaluated range of photon doses (0.2 to 20 cGy) and heating rates (7 to 25 K/s), the behavior of the dosimetric peak was consistent with the predictions of the Randall-Wilkins first-order kinetic model. In particular, it was confirmed that the activation energy of the dosimetric peak is independent of the heating rate and irradiation dose, as expected from this model. The mean activation energy obtained for peak 5 was 2.27 ± 0.08 eV. The area under the experimental glow curves for the same dose remained stable regardless of the heating rate used, indicating that the thermal quenching effect did not have a significant influence within the studied range. By fixing the heating rate and varying the dose, it was found that the integral was proportional to the irradiation dose, as expected.

Investigation of Thermal Quenching Effect for Lithium Fluoride (LiF) Type Dosimeters

“…Similarly, TLD-100 was not affected by thermal quenching at 10mGy when ROI was used. In this regard, the results obtained for TLD-100 were consistent with the literature of [11][12][13]. However, thermal quenching was observed only at the 10mGy when only the total area value was considered.…”

“…Although partial increases were observed in the initial heating rates for TLD-600 and TLD-700, the area values in general varied between 1.00 and 1.10 (Figure 4c,d). As a result, all dosimeters did not show thermal quenching effect at 1000mGy as opposed to 10mGy over the total area Most thermal quenching studies for TLD-100 in the literature generally do not show thermal quenching for in the order of Gy [11][12][13]. In the study performed by Caprile et al [13] in the order of mGy, the area of the peak did not change according to the heating rate, that there was no thermal quenching.…”

“…As a result, all dosimeters did not show thermal quenching effect at 1000mGy as opposed to 10mGy over the total area Most thermal quenching studies for TLD-100 in the literature generally do not show thermal quenching for in the order of Gy [11][12][13]. In the study performed by Caprile et al [13] in the order of mGy, the area of the peak did not change according to the heating rate, that there was no thermal quenching. Apart from this, there are rare studies reporting existence of thermal quenching in TLD-100 [14].…”

“…The results showed that all the peaks were not affected by thermal quenching. According to another study for TLD-100 performed by Caprile et al [13], the variation in the area of dosimetric peak (peak 5) was investigated for four heating rates (7,10,15 and 25°C/s) for the dose of 0.2, 2 and 20cGy. No significant change was observed attributable to thermal quenching, although a slight decrease in intensity was observed.…”

Analytical model for photon peripheral dose estimation in radiotherapy treatments

“…Finally, after the general model was trained to absorbed doses measured with the same TLD-700 used for fitting the basic model parameters, a totally independent validation was performed under the measurement conditions in table 2. Measurements in these cases were carried out using an independent dosimetric system based on pairs of TLD-100 dosimeters [21]. The TLD-100 readings were firstly converted into photon-absorbed doses through the calibration factor f=0.101 11 Gy/μC, obtained using a 6 MV beam.…”