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Fine-tuning investigation of the dosimetric parameters in LiF:Mg,Ti )TLD- 100): Dose response as a function of cooling, heating, and dose rates
Bokobza Yogev1; yogoev3@gmail.com
Prof. Oster Leonid1, Prof. Yigal S. Horowitz2
1Sami Shamoon College of Engineering, Be’er-Sheva, Israel. 2 Ben-Gurion University of the Negev, Be’er-Sheva, Israel.
An experimental investigation into the possibility of dose-rate effects in the thermoluminescent )TL( response of LiF:Mg,Ti )TLD-100( was conducted. This investigation was motivated by theoretical simulations predicting the possible presence of dose-rate effects coupled with the lack of detailed experimental studies. The dose rate was varied by changing the source to sample distanceand using attenuators and 137Cs sources with various levels of activity. A carefully controlled experimental investigation was then carried out by the “Needle in the Haystack“ group at the Ben-Gurion University of the Negev )BGU( and the Sami Shamoon College of Engineering )SCE(. Four levels of dosage, in the linear dose response region, were studied at 10-2 Gy, 1.5 x 10-2 Gy, 0.1 Gy, and 0.5 Gy. These investigations did not show dose-rate effects to within precision measurements of ~ 5-10% )1 SD(. At 1.5 x 10-2 Gy, the dosage rate was varied by five orders of magnitude from 4.9 x 10-3 Gy s-1 to 4.9 x 10-8 Gy s-1. At the other dosage levels, a one to two order of magnitude difference in dosage rate was achieved. It was deemed necessary to carry out an additional dose-rate study at a higher level, specifically at 15 Gy. This additional dose range is important in clinical radiation dosimetry, where accuracy is of great importance. I personally carried out the new experiment, as part of my M.Sc. research. Within a measurement uncertainty of 5%-10%, no dose-rate effects were observed in any of the experimental measurements and no changes were seen in the observed shapes of the glow curves. These results are encouraging with respect to the accurate and reproducible use of LiF:Mg,Ti under various experimental conditions of irradiation.
One of the objectives of this study was to investigate the possible effects resulting from different heating rates. The analysis of the data revealed no significant variations in the maximum intensity of glow peak 5 )IMAX( as a function of the heating rate. This finding is consistent with previous studies, which indicated that peak 5 obeys first-order kinetics. However, noteworthy distinctions were observed in the shape of the glow curve leading to observable shifts in the temperature at maximum intensity )Tmax( with varying heating rates. This suggests that the shape of the glow curve )the relative intensity of the various glow peaks( is sensitive to changes in the heating rate. These findings will, hopefully, contribute to a better understanding of the TL characteristics of LiF:Mg,Ti. Further investigations and analyses are recommended for deeper insights into the underlying mechanisms governing these observations.
The cooling rate to room temperature, following the 400oC pre-irradiation anneal, is known to affect the TL properties of LiF:Mg,Ti )TLD-100(, as a result of the migration and clustering of defects during the cooling process. In this investigation, the dose response over the dose ranges from 0.76 Gy to 50 Gy, in both naturally-cooled and the much slower furnace-cooled samples, has been measured. The average precision in three separate, independent studies was essentially identical
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