engleski

Influence of thermal annealing on the characteristics of different Al2O3 thermoluminescence dosimeters.

The method of thermal annealing is indispensable in thermoluminescence (TL) dosimetry for obtaining reliable and reproducible results. Depending on the crystal structure of the dosimeter material as well as the kind and concentration of the activator, TL dosimeters based on Al2O3 can be used in different dose ranges. In this work the influence of various parameters of annealing on the properties of TL dosimeters (sensitivity, reproducibility, the shape of the glow curve) was investigated. Three types of TL dosimeters based on Al2O3: Al2O3:C, Al2O3:Mg, Y with 0.5% and 1% of activator, respectively were investigated. The way of thermal annealing (temperature, heating rate and cooling rate) significantly affected the sensitivity and reproducibility of the TL response of Al2O3:C while the same parameters had no influence on the characteristics of Al2O3:Mg, Y dosimeters. Because of the elimination of F-centres1 both on the surface and inside the Al2O3:C crystal, high temperature annealing (900 &ordm ; C) caused a significant (10-50%) sensitivity decrease. This process was irreversible. The optimum annealing procedure was found as follows: ● Al2O3:C 270 &ordm ; C /35 (reading cycle) ● Al2O3:Mg, Y (0.5%) 600 &ordm ; C/ 1 h (high heating and low cooling rate) ● Al2O3:Mg, Y (1%) 600 &ordm ; C/ 1 h (high heating and low cooling rate). The comparison of dosimetric characteristics in case of an optimum treatment gave the following results: ● relative TL sensitivity increases in the series Al2O3:Mg, Y (0.5%): Al2O3:Mg, Y (1%): Al2O3:C =1:2:1000, reproducibility of the calibration factor (expressed as the standard deviation of the measurements) is less than 5% for all types of TL dosimeters.

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