The Reusability of Solid Thermoluminescent Dosimeters and Its Relation to the Maintenance of TL Standards

Abstract

Widespread use of LiF in personnel dosimetry has generated a requirement that material be selected on a continuing basis which has the same sensitivity as that already deployed. The preservation of TL standards over a long period requires that the standard be reusable without change. Studies have been made to determine the effect ofhandling, heating, cleaning and exposure to radiation on the lifetime of solid LiF dosimeters.Handling with tweezers has been found to produce abrasions and to change the sensitivity of the dosimeters by as much as 0.1 % for each time they are grasped by metal tweezers. The use of vacuum handling tools avoids such changes. While significant changes in sensitivity occur upon annealing, the long term effects ofmultiple readout cycles do not damage the dosimeter. Dosimeters have been subjected to 1200 readout cycles without change in sensitivity. Based on these results, a system of standardization of materials has been devised which should provide for maintenance of a TL light standard for many years.

Experimental and Monte Carlo determination of the TG-43 dosimetric parameters for the model 9011 THINSeed™ brachytherapy source

“…TLD-100 microcubes were used for all phantom measurements and were handled with vacuum tweezers. 18,19 All dosimeters were fully annealed before and after each experiment at 400°C for 1 h, quickly cooled on aluminum plates, followed by an 80°C anneal for 24 h. Dosimeters were read 24 h after exposure using a Harshaw model 5500 TLD reader which uses hot nitrogen gas to heat the TLDs. The timetemperature profile included an initial heating to 50°C followed by a data collection region using 13°C s −1 temperature increase and a maximum temperature of 350°C.…”

Dosimetric characterization and output verification for conical brachytherapy surface applicators. Part I. Electronic brachytherapy source

“…TLD-100 (LiF: Mg, Ti) microcubes were used for all phantom measurements and were handled with vacuum tweezers. 41,42 All dosimeters were fully annealed before and after each experiment at 400 • C for 1 h, quickly cooled on aluminum plates, followed by an 80 • C anneal for 24 h. Dosimeters were read 24 h after exposure using a Harshaw model 5500 TLD reader which uses hot nitrogen gas to heat the TLDs. The time-temperature profile included an initial heating to 50 • C followed by a data collection region using a 13 • C s −1 temperature increase and a maximum temperature of 350 • C. Each cube was marked on one edge with a pencil for consistency in positioning during readout.…”

Long Term Recycling Characteristics of LiF (TLD-100) Dosimeter Material

“…No cleaning procedures were performed at any time, to eliminate the possibility of introducing an extraneous variable into the experiments. Cox et al (Co76) have demonstrated that a decrease in TL intensity of nearly 25% occurs due to rough handling over 50 readout cycles. In our study, extreme care was used, and in no case could surface scratches be shown to affect the TL response.…”

“…The recent data of Cox et al (Co76) indicate that if solid LiF dosimeters are not annealed but are simply cycled through a 30 sec readout procedure to 240"C, they could be re-used up to 1200 times with only a 5% decrease in sensitivity. Of course, few workers would use a group this many times without recalibration.…”

“…The continued re-use of solid TL dosimeters with the standard 400°C annealing cycle is known to produce changes in sensitivity (Co76). This is related to the fact that the heating and cooling processes can cause changes in the concentration of lattice defects in such samples (St75).…”