On the determination of the post-irradiation time from the glow curve of TLD-100

Abstract

The ratio of peak 3 to the sum of peaks 4 + 5 in TLD-100 was measured for various pre-irradiation and post-irradiation time periods, under conditions characteristic of routine personal dosimetry. It was confirmed that the value of this ratio depends only on the elapsed time between the prior readout and the present one, independent of the moment when the irradiation took place during the total time interval (storage time). This effect indicates that fading of peak 3 seems to be due mainly to changes in the unoccupied traps, and not to decay of trapped charges, being almost independent of the presence of electrons or holes in the traps. This observation leads to the conclusion that the suggestions in the past to use the decay of peak 3 in TLD-100 for the measurement of the elapsed time between irradiation and readout may have been wrong. On the other hand, the decay of peak 2 can be used to measure the elapsed time from irradiation, since the rate of decay is different when related to pre-irradiation and post-irradiation times, indicating a much higher decay rate of the trapped charges (Randall-Wilkins decay). However, because of the fast decay rate of peak 2, its use for determination of the elapsed time since irradiation is of little practical significance.

Advantages and disadvantages of luminescence dosimetry

“…Budzanowski et al (1999) demonstrated that by deconvoluting the MCP-N (LiF:Mg,Cu,P) glow curve it is possible to determine the time elapsed since exposure up to about 40 days using the peak 3/peak 4 and peak 2/peak 4 ratios. Weinstein et al (2003) draw similar conclusions, pointing out difficulties in using peak 2 in TLD-100 for this purpose. This feature is still not used in routine personal dosimetry but it could be applied in some special circumstances, e.g.…”

Dose response linearity and practical factors influencing minimum detectable dose for various thermoluminescent detector types

“…When using the entire integrated glow curve, it should be noted that peaks 2 and 3 in LiF:Mg,Ti fade very quickly postirradiation, causing a much faster approach to the limits. This may be remedied by considering peaks 4 and 5 only, though this would cause problems with dosimetry applications requiring other peaks, such as the determination of post-irradiation fading time, which requires peak 2 [14]. In general, over a 90 day deployment period, a prompt dose of below 75 lGy caused crossover with the detection limit within 90 days, while a prompt dose of above 75 lGy did not cross the detection limit but did cross the determination limit within 90 days.…”

“…If such a program is necessary for the desired dosimetry application, such as for determination of post-irradiation time in LiF:Mg,Ti, which requires the measurement of the areas of peaks 2, 3, 4, and 5 [14] and no other limit applies, some dosimetry applications may not be possible once the individual peaks in a glow curve are no longer separable by the computer.…”

Technical note: High‐dose and ultra‐high dose rate (UHDR) evaluation of Al2O3:C optically stimulated luminescent dosimeter nanoDots and powdered LiF:Mg,Ti thermoluminescent dosimeters for radiation therapy applications

“…13 A potential drawback in the use of TLDs and Gafchromic film are that they demonstrate a strong temporal dependence in their measured signal after irradiation and thus require that the user wait for some amount of time for the signal to stabilize before measurements are recorded. 1,2,[14][15][16][17][18][19] Optically stimulated luminescent dosimeters (OSLDs) are another type of radiation detector that are widely used clinically for dose verification after the delivery of ionizing radiation in conventional dose rate (CONV) RT. Although the use of Al 2 O 3 :C OSLDs is fairly common in routine clinical practice, 20 their use and characterization in UHDR conditions has only been performed in a continuous radiation delivery proton FLASH pencil beamline with average dose rates ranging from 1 to 9000 Gy/s for OSLDs, with demonstrated dose-rate independence.…”