Elsevier

Radiation Measurements

Volume 47, Issue 2, February 2012, Pages 185-189
Radiation Measurements

Newly developed highly sensitive LiF:Mg,Cu,Si TL discs with good stability to heat treatment

https://doi.org/10.1016/j.radmeas.2011.12.003Get rights and content

Abstract

The preparation method and some dosimetric properties of the new LiF:Mg,Cu,Si discs are presented. The effect of heat treatments on LiF:Mg,Cu,Si was investigated. The shape of the glow curve for LiF:Mg,Cu,Si is similar to that for standard LiF:Mg,Cu,P (GR-200A), and shows minimal differences when annealed in the range from 260 °C to 290 °C for 10 min. The TL sensitivity for LiF:Mg,Cu,Si is much lower than that for GR-200A, but is 35 times larger than that for TLD-100 and is slightly higher than that for HMCP. The height of the high-temperature peaks for LiF:Mg,Cu,Si is not only lower than that for GR-200A, but also lower than that for HMCP. The glow curve shape of LiF:Mg,Cu,Si annealed at 260 °C for different times shows minimal differences and TL response remains stable. These results indicate that the new LiF:Mg,Cu,Si disc has a good stability to thermal treatments and a lower residual TL signal.

Highlights

► The TL sensitivity for LiF:Mg,Cu,Si is 35 times larger than that for TLD-100. ► Glow curve shows minimal differences in the range from 260 °C to 290 °C. ► The temperature between 260 °C and 290 °C can be used to treat LiF:Mg,Cu,Si. ► LiF:Mg,Cu,Si has a good stability to thermal treatments and a lower residual TL signal.

Introduction

LiF-type thermoluminescence (TL) dosimeters have been widely studied for their advantages of TL response and good tissue equivalence. Studies with LiF:Mg,Cu,P have been extensively reported, as this material has the highest sensitivity in the LiF family, but any high-temperature thermal annealing or TL measurement above 240 °C leads to a loss of sensitivity and changes in the glow curve (Yang et al., 2003). Therefore, the identification of new dosimeters that retain high sensitivity and are more stable has been of major interest.

It was reported (Tang et al., 2008) that a new LiF:Mg,Cu,P formulation with enhanced thermal stability allows heating of the material to higher temperatures than that originally employed for the well-known GR-200A dosemeter, practically without losses in sensitivity. The residual signal of the new formula is approximately five-fold lower than for the GR-200A, however its TL sensitivity is approximately half of that for the GR-200A.

LiF crystals doped with Mg, Cu and Si impurities was first developed in Japan (Nakajima et al., 1978), however it was not attractive because of its low sensitivity and other limitations. At the 12th International Conference on Solid State Dosimetry, it was reported (Nam et al., 1999) that LiF:Mg,Cu,Na,Si with high TL sensitivity was developed in Korea. A high sensitivity phosphor LiF:Mg,Cu,Na,Si with low residual signal and good stability to heat treatment developed at Solid Dosimetric Detector and Method Laboratory (DML) had been reported in 13th International Conference on Solid State Dosimetry (Tang et al., 2002). It was found (Tang, 2003) that thermal susceptibility of LiF:Mg,Cu,Na,Si appears to be associated with the Na concentration, the lower the Na concentration, the less sensitive is the TL to annealing temperature and the optimum Na dopant concentration was found to be 0%. In 2003, a new phosphor LiF only doped with Mg, Cu and Si was investigated at DML.

The dosimetric characteristic of LiF:Mg,Cu,Si developed in Korea (Lee et al., 2006) was reported. It was founded that LiF:Mg,Cu,Si can be heated up to 300 °C without any loss of TL sensitivity, however the glow curve of LiF:Mg,Cu,Si annealed at 300 °C was quite different from that at 260 °C and the height of main peak of LiF:Mg,Cu,Si annealed at 300 °C dropped to about 70% of that at 260 °C. Recently the optimization of preparation procedure of LiF:Mg,Cu,Si for improving reusability was reported (Kim et al., 2010).

In this study, a new LiF:Mg,Cu,Si disc was developed at DML. The preparation method and some dosimetric properties (sensitivity and residual) of the new LiF:Mg,Cu,Si TL material are presented. The effect of heat treatments on the glow curve structure and TL sensitivity for LiF:Mg,Cu,Si was investigated. These thermal treatments were for the best TL stability purpose to thermal treatments. The main aim of this study is to investigate the stability of LiF:Mg,Cu,Si to heat treatment.

Section snippets

Materials and methods

LiF:Mg,Cu,Si TL phosphor was prepared as follows: Lithium fluoride of a special grade on the market as the material. This material was mixed with activators, MgF2 (0.6 mol%), CuF2 (0.03 mol%), and SiO2 (0.9 mol%). The mixture in a platinum crucible was heated at 1050 °C in nitrogen gas after being dried at about 100 °C for 5 h. The reaction tube was constructed of quartz. After a period of 30 min in the molten stage, the sintered material in the crucible was quickly quenched to room temperature

TL glow curves

Fig. 1 shows the glow curves for the standard LiF:Mg,Cu,P GR-200A, the HMCP and LiF:Mg,Cu,Si. Pre-irradiation annealing programs of 240 °C for 10 min for GR-200A and 260 °C for 10 min for HMCP and LiF:Mg,Cu,Si were used. Readout programme (i) for plotting glow curves was used.

The shape of the glow curve for LiF:Mg,Cu,Si is similar to that for GR-200A. The glow curve for LiF:Mg,Cu,Si consists of several overlapping glow peaks, namely low-temperature peaks (nos. 2 and 3), the main dosimetric peak

Conclusion

The shape of the glow curve for the new LiF:Mg,Cu,Si disc is similar to that for standard LiF:Mg,Cu,P (GR-200A), and shows minimal differences when annealed in the range from 260 °C to 290 °C for 10 min. The height of the main peak for LiF:Mg,Cu,Si is significantly lower than that for GR-200A, however higher than that for HMCP. The TL sensitivity for LiF:Mg,Cu,Si is much lower than that for GR-200A, but is 35 times larger than that for TLD-100 and is slightly higher than that for HMCP. The

Acknowledgements

The authors wish to thank Professor W. Shen, Professor B. Huang, Mrs. Fan, Mrs. Shi and Mrs. Lu for their kind help in the experiments.

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