Thermoluminescence efficiency and glow curves of Cr-doped Al2O3 ceramic TLD for a wide linear energy transfer range

https://doi.org/10.1016/j.radmeas.2020.106356Get rights and content

Highlights

  • •

    The relative TL efficiencies of Cr-doped Al2O3 ceramic TLDs exhibited different trends for particle beams.

  • •

    Their shape of the glow curve remains the same for a wide LET range.

  • •

    In order to clarify the mechanism responsible for the change of the TL intensity, further studies are needed.

Abstract

We investigated the thermoluminescence (TL) efficiency and the glow curve of Cr-doped alumina (Al2O3) ceramic thermoluminescent dosimeters (TLDs) for heavy charged particles. The TLDs were irradiated with beams of protons, helium, and carbon ions. A 6-MV X-ray was used as the reference radiation for investigating the relative TL efficiency. The relative TL efficiency reaches its peak when the linear energy transfer (LET) is approximately 6 keV/μm and decreases with increasing LET. Moreover, the relative TL efficiency was 1.09 for the helium beam (LET: 11.5 keV/μm) and 1.22 for the carbon beam (LET: 13.3 keV/μm). This indicates that the relative TL efficiency of a Cr-doped Al2O3 ceramic TLD varies not only with the LET but also with the particle species. In order to investigate the relationship between the trap center of the Cr-doped Al2O3 ceramic TLD and the LET, the glow curve for each irradiation condition was also measured. As a result, the shape of the glow curve remained the same for a wide LET range, between 0.5 keV/μm and 128 keV/μm.

Introduction

Heavy charged particle (HCP) therapy has the advantages of allowing higher local control of the tumor and causing less damage to normal tissues. Pre-treatment dose verification is necessary for preventing mismatches between planned and delivered doses. Ionization chambers have been used for point-by-point verification of the dose with high accuracy. However, the large effective volume of the ionization chamber makes it difficult to obtain the dose distribution with high spatial resolution.

The Cr-doped Al2O3 ceramic thermoluminescent dosimeter (TLD) has high thermoluminescence (TL) sensitivity, high reproducibility, and high spatial resolution, and is available at a reasonable price. In addition, the Cr-doped Al2O3 ceramic TLD can be used as a two-dimensional (2D) dosimeter by means of a custom TL imaging measurement system (Shinsho et al., 2018).

We previously investigated the dose-response linearity and linear energy transfer (LET) dependence of a Cr-doped Al2O3 ceramic TLD using several HCP and found that the TLD has a large LET dependence (Koba et al., 2018). Therefore, it is difficult to directly measure the dose distribution of HCPs. Nevertheless, it is possible to estimate the LET in HCP therapy according to the combination of the Cr-doped Al2O3 ceramic TLD and a TLD showing different LET dependency. If both TLDs are capable of 2D measurement, the spatial distribution of average LET values can be measured. In our previous study, the LETs of Cr-doped Al2O3 ceramic TLDs for different species of heavy charged particle were investigated with only a fixed energy. In order to estimate the LET distribution, the information of the LET dependence for heavy charged particles with different energies is necessary. Therefore, the present study attempts to investigate the LET dependence in the TL efficiency and the glow curve shape in detail.

Section snippets

Cr-doped Al2O3 ceramic thermoluminescent dosimeter

The Cr-doped Al2O3 ceramic TLDs (Chiba Ceramic Mfg. Co., Ltd.) were composed of Al2O3 (>99.5 wt%) with 0.05 wt% Cr2O3 added. The dimensions of the TLDs were 11 mm × 11 mm × 0.7 mm. The bulk density and effective atomic number of the TLDs were 3.7 g/cm3 and 11.14, respectively. The glow peak temperature was approximately 300 °C. The TLDs were annealed at 1,000 °C for 1 h before irradiation.

Irradiation experiments

Irradiation experiments were performed at the Heavy Ion Medical Accelerator in Chiba (HIMAC) at the

Thermoluminescence efficiency of a Cr-doped Al2O3 ceramic thermoluminescent dosimeter

Fig. 2 shows the relative TL efficiency of Cr-doped Al2O3 ceramic TLD to the LET in water. The relative TL efficiency for the proton beam increased as the LET increased. The relative TL efficiency for the helium beam reached its peak when the LETs was approximately 6 keV/μm and then decreased with increasing LET. The relative TL efficiency for the carbon beam decreased as the LET increased. The LET dependence of Cr-doped Al2O3 ceramic TLD exhibits a different tendency for each particle species.

Conclusion

The present study investigated the relative TL efficiency and the glow curves of Cr-doped Al2O3 ceramic TLDs for different LETs. The relative TL efficiency of the Cr-doped Al2O3 ceramic TLD varies with not only the LET but also the particle species. The relative TL efficiency was 1.09 for the helium beam (LET: 11.5 keV/μm) and 1.22 for the carbon beam (LET: 13.3 keV/μm). On the other hand, the shape of the glow curve was found to be not dependent on the particle type and the LET. Further

Acknowledgements

The experiment of the present study was conducted as part of the Research Project with Heavy Ions at NIRS-HIMAC.

References (7)

There are more references available in the full text version of this article.

Cited by (1)

  • Properties of phototransferred thermoluminescence of Al<inf>2</inf>O<inf>3</inf>:Cr

    2023, Physica B: Condensed Matter
    Citation Excerpt :

    A series of studies have demonstrated the efficacy of Al2O3:Cr ceramics for high dose dosimetry using x-rays [19–21], heavy charged particles (HCP) [22], or thermal neutrons [23]. The TL of Al2O3:Cr exposed to x-ray or HCP irradiation is intense [22]. In particular, Shinsho et al. [20] showed that the TL intensity of Al2O3 when doped with Cr is fivefold that of the undoped variety.

View full text
© 2020 Elsevier Ltd. All rights reserved.