Recent developments in phosphate materials for their thermoluminescence dosimeter (TLD) applications

Synthesis, characterization and thermoluminescence properties of LiCaPO4 phosphor for ionizing radiation dosimetry

Many minerals and compounds show thermoluminescence (TL) properties but only a few of them can meet the requirements of an ideal dosimeter. Several phosphate materials have been studied for low-dose dosimetryin recent times. Among the various phosphates, ABPO4-type material shows interesting TL properties. In this study, an ABPO4-type (A = Lithium, B=Calcium) phosphor is synthesized using a modified solid-state diffusion method. Temperature is maintained below 800 °C in every step of phosphor preparation to obtain the pure phase of Lithium calcium phosphate (LiCaPO4). The purpose of this work is to synthesize LiCaPO4 using a simple method, examine its structural and luminescence properties in order to gain a deeper understanding of its TL characteristics. The general TL properties, such as TL glow curve, dose linearity, sensitivity, and fading, are investigated. Additionally, this study aims to determine various kinetic parameters through Glow Curve Deconvolution (GCD) method using the Origin Lab software together with the Chen model. XRD analysis confirmed the phase purity of the phosphor with a rhombohedral structure. Lattice parameters, unit cell volume, grain size, dislocated density, and microstrain were also calculated from XRD data. Raman analysis and Fourier Transform Infrared analysis were used to collect information about molecular bonds, vibrations, identity, and structure of the phosphor. To investigate TL properties and associated kinetic parameters, the phosphor was irradiated with 6.0 MV (photon energy) and 6.0 MeV (electron energy) from a linear accelerator for doses ranging from 0.5 Gy to 6.0 Gy. For both photon and electron energy, TL glow curves have two identical peaks near 200 °C and 240 °C.The TL glow curves for 0.5 Gy-6 Gy are deconvoluted, then fitted with the appropriate model and then calculated the kinetic parameters. Kinetic parameters such as geometric factor (μg), order of kinetics, activation energy (E), and frequency factor (s) are obtained from Chen's peak shape method. The dose against the TL intensity curve shows that the response is almost linear in the investigated dose range. For photon and electron energy, the phosphor is found to be the most sensitive at 2.0 Gy and 4.0 Gy, respectively. The phosphor shows a low fading and after 28 days of exposure, it shows a signal loss of better than 3%. The studied TL properties suggest the suitability of LiCaPO4 in radiation dosimetry and associated fields.

Electron beam detection in radiotherapy using a capacitor dosimeter equipped with a silicon photodiode

In this study, a newly developed capacitor dosimeter was evaluated using electron beams commonly utilized in radiotherapy. The capacitor dosimeter comprised a silicon photodiode, 0.47-μF capacitor, and dedicated terminal (dock). Before electron beam irradiation, the dosimeter was charged using the dock. The doses were measured without using a cable by reducing the charging voltages using the currents from the photodiode during irradiation. A commercially available parallel-plane-type ionization chamber and solid-water phantom were used for dose calibration with an electron energy of 6 MeV. In addition, the depth doses were measured using a solid-water phantom at electron energies of 6, 9, and 12 MeV. The doses were proportional to the discharging voltages, and the maximum dose difference in the calibrated doses measured using a two-point calibration was approximately 5% in the range of 0.25-1.98 Gy. The depth dependencies at energies of 6, 9, and 12 MeV corresponded to those measured using the ionization chamber.

Rhyolite as a Naturally Sustainable Thermoluminescence Material for Dose Assessment Applications

Thermoluminescence characteristics of natural rhyolite have been studied. Dose response at a wide dose range of 0.5–2000 Gy has been determined. Minimum detectable dose and thermal fading rate are evaluated. Glow curve deconvolution is conducted after determining the best read-out conditions. The repeated initial rise (RIR) method is used to detect the overlapping peaks, and a glow curve deconvolution procedure is used to extract the thermoluminescence parameters of rhyolite. According to the findings, rhyolite glow curves show five interfering peaks corresponding to five electron trap levels at 142, 176, 221, 298, and 355 °C, respectively, at a heating rate of 3 °C/s. The obtained kinetic order for the deconvoluted peaks showed mixed-order kinetic. The reported results might be useful to introduce rhyolite as a natural sustainable material for radiation dosimetry applications.

Thermoluminescence Dosimetric Attributes of Yb3+ Doped BaO-ZnO-LiF-B2 O3 Glass Material After Er3+ Co-doping

Motivated by our previous study on Sm³⁺ ions as thermoluminescence (TL) sensitizers to the BaO-ZnO-LiF-B₂ O₃ -Yb₂ O₃ glass system, in current study we examine the effect of Er³⁺ ion co-doping on the TL characteristics of this glass system. The 4f-4f electronic transitions of the Er³⁺ and Yb³⁺ ions were confirmed via the optical absorption spectrum. Notably, the use of Yb³⁺ -Er³⁺ ions failed to improve the TL intensity, sensitivity, and trap density. However, they enabled the glass system to function as an activator-quencher system. The linearity range and effective atomic number remained unaffected after co-doping. In addition, the problem of anomalous fading caused a remnant signal of just 58% after a week of storage of the Yb³⁺ mono-doped glass. This was resolved by the optimum co-doping of Er³⁺ ions to achieve an 89% signal. The co-doping of Er³⁺ ions to the BaO-ZnO-LiF-B₂ O₃ -Yb₂ O₃ glass system regulated its thermal stability and therefore supplemented its potential for radiation monitoring in food processing and retrospective dosimetry.