Optical absorption and thermoluminescence studies in 100 MeV swift heavy ion irradiated CaF2 crystals

Pure and Ytterbium (Yb) doped Calcium fluoride (CaF₂) single crystals were irradiated with 100 MeV Ni⁷⁺ ions for fluences in the range 5 × 10¹¹-2.5 × 10¹³ ions cm⁻². The irradiated crystals were characterized by Optical absorption (OA) and Thermoluminescence (TL) techniques. The OA spectra of ion irradiated pure CaF₂ crystals showed a broad absorption with peak at ∼556 nm and a weak one at ∼220 nm, whereas the Yb doped crystals showed two strong absorption bands at ∼300 and 550 nm. From the study of OA spectra, the defect centers responsible for the absorption were identified. TL measurements of Ni⁷⁺ ion irradiated pure CaF₂ samples indicated a strong TL glow with peak at ∼510 K. However, the Yb doped crystals showed two TL glows at ∼406 and 496 K. The OA and TL intensity were found to increase with increase of ion fluence upto 1 × 10¹³ ions cm⁻² and thereafter it decreased with further increase of fluence. The results obtained are discussed in detail.     

Precision and accuracy of two luminescence dating techniques for retrospective dosimetry: SAR-OSL and SAR-ITL

Luminescence techniques based on thermally or optically stimulated signals are used extensively for estimating the equivalent dose (ED) of quartz samples for dating and retrospective dosimetry. This paper presents simulations of two luminescence dating protocols which use single aliquots of the quartz samples. The first protocol is the well-known single-aliquot regenerative optically stimulated luminescence (SAR-OSL) protocol for quartz. The second protocol was developed more recently and is based on a thermoluminescence (TL) signal measured under isothermal conditions (termed the SAR-ITL technique). The simulations are carried out using a recently published comprehensive kinetic model for quartz, consisting of 11 electron and hole traps and centers. The complete sequence of the two experimental protocols is simulated using the same set of kinetic parameters. The simulated dose response curves for the two protocols are found to be very similar to published experimental data. The relative intrinsic accuracy and precision of the two techniques is estimated by simulating one hundred random variants of the natural samples, and by calculating the equivalent doses using each technique. The 100 simulated natural variants are generated by keeping the transition probabilities between energy levels fixed, while allowing simultaneous random variations of the concentrations of the 11 energy levels. The SAR-OSL protocol was found to be intrinsically both more accurate and more precise than the SAR-ITL protocol. We investigate several experimental factors which affect the precision and accuracy of the two protocols. New simulations are presented for commonly used sensitivity tests consisting of successive cycles of sample irradiation with the same dose, followed by measurements of the sensitivity corrected L/T signals. These new simulations provide valuable insight into the previously reported sensitivity changes taking place during application of the SAR-ITL protocol.     

热释光缺陷模型的探讨

热释光物理机制的描述及相关理论模型的建立依赖于所采用的缺陷模型.热释光动力学模型基于固体能带理论和孤立点缺陷的假设,完全不涉及介质中的缺陷结构和空间分布.实际应用中,动力学模型参数并不能给出确切的意义,对许多热释光物理现象也无法解释.本文基于掺入稀土的碱土硫酸盐磷光体的系统实验研究,分析了热释光三维发光谱和剂量响应非线性特性,结果显示,大多数热释光磷光体中缺陷是以缺陷复合体的形式存在,本征缺陷和掺入杂质构成的缺陷复合体是热释光多阶段随机过程的基本作用单元,表明热释光磷光体的发光特性和剂量响应非线性特性与缺陷复合体的结构密切相关.     

Unusual heating rates,dose responses and kinetic parameters detected on thermoluminescence from YAl3(BO3)4:Sm3+ phosphors

This study focused on the thermoluminescence (TL) characteristics of YAl₃(BO₃)₄ (YAB) phosphors modified with various contents of Sm³⁺ ions. The TL response of the YAB: Sm³⁺ phosphors exposed to beta irradiation was measured across the temperature range of 25–500 °C, exhibiting three TL maxima at 70, 235, and 408 °C. Preheating protocol was also carried out to remove the low temperature TL peak followed by further experiments with the two-remaining high-temperature peaks. In the TL measurements conducted with variable heating rates (HR) between 0.1 and 5 °Cs^-1, an anomalous heating rate behaviour was observed. A semi-localized transition model was used to address this feature. There was a standard deviation of less than 5% in the reusability measurements. The results of the kinetic parameters obtained by initial rise (IR) and various heating rate (VHR) methods were compared with those obtained by glow curve deconvolution (GCD) method. T_m-T_stop analysis revealed a continuous distribution of trap levels with a trap depth ranging from 1.35 to 2.20 eV. Through the use of GCD, the glow curve was found to demonstrate general order kinetics and consist of seven superimposed traps. The values of the kinetic parameters obtained for the glow curve agreed with those obtained by other methods excluding the VHR method encountering an anomalous impact. The results obtained from these tests showed that the sample could be successfully used for TL dosimetry applications.     

Photoluminescence and thermoluminescence studies of Mg2SiO4:Eu nano phosphor

Nanoparticles of Eu³⁺ doped Mg₂SiO₄ are prepared using low temperature solution combustion technique with metal nitrate as precursor and urea as fuel. The synthesized samples are calcined at 800 °C for 3 h. The Powder X-ray diffraction (PXRD) patterns of the sample reveled orthorhombic structure with α-phase. The crystallite size using Scherer's formula is found to be in the range 50-60 nm. The effect of Eu³⁺ on the luminescence characteristics of Mg₂SiO₄ is studied and the results are presented here. These phosphors exhibit bright red color upon excitation by 256 nm light and showed the characteristic emission of the Eu³⁺ ions. The electronic transition corresponding to ⁵D₀ → ⁷F₂ of Eu³⁺ ions (612 nm) is stronger than the magnetic dipole transition corresponding to ⁵D₀ → ⁷F₁ of Eu³⁺ ions (590 nm). Thermoluminescence (TL) characteristics of γ-rayed Mg₂SiO₄:Eu³⁺ phosphors are studied. Two prominent and well-resolved TL glows with peaks at 202 °C and 345 °C besides a shoulder with peak at ∼240 °C are observed. The trapping parameters-activation energy (E), order of kinetics (b) and frequency factor (s) are calculated using glow curve shape method and the results obtained are discussed.     

Germination test for identification of irradiated garlic

Ionising radiation can be used to inhibit the sprouting of garlic. This study investigates whether a simple germination test can be used to detect irradiated garlic. The results show that the germination test can be used as a detection method for garlic irradiated in the dormancy period. Detection is even reliable for samples treated with 25 Gy. For garlic irradiated after the dormancy period the germination test does not function properly. However, in this case the sprout-inhibiting effect of irradiation is also inadequate. For some samples, standard detection methods such as thermoluminescence, electron spin resonance and photostimulated luminescence were also applied. Whereas thermoluminescence measurements unequivocally proved the radiation treatment, electron spin resonance and photostimulated luminescence were not conclusive.     

Identifying irradiated oysters by luminescence techniques (TL & PSL)

This study shows an exhaustive comparison of different methods, based on luminescence techniques, to identify X-ray irradiated oysters at five different dose levels in the range 0.1-2 kGy and suggests a simple, fast and sequential routine analysis protocol. A total number of 50 oysters from North Sea, including 10 control samples, were analysed by using two photo-stimulated luminescence (PSL) methods (named A and B) and three thermoluminescence (TL) methods (named C, D and E), either on constituents or contaminating minerals from shells and intestines. Setting a lower threshold value T1 (1000 counts/60s) all of control specimens gave negative screening results while photo counts from irradiated samples were found to be higher than upper threshold T2 (4000 counts/60s), except at the lowest dose level 0.1 kGy for procedure A. All PSL calibrated analysis were successful and a sensitivity index was also determined to better classify obtained data according to the revised European Standard (EN 13751:2009). TL ratios, Glow 1 over second Glow 2, the latter after irradiating at 1 kGy and remeasuring the same minerals for each sample, showed values less than 0.1 related to untreated samples or higher than 0.1 for irradiated ones. Reported procedures were also tested over 60 days, longer than oyster shelf life confirming the applicability and feasibility of the proposed methods.     

Green synthesis,structural and luminescent characterization of BaZrO3:Eu3+ nanoparticles

This paper presents experimental results of the structural, morphological, and luminescence characterization of Eu³⁺ doped BaZrO₃ powders produced by the green synthesis method. The highly crystalized cubic structure perovskite powders of the formula BaZrO₃ were synthesized by the chemical hydrothermal method. The phase of the compound and the average particle size were determined using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Powder samples were characterized also by photoluminescence (PL) and thermoluminescence (TL) techniques. Results showed that BaZrO₃ crystallizes in its perovskite cubic phase, with a crystal size circa 40 nm. The presence of each element of the compound was confirmed by the energy disperse spectroscopy (EDS) technique. The PL emission spectra, at room temperature, were obtained using 395 nm as excitation wavelength. The spectra showed the characteristic emissions of Eu³⁺ ion. The intensity of the PL emission spectra varies with the Eu³⁺ concentration and shows a maximum luminescence efficiency when the synthesis of BaZrO₃ was performed using a content of 5 mol% Eu³?. The thermoluminescence data shows that at the heating rate of 10 °C/s, BaZrO₃:Eu³⁺ doped with 5% of dopant concentration exhibits two TL peaks: first of them rapidly decaying peaks at about 110 °C and a high sensitivity peak at 235 °C TL. The correlation between luminescence intensity and concentration quenching of the prepared phosphor was investigated. Present findings substantiate the ability of the BaZrO₃ nanopowder sample to be a promising candidate for luminescence applications.