TL properties of anhydrous CaSO4:Tm improvement

CaSO4:Tm is excellent phosphors for dosimetry of ionising radiations due to their high sensitivity, wide dose range (from 10^?6 to 1 Gy), relatively simple trap structure, good chemical, thermal and physical stability and ease of preparation. Since 1968 have been developed new methods of preparing aim to increase the sensitivity and the linearity of the CaSO₄:Tm thermoluminescence. The objective of this work is to obtain single crystals of CaSO₄:Tm under controlled crystal growth conditions, such as temperature, atmosphere and velocity, aiming to improve the TL sensitivity of the crystals and investigate its dosimetric properties in order to evaluate the applicability of this material to dosimetry.     

Thermally stimulated luminescence studies of undoped,Cu- and Mn-doped CaSO4 compounds

Thermally stimulated luminescence (TSL) of undoped and doped CaSO₄ with activators such as Cu and Mn has been investigated. The polycrystalline samples of undoped and doped CaSO₄ are prepared by the melting method. The formation of CaSO₄ compound is confirmed by X-ray diffraction and Fourier transform infrared studies. Scanning electron microscopic studies of CaSO₄ are also carried out.

The TSL glow curves of undoped CaSO₄, Cu- and Mn-doped CaSO₄ are studied. Comparison of the thermoluminescence (TL) intensity of the most intensive glow peak of Cu-doped CaSO₄ compound with that of undoped CaSO₄ shows that addition of Cu impurity in CaSO₄ compound enhances the TL intensity by about four times. However, the addition of Mn impurity to undoped CaSO₄ increases the TL intensity by about three times when compared with that of undoped CaSO₄. The TL-dose dependence of all three samples was studied and was observed to be almost linear in the studied range of irradiation time. Among the samples studied, namely undoped CaSO₄ and Cu- and Mn-doped CaSO₄, Cu-doped CaSO₄ is found to be the most sensitive. The trap parameters, namely order of kinetics (b), activation energy (E) and frequency factor (s) associated with the most intensive glow peaks of CaSO₄:Mn, CaSO₄:Cu and CaSO₄ phosphors were determined using the glow curve shape (Chen's) method.     

Structural analysis, TSL studies and evaluation of trapping parameters of Cu activated CaSO4

The XRD and SEM and TSL studies of the as prepared pure, Cu and Mn doped CaSO₄ have been carried out. From the comparative TSL studies it has been seen that the 137 °C glow peak of CaSO₄:Cu is superior to undoped and Mn doped CaSO₄ compounds as well as other Cu doped alkaline earth sulphates. Evaluation of trapping parameters of the most intensive glow peak Cu (0.5 mol%) doped CaSO₄ is accomplished by a technique named isothermal luminescence decay method and comparison of these parameters with the previously calculated trapping parameters by glow curve shape method (Chen’s method) have been done. It is observed that the most intensive glow peak of Cu doped CaSO₄ is found to obey second order kinetics, because of availability of vacant traps for retrapping to take place. Moreover the effect of various doping concentration of Cu on the TSL glow curve and reproducibility of Cu doped CaSO₄ has also studied.     

TL and EPR studies of CaSO4:Dy phosphor to investigate its efficacy in measurement of food irradiation dose at sub-ambient temperatures

The effects of sub-ambient temperatures of irradiation and dose response of CaSO₄:Dy phosphor was investigated. The irradiation dose in the range 0.5–7.0 kGy was chosen to meet the requirement of commercial food irradiation at low temperature. Commercially available phosphor showed no significant change in glow curve structure with low temperature of irradiation. In order to enhance the sensitivity of the low temperature glow peak (142 °C), the phosphor was subjected to different post-preparation thermal treatments at 700–900 °C. The change in glows and improvement in dose response characteristics were explained by Electron Paramagnetic Resonance (EPR) spectroscopy. At sub-ambient temperature of irradiation, the behavior of thermally treated CaSO₄:Dy phosphor with increasing dose revealed improved linear response of the low temperature glow peak and could be an efficient dosimetry system for the food commodities irradiated at low temperatures.     

Luminescence and evaluation of trapping parameters in NaMgSO4Cl: X (X=Cu or Ce) phosphor

Thermoluminescence (TL) characteristics of recently developed high sensitive mixed halosulphate phosphors, NaMgSO₄Cl: Cu and NaMgSO₄Cl: Ce were studied in comparison with CaSO₄: Dy in order to assess the possibility of their use in personal monitoring and TLD phosphors at very low dose of 5 Gy. It was found that NaMgSO₄Cl: Cu is 5.59 times and NaMgSO₄Cl: Ce is 6.18 times more sensitive as compared to standard CaSO₄: Dy. UV photo-excited luminescence from Cu to Ce doped NaMgSO₄Cl halosulphate phosphors has been investigated. The intense emission of the spectrum is assigned to electronic transitions 3d⁹4s¹→3d¹⁰ in monovalent copper ion and 5d→4f in Ce³⁺ ions. Increase in PL peak intensity suggesting that Cu and Ce play an important role in PL emission in the present matrix. These phosphors were synthesized by the wet chemical method. XRD, photoluminescence (PL) and thermoluminescence (TL) characterization of phosphors has been reported in this paper. The preparation of an inexpensive and high sensitive NaMgSO₄Cl: Cu and NaMgSO₄Cl: Ce with TL glow peaks for different concentrations are observed between 160 and 195 °C and between 200 and 225 °C, respectively, exposed to gamma-rays of ⁶⁰Co for their thermoluminescence (TL) properties. The glow curves have been recorded at a heating rate of 2 K s^?1 and irradiated at a dose rate of 0.995 kGy h^?1 for 5 Gy. In present study the trapping parameters such as order of kinetics (b), activation energy (E) and frequency factors (s) have been calculated for the 195 and 200 °C glow peaks of NaMgSO₄Cl: Cu and NaMgSO₄Cl: Ce, respectively by using Chen's method. The paper discusses the luminescence of Cu⁺ and Ce³⁺ by simple method of incorporation in NaMgSO₄Cl host.     

Thermoluminescence of rare earth activated CdSO4, SrSO4 and BaSO4

The thermoluminescence (TL) of rare earth (RE) activated sulfates of Cd, Sr and Ba was studied above room temperature. Many of the phosphors prepared exhibit an extremely bright TL following X-irradiation (most notably with Sm, Eu, Tb, Dy and Tm dopants), having an efficiency comparable to that of the highest sensitivity phosphors available for TL dosimetry, and exhibiting activator-induced glow peaks between 405 and 480°K. In a given lattice, the RE³⁺ ions produce a characteristic glow peak at the same temperature (independent of the particular RE ion), whereas Eu²⁺ produces a single glow peak at a different temperature. A decrease in glow peak temperature with increasing interatomic spacing was observed in the homologous SrSO₄-BaSO₄ system - this shift being most pronounced in the Eu²⁺ -doped materials. TL emission spectra were obtained for trivalent Sm, Tb, Dy and Tm and for divalent Eu in these sulfates (and also in CaSO₄).     

TL and OSL studies on lithium borate single crystals doped with Cu and Ag

Lithium borate (LBO) single crystals doped with Cu and Ag (0.25 mol% each) (Li₂B₄O₇:Cu,Ag) are grown by the Czochralski method. The thermoluminescence readout on Li₂B₄O₇:Cu,Ag crystals showed three glow peaks at～375, 441 and 516 K for the heating rate of 1  K/s. The thermoluminescence sensitivity of the grown Li₂B₄O₇:Cu,Ag single crystals is found to be 5 times TLD-100 and a linear dose response in the range 1 mGy to 1 kGy. The glow curve deconvolution reveals nearly first order kinetics for all the three peaks with trap depths 0.77, 1.25 and 1.34 eV respectively and corresponding frequency factors 1.6×10⁹, 1.3×10¹³ and 6.8×10¹¹ s^?1. The continuous wave optically stimulated luminescence (CW-OSL) measurements were performed on the LBO:Cu,Ag single crystals using blue light stimulation. The traps responsible for the three thermoluminescence peaks in Li₂B₄O₇:Cu,Ag are found to be OSL sensitive. The qualitative correlation between TL peaks and CW-OSL response is established. The photoluminescence studies show that in case of co-doping of Ag in LBO:Cu the emission at 370 nm in Cu states dominates over the transitions in Ag states implying doping of Ag plays a role as sensitizer when co-doped with Cu and increases overall emission.     

Evaluation of TL response and intrinsic efficiency of TL dosimeters irradiated using different phantoms in clinical electron beam dosimetry

The TL response of LiF:Mg,Ti microdosimeters and CaSO₄:Dy dosimeters were studied for 12 MeV electron beams using PMMA, liquid water and solid water (SW) phantoms. The different phantom materials affect the electron spectrum incident on the detector and it can alter the response of dosimeters to different radiation types, so this fact should be considered in clinical dosimetry. The dosimeters were irradiated with doses ranging from 0.1 up to 5 Gy using a Varian Clinac 2100C linear accelerator of Hospital Israelita Albert Einstein – HIAE using a 10 × 10 cm² field size and 100 cm source-phantom surface distance, with the dosimeters positioned at the depth of maximum dose. The TL readings were carried out 24 h after irradiation using a Harshaw 3500 TL reader. This paper aims to compare the TL response relative to ⁶⁰Co of the dosimeters for different phantoms used in radiotherapy dosimetry. CaSO₄:Dy dosimeters presented higher TL sensitivity relative to ⁶⁰Co and intrinsic efficiency than microLiF:Mg,Ti dosimeters for all phantoms.     

Influence of Li dopants on thermoluminescence spectra of CaSO4 doped with Dy or Tm

Thermoluminescence emission spectra are presented for lithium doped variants of CaSO₄:Dy or CaSO₄:Tm dosimetry material. All three dopants (Li, Dy and Tm) variously introduce different changes in both the glow peak temperatures and the luminescence efficiency. In every case the emission signals display the line emission characteristic of the rare earth ions. At temperatures below ∼50 K the relative peak intensities differ for Dy and Tm doped samples, and there are small temperature shifts between the Dy:Li and Tm:Li co-doped materials. Above room temperature the rare earth ions do not show peak temperature movements when co-doped with lithium. However they do influence the peak temperature by ∼5 °C when they are the sole dopant. Inclusion of lithium dramatically moves the high temperature glow peak from ∼200 °C down to 120 °C. All these changes are consistent with a single defect model in which the trapping sites and luminescence occur within the complexes formed of the rare earth ion, an intrinsic sulphate defect and lithium. The evidence and rationale for such a model are presented. There is discussion which suggests that such defect complexes are the norm in thermoluminescence.     

Cu+ emission in Li2BPO5 material for thermoluminescence dosimetry

In this study, Li₂BPO₅ doped with Cu and that co-doped with Mg are synthesized by the wet chemical technique and exposed to γ rays of ⁶⁰Co to determine their thermoluminescence (TL) properties. The X-ray diffraction technique shows the crystalline nature of the prepared material. The photoluminescence (PL) emission spectra of Li₂BPO₅:Cu phosphor show the strong prominent peak at 368 nm in the violet region of the visible spectrum due to the transition of 3d⁹4s¹ ? 3d¹⁰ of monovalent copper ion. The PL emission of Li₂BPO₅:Cu is enhanced by the addition of Mg. The TL glow curves of γ-irradiated Li₂BPO₅:Cu sample show one glow peak at 143°C, indicating that only one set of traps is being activated within the particular temperature range each with its own value of activation energy (E) and frequency factor (s). The trapping parameters associated with the prominent glow peak of Li₂BPO₅:Cu are calculated using the glow curve shape (Chen's) method. The release of hole/electron from defect centers at the characteristic trap site initiates the luminescence process in these materials. A linear TL response is observed in Li₂BPO₅:Cu in a long span of exposures. The sensitivity of Li₂BPO₅:Cu sample is observed to be 7.8 times that of (TLD-100) LiF:Mg, Ti.     

Unified picture of the distribution of electric field gradients at Cu, O, and Tm sites in ReBa2Cu3O7−δ

An abundant set of published experimental NMR/NQR data on electric field gradients in ReBa₂Cu₃O_7−δ high temperature conductors, where Re=Y and Tm, is used as a test for the singlet-correlated band theory. Because of the unusual spectral weight (“capacity”) of this band, it has been possible to match the number of holes per lattice site to photoemission data on the energy spectrum and the location of the Fermi level. In the framework of a unified picture of the distribution of holes (charges) it has been possible for the first time to explain satisfactorily the observed electric field gradients at the Cu(1), Cu(2), O(1), O(2), O(3), and O(4) sites, as well as NMR and inelastic neutron scattering data on the crystal electric field at the Tm ions. Zh. éksp. Teor. Fiz. 111, 144–157 (January 1997)     

Energy transfer process in CaSO4:Tb,Ce phosphor

Thermoluminescence (TL) and photoluminescence studies have been carried out on CaSO₄:Tb, CaSO₄:Ce and CaSO₄:Tb,Ce phosphors with the aim of studying energy transfer process in the CaSO₄:Tb,Ce phosphor. CaSO₄:Tb,Ce shows TL peaks at 150, 220, 320 and 400°C. Changes in Tb and Ce concentrations influence the relative heights of these glow peaks. Co-doping with 0.1 mol% of Ce in CaSO₄:Tb enhances the sensitivity of 320^oC TL peak by a factor of 15. Fluorescence results show that there is energy transfer from Ce to Tb ion. The defect centres formed in CaSO₄:Tb,Ce phosphor are studied using electron spin resonance technique. The 320^oC glow peak correlates with a centre (SO₃⁻radical) with g-values: g_||=2.0061 and g_⊥=2.0026.     

Feasibility study of CaSO4:Eu,CaSO4:Eu,Ag and CaSO4:Eu,Ag(NP) as thermoluminescent dosimeters

This work evaluates the dosimetric properties of crystals of CaSO₄ doped with unusual elements, such as europium (Eu) and silver (Ag), including their nanoparticle forms, after the incorporation of glass or Teflon and compares them with well-known thermoluminescent dosimeters (TLD). X-ray diffraction analyses showed that samples of doped CaSO₄ exhibit only a single phase corresponding to the crystal structure of anhydrite. Optical spectroscopy confirmed the presence of Eu³⁺ in the crystal matrix and a luminescent gain due the presence of silver nanoparticles. The composites showed thermoluminescent emission glow curves, with a single peak centered at approximately 200 °C for pellets with Teflon and at 230 °C for pellets with glass. The dosimeters based on calcium sulfate doped with europium and silver nanoparticles provided the most intense thermoluminescent (TL) emission of the composites studied. In comparison with commercial TLD, such as LiF:Mg,Ti and CaSO₄:Dy, the CaSO₄:Eu,Ag(NP)+glass produced in this work presented similar low detection limits and higher sensitivity. The new methods for the preparation of dosimeters and the incorporation of glass are shown to be viable because all of the samples presented a linear, reproducible and first order kinetic TL emission.     

自旋阀型[NiFe/Cu/Co/Cu]多层膜的磁电阻、矫顽力和稳定性研究

用电子束蒸镀工艺制备了自旋阀型［NiFe/Cu/Co/Cu］_N多层膜．研究了工艺过程及磁层、非磁层厚度和矫顽力对磁电阻的影响．还研究了磁电阻的稳定性和降低中心磁场等问题．用较优化的方法，制备了中心磁场为（10—20）（10³/4π）A/m，优值大于0.2%（（10³/4π）A/m）^-1的多层膜．实验表明，磁电阻随磁场的变化在中心区内是可逆的．经200℃退火15min，中心磁场略有减小，磁电阻稍有增加．一些样品经一年多老 关键词：     

Coil-less fluxgate effect in CoNiFe/Cu wire electrodeposited under torsion

Co₁₉Ni_49.6Fe_31.4 layer was electrodeposited onto a twisted Cu wire and helical anisotropy was induced in the magnetic Co₁₉Ni_49.6Fe_31.4 shell. The magnetic and coil-less fluxgate (CF) properties are presented. The Co₁₉Ni_49.6Fe_31.4/Cu wire, produced at zero torsional strain, shows a CF output of nearly zero. The samples produced under torsional strains of 29.5π and 59π rad/m show a linear change in CF output in the low-frequency range. At higher frequencies the CF output shows two linear ranges. A maximum sensitivity of 150V/T is observed at 20 kHz driving-current frequency and 67 mA driving current for a wire produced under 59π rad/m torsional strain. It is also found that the slope of the CF curve depends on the direction of induced anisotropy.     

Thermoluminescence characteristics of inorganically and organically capped ZnS:Cu nanophosphors

ZnS:Cu nanophosphors were prepared by wet chemical methods and characterized by X-ray diffraction (XRD). The typical morphologies of the nanophosphors were investigated by scanning electron microscopy (SEM). The thermoluminescence (TL) properties of inorganically and organically passivated ZnS:Cu nanophosphors were investigated after γ-irradiation using a ⁶⁰Co source at room temperature. The TL glow curve of capped ZnS:Cu showed variation in TL peak and intensity as the capping agent was changed. Amongst the synthesized samples the TL glow curve of SiO₂ capped ZnS:Cu showed the highest TL intensity. It has been found that TL response of SiO₂ capped ZnS:Cu is linear in the range 10-550 Gy. A discussion of the obtained results is also presented.     

Optically stimulated luminescence from CaSO4:Eu – Preliminary results

A new OSL phosphor CaSO₄:Eu was developed. The phosphor shows good OSL sensitivity which is about 55% of commercially available Al₂O₃:C. The phosphor also shows good TL sensitivity and the dosimetric peak, which appears around 186 °C, has sensitivity nearly 50% of Al₂O₃:C. After OSL readout of the irradiated sample, the TL peak around 250 °C depletes completely, with partial depletion of peak around 186 °C. Since the traps responsible for the high temperature peak are involved for the observed OSL, the sample shows low post-irradiation fading. The OSL decay is similar to Al₂O₃:C. Thus this phosphor due to its good OSL sensitivity, linear dose response, low fading and simple preparation technique could be useful for radiation dosimetry applications.     

Magnetism and unusual Cu valency in quadruple perovskites

We study a selection of Cu-containing magnetic quadruple perovskites (CaCu₃Ti₄O₁₂ LaCu₃Fe₄O₁₂, and YCu₃Co₄O₁₂) by ab initio calculations, and show that Cu is in an effective divalent Cu(II)-like state or a trivalent Cu(III) state depending on the choice of octahedral cation. Based on the electronic structure, we also discuss the role of Mott and Zhang-Rice physics in this materials class.     

α-Al2O3:C晶体的热释光和光释光特性

以高纯α-Al₂O₃和石墨为原料,采用温梯法生长了α-Al₂O₃：C晶体,使用Ris TL/OSL-DA-15型热释光和光释光仪研究了其热释光和光释光特性.α-Al₂O₃：C晶体在462K附近有单一热释光峰,发射波长位于410nm.随着辐照剂量的增加,热释光强度逐渐增强,462K的热释光特征峰位置保持不变.α-Al₂O₃：C晶体的 关键词： 2O₃：C')" href="#">α-Al₂O₃：C 热释光 光释光     

Experimental determinations of beta attenuation in planar dose geometry and application to ESR dating of tooth enamel

Two experiments were performed to determine the distribution of beta dose in a target medium as a function of distance from a planar source (2π geometry). In Experiment 1 planar absorbers were used to simulate depth in the target medium, and the attenuated dose that penetrated the intervening absorbers was detected using thermoluminescence from CaSO₄:Tm. In experiment 2 pellets of powdered tooth enamel were situated in a cavity in solid tooth enamel. Dose response of the electron spin resonance (ESR) signals in the pellets allowed direct detection of dose distribution within the target medium. The dose distributions were found to agree more closely with Monte Carlo calculations and with one-group transport theory (Prestwich et al., 1997 and Brennan et al., 1997) than with approximations used widely in ESR dating applications (Grün, 1986). Although the latter were supported by experiments by Aitken et al. (1985), the results of experiment 1 provided data to suggest that departure from 2π geometry was unacceptably large in the Aitken et al. (1985) configuration. The beta doses obtained by one-group theory in typical target volumes of enamel were 17 to 40% lower than those obtained using the Grün approximation. It was concluded that one-group transport theory provides the best available routine tool for calculations of beta dose attenuation in near-planar target materials (e.g. tooth enamel and shell) irradiated by natural sources, although Monte Carlo methods are better and could eventually be introduced into the ROSY ESR dating program (Brennan et al., 1997). It was also concluded that a revision of previously published ESR ages using one-group transport for beta dosimetry will be needed. For cases where the U concentrations in enamel are generally low (less than a few ppm), previously published ESR ages on tooth enamel are systematically too young by 5–30%.