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.     

Thermoluminescent analysis of CaSO4:Tb,Eu crystal powder for dosimetric purposes

The motivation of this work was to produce crystals of CaSO₄ doped with an unusual combination of RE elements such as terbium (Tb) and europium (Eu) in different concentrations, and analyze its thermoluminescent (TL) properties. The crystals were produced by the slow evaporation route using calcium carbonate (CaCO₃) as precursor, and incorporating the dopants (Tb₂O₃ and Eu₂O₃) in a solution of sulfuric acid, that is evaporated and collected again, leaving just CaSO₄:Tb,Eu crystal powder. The terbium and europium ions were incorporated in concentration ratios of 1:1, 2:1 and 5:1 (weight proportions). X-ray diffraction analyses showed that samples of doped CaSO₄ exhibit only a single phase corresponding to the crystal structure of anhydrite. The radioluminescence confirmed the presence of Tb³⁺ and Eu²⁺ in the crystal matrix. The CaSO₄:Tb,Eu crystal powders showed TL emission glow curves with three peaks centered around 170 °C, 270 °C and 340 °C, after irradiation with a ⁹⁰Sr/⁹⁰Y source. Thermoluminescent (TL) characteristics such as linearity, reproducibility and fading were evaluated. Samples produced with concentration ratio of 2:1 of Tb and Eu showed the highest TL intensity. The produced CaSO₄:Tb,Eu samples present TL properties useful for dosimetric purposes.     

基于TL494开关电源的设计

开关电源主回路将输入的15VAC电压整流滤波所得的直流电压通过升压斩波电路,变换为25-30VDC输出。主控制器为PIC16F877A单片机。整个系统由整流滤波电路、DC-DC变换器、控制电路、按键显示等模块组成。主控制器和TL494以闭环形式控制DC-DC变换电路,实现输出电压稳定可调。该电源还具有过流保护、自恢复、软启动和短路报警功能。     

Combined measurement of dose and α/γ radiation-field-components using the shape of composite peak 5 in the glow curve of LiF:Mg,Ti

The shape of composite peak 5 in the glow curve of LiF:Mg,Ti (TLD-100), specifically, the ratio of the intensity of peak 5a to peak 5, is employed to separately estimate the gamma and alpha particle components in a mixed radiation field. A blind test demonstrates the reasonable accuracy of the technique which yields results between 3.8% and 30%.     

Intercomparison of Gafchromic™ films,TL detectors and TL foils for the measurements of skin dose in interventional radiology

Several passive solid state dosemeters, such as Gafchromic™ films and thermoluminescence (TL) detectors, are used to estimate and monitor patient skin doses in interventional radiology. To determine the suitability of XR-TypeR Gafchromic™ films and of detectors based on TL materials: pellets, chips and foils to measure skin dose, an intercomparison exercise has been organized within European Dosimetry Radiation Group – Working Group 12 “European Medical ALARA Network” (EURADOS WG12). To test response detectors were exposed to X-ray beams of energies and qualities applied clinically. A blind test was also performed to investigate the accuracy of the dose estimate by detectors exposed to unknown doses. We found the response of films to be strongly dependent on beam quality and filtration (increasing by up to 80% with respect to reference beam quality). The response of TL detectors was found to be less dependent on beam quality (less than 25% variation), with TL foils showing less than 10% variation with respect to reference beam quality. To accurately estimate patient skin doses in interventional radiology it is important to choose the quality of the calibration beam to be as close as possible to the quality of beams actually applied in clinical work.     

Beta-delayed neutron spectra for application in reactor technology,nuclear physics and astrophysics

Recent developments in ß-delayed neutron (DN) spectroscopy are reviewed, and the importance of DN energy spectra for various problems in reactor physics, nuclear physics and astrophysics is discussed.     

Spatially-resolved thermoluminescence from snail opercula using an EMCCD

In recent years opercula of the snail species Bithynia tentaculata have been shown to emit thermoluminescence (TL) signals that can be used to determine equivalent dose, and may be capable of dating events throughout the entire Quaternary period. Concentric growth lines are a notable feature of almost all B. tentaculata opercula, but it is not known whether the luminescence emitted by the opercula is influenced by these structures. This study uses a newly developed EMCCD imaging system to measure the TL signals from opercula. A combination of microscopic analysis of the opercula using visible imagery, and measurement of the TL using the EMCCD system has been undertaken. Variations in TL intensity and equivalent dose (D_e) are seen, but the two are not correlated. Changes in TL intensity broadly mimic the concentric growth structures, but the largest variations in intensity are between different margins of the opercula, not individual growth bands. The EMCCD system makes it possible to produce a two dimensional map of the D_e measured from an operculum. Dose recovery experiments give D_e values that are consistent with each other across the whole opercula. Measurement of the D_e arising from irradiation in nature shows significant variability across a single operculum, but at present the reason for this variability is unknown.     

DC-DC稳压电源的制作

本文制作了以TL494芯片为核心的直流变换直流（DC-DC）稳压电源.该电源实现了输入24 V电压,输出12V的降压、稳压功能.同时,该电路还具有短路保护,过流保护功能.其工作稳定、效率高、性能良好,参数指标符合设计的基本要求.     

Thermally assisted OSL (TA-OSL) reproducibility in Al2O3:C and its implication on the corresponding thermoluminescence (TL) reproducibility

Thermally assisted optically stimulated luminescence (TA-OSL) method is an excellent advancement of high-dose luminescent dosimetry with involvement of very deep traps. This specific method has been reported to be very efficient for the cases of anion deficient alumina doped with carbon and quartz. Nevertheless, reproducibility and sensitivity changes have been previously studied only for the case of quartz. In the present study, reproducibility was studied in both terms of quantitative and qualitative features, such as signal intensity and glow curve shape respectively, for both TL and TA-OSL signals on various TLD 500 dosimeters. Finally, for the case of the TL signal, sensitivity changes were studied with and without applying TA-OSL, towards studying the impact of the TA-OSL on the main dosimetric TL signal.     

Electron paramagnetic resonance and the thermoluminescence emission mechanism of the 280 °C peak in natural andalusite crystal

Samples of natural andalusite (Al₂SiO₅) crystal have been investigated in terms of thermoluminescence (TL) and electron paramagnetic resonance (EPR) measurements. The TL glow curves of samples previously annealed at 600 °C for 30 min and subsequently gamma-irradiated gave rise to four glow peaks at 150, 210, 280 and 350 °C. The EPR spectra of natural samples heat-treated at 600 °C for 30 min show signals at g=5.94 and 2.014 that do not change after gamma irradiation and thermal treatments. However, it was observed that the appearance of a paramagnetic center at g=1.882 for the samples annealed at 600 °C for 30 min followed gamma irradiation. This line was attributed to Ti³⁺ centers. The EPR signals observed at g=5.94 and 2.014 are due to Fe³⁺. Correlations between EPR and TL results of these crystals show that the EPR line at g=1.882 and the TL peak at 280 °C can be attributed to the same defect center.     

Non-resonant X-ray/laser interaction spectroscopy as a method for assessing charge competition, trapping and luminescence efficiency in wide band-gap materials

Using a conventional fast-shuttered laboratory X-ray source in combination with pulsed laser diode modules, the possibilities for undertaking X-ray/laser interaction spectroscopy in wide band-gap luminescent materials are explored. It is shown that in such materials, a variety of X-ray/laser timing sequences can extract complimentary information regarding the charge-carrier trapping, de-trapping and recombination processes. The effects on the luminescence are illustrated for six example materials (YPO₄:Ce,Sm, Lu₃Al₅O₁₂:Pr, Al₂O₃:C, natural sodium feldspar NaAlSi₃O₈, cubic BN and type IIa natural diamond). By ramping the temperature from 10 to 320 K during repeated X-ray pump/laser-probe activation cycles, a rapid assessment can be made of the important thermally dependent changes to the charge carrier trapping competition processes.     

SrSO4:Eu磷光体的光释光特性

研究了通过掺杂得到的SrSO4:Eu(01mol%)的粉末样品的光释光(OSL)特性.用90Sr的β射线辐照0116—116kGy后，测定了恒定光源激发的光释光发光曲线(CW-OSL)和线性光源激发的光释光发光曲线(LW-OSL)，对发光曲线分析均得到了四种陷阱成分.采用复合作用响应函数得到SrSO4:Eu辐射剂量响应为线性-亚线性.测量了温度对OSL信号的影响，结果表明OSL信号的温度稳定性很好，最灵敏读出温度约为180℃，说明这时OSL信号来自热激发和光激发的共同作用.用60Coγ辐照100Gy后，测量了热释光(TL)三维光谱，确定了发光波长主要位于375nm，可以确定这是来自于Eu2+能级跃迁的发光. 关键词： 光释光 热释光 SrSO4:Eu     

An algorithm for unified analysis on the thermoluminescence glow curve

An algorithm was developed to integrally handle excitation by radiation, relaxation and luminescence by thermal or optical stimulation in thermoluminescence (TL) and optically stimulated luminescence (OSL) processes. This algorithm reflects the mutual interaction between traps through a conduction band. Electrons and holes are created by radiation in the beginning, and these electrons move to the trap through the conduction band. These holes move to the recombination center through a valence band. The ratio of the electrons allocated to each trap differs with the recombination probability and these values also relevant to the process of luminescence. Accordingly, the glow curve can be interpreted by taking the rate of electron–hole pairs created by ionizing radiation as a unique initial condition. This method differs from the conventional method of interpreting the measured glow curve with the initial electron concentration allocated to each trap at the end of irradiation. A program using the Visual Studio's C# subsystem was made to realize such a developed algorithm. To verify this algorithm it was applied to LiF:Mg,Cu,Si. The TL glow curve was deconvoluted with a model of five traps, one deep trap and one recombination center (RC).     

In-phantom neutron dose distribution for bladder cancer cases treated with high-energy photons

This work presents an estimation of the neutron dose distribution for common bladder cancer cases treated with high-energy photons of 15 MV therapy accelerators. Neutron doses were measured in an Alderson phantom, using TLD 700 and 600 thermoluminescence dosimeters, resembling bladder cancer cases treated with high-energy photons from 15 MV LINAC and having a treatment plan using the four-field pelvic box technique. Thermal neutron dose distribution in the target area and the surrounding tissue was estimated. The sensitivity of all detectors for both gamma and neutrons was estimated and used for correction of the TL reading. TLD detectors were irradiated with a Co⁶⁰ gamma standard source and thermal neutrons at the irradiation facility of the National Institute for Standards (NIS). The TL to dose conversion factor was estimated in terms of both Co⁶⁰ neutron equivalent dose and thermal neutron dose. The dose distribution of photo-neutrons throughout each target was estimated and presented in three-dimensional charts and isodose curves. The distribution was found to be non-isotropic through the target. It varied from a minimum of 0.23 mSv/h to a maximum of 2.07 mSv/h at 6 cm off-axis. The mean neutron dose equivalent was found to be 0.63 mSv/h, which agrees with other published literature. The estimated average neutron equivalent to the bladder per administered therapeutic dose was found to be 0.39 mSv Gy^?1, which is also in good agreement with published literature. As a consequence of a complete therapeutic treatment of 50 Gy high-energy photons at 15 MV, the total thermal neutron equivalent dose to the abdomen was found to be about 0.012 Sv.     

Effects of high-temperature annealing on ESR properties of solid solutions of garnet minerals

A garnet (G7) silicate mineral belonging to pyralspite subgroup was studied using the technique of electron spin resonance (ESR). This study shows that iron is present in G7 as isolated species as well as species coupled by dipolar interactions. The ESR data shows a gradual increase of cluster of Fe³⁺ ions accompanied by decrease of dipolar interactions and increase of possible exchange interactions at high temperature. The Fe²⁺→Fe³⁺ oxidation process occurs in the garnets as a function of annealing temperature. Thermoluminescence (TL) peaks at approximately 190 and 340 °C are observed in the irradiated G7 garnet. Investigations using the technique of ESR were carried out to identify the centers involved in the TL process.     

Role of fluorescent lamp phosphors in accidental radiation monitoring

The present paper reports studies on the applicability of fluorescent lamp phosphors in accidental radiation dosimetry. Strontium orthophosphate, which is used as one of the components in the fluorescent lamps, has been studied for its thermo-luminescence (TL) characteristics on exposure to different doses of beta irradiation. The analysis of the TL glow curve of the phosphor, with a well-defined glow peak at 553 K, and other experiments carried out have proved the utility of strontium orthophosphate as dosimetric material in the range of 10–200 Gy. It has been observed that the material satisfies most of the fundamental criteria for a good TLD-material. A fluorescent lamp developed with this material as TLD grade lamp phosphor is thus expected to serve twin purposes of providing illumination and monitoring the radiation released during a nuclear accident.     

Thermoluminescence glow curve deconvolution of LiF:Mg,Cu,Si with more realistic kinetic models

Thermoluminescence (TL) glow curves of LiF:Mg,Cu,Si were deconvoluted with the introduction of enhanced physical model which envisages that both electrons and holes, produced by ionization radiation and trapped at the respective traps, can be thermally released into the conduction and the valence band, respectively and the holes may also radiatively recombine with electrons at the electron recombination centers. The model is more generalized than the ordinary trap interaction model which only permits the traffic of electrons through the conduction band. An effective numerical analysis method was developed to calculate the glow curve to be compatible with the measured curves. The validity of the numerical method was verified through artificially generated TL glow curves for a wide range of trap parameters. In order to identify TL kinetics of LiF:Mg,Cu,Si with higher accuracy, its glow curves were deconvoluted for two more generalized models, namely, the Schön–Klasens model and the Chen–Pagonis–Lawless model as well as the ordinary trap interactive model. The parameters in the more generalized multi-trap multi-recombination center (MTMR) model were found to be consistent with the quasi-static approximation(QSA) method.     

Investigation of the optical absorption dose response of LiF:Mg,Ti (TLD-100) and the role of V centers in F center (5.08 eV) bleaching

The optical absorption (OA) dose response of irradiated LiF:Mg,Ti has been measured over the dose range from 100 Gy to 1.4 M Gy. Measurements at high dose indicate that the 4.0 eV band is actually a composite band at 3.84 eV and 4.3 eV. Bleaching experiments at 5.08 eV (F band) support the participation of V₃ centers in the relaxation mechanisms following the bleach. The results are interpreted in the framework of a spatially correlated trapping center/luminescent center giving rise to composite peak 5 in the glow curve.     

Thermoluminescence glow-curve characteristics of LiF phosphors at high doses of gamma radiation

High doses of ionising radiation are becoming increasingly common for radiation-processing applications of various medical, agricultural and polymer products using gamma and electron beams. The objective of this work was to study thermoluminescence (TL) glow-curve characteristics of commonly used commercial LiF TL phosphors at high doses of radiation with a view to use them in dosimetry of radiation-processing applications. The TL properties of TLD 100 and 700 phosphors, procured from the Thermo-Scientific (previously Harshaw) company, have been studied in the dose range of 1–60 kGy. The shift in glow peaks was observed in this dose range. Integral TL responses of TLD 100 and TLD 700 were found to decrease as a linear function of dose in the range of 5–50 kGy. The paper describes initial results related to the glow-curve characteristics of these phosphors.