不同退火温度的Al_2O_3:C薄膜热释光和光释光性能

α-Al_2O_3:C晶体的热释光和光释光性能优越,但其制备要求高,需高温和高还原气氛.与α-Al_2O_3:C晶体性能接近的α-Al_2O_3:C陶瓷,热释光峰不单一.本文采用两次阳极氧化法在0.5 mol/L的草酸溶液中5℃恒温制备高度均匀有序的多孔Al_2O_3:C薄膜,主要研究不同退火温度对其热释光和光释光特性的影响.结果表明,经不同温度退火后的Al_2O_3:C薄膜均为非晶结构;不同退火温度的Al_2O_3:C薄膜热释光的主发光峰约在310℃左右,符合通用级动力学模型.600℃退火后的Al_2O_3:C薄膜热释光灵敏度最强,其热释光剂量曲线在1-10 Gy范围内具有很好的线性响应,在剂量10-120 Gy范围内出现超线性响应;在相同的辐照剂量下,随着退火温度的升高(≤600℃)光释光的初始发光强度逐渐增强.不同退火温度的Al_2O_3:C薄膜光释光衰减曲线都呈典型的指数衰减且快衰减速率相比α-Al_2O_3:C晶体显著加快.600℃退火后的Al_2O_3:C薄膜光释光灵敏度最强,其光释光剂量响应曲线在1-200 Gy整体上都具有很好的剂量线性关系.与热释光相比,Al_2O_3:C薄膜的光释光具有更宽的线性剂量响应范围.此研究为Al_2O_3:C薄膜作为光释光辐射剂量材料做出了有益的探索.     

不同粒径α-Al2O3:C晶态粉体热释光和光释光特性

本文探讨了α -Al₂O₃:C晶态粉体的辐照剂量效应, 使用RisøTL/OSL-DA-15 型热释光和光释光仪研究其热释光和光释光特性, 结果发现, 相同粒径的α-Al₂O₃:C晶态粉体具有单一热释光峰, 且随着辐照剂量的增加热释光强度不断增加, 但热释光峰位置保持不变, 符合一级动力学模型; 而在相同的辐照剂量和测试条件下, 随着α -Al₂O₃:C晶态粉体粒径的减小, 其热释光强度先增强后减弱, 热释光峰却逐渐增加至趋于稳定, 表明粒度为40—60 μ的α -Al₂O₃:C晶态粉体具有最佳的热释光效应. 同时α -Al₂O₃:C晶态粉体的光释光特性的研究发现, 其光释光曲线具有典型的指数衰减特征, 粒径对其光释光强度和衰减速率的影响符合浅电子陷阱能级理论.     

热释光和光释光发光谱的测量

介绍了自行研制的计算机化热释光和光释光三维光谱测量装置的系统结构及其工作原理.在计算机的控制下,通过精密加热器或激发光源以热激发或光激发的方式使样品发光.从样品发出的光经过光路和光栅分光系统后,形成光谱,被高灵敏度的CCD采集,再将光谱图像模拟信号变为可以直接用计算机进行数据处理的数据信号.波长范围200~800nm,波长分辨率优于2nm,人机界面友好,操作方便.利用热释光和光释光三维光谱测量装置测量了SrSO₄:Eu(0.1%,摩尔分数)和CaSO₄:Eu(0.1%,摩尔分数)的光释光发光谱和热释光发光谱,得到SrSO₄:Eu的光释光发光波长与热释光发光波长均为375nm,而CaSO₄:Eu的光释光发光波长与热释光发光波长均为385nm,说明热释光和光释光具有相同的发光中心,均来自于Eu²⁺的能级跃迁.同时在CaSO₄:Eu的热释光发光谱中还观察到了Eu³⁺的发光.与二维发光曲线相比较,通过对三维热释光和光释光发光谱的研究,可以得到更丰富的信息,这有助于对热释光和光释光发光机制进行更深入的研究.     

Optical and dosimetric properties of variously doped SrF2 crystals

Optical properties and irradiation effects of Nd³⁺-, Pr³⁺-, Tb³⁺- and Tm³⁺-doped SrF₂ crystals and their possible application to solid-state dosimetry were studied and compared to those induced in pure SrF₂ crystals. Optical absorption, thermoluminescence (TL), X- and light-induced luminescence (XL and PL) as well as optically stimulated luminescence and phototransferred TL (OSL and PTTL) were measured in the various samples. Special attention was given to effects of monochromatic vacuum ultraviolet (VUV) radiation. TL was excited in the pure and doped samples by X and β rays as well as by VUV radiation. TL peaks appeared after VUV irradiation at the same temperatures and with the same thermal activation energies as after X or β irradiation, indicating that they are due to the same processes. The VUV excitation spectra showed two maxima at about 145 and 130 nm. Comparison of the TL sensitivities of the various TL materials, showed that the sensitivity of SrF₂:Pr³⁺ was by more than an order of magnitude higher than that of the known LiF:Mg,Ti (TLD-100) phosphor. The sensitivity of pure and of the Nd, and Tb-doped SrF₂ were by a factor of 2–4 higher than that of the TLD-100 and that of SrF₂:Tm was slightly lower. The main emission bands of SrF₂:Pr³⁺ are located in a convenient spectral region between 460 and 640 nm, where most of the standard photomultipliers are sensitive. The dose dependence of the 460 K TL peak in SrF₂:Pr³⁺ is nearly linear in a wide range up to above 27 000 Gy.     

Radioluminescence (RL) behaviour of Al2O3:C-potential for dosimetric applications

The radioluminescence (RL) of carbon doped aluminium oxide (Al₂O₃:C) TL dosimeter material (TLD-500) was investigated using a ¹³⁷Cs conversion electron source (which also emits β and γ) for simultaneous irradiation and luminescence excitation. Furthermore, RL dosimetry characteristics of this material were studied. The main RL emission occurs at 420 nm. That matches the known main TL and OSL emissions for this material as well as an emission that was investigated in earlier RL studies, excited at higher energies (4 MeV electrons) and very high pulse delivered doses (≈800 kGy·s⁻¹). Furthermore, the saturation dose for the main peak is reached at the dose level of ≈80 Gy as known from TL and earlier RL investigations. Other peaks at 700 and 790 nm and broad emission bands at photon energies higher than 3.00 eV and others between 2.00 and 2.50 eV were observed. The 700 nm emission shows growth also at higher dose levels, and saturates at an estimated dose of ≈800 Gy. The 790 nm emission reaches its maximum intensity at ≈10 Gy absorbed dose. The reported results give an outlook to the usability and the potential of Al₂O₃:C combined with RL measurements for radiation dosimetry as well as for beta source calibration, using radioluminescence.     

The response of thermally and optically stimulated luminescence from Al2O3:C to high-energy heavy charged particles

The thermoluminescence (TL) and optically stimulated luminescence (OSL) response of Al₂O₃ dosimeters to high-energy heavy charged particles (HCP) has been studied using the heavy ion medical accelarator at Chiba, Japan. The samples were Al₂O₃ single-crystal chips, of the type usually known as TLD-500, and Luxel^TM dosimeters (Al₂O₃:C powder in plastic) from Landauer Inc. The samples were exposed to ⁴He (150 MeV/u), ¹²C (400 MeV/u), ²⁸Si (490 MeV/u) and ⁵⁶Fe (500 MeV/u) ions, with linear energy transfer values covering the range from 2.26 to 189 keV/μm in water and doses from 1 to 100 mGy (to water). A ⁹⁰Sr/⁹⁰Y beta source, calibrated against a ⁶⁰Co secondary standard, was used for calibration purposes. For OSL, we used both continuous-wave OSL measurements (CW-OSL, using green light stimulation at 525 nm) and pulsed OSL measurements (POSL, using 532 nm stimulation from a Nd:YAG Q-switched laser). The efficiencies (η_HCP,γ) of the different HCPs at producing OSL or TL were observed to depend not only upon the linear energy transfer (LET) of the HCP, but also upon the sample type (single crystal chip or Luxel^TM) and the luminescence method used to define the signal—i.e. TL, CW-OSL initial intensity, CW-OSL total area, or POSL. Observed changes in shape of the decay curve lead to potential methods for extracting LET information of unknown radiation fields. A discussion of the results is given, including the potential use of OSL from Al₂O₃ in the areas of space radiation dosimetry and radiation oncology.     

LiMgPO_4:Tm,Tb的热释光和光释光陷阱参数

采用高温固相法合成了LiMgPO_4:Tm,Tb粉末样品,测定了热释光陷阱参数激发能E和频率因子s.用脉冲退火和多次退火方法研究了其光释光陷阱参数E和s,并与用多速法得到的热释光的结果进行了比较.对不同β射线剂量照射的样品发光曲线的研究表明,300°C高温峰属于一级动力学发光峰.通过对热释光和光释光陷阱的相关性研究表明,经200°C预热的热释光信号(对应于300°C高温峰)和光释光信号很有可能来自于同一深度的陷阱.     

TL, OSL, and phototransferred TL in beta-irradiated anion-defective Al2O3

The behavior of TL, OSL and PTTL under thermal and/or optical stimulation in beta-irradiated -Al₂O₃ was investigated. The noticeable change of the shape of the main TL peak after thermal or optical stimulation clearly shows that this peak is related to at least two traps. The OSL curves recorded after preheating up to a given increased end temperatures are described by two exponential decays curves. The first one is associated to the decay of the traps responsible for the main TL peak. The second exponential is related with the phototransfer from the deep to the main traps. A simple model of the OSL process, based on simultaneous refilling of shallow traps and their reverse filling due to phototransfer from deep traps, under illumination with light is proposed. The model describes well the obtained experimental data.     

Advances in luminescence instrument systems

We report on recent advances in the development of luminescence measurement systems and techniques at Risø. These include: (1) optical stimulation units based on new-generation powerful blue light (470 nm) emitting diodes providing up to 28 mW/cm² for OSL measurements; (2) an infrared (830 nm) laser diode unit providing up to 400 mW/cm² for stimulation of feldspars; and finally (3) an optical stimulation attachment based on a focused solid state green (532 nm) laser for rapid OSL measurements of individual sand-sized single grains of a sample. Facilities for heating samples during beta irradiation and performing linearly modulated OSL measurements have also been incorporated into the system.     

MSO4:Eu2+(M =Mg,Ca, Sr,Ba)的等电子陷阱与热释光特性

在硫酸盐掺入稀土元素的研究中, 得到了几种掺入Eu²⁺的碱土金属硫酸盐磷光体MSO₄:Eu²⁺ (M =Mg, Ca, Sr, Ba), 这组磷光体具有与掺入三价稀土离子(Tm³⁺, Dy³⁺, Eu³⁺)的碱土金属硫酸盐截然不同的热释光特性, 热释光三维发光谱中只呈现一个热释光峰, 对γ和βup辐射的热释光剂量响应为线性-亚线性响应. 结果清楚地显现出Eu²⁺对碱土金属阳离子的等价取代而形成的等电子陷阱对这些磷光体的热释光特性起了关键性的作用, Eu²⁺等电子陷阱与基质中的本征缺陷SO₄^2-形成的缺陷复合体作为热释光多阶段过程的基本作用单元, 基本上产生一次作用热释光事件. SrSO₄:Eu²⁺是一种典型的等电子陷阱发光的磷光体, 它具有相当高的热释光和光释光发光效率.     

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     

Luminescence and OSL study of the inorganic compounds Tl-doped (NH4)2BeF4 and (NH4)2SiF6

The search of materials with efficient optically stimulated luminescence (OSL) properties and a high hydrogen content for fast neutron dosimetry has led to the development of Tl⁺-doped ammonium salts (NH₄)₂SiF₆ and (NH₄)₂BeF₄. Preliminary OSL studies have shown that the OSL in (NH₄)₂SiF₆:Tl⁺ and (NH₄)₂BeF₄:Tl⁺is efficient. In order to optimise the OSL emission and its detection, the identification of the luminescent centres in the OSL process is necessary. This study focuses on the identification of the luminescent centres associated with Tl⁺ based on optical studies in the vacuum UV (VUV) at different temperatures.     

Superlinear dose response of thermoluminescence (TL) and optically stimulated luminescence (OSL) signals in luminescence materials: An analytical approach

The phenomenon of superlinear dose response of thermoluminescence (TL) and optically stimulated luminescence (OSL) signals has been reported for several important dosimetric materials. We develop new analytical equations for the filling of traps and centers during irradiation and for the read-out stage of annealed luminescence materials, within the context of a two-trap and two-center model. The equations are applicable for both TL and OSL signals in annealed dosimetric materials, and are derived under the assumptions of low irradiation doses and dominant strong retrapping (weak recombination) processes. For low doses all traps and centers display linear dose response, which leads to quadratic dose response of the integrated TL/OSL signals. A new analytical expression is presented for this well-known quadratic dose dependence, in terms of the kinetic parameters in the model. The effect of elevated irradiation temperature on the integrated TL/OSL signals is also considered, and analytical expressions are obtained for this situation as well. A new type of dose-rate effect is reported based on the modeling results, which is due to irradiation during elevated temperatures. The accuracy of the analytical expressions is verified by comparing with the results of numerical simulations.     

Thermoluminescence and optically stimulated luminescence disadvantages of α-Al2O3:C crystal grown by the temperature gradient technique

Recently, α-Al₂O₃:C crystal with highly sensitive thermoluminescence (TL) and optically stimulated luminescence (OSL) has been successfully grown by the temperature gradient technique. This paper investigates the heating rate dependence of TL sensitivity, light-induced fading of TL signals and thermal stability of OSL of α-Al₂O₃:C crystals. As the heating rate increases, the integral TL response decreases and the dosimetric glow peak shifts to higher temperatures in α-Al₂O₃:C crystals. Light-induced fading of TL increases with the irradiation dose, and TL response decreases as the exposure time increases, especially in the first 15 minutes. With the increasing intensity of the exposure light, the TL fading of α-Al₂O₃:C crystal increases sharply. The OSL response of as-grown α-Al₂O₃:C crystal is quite stable below 373 K and decreases sharply for higher temperatures.     

TL and OSL dosimetric properties of Opal gemstone for gamma radiation dosimetry

In this work, the response of the natural material Opal was studied in relation to its thermoluminescence (TL) and optically stimulated luminescence (OSL), after exposure to the gamma radiation of a ⁶⁰Co source. The structure of the powdered Opal was verified using the X-ray diffraction, scanning electronic microscopy and energy-dispersive X-ray spectroscopy techniques. The material, in its stone form, was turned into powder and mixed to Teflon (also in powder) in three different concentrations, and then pellets were manufactured. The aim of this work was to evaluate the response of these pellets in high-doses of gamma radiation beams, and to observe their possible application as dosimeters, using the TL and OSL techniques. The dosimetric properties of the samples were analyzed by means of different tests, as: TL emission curves and OSL signal decay curves, reproducibility of TL and OSL response, minimum detectable dose, TL and OSL dose–response curves (5 Gy–10 kGy), and fading. The results obtained in this work, for the TL and OSL phenomena, demonstrated that the pellets of Opal + Teflon present an adequate performance e possibility of use as dosimeters in beams of high-dose gamma radiation.     

Characteristics of TL and PTTL glow curves of gamma irradiated pure Li2B4O7 single crystals

The TL glow curve of X-ray irradiated pure and Cu-doped Li₂B₄O₇ shows that the most intense TL peak is at 160°C. In the present work the characteristics of the TL and PTTL glow curves from gamma irradiated pure Li₂B₄O₇ single crystal samples (prepared by Mitui Kinzoku Kougyo, Japan) have been studied. The samples were irradiated with different gamma doses (from 0.5 up to 500 Gy) using a ⁶⁰Co gamma ray source at a dose rate of 78 Gy h⁻¹. The TL glow curve shows three intense peaks (at 160°C, 260 and 305°C) and three weak ones (at 110, 140 and 220°C). The most intense TL peak is at 160°C, which agrees with the TL glow curve from X-ray irradiated samples [Kutomi Y. and Tomita A. (1990) TSEE and TL of Li₂B₄O₇:Cu single crystals. Radiat. Prot. Dosim. 33, 347–350]. The 305°C peak in gamma irradiated samples also appears to be very intense, which indicates its possible use in high-dose high-temperature dosimetry. Further, the characteristics of the PTTL glow curve have been studied as a function of ultraviolet exposure and number of repeated PTTL cycles.     

Application of the optically stimulated luminescence (OSL) technique in space dosimetry

This paper reviews the state of the optically stimulated luminescence (OSL) technique for space dosimetry applications, focusing on the properties of carbon-doped aluminum oxide (Al₂O₃:C). New data presented include the most complete and recent values for the relative efficiency η_HCP,γ for heavy charged particles as a function of the incident radiation's linear energy transfer (LET), obtained through ground-based experiments at heavy ion accelerators. We also discuss the factors influencing the OSL efficiencies, the LET-dependent properties of Al₂O₃:C, and the experience gained from past space experiments using Al₂O₃:C. The characterization of the OSL efficiency values as a function of LET allows the use of the OSL of Al₂O₃:C in combination with plastic nuclear track detectors for personal dosimetry of astronauts, as proposed by the NCRP Report 142.     

Spectroscopy of the gamma and X ray leakage radiation from the built-in sources of a Risø TL/OSL reader

In this work we evaluate the intensity and the spectral shape of the leakage radiation from the built-in beta and alpha sources of a Risø TL/OSL reader. LiF (TLD-100), fluorite-based pellets and Al₂O₃:C detectors were used in order to determine the dose rate delivered to the dosimeters when the sources are closed. The leakage spectra under both alpha and beta sources were registered with a CdTe semiconductor detector. The spectrum measured under the beta source shows the X-ray beam generated by the interaction of the beta particles with the lead used to shield the source. Besides, the 59.4 keV gamma ray from ²⁴¹Am was registered under the alpha source. Dose rates from 50 to 100 μGy/h were obtained for the dosimeter positions in the turntable under the beta and the alpha sources with the luminescent dosimeters.     

Characterization of the Risø TL/OSL DA-20 reader for application in TL dosimetry

The automated Risø TL/OSL Reader Model DA-20, often used in dating and retrospective dosimetry, was examined for possible applications in thermoluminescent dosimetry related to radiation protection. The investigations revealed that performance of the DA-20 is comparable with that of the Harshaw 3500 manual reader, which was used as a reference instrument. All studied parameters, like stability, reproducibility, low-dose measuring capabilities, were at the same level or only somewhat inferior to those of Harshaw 3500. In particular, using the highly-sensitive LiF:Mg,Cu,P dosimeters, it is possible to measure doses at the microgray level.The DA-20 reader possesses built-in alpha and beta sources, which cause an increased radiation background. At positions just under the closed sources the dose-rate rises to about 50 μGy/h. When the ⁹⁰Sr/⁹⁰Y source is open a quite high dose-rate of 100 mGy/h was measured at the position adjacent to the one being irradiated. Additionally the TLD response to the background radiation significantly depends on the TLD type (atomic number), as the radiation leaking through shielding is composed of low-energy photons. The dose-rate under the closed ²⁴¹Am source was over 10 times higher, when measured with CaF₂ dosimeters, than with LiF.In spite of these problems, the DA-20 reader due to its good stability, reproducibility and sensitivity, combined with such obvious benefits as a 48-dosimeter carousel, temperatures up to 700 °C and full automatics of measurements control, encourages the opinion that the DA-20 Risø reader can be successfully used in practical dosimetric measurements.     

OSL and TL retrospective dosimetry with a fluorapatite glass-ceramic used for dental restorations

Optically Stimulated Luminescence (OSL) and Thermoluminescence (TL) properties of a fluorapatite glass-ceramic have been investigated, with a view to developing a dose assessment technique for medical triage following unplanned exposures of individuals to ionizing radiation. The ceramic is an innovative material used in dental prostheses and restorations. It is strongly sensitive to radiation and the intensity of both the OSL and TL signals are proportional to the absorbed radiation dose. We focused on the optimization of the measuring procedure and investigated characteristics such as reproducibility, fading, minimum detectable dose (MDD), dose response and photon energy response of TL and OSL signals. The dental ceramic exhibited very good reproducibility (<5% at 2σ level) when measured and a linear dose response for a wide range of doses (50 mGy–20 Gy). The MDD values for the samples investigated were ∼5 mGy. The material is not tissue equivalent and the OSL and TL signals are strongly dependent on incident photon energy. Both the luminescence signals exhibited significant fading during the first few hours after irradiation. Its rate was dependent on the parameters of measurement. The results indicate that the material can be used for the purposes of accident dosimetry, however, the fading and photon energy response have to be properly corrected for a reliable dose assessment.