光释光断代

系统介绍了光释光断代的原理,方法和应用技术,光释光是结晶固体的特征发光性质,由这个性质对光的敏感,加上它发射出的光子的数目正比于晶体接受的来自环境中的辐射剂量,因此,我们可以利用这个方法来测定沉积地层中该发光矿物的存在年龄。     

释光断代的可靠性分析

释光断代是一种测年方法,利用的主要是石英等矿物晶体对放射性辐射的次级响应规律.该方法不受其他因素干扰,断代时间基本涵盖第四纪范围,而且适用样品广泛,在细颗粒沉积物测年方面方法独特,在一定程度上弥补了测年工作中的某些空缺,受到第四纪、考古、地震、水文、环境演变等专业研究人员的重视.不过,其断代数据时有偏差,引起应用人员的困惑.本文试图对此进行一些分析和讨论.     

选频光释光——特征波长光释光测定年龄的技术

光释光是结晶固体的特征发光性质,不同固体在不同波长的激发光源作用下,释放出来的光子的波长也是不同的。介绍了一种利用矿物的特征光释光测定年龄的方法。首先是采用BG1999光释光谱仪选定激光光源。确定释放光子的频率,再用矿物的特征光释光谱作年龄测定。利用这一技术获得的年龄数据不仅准确度高,而且可信度大。     

油气勘察样品的多波段激发光释光曲线特征

在热释光研究和应用的基础上,重点探讨了光释光方法在油田勘察中应用的可行性.实验采用的激发波段分别为514 nm、600nm、685nm、740nm和800nm,数据采集时间分别为5s、10s、15s、20s、25s、30s和35s.结果表明,同一个样品,经过不同能量的激光激活,可以得到数个不同水平的光子响应.由此证明,光释光发光曲线与热释光发光曲线都是不同能级陷阱中的电子跃迁表现.     

荧光玻璃、热释光和光释光探测器性能比较

介绍了荧光玻璃探测器、热释光探测器和光释光探测器基本原理和近期发展,并总结了荧光玻璃、热释光探测器、光释光探测器的优缺点.荧光玻璃最大优点是长期稳定性好和可多次读取.热释光和光释光探测器具有灵敏度高、低探测阈、较好的稳定性和能量响应、环境适应性强等优点.但与LiF:Mg,Cu,P相比,α- Al2O3:C光释光探测器对...     

Daybreak 2200型自动化光释光测量仪的初步定量评估

确认和定量检验释光自动化测量系统的性能指标和系统误差是释光年代学实验室非常重要的一项工作.用细颗粒石英和热释光CaSO4:Tm剂量片对Daybreak 2200型自动光释光测量仪长时间光激发/辐照对比邻测样的影响以及辐照泄漏、辐照源开关时间作了系统检测.长时间蓝光激发时比邻测样细颗粒石英发生非线性光晒退,激发10ks时其OSL信号损失不大于15%(光强为最大功率的95%),而对更远位置的测样则几乎无影响.机载90Sr/90Y β放射源在长时间辐照时对比邻测样的影响约为0.02%,对更远位置的样品几乎无影响.Daybreak 2200型测量仪机载β源的快门开关时间约为0.22s(相当于～0.01Gy),β放射源在快门关闭时的泄漏极其微弱,测量时可不予考虑.12个代表性测片位置在测量时具有非常好的一致性,相对标准偏差不超过3%,具有非常低的系统误差.     

水成沉积物EM-OSL与TL释光曲线相似性研究

基于单陷阱单复合中心(OTOR)模型,通过理论分析及采用合适的参数组,并采用R软件模拟,形成水成沉积物的指数调制光释光(EM-OSL)曲线和热释光(TL)曲线,并进一步横向比较它们的各项峰形参数,以分析它们的相似性.初步研究结果表明:基于OTOR模型的条件下,水成沉积物的指数调制光释光曲线和热释光曲线的各项峰形参数极为...     

湖光岩砂石的释光剂量研究

采集湖光岩玛尔湖周围部分岩洞内的岩样及岩壁下和湖岸边的砂土样品,用粗颗粒法测量它们的热释光和光释光;用复合作用剂量响应模型分析热释光和光释光剂量响应,并计算对应的热释光和光释光古剂量。结果表明:相同采样点的样品,热释光和光释光古剂量间都存在一些差异;不同采样点样品的释光剂量相差很大;热释光古剂量测量值较准确的样品,光释光古剂量测量值与热释光测量值无显著的数量级差别。此测量分析对第四纪火山考古有一定参考意义。     

α-Al_2O_3:C单晶的β辐射热释光与光释光性能研究

以高纯碳粉作为碳源直接加入原料,采用导模法(EFG)生长了α-Al2O3:C单晶。研究了晶体经过低剂量β射线辐照后的热释光与光释光特性,α-Al2O3:C单晶的热释光发光曲线在350 K、540 K和689 K附近有3个热释光峰,540 K附近为主要热释光峰,689 K附近为新的热释光峰,发现晶体的陷阱能级深度发生变化并产生了新深度的陷阱能级;随着β吸收剂量的增加,发光强度也随之增强,但是3个热释光峰温位置大致保持不变。在多次连续同剂量辐照过程中,随着辐照次数的增加,主热释光峰强度增强,峰温向高温方向偏移。α-Al2O3:C单晶的光释光衰减曲线呈指数变化,其由前期快衰减部分和后期慢衰减部分组成,快衰减部分衰减速率随着吸收剂量的增加变化很小,而慢衰减部分衰减速率则有较为明显的减慢。在低剂量范围内(低于10Gy),热释光和光释光过程灵敏度不随吸收剂量而变化,剂量响应曲线呈线性的特点。     

古代瓷器热释光测定年代研究

叙述了热释光断代中采用前剂量技术测定瓷器的年代，着重研究了瓷片深度剂量的变化，１１０℃ＴＬ峰的热激活特性、古剂量的测定和年剂量的估算。结果表明，这项技术能用于古代瓷器的真伪鉴定，但准确度和精度不及陶器。另外，前剂量技术中一些复杂因素，也是导致年代测定误差大的可能原因。     

Investigation of OSL signals from very deep traps in unfired and fired quartz samples

This paper presents an attempt to isolate experimentally optically stimulated luminescence (OSL) signals which may originate from very deep traps (VDT) in quartz samples. As VDT we consider those traps which are responsible for TL glow peaks with a peak maximum temperature above a TL readout temperature of 500 °C. The basic experimental procedure used to isolate OSL signals from VDT is heating the quartz samples to 500 °C immediately before measuring the OSL signal. The study was carried out on eight quartz samples of very different origins; it is found that all eight samples exhibit OSL signals from VDT, and for a wide region of OSL stimulation temperatures. The OSL signal from VDT depends strongly on the type of quartz sample studied and on whether the sample was fired at high temperatures or not. The behavior of the OSL signal from VDT as a function of the stimulation temperature is found to be very different in fired and unfired samples. The thermal activation energy E for the OSL signals from VDT is obtained in both fired and unfired samples. The OSL signal from VDT in quartz samples fired at 800 °C for 1 h is very high, and the OSL curves consist of three well-defined components and a fourth slow component which is rather poorly resolved. The dose response of these components is obtained using a computerized deconvolution procedure for the dose region 0.5-300 Gy. The results are of importance for dating of ancient fired ceramics, since OSL signals from VDT could potentially extend appreciably the equivalent dose region toward both lower and higher values.     

Optically stimulated luminescence (OSL) of Lu2SiO5:Ce powder: A preliminary study

Optically stimulated luminescence (OSL) of Lu₂SiO₅:Ce powder (Phosphor Technology Ltd., UK) has been measured by Risø TL/OSL Reader (TL-DA-15). Upon blue photon stimulation (λ_ex ∼470 nm) the material shows strong OSL signal that can detect β-irradiation right up to the dose of ∼0.2 Gy.A brief discussion on this finding is presented by comparing the thermoluminescence of the system with and without optical stimulation. The two key important parameters namely, trap-depth (E) and frequency factor (s) of the main peaks that occur at 85 and 232 °C are determined.     

Simulations of thermally transferred OSL signals in quartz: Accuracy and precision of the protocols for equivalent dose evaluation

Thermally-transferred optically stimulated luminescence (TT-OSL) signals in sedimentary quartz have been the subject of several recent studies, due to the potential shown by these signals to increase the range of luminescence dating by an order of magnitude. Based on these signals, a single aliquot protocol termed the ReSAR protocol has been developed and tested experimentally. This paper presents extensive numerical simulations of this ReSAR protocol. The purpose of the simulations is to investigate several aspects of the ReSAR protocol which are believed to cause difficulties during application of the protocol. Furthermore, several modified versions of the ReSAR protocol are simulated, and their relative accuracy and precision are compared. The simulations are carried out using a recently published kinetic model for quartz, consisting of 11 energy levels. One hundred random variants of the natural samples were generated by keeping the transition probabilities between energy levels fixed, while allowing simultaneous random variations of the concentrations of the 11 energy levels. The relative intrinsic accuracy and precision of the protocols are simulated by calculating the equivalent dose (ED) within the model, for a given natural burial dose of the sample. The complete sequence of steps undertaken in several versions of the dating protocols is simulated. The relative intrinsic precision of these techniques is estimated by fitting Gaussian probability functions to the resulting simulated distribution of ED values. New simulations are presented for commonly used OSL sensitivity tests, consisting of successive cycles of sample irradiation with the same dose, followed by measurements of the sensitivity corrected L/T signals. We investigate several experimental factors which may be affecting both the intrinsic precision and intrinsic accuracy of the ReSAR protocol. The results of the simulation show that the four different published versions of the ReSAR protocol can reproduce accurately the natural doses in the range 0-400 Gy with approximately the same intrinsic precision and accuracy of ∼1-5%. However, these protocols underestimate doses above 400 Gy; possible sources of this underestimation are investigated. Two possible explanations are suggested for the modeled underestimations, possible thermal instability of the TT-OSL traps, and the presence of thermally unstable medium OSL components in the model.     

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.     

凉水河畔热释光断代结果比较

对样品进行光晒退处理后测定热释光(TL)强度,得到TL断代结果。实验表明记年累积起点消楚,回零完全的标本是TL断代理想的测试对象。光晒退校正可获得可靠的TL断代结果,但河流沙土等地质标本在记年累积不太明确时将导致测年结果不准确。     

A versatile integrated system for thermoluminescence and optically stimulated luminescence measurements

A versatile integrated reader system for TL and OSL measurements of phosphor materials has been described for luminescence research applications. The developed integrated reader system works either in TL or OSL or TL-OSL mode. In the OSL operation, besides the conventional CW-OSL, POSL and LM-OSL modes a novel non-linear OSL (NL-OSL) method has been incorporated in the reader system. The optical stimulation unit consists of four high power LEDs fitted in four channels and optically focused on the sample. Each of the LED is capable of delivering up to 80 mW/cm² light power at the sample position. The LEDs with peak wavelength λ_p ≈ 470 nm and 530 nm and Δλ ≈ 20 nm have been used for optical stimulation of the samples. A PID temperature controller has been used for generating and controlling user defined heating profiles for the TL measurements in the reader system. The reader system covers a wide dynamic dose range of 10 μGy to 10³ Gy for TL/OSL measurements. The OSL grade α-Al₂O₃:C phosphor was used to test the reader system and investigate its impact on low dose assessment for personnel and environmental monitoring. The design concept of the reader system and the results of dose measurements are discussed.