Assessing conservation practices in Amalacaxco Gorge (Izta-Popo National Park, Central Mexico) using fallout 137Cs and Optically Stimulated Luminescence (OSL)

This study aims to assess conservation practices in Izta-Popo National Park(Central Mexico) by evaluating the mechanisms of sediment transfer. We applied a methodology based on fallout ^(137)Cs and optically stimulated luminescence(OSL) analysis. This was tested in the upper catchment of Amalacaxco Gorge, selected for being one of the sectors of the park in which man-made actions have been implemented in last decades to favor forest growth in the alpine grassland and to reduce the effect of water runoff. We quantified the ^(137)Cs activity using gamma and beta spectrometry of fine sediment grains extracted from the surface of parcels of 0.4 m2 in areas of natural forest, natural alpine grassland, alpine grassland with conservation practices, ravines and trails. In general, ^(137)Cs values increases as local slope decreases as it was expected. The natural forest is the most stable area in terms of soil erosion and sediment accumulation and, mean ^(137)Cs activity was taken as reference to assess cumulative zones, with higher ^(137)Cs values and erosive, with lower. We found that trails are accumulative surfaces but in other areas, erosion predominates. Man-made ditches, trenches and afforestation in the alpine grassland have higher ^(137)Cs values than thenatural grassland, which indicates that conservation practices are limiting the sediment transfer from hillslopes to channels, however, soil retention is less than in the natural grassland. Additionally, we evaluated the luminescence(OSL) values obtained from samples extracted from the sediment transported in ravines that are cutting into different sectors of the study area to assess the grade of resetting of fluvial materials. These luminescence results indicated that the sediment transported in ravines that are cutting into the natural forest and alpine grassland is bleached more efficiently than the sediment transported in the alpine grassland with conservation practices. Results of fallout ^(137)Cs and luminescence strongly suggest that man-made actions in this part of the Izta-Popo National Park are dramatically modifying the natural mechanisms of sediment transfer and favoring soil erosion. We conclude that made ditches, trenches and afforestation are not an effective conservation practice in Amalacaxco Gorge because they are promoting soil erosion instead of reducing it.

Late Pleistocene aeolian activity in Haitan Island, Southeast China: Insights from optically stimulated luminescence dating of coastal dunes on marine terraces

The 'Old Red Sand' is a type of semicemented medium-fine sandy sediment that is red(10R_4/8) or brown red(2.5YR_4/8) in colour and is found in late Quaternary deposits. The sediments have distinctive characteristics and are a critical archive for understanding climatic changes in the coastal areas of East Asia. The ages of the late Quaternary aeolian sand dunes from Haitan Island in the coastal area of South China are still in debate. In this study, three sets of marine terraces were identified in the northern region of Haitan Island. Aeolian dune sands are well preserved on the top of these terraces. Quartz Optically Stimulated Luminescence dating and the distribution of the formation ages demonstrated that the palaeo-dunes are deposits from the middle-late period of the Late Pleistocene(Q_3^(2-3)). The period may be divided into three stages, 100-90 ka, 70-60 ka, and 40-20 ka, in which the palaeo-dunes of the first two stages are more widespread and were formed separately during a low-sea level period of the Marine Isotope Stages 5 b and 4. Several depositional palaeo-flood event records were preserved during the last stage due to the increasing gradient of mountain gullies formed during the Last Glacial Maximum.

The study on optically stimulated luminescence dosimeter based on the SrS:Eu,Sm and CaS:Eu,Sm

With the increasing use of nuclear energy, there is a need for a wider range of efficient dosimeters for radiation detection and assessment. There has been a tremendous growth in the development of radiation detectors and devices in the past few decades. In recent years, the development of new materials for radiation dosimetry has progressed significantly. Alkaline earth sulfides （AES） have been known for a long time as excellent and versatile phosphor materials. In the present investigation, a number of phosphor samples such as mono-, binary and ternary sulfides of alkaline earths （II^a-VI^b） have been prepared and their TL properties have been studied with respect to exposure （x-ray） response and fading. In this paper, some results on SrS：Eu, Sm and CaS：Eu, Sm phosphors are presented. A type of novel OSL dosimeter is described. The dosimeter takes advantage of the characteristics of charge trapping materials SrS：Eu, Sm and CaS：Eu, Sm that exhibit optically stimulated luminescence （OSL）. The measuring range of the dosimeter is from 0.01 to 1000 Gy. The OSL dosimeters provide capability for remote monitoring radiation locations which are difficult to access and hazardous. This equipment is relatively simple, small in size and has low power consumption. The device is suitable for space radiation dose exploration. In addition, it also can be used in IC and other radiation occasions and has good prospects.

Optically stimulated luminescence dosimeter based on CaS:Eu,Sm

Alkaline earth sulfides (MgS,CaS and BaS) crystal doped with rare-earth ions is an optically stimulated luminescence dosimeter with very high sensitivity,short time constant of the optically stimulated luminescence (OSL) separated perfectly from the stimulation.In this paper,an OSL dosimeter is described.It has linear dose response from 0.01 to 1000 Gy.The equipment,relatively simple and small in size is promising for applications in space exploration and for high dose irradiation and dangerous irradiation conditions.

Optically stimulated luminescence dating of young glacial sediments from the eastern Qinghai-Tibetan Plateau

Poor bleaching is a significant problem for Optically Stimulated Luminescence(OSL) dating of glacial sediments. Five young glacial samples(including two modern analogues) from different depositional settings were collected beyond the Yingpu Glacier in the eastern Qinghai-Tibetan Plateau. De was determined using different OSL methods. The luminescence characteristics and dating results showed that the large aliquot quartz Blue Stimulated Luminescence(BSL) is more applicable than polymineral infrared stimulated luminescence(IRSL) method. Small aliquot quartz BSL results showed poor luminescence properties due to low luminescence sensitivity of quartz in this area. The dating results also indicated that glaciofluvial samples deposited close to ice margin(~40 m and ~700 m) and supraglacial debris dominated lateral moraine samples are relatively well-bleached, whereas samples from ground moraine and low terminal moraine were poorly bleached, probably due to containing subglacial and englacial debris. The residual doses of glaciofluvial and lateral moraine crest samples were below a few Gy and age overestimations were below a few hundred years. The ground moraine and low terminal moraine samples had residual doses as high as ~110 Gy, and ages were overestimated by ~15-17 ka.

Thermoluminescence and optically stimulated luminescence disadvantages of α-Al_2O_3: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.

External and Environmental Radiation Dosimetry with Optically Stimulated Luminescent Detection Device Developed at the SCK.CEN

The laboratory of Radiation Dosimetry and Calibration of the Belgian Nuclear Research Centre (SCK.CEN) is using thermoluminescence dosimetry for more than thirty years for routine measurements and for R&D investigations. In 2002, it has developed an experimental device based on the optically stimulated luminescence (OSL) technique. This device is working with AL2O3:C crystals stimulated by the green line (488 nm) emitted by a 150 mW argon laser. This paper describes this device, its characteristics, some applications in space dosimetry and the R&D works initiated in this field during the next few years.

全新世以来察尔汗盐湖沉积物的OSL年代学研究

察尔汗盐湖沉积物记录了柴达木盆地晚更新世以来的环境演化信息,但全新世以来沉积剖面的研究比较稀少且相关年代数据也比较缺乏。在察尔汗盐湖别勒滩区段东部,别勒滩区段西部和达布逊区段东部的沉积剖面中各发现2层细碎屑夹层,采集了相应的光释光样品,以研究察尔汗盐湖全新世时期的沉积年代。结果表明,察尔汗盐湖达布逊区段东部剖面(DBX)的2个碎屑层分别形成于6.2 ka(8.90 m)和2.8 ka(1.96 m),别勒滩区段东部剖面的2个碎屑层分别形成于2.9 ka(3.20 m)和0.9 ka(1.40 m),别勒滩区段西部剖面的2个碎屑层分别形成于2.4 ka(3.10 m)和0.7 ka(1.50 m)。由于晚第四纪盐湖沉积松散且易溶造成样品的成分及来源复杂等影响,造成了剖面OSL数据远小于14C、U-Th测年数据(8~9 ka)。3个剖面沉积速率计算表明,察尔汗盐湖达布逊区段沉积速率大于别勒滩区段,而别勒滩区段东部的沉积速率高于西部,察尔汗盐湖与东台吉乃尔盐湖的沉积速率整体上保持一致。

基于OSL原理的Al_(2)O_(3):C核辐射剂量测量系统研究综述

核辐射剂量测量是辐射监测中的一项重要内容。基于光释光(Optically Stimulated Luminescence,OSL)原理搭建掺碳氧化铝(Al_(2)O_(3):C)核辐射剂量测量系统的相关研究迄今已有数十年的历史。该系统将Al_(2)O_(3):C中存储的辐射能量以光信号的形式释放,之后使用光电转换器件将光信号转换为电信号,通过对电信号的采集分析实现辐射剂量的测量,具有灵敏度高、远程探测、保护人员安全、抗电磁干扰等优势。本文介绍了该系统在国防、医疗剂量及个人剂量监测等领域的研究成果,探讨了其未来发展趋势,以期对OSL核辐射剂量测量系统的研究人员提供参考借鉴。

Optically stimulated luminescence of Dy^3+-doped NaCaPO4 glass-ceramics

Dy^3+-doped glass-ceramics containing NaCaPO4 crystals were successfully fabricated by heat treatment at base glass,and the luminescence properties were investigated for potential applications in radiation measurements.The photo luminescence(PL)excitation and emission spectra exhibit transitions related to Dy^3+ions corresponding to the strongest excitation and emission wavelengths at 351 and 575 nm,respectively.The CW-OSL properties as a function of dopant concentration,pre-heating temperature,pre-heating time and signal fading were investigated.The most appropriate Dy^3+ion concentration was found to be 0.25 mol%.The TL glow curves have a broad peak feature peaking at 195±5℃.The fading of the OSL signal would keep stable in five days with the intensity value of about 76.11%.The samples also exhibit good signal reusability and a broad linear dose response range(0.02-1000 Gy).

Tracing mechanism of optically and thermally stimulated luminescence in Lu2O3:Tb,M（M=Hf,Zr,Ti）ceramic storage phosphors

A series of energy storage phosphors,Lu2O3:Tb,M(M=Hf,Zr,Ti),were investigated by means of photoand thermoluminescence techniques to compare the effect of the co-dopant from the same group of periodic table of elements on charge carriers trapping capability and trap parameters.Most of the investigated processes were tracked individually for the Tb3+in the two different metal sites offered by the Lu2O3 host-noncentrosymmetric C2 and centrosymmetric C3i.It is proved that both Tb3+ions participate in hole trapping and electrons are immobilized in traps whose depths are defined by the codopant.Deepest traps,~1.79 eV,appear upon Ti addition,while Zr and Hf generate traps of very similar,~1.40-1.44 eV,depths.The stored energy may be released not only by means of thermal stimulation but also upon the impact of optical photons.Light from the 390-430 nm range of wavelengths was found the most efficient in the latter process.Also deep red radiation of 780 nm releases most of the trapped electrons in Zr/Hf co-doped ceramics but is much less effective in the case of Tb,Ti material.Consistent scheme of electronic levels engaged in charge carriers trapping and subsequent generation of thermoand optically stimulated luminescence was constructed.

Dose-rate dependence of optically stimulated luminescence signal

Optically stimulated luminescence （OSL） is the luminescence emitted from a semiconductor during its exposure to light. The OSL intensity is a function of the total dose absorbed by the sample. The dose-rate dependence of the OSL signal of the semiconductor CaS doped Ce and Sm was studied by numerical simulation and experiments. Based on a one-trap/one-center model, the whole OSL process was represented by a series of differential equations. The dose-rate properties of the materials were acquired theoretically by solving the equations. Good coherence was achieved between numerical simulation and experiments, both of which showed that the OSL signal was independent of dose rate. This result validates that when using OSL as a dosimetry technique, the dose-rate effect can be neglected.

The fluorescence and thermoluminescence characteristics of α-Al_2O_3:C ceramics

This paper reports that polycrystalline （α-Al2O3：C ceramics are fabricated by conventional ceramics process. The excitation, emission spectra, thermoluminescence （TL） and optical stimulated luminescence （OSL） of α-Al2O3：C polycrystalline ceramics are investigated. There exists 410nm maximum emission peak which is caused by recombination of an electron with F＋ centre to produce an excited F centre. The samples show three clear TL glow peaks at 405, 493 and 610 K. The attenuation constant of exponentially decaying fast component （τ1） and slow component（τ2） of OSL curve are 8.43s and 41.73s, respectively. Those fluorescence and thermoluminescence characteristics are similar with α-Al2O3：C crystal.

Quartz luminescence dating of a centennial coastal foredune from Changle in Fujian Province,East China Sea

The Aeolian foredunes in the southern coast of China are records of paleoenvironmental changes for marine monsoon region. Intensive studies have been conducted to decipher their formation and paleoenvironmental implications in which chronology played a key role. However, robust dating results are still limited due to the scarcity of organic materials for radiocarbon and the limited application of quartz optically stimulated luminescence(OSL). Here, we collected 11 OSL samples and 140 grainsize samples from the Changle section with a thickness of 7 m from a coastal foredune in Fujian Province. The dating results indicated that the section spanned a time period from 0.32±0.04 ka(depth of 700 cm) to 0.18±0.02 ka(depth of 80 cm), after removal of age outliers. According to the OSL ages and sedimentary structural characteristics, the section could be divided into two stages, i.e. the stable accumulation period with an age range of 0.32-0.18 ka from the depth of 700 cm to 80 cm, and the activation period above the depth of 60 cm, at which the dune erosion was retained. The foredune development due to increased transport of dune sediment at the top part of the section was the result of recent human activities.Inside the foredunes, normal cross-bedding was generated by seasonal changes in wind direction.Seasonal changes in the wind direction were the primary cause for various sedimentary bedding within the dunes.

土壤光释光测量方法在特拉敖包砂岩型铀矿产地的试验研究

文章以探索新型铀矿放射性勘查技术方法的试验效果为目的,在特拉敖包砂岩型铀矿产地开展了土壤光释光测量方法的试验研究。通过数据处理,综合地质、钻孔和物探相关先验信息,分析评价了土壤光释光测量方法在砂岩型铀矿勘查中的应用效果。试验结果显示:土壤光释光测量等效剂量数据非正态分布,不适宜采用逐步剔除法进行数据异常下限的计算;对数处理后的数据符合近似正态分布,可根据数据分布特征进行异常下限的估算。在铀矿体上方及其附近,存在土壤光释光测量等效剂量异常,表明该方法在砂岩型铀矿勘查领域具有较好的发展前景。通过对异常成因的分析,提出通过不同深度样品等效剂量差的矿致释光异常识别方法。

基岩断层面黏滑和蠕滑时岩石表层光释光信号模拟

重建断层的黏滑(seismic slip)和蠕滑(creep)历史对于更好地了解断层活动和地震危险性评估至关重要。近年来,利用大地测量技术研究活动断层的蠕滑和黏滑过程成为一个研究热点。然而,在地质历史时期(如百年尺度以上),如何判断活动断层的滑动方式(黏滑或蠕滑),并获取其滑动速率仍然是一项挑战。文中基于近十年来发展的岩石表层光释光测年方法,结合内蒙古狼山断裂花岗岩样品的光释光晒退参数进行理论模拟,得到了基岩正断层发生黏滑、蠕滑和崩积楔侵蚀等情形的光释光晒退模型。模拟结果表明,该方法能够有效区分断层的黏滑和蠕滑,获得相应的活动期次和位移量,并且有潜力记录崩积楔侵蚀。文中还分析了该方法区分断层活动方式、期次的时间分辨率和获得位移量的空间分辨率。

北京平谷山前河流阶地发育序列、形成时代及地质意义

河流阶地是研究河流演化、构造运动的良好载体,虽然北京地区第四纪地质研究程度较高,但北京东部地区对河流阶地的相关研究资料较少。笔者等以北京平谷燕山山前发育的泃河、黄松峪石河、将军关石河为研究对象,通过野外地质调查、光释光测年技术(OSL)详细划分了上述河流阶地的发育序列,在此基础上讨论了部分河流阶地的形成时代、阶地成因及河流阶地对燕山隆升的响应等地质问题,认为泃河南岸发育有3级阶地,北岸发育2级阶地;黄松峪石河最多发育有6级阶地;将军关石河发育有5级阶地。将军关石河至晚形成于中更新世晚期(161.7±7.7 ka BP),黄松峪石河至晚形成于晚更新世早期(121.2±5.4~100.3±4.1 ka BP),泃河至晚形成于晚更新世中期(79.4±3.3~70.8±3.4 ka BP)。泃河、黄松峪石河、将军关石河各级阶地的形成受到了古气候变化和燕山隆升的双重影响,平谷地区燕山在中更新世晚期以来,一直处于隆升的状态,晚更新世早期时隆升速率达到最大,可达0.24~0.34 mm/a,晚更新世中期时隆升速率降低,0.18~0.24 mm/a。以上成果对研究北京东部河流阶地发育特征、形成时代具有重要参考价值,也为中更新世晚期以来燕山的隆升提供了新的证据。

植硅体释光信号特征及其对测年应用的启示

中国西部青藏高原等地区往往缺乏可供AMS^(14)C测年的炭屑、植物残体等物质,开展传统的^(14)C测年有一定难度。然而,这些地区的现代地表常生长着大量草本植物,在其第四纪沉积物中均发现了丰富的植硅体。探索新的植硅体测年技术流程,可为中国西部地区的第四纪沉积物提供新的有效测年途径。植硅体以其自身的广泛分布性、结构稳定性和保存完整性,在测年应用中具有特殊优势,尤其是植硅体碳可用于^(14)C测年。然而,植硅体碳的^(14)C年龄存在高估问题,这可能是由于前处理过程中的快速氧化作用和高温作用破坏了其结构的稳定性和封闭性,需依据其化学组成和某些物理性质变化识别其结构在高温环境下的细微改变。植硅体作为特殊的非晶质含水SiO_(2),其热释光(Thermoluminescence,TL)与光释光(Optically stimulated luminescence,OSL)信号具有测年潜力,可作为直接比对和替代植硅体^(14)C测年法的另一测年手段,同时其释光性质变化可能对识别其物理结构变化具有参考价值。文中以从干稻草中提取的现代植硅体样品为例,对其进行了一系列条件实验,从而确定了植硅体OSL与ITL_(165)信号的具体测试流程,并进行了不同给定剂量的剂量恢复实验,以探讨其剂量-信号的响应关系及测试流程的可行性和可靠性。结果表明,天然植硅体颗粒存在稳定且易晒退的OSL信号,在较高给定剂量(850Gy)的条件下植硅体存在较显著且稳定的_(165)℃TL峰,OSL信号与ITL_(165)信号均有潜力应用于测年研究,但需要已知年龄的样品进行检验。与此同时,不同退火温度加热后的ITL_(500)曲线具有识别植硅体释光性质和物理结构变化的潜力,退火温度升高至300~350℃时植硅体的结构开始发生改变,至约600℃时已发生不可逆的结构改变且逐渐敏化。这也意味着在提取植硅体的过程中应尽可能使用湿式氧化法而非干灰化法,以避免植硅体的结构封闭性遭受破坏,从而造成植硅体碳的AMS^(14)C年龄被高估。

郑州市隐伏构造精细探测技术应用研究

隐伏构造格架空间形态主要由深部孕震环境分析及浅部浅层定位等多组合方法进行精细探测,研究目标区断裂构造活动时代。深部空间特征主要由大地电磁测深与深反射地震推断解释,浅层空间特征由浅层地震勘探与地质钻孔联合勘探,地层年代主要通过地层岩性、沉积颜色、光释光测年等,综合分析研究确定地层错段的最新时代。本文以郑州市某隐伏构造活动性探测与评价为研究基础,通过组合方法探明地下埋藏的隐伏活断层,揭示其精确空间位置、活动时间,判定该构造为第四系早中期的隐伏断裂,为城市评估活断层危险性和危害性提供了依据,并对其他城市隐伏区活动断层探测有一定的借鉴意义。

光释光(OSL)测年技术的初步实验研究

提出了基于X射线激发的光释光测年原理，据此进行了初步实验研究。研究表明，利用X射线是可以激发辐射样品使其产生光释光信号的。