共查询到19条相似文献，搜索用时 109 毫秒
1.
珊瑚礁生态系统拥有较高的生物多样性,为人类提供了丰富的生物资源及生态服务功能与价值。我国多处滨海核电站周边存在造礁珊瑚,而南海珊瑚岛礁也是未来海上漂浮核电站重要的潜在应用场景。基于在珊瑚礁中14C、90Sr和137Cs的已有研究,分析了珊瑚礁中关键人工放射性核素的研究动态,提出了基于核素在珊瑚骨骼与海水分配系数的分类原则,探索了低度(137Cs)、中度(129I)和高度(14C>239+240Pu>90Sr,236U)富集的三大类核素在珊瑚骨骼中的富集规律,利用欧盟的ERICA模型开展上述人工放射性核素和天然放射性核素210Po对珊瑚虫的辐射剂量评估,定量计算不同核素对珊瑚虫的剂量率排序依次为14C>90Sr>137Cs>239+240Pu> 相似文献
2.
运用γ谱仪,对采自福建省兴化湾外近海海域的D37和FJ3-12孔进行了 210Pb 、226Ra和 137Cs 活度的测试,得到这3种核素活度随深度变化特征。分别运用 210Pb 法的CFCS模式(恒定通量恒定沉积模式,Constant Flux and Constant Sedimentation)和CRS模式(恒定供给速率模式,Constant Rate of Supply)以及 137Cs 时标法计算平均沉积速率,发现3种方式的计算结果存在一定差异。在排除粒度变化对核素剖面的影响后,对比不同取样深度的结果发现,指数衰减剖面不完整度(取样深度未达 210Pb 的本底值区)对运用CFCS和CRS模式计算平均沉积速率均有不利影响,其中对CRS模式的影响随剖面不完整性愈强而愈显著。为此提出了相关校正方法作为参考,即先根据CFCS模式估算平均沉积速率和相应的210Pbex累积量,再通过CRS法建立钻孔年龄框架,由此可计算得出D37和FJ3-12孔的平均沉积速率分别为2.76cm/yr和4.53cm/yr。 相似文献
3.
格尔木河222Rn同位素变化及其对地表水-地下水交互关系的指示意义 总被引：2，自引：0，他引：2
我国西北内陆干旱区水资源匮乏,生态环境脆弱,在全球气候变化和人类活动干扰背景下,采用同位素方法进行精细尺度地表水-地下水交互作用研究是探求当地水循环变化和水资源管理的基本要求。通过测量格尔木河流域河水、地下水样品2019年5月和8月的222Rn浓度和典型断面流量,结果发现：山区河段河水222Rn浓度最高,平均值为948.72 Bq·m-3,指示基岩裂隙水是山区河段重要补给来源;山前冲洪积扇河水222Rn浓度最低,平均值为76.71 Bq·m-3,地下水补给较少;溢出带地区河水222Rn浓度上升至平均676 Bq·m-3,地下水溢出补给河水,向下至细土平原,河水222Rn浓度呈下降趋势。时间变化上,8月与5月相比,河水222Rn浓度下降,表明地下水补给减少。溢出带S1~S2河段河水与地下水交互关系以双向转化为主,基于质量守恒原理计算河水与地下水交互通量,5月和8月累积河水渗漏通量分别为3.87 m3?s-1和0.9 m3?s-1,地下水补给通量分别为0.51 m3?s-1和0.47 m3?s-1,河水渗漏强度大于地下水补给,二者交互通量存在时空差异。 相似文献
4.
通过在区域开展地下水同位素、水化学取样分析，研究了平谷泃河和洳河冲洪积扇地下水循环演化特征。分析结果显示：本次所取水样pH值为7.6～8.1，为中性水；阳离子含量均以Ca2+、Mg2+为主，占70%以上，阴离子含量以HCO3-为主，占82%以上，所取水样地下水水化学类型均为HCO3·Ca·Mg型。研究区浅层第四系松散孔隙水δ2H值和δ18O值分别为64.9‰、9.08‰，深层第四系松散孔隙水δ2H值和δ18O值分别为67.6‰、δ18O值，基岩岩溶水δ2H值和δ18O值分别为64.5‰、9.36‰。基岩岩溶水稳定同位素含量均值与浅层地下水比较接近；浅层第四系松散孔隙水14C含量为46.7%～93.1%，深层水第四系松散孔隙水14C含量为40.23%～61.13%，基岩岩溶水... 相似文献
5.
利用ARD型γ能谱仪对辽宁省大连市区地表天然放射性核素238U、232Th、40K含量进行了现场测量.调查结果显示，大连市区238U、232Th、40K比活度平均值分别为23.09 Bq/kg（范围值1.24~151.91 Bq/kg）、18.99 Bq/kg（范围值0.41~92.57 Bq/kg）、386.39 Bq/kg（范围值31.30~1095.50 Bq/kg），均显著低于全国和世界的平均值.在测得的238U、232Th、40K含量基础上，计算了距地面1 m高处空气中γ辐射吸收剂量率、外照射指数、内照射指数和年有效剂量等参数，并据此对大连市区天然放射性水平进行了评价.空气中γ辐射吸收剂量率（Dr）平均值为39.04 nGy/h，远低于全国（81.5 nGy/h）和世界（80 nGy/h）平均水平.外照射指数、内照射指数平均值分别为0.23、0.12，均远小于国家对建筑材料外照射指数的限值1.年有效剂量为0.048 mSv，远低于世界年平均有效剂量（0.46 mSv）以及公众外照射年有效剂量（1.0 mSv）的限值.评价结果表明，大连市区地表天然放射性辐射处于安全的水平. 相似文献
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7.
干旱地区空气中氚浓度测定方法研究 总被引：1，自引：0，他引：1
空气中3H以水蒸气形态存在,环境中气氚的测定先是把空气中3H收集起来,再在收集液中加入闪烁液,用低本底液闪谱仪测量水样中3H浓度,然后换算成空气中3H浓度. 相似文献
8.
洞庭湖区水系发达,水文地质条件复杂,人类活动强烈,地表水和地下水的水力联系变化频繁,其研究的难度以及由此造成的研究不足影响了对湖区地下水赋存和运动规律的深入认识。本文以洞庭湖整体为研究对象,采用水位动态分析和氡(222Rn)同位素示踪法,定性和定量研究枯水期洞庭湖区地表水与地下水的交互作用关系与交互通量。枯水期洞庭湖区水位和氡浓度空间分布特征指示研究区内地下水向湖水排泄,尤以东洞庭湖最为显著。氡箱模型计算结果显示枯水期地下水排泄222Rn通量为455.09 Bq/(m2·d),占总输入222Rn通量的60.07%,地下水排泄总量为0.29×108 m3/d,平均排泄速率为56.27 mm/d,地下水排泄对湖水的贡献率为7.04%。敏感性分析表明：风速、地下水和湖水222Rn浓度以及湖面面积等参数较为敏感,合理布置取样点并提高敏感参数测量准确度能提高模型计算结果的可靠度。氡同位素示踪法物理意义明确、操作过程简便,是研究复杂区域地下水补、... 相似文献
9.
用镭同位素评价海水滞留时间及海底地下水排泄 总被引：3，自引：0，他引：3
海底地下水排泄(submarine groundwater discharge, SGD)难以直接测量, 镭同位素和氡-222等天然示踪剂使得间接评价SGD通量成为可能.为了评价五缘湾的水体滞留时间和SGD通量, 实测了湾内海水、湾外海水和地下水中224Ra和226Ra的活度, 利用224Ra和226Ra半衰期的差异, 采用224Ra与226Ra的活度比值计算湾内水团的年龄和平均滞留时间, 利用224Ra和226Ra的质量平衡模型计算SGD通量.五缘湾13个站位的水团年龄在0.6~2.4 d之间, 湾顶水团年龄相对较大, 平均海水滞留时间1.4 d.地下水输入五缘湾的224Ra和226Ra通量分别为5.17×106 Bq/d和5.28×106 Bq/d, 将该通量用地下水端元的活度转换成为SGD通量分别是0.21 m3/m2/d(224Ra平衡模型)和0.23 m3/m2/d(226Ra平衡模型), 两种模型的结果较接近, 其平均值0.22 m3/m2/d可作为五缘湾的海底地下水排泄通量. 相似文献
10.
湖泊沉积中的10Be含量变化——有助于识别第四纪古冰川的有无 总被引：1，自引：1，他引：0
20世纪50-70年代核试验产生的137Cs尘埃,在现代冰川和非冰川湖泊沉积剖面中的深度分布存在明显差异.同理,大气宇宙射线成因的长半衰期10Be尘埃,在第四纪冰川和非冰川湖泊沉积剖面中的深度分布也应存在差异.第四纪冰川湖泊,冰期时流域内冰雪和10Be的累积量大于消融量,间冰期时冰雪和10Be的消融量大于累积量.因此,冰川湖泊冰期的10Be入湖通量小于间冰期.湖泊沉积剖面10Be浓度的波动,很可能表征流域内冰雪消融与累积的变化.非冰川湖泊,不存在冰川的累积与消融对10Be入湖通量的影响.开展第四纪冰川与非冰川湖泊沉积10Be含量变化的对比研究,有可能为破译中国东部中低山区古冰川和青藏高原大冰盖的世纪之争提供新的证据. 相似文献
11.
Temporal Variation in Sr and 87Sr/86Sr of Yangtze River: An Example from Datong Hydrological Station
Temporal variation of dissolved 87Sr/86Sr in the Yangtze River is poorly understood compared to other Tibetan rivers. In this study, dissolved Sr and 87Sr/86Sr were measured from a temporal series of water samples collected biweekly at Datong Hydrological Station over a period of one year. Our results show that Sr concentration in the Yangtze River ranges from 1.74 to 2.92 μmol/L with 87Sr/86Sr of 0.710125 to 0.710965. The Sr concentration and 87Sr/86Sr shows a distinct seasonal variation, with a general increase in 87Sr/86Sr ratios from summer to winter and some fluctuations during July and December, then followed by a gradually decrease till the next rainy season. The seasonal variation results from the variation of contributions from different sub-basin due to the spatially and seasonally variable rainfall across the basin. During the flood season, more contribution from upper reach (low 87Sr/86Sr values) due to the strong rainfall decreases the 87Sr/86Sr ratio at lower reach. While the severe drought which happened in the middle-lower reaches (high 87Sr/86Sr values) from January to May explains the decrease in the later part of the data by the decrease of the contribution from middle-lower reaches. The discharge weighted annual 87Sr/86Sr and annual Sr flux of the Yangtze River based on the time series data are 0.710628 and 1.9×109 mol/a, respectively. It was also indicated that dissolved 87Sr/86Sr in the Yangtze River is well correlated to the extreme climate events and might contribute to our explanation for reconstructing past climatic changes by using 87Sr/86Sr ratios of the sedimentary record in the delta . 相似文献
12.
The hydrochemical interaction between groundwater and lakewater influences the composition of water that percolates downward from the surficial aquifer system through the underlying intermediate confining unit and recharges the Upper Floridan aquifer along highlands in Florida. The 87Sr/86Sr ratio along with the stable isotopes, D, 18O, and 13C were used as tracers to study the interaction between groundwater, lakewater, and aquifer minerals near Lake Barco, a seepage lake in the mantled karst terrane of northern Florida. Upgradient from the lake, the 87Sr/86Sr ratio of groundwater decreases with depth (mean values of 0.71004, 0.70890, and 0.70852 for water from the surficial aquifer system, intermediate confining unit, and Upper Floridan aquifer, respectively), resulting from the interaction of dilute oxygenated recharge water with aquifer minerals that are less radiogenic with depth. The concentrations of Sr2+ generally increase with depth, and higher concentrations of Sr2+ in water from the Upper Floridan aquifer (20–35 μg/L), relative to water from the surficial aquifer system and the intermediate confining unit, result from the dissolution of Sr-bearing calcite and dolomite in the Eocene limestone. Dissolution of calcite [δ13C = −1.6 permil (%o)] is also indicated by an enriched δ13CDIC(-8.8 to -11.4% o) in water from the Upper Floridan aquifer, relative to the overlying hydrogeologic units (δ13CDIC < -16%o).
Groundwater downgradient from Lake Barco was enriched in 18O and D relative to groundwater upgradient from the lake, indicating mixing of lakewater leakage and groundwater. Downgradient from the lake, the 87Sr/86Sr ratio of groundwater and aquifer material become less radiogenic and the Sr2+ concentrations generally increase with depth. However, Sr2+ concentrations are substantially less than in upgradient groundwaters at similar depths. The lower Sr2+ concentrations result from the influence of anoxic lakewater leakage on the mobility of Sr2+ from clays. Based on results from mass-balance modeling, it is probable that cation exchange plays the dominant role in controlling the 87Sr/86Sr ratio of groundwater, both upgradient and downgradient from Lake Barco. Even though groundwater from the three distinct hydrogeologic units displays considerable variability in Sr concentration and isotopic composition, the dominant processes associated with the mixing of lakewater leakage with groundwater, as well as the effects of mineral-water interaction, can be ascertained by integrating the use of stable and radiogenic isotopic measurements of groundwater, lakewater, and aquifer minerals. 相似文献
13.
137Cs及210Pbex方法湖泊沉积计年研究新进展 总被引：38，自引：1，他引：38
The 137Cs and 210Pbex techniques are widely employed for dating recent sediments of lakes. There is important provision to gain dating results correctly with the sampling device of no-disturbing sediments and the sample separation of high precision. The secondary peak of 137Cs in sediment horizon of 1975 could be as an assistant dating time marker. Most part of 137Cs in sediments is at stable position which provides reliability for 137Cs dating time marker. The post-depositional remobilization of 210Pb could lead to the lower rate of sediment accumulation in seasonal anoxic hypolimnia of lakes.The transformation of Pb species has provided the geochemical condition of its diffusion in the processes of early diagenesis. The diffusion mechanism of Pb-Po is controlled by cycling Fe-Mn, respectively. 相似文献
14.
纹层计年与137Cs、210Pb法对比研究东北二龙湾玛珥湖现代沉积速率 总被引：1，自引：0，他引：1
通过对东北二龙湾玛珥湖顶部无扰动岩心显微研究,证明此岩心发育有良好的年纹层。据精确统计,0~5.5 cm间为36个年纹层,纹层计年的误差为4％~7％,年纹层厚度为1.1~2 mm不等,平均沉积速率为1.53 mm/a,5.5 cm处对应于1965年。而二龙湾沉积物（从6.5 cm到5.5 cm)岩心的137Cs比活度值急剧增加,从（4.67±0.29） dpm/g增加到（12.06±0.47） dpm/g,在5.5 cm处有一个较为明显的蓄积峰值,这一峰值被确认对应为1963年全球137Cs散落的高峰期。另外据210Pbex比活度CIC模式,5.5 cm处约为1962年,这和137Cs比活度曲线的1963年时标相一致。印证了纹层计年的精确性,完全可以建立高分辨率时间序列。 相似文献
15.
An assessment of the groundwater in areas underlain by pegmatite in Ede, southwestern Nigeria was carried out to determine the concentration of Potassium-40 (40K), Uranium-238 (238U) and Thorium-232 (232Th) radionuclides. In the earlier work, it was established that zircons in these pegmatites have suffered a high degree of metamictization that has enhanced continuous loss of some radionuclides since the time of emplacement of the pegmatite host rock to the present. The aim of this work is to determine whether or not there is corresponding increase in the concentration of radionuclides in groundwater in the study area. Fifteen groundwater samples were collected from both hand dug wells and boreholes in the area. Ten samples were from Ede town, two samples each from nearby communities of Iddo and Ekuro and one from Iwoye, where the bedrocks were not pegmatites. All the 15 samples were analyzed with the Sodium Iodide scintillator (NaI [Tl]) detector at the Centre for Energy Research and Development, Obafemi Awolowo University, Ile-Ife, Nigeria. The results showed varying concentrations of the radionuclides in the water samples. Activity concentrations of Potassium-40 (40K) indicated an average value of 17.149 Bq/L for samples from Ede, 9.265 Bq/L for Iddo, 6.6 Bq/L for Ekuro, while Iwoye has a value of 21.21 Bq/L. The Uranium-238 (238U) series had an average value of 13.64 Bq/L for Ede, 13.49 Bq/L for Ekuro, 11.685 Bq/L for Iddo and 12.04 Bq/L for the lone sample from Iwoye. Thorium-232 (232Th) series had an average value of 11.182 Bq/L for Ede, while average values of 7.79 Bq/L and 9.025 Bq/L, respectively, were recorded for Iddo and Ekuro and 12.25 Bq/L for Iwoye. The annual effective dose level of 40K is generally below the World Health Organization (WHO) recommended dosage of 0.1 mSv/y except for three locations, while those of 238U and 232Th are in excess of the standard values. The high radionuclides in the groundwater in the study area were not due to anthropogenic sources but directly due to geological processes which release the radioisotopes from rocks after weathering, continuous loss from metamict minerals and natural lateral mobility from regions of radionuclides’ release to other areas. There is thus the need to carry out systematic studies of the radionuclides concentrations on regional scale in the area which could lead to investigating on both short- and long-term health effects on organic species in these areas, and development of purification systems before utilizing water from the areas for domestic and industrial purposes. 相似文献
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137 Cs示踪技术广泛地应用于农耕地土壤侵蚀研究，目前已建立了许多运用 137 Cs估算土壤侵蚀速率的模型。这些模型主要分为两类：经验模型与理论模型。其中理论模型中的质量平衡模型应用较多。质量平衡模型主要有：Wal l ing模型、张信宝模型、杨浩模型和周维芝模型。重点讨论这 4种质量平衡模型的异同。详细阐述了这四种模型的建立过程，并用图形模拟的方法给出各个模型所刻画的土壤侵蚀速率与土壤剖面中 137 Cs相对损失率的关系。分析表明，尽管各个模型在建立的假设和方法上以及对 137 Cs沉降过程的处理上存在一定程度的差异，但是各个模型所
刻画的土壤侵蚀速率与土壤剖面中 137 Cs相对损失率的关系实质上都是幂函数的形式，而且这 4条曲线的走势基本一致，各自计算的土壤侵蚀速率差异也较小。因此，在利用 137 Cs技术示踪农耕地土壤侵蚀速率时，这 4个模型都可以应用。 相似文献
17.
ne river: a snapshot of the situation during winter 1994/95Artificial radionuclides (60 Co, 106 Ru, 134 Cs and 137 Cs) produced in the nuclear power plants along the Rhne valley have been detected in most of the 35 sediment samples collected from the shores of the Rhne river in southern France. In one sample traces of 241 Am were found, suggesting the presence of transuranic elements. The wide use of river water for irrigation and the occasional big inundations of the Rhne have spread the artificial radionuclides over huge areas, quite far behind the river shores. Although artificial radionuclides are present in fields where food crops are collected, their activity is currently considerably lower than the activity of the natural radionuclides present in the river sediment. 相似文献
18.
黄土物源研究对揭示第四纪以来东亚大气环流格局的演化和构造—气候之间的相互作用具有重要意义。目前已应用多种物源示踪方法对黄土物源开展了大量研究,但对黄土物源时空差异规律及其动力学机制尚未取得较为一致的认识。在综合分析黄土物源研究现状的基础上,重点从影响87Sr/86Sr值和 143Nd/144Nd 值组成及单颗粒碎屑锆石U-Pb年龄谱构成的因素角度,分析了第四纪黄土的物源及可能变化,获得以下认识: (1)第四纪黄土沉积物的87Sr/86Sr值变化幅度可达0.002 580~0.004 949,远远超出实验室分析测试误差(<0.000 018)或由Sr同位素衰变带来的影响(2.6 Ma时段小于0.000 026,1个冰期旋回小于0.000 001); 143Nd/144Nd 值亦发生了较显著变化(0.000 095~0.000 240),其变化幅度远大于实验室的分析测试误差(<0.000 010)及衰变导致的 143Nd/144Nd 值(<0.000 013)变化。因此,在黄土中检测到的Sr-Nd同位素组成的变化应具有较明确的地质意义。(2)第四纪黄土沉积物中无论全岩还是主要粒径组分的87Sr/86Sr值和 143Nd/144Nd 值的变化都与气候代用指标变化不同步,难以从气候变化角度进行解释,可能更多地反映了源区的变化。(3)与Sr-Nd同位素示踪体系相比,单矿物或单颗粒的物源示踪体系对物源区变化的响应更为敏感,在追踪第四纪黄土沉积物源区时空差异方面具有较明显的优势。(4)基于碎屑锆石U-Pb年龄谱对黄土物源的有限研究揭示黄土高原的黄土在地质历史时期可能发生了原始物源区显著的时空分异,特别是不同剖面都反映出了1.2 Ma前后黄土主要源区的变化,表明通过锆石U-Pb年龄谱研究黄土物源时空差异规律具有揭示岩石圈、大气圈、水圈耦合作用过程及历史的巨大潜力。 相似文献
19.
Wan Guojiang Zheng Xiangdong Lee H N Bai Z G Wan Enyuan Wang Shilu Yang Wei 《地球科学进展》2010,25(5):492-504
It′s essential to measure air concentrations and depositional fluxes of environmental radionuclides in different regions for modeling global contamination transfer and validation, tracing deposition process and dating, referencing watershed erosion trace and assessing natural radiation of ecosystem. This study introduces the research background and methods and explains weekly variations of 210Pb and 7Be concentrations in surface air and precipitation at Mt. Guanfeng/Guiyang since 2001. The results indicate that 210Pb and 7Be concentrations in surface air fluctuate periodically at 2~6 week interval because of the meteorological condition changes. The annual trend in 210Pb air concentration is overall influenced by air temperature variation and periodical rainfall. 7Be air concentration varies up and down regualarly. The synchronization of low concentrations for both 210Pb and 7Be in surface air and high ratio (210Pb/7Be ≥ 0.8) indicate oceanic poor 210Pb-7Be air mass invasion. The synchronization of high concentrations of 210Pb and 7Be in surface air and low ratio (210Pb/7Be ≤ 0.7) implies rich 7Be air mass invasion from altostratus atmosphere. Weekly concentrations of 210Pb and 7Be in precipitation and the Kd coefficients are high in late Autumn to Spring, and low in late Spring to Autumn. Although 210Pb and 7Be concentrations vary seasonally, their weekly concentrations in precipitation increase with that of air concentration. The 210Pb and 7Be weekly concentrations for seasonal division is about 0.2 Bq/L and 1 Bq/L, respectively. However, the Kd coefficient decreases when 210Pb and 7Be air concentrations increase. Deposition of 210Pb and 7Be with precipitation mainly take place in Spring and Summer; The weekly fallout of 210Pb and 7Be increases with increasing precipitation; the increase of 7Be is triple of that of 210Pb and 2.5 when precipitation nears to zero. The weekly-high fallout of 210Pb and 7Be with precipitation corresponds with the dramatic decrease of their air concentrations within or vicinal weeks. The ratio of 210Pb to 7Be in rainfall is overall ≤ 0.5 and varies synchronously with the ratio in surface air, indicating that the two radionuclides are cleaned by precipitation from air at close speed. In the extreme freezing disaster in 2008, both 210Pb and 7Be air concentrations were low and coupling with coexist of low concentration of aerosol and high nuclides activities. Weekly concentration of 7Be in surface air at Mt. Guanfeng demonstrates the anticipated concentration level in the low-latitude and high-elevation region; the short-term fluctuations of 7Be concentration indicated the hysteresis was influcenced by the strong air current submersion and the low-elevation air mass rising differently at Mt. Guanfeng and Mt. Waliguan. 相似文献