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1.
To study the Pu concentration and isotope ratio distributions present in China, the 239+240Pu total activities and 240Pu/239Pu atom ratios in core soil samples from Hubei Province in central China were investigated using Accelerator Mass Spectrometry (AMS). The activities ranged from 0.019 to 0.502 mBq g−1 and the 239+240Pu inventories of 45 and ∼55 Bq m−2 agree well with that expected from global fallout. The 240Pu/239Pu atom ratios in the soil ranged from 0.172 to 0.220. The ratios are similar to typical global fallout values. Hence, any close-in fallout contribution from the Chinese nuclear weapons tests, mainly conducted in the 1970s, must have either been negligible or had a similar 240Pu/239Pu ratio to that of global fallout. The top 10 cm layer of the soil contributes ∼90% of the total inventory and the maximum concentrations appeared in the 2-4 cm or 4-6 cm layers. It is suggested that climatic conditions and organic content are the two main factors that affect the vertical migration of plutonium in soil.  相似文献   
2.
We consider one and two-dimensional minimal models in plankton dynamics. The influence of oscillating boundary forcing functions as agents for triggering pattern formation is discussed. In particular it is found that in these conditions population waves arise for one dimensional models, while for two dimensional models, different amplitudes and frequencies in the boundary forcing generate definite patterns, mimicking the boundary term. This happens even though the model we investigate is very simple. The emergence of these features is an interesting metaphor for the fundamental biological problem of how pattern formation processes may be inevitable in natural heterogeneous ecosystems.  相似文献   
3.
AMS方法在大气气溶胶来源研究中的应用   总被引:8,自引:0,他引:8  
在我国自己建立的加速器质谱计(AMS)技术的基础上,利用^14C的特征的生物来源示踪性能,将AMS技术运用于我国大气气溶胶来源的研究,我们建立了大气气溶胶采样--石墨碳制备-AMS测定的全部样品处理过程,对北京市中关村地区、东单地区在采暖期和非采暖期的气溶胶样品和湖南南岳、山东青岛的气溶胶及这些地区的地表土进行了AMS测定,将多元统计方法与AMS方法相结合,从中分析这些样品中微量元素组分和含碳 分  相似文献   
4.
湖泊沉积物是研究古气候、古环境的理想对象。本文选取鹤庆湖泊沉积物开展了样品BeO制备的实验研究。通过对比黄土提取~(10)Be的思路,利用条件实验确定了先沉淀去除常量元素,再进行阳离子交换的新的实验流程。加速器质谱仪的测量结果表明该流程有效可靠,为下一步拓展湖泊~(10)Be环境示踪的新方向提供了实验方法基础。  相似文献   
5.
利用先进的高分辨飞行时间气溶胶质谱仪(High Resolution Time-of-Flight Aerosol Mass Spectrometer,HR-To F-AMS),于2017年9月8日—2017年10月8日对上海市城区开展了亚微米级颗粒物化学组分、粒径及其污染来源的在线测量.结果表明,观测期间上海城区亚微米颗粒物质量浓度平均为(22.0±17.2)μg·m-3;其中,有机物是PM1的主要贡献者,平均占总颗粒物浓度的49.3%,硫酸根、硝酸根和铵根的占比分别为24.2%、10.5%和9.7%.上海城区亚微米级颗粒物中无机盐组分类(硝酸根,硫酸根和铵根)具有较为一致的粒径分布,峰值粒径主要集中在空气动力学粒径500~600 nm.有机物的粒径分布峰值位于空气动力学粒径400~500 nm,且在小粒径范围内有较高的有机物浓度,表明存在一定程度的一次排放.观测期间有机气溶胶呈现明显的多峰分布,硫酸根、铵根和氯离子呈白天低、夜间高的特点,而硫酸根和黑碳的日变化并不明显.基于高分辨率有机质谱计算得到上海城区有机气溶胶氧碳比(O/C)的平均比值为0.37;有机物与有机碳(OM/OC)的平均比值1.65.利用正矩阵因子解析(PMF)模型对有机气溶胶高质量分辨率质谱进行来源解析,得到4类有机气溶胶:HOA(还原态有机气溶胶)、COA(餐饮源有机气溶胶)、MO-OOA(高氧化性有机气溶胶)和LO-OOA(低氧化性有机气溶胶),分别占有机气溶胶总量的15%、20%、32%和26%,说明观测期间上海城区有机气溶胶主要来自二次气溶胶的贡献.  相似文献   
6.
The experimental study on ozonation of ethylenethiourea(ETU) is conducted.The reaction of gas-phase ETU with 0.63 × 10-6 mol/L ozone is carried out in a 200-L reaction chamber.The secondary organic aerosol(SOA) resulted from the ozonation of gas-phase ETU is observed with a scanning mobility particle size(SMPS).The rapid exponential growth of SOA reveals that the atmospheric lifetime of ETU vapor towards ozone reaction is less than four days.The ozonation of dry ETU particles,ETU-contained water droplets an...  相似文献   
7.
A study has been carried out to assess the potential of using fallout plutonium (Pu), which originated from atmospheric nuclear-weapons tests, as a tool to investigate recent erosional processes within the lower Cotter water-supply catchment in the Australian Capital Territory. This catchment, which was predominantly pine plantation, was severely affected by a major bush fire in 2003. Accelerator mass spectrometry has been used to measure Pu in soil samples collected from a number of sites across the catchment. The results indicate that less than 1 cm of surface soil had been lost since the early 1960s over much of the catchment. Areas of more erodible soil have, however, lost 2-4 cm of topsoil, and a loss of ∼6 cm of soil was identified at one particular site.  相似文献   
8.
9.
14C是广泛存在于环境中的主要放射性核素,由于14C半衰期很长(5 730年)且参与地质系统中的迁移及食物链碳循环,因此14C受到人们的日益关注,建立可靠的14C测量方法成为环境监测中的一项重要工作内容.由于水中含碳量较低,且14C是低能纯β辐射体,给水中的14C测量带来一定困难.综合调研国内外水中14C分析方法,在详细阐述水中无机14C和有机14C的各种样品制备及测量方法的基础上,对鼓泡法和沉淀法、高温氧化法和加热过硫酸盐氧化法、CaCO3沉淀法、直接吸收法、苯合成法和加速器质谱法的原理及优缺点进行了分析评述,并讨论了方法中可能存在的问题,有助于实验室选用最佳的方法.  相似文献   
10.
Natural organic matter, such as humic and fulvic acids and humin, plays a key role in determining the fate and mobility of radioiodine in soil and sediments. The radioisotope 129I is continuously produced and released from nuclear fuel reprocessing plants, and as a biophilic element, its environmental mobility is strongly linked to organic matter.Due to its long half-life (15.7 million years), 129I builds up in the environment and can be traced since the beginning of the nuclear era in reservoirs such as soils and marine sediments. Nevertheless, partition of the isotope between the different types of organic matter in soil and sediment is rarely explored. Here we present a sequential extraction of 129I and 127I chemical forms encountered in a Danish soil, a soil reference material (IAEA-375), an anoxic marine sediment from Southern Norway and an oxic sediment from the Barents Sea. The different forms of iodine are related to water soluble, exchangeable, carbonates, oxides as well as iodine bound to humic acid, fulvic acid and to humin and minerals. This is the first study to identify 129I in humic and fulvic acid and humin. The results show that 30-56% of the total 127I and 42-60% of the total 129I are associated with organic matter in soil and sediment samples. At a soil/sediment pH below 5.0-5.5, 127I and 129I in the organic fraction associate primarily with the humic acid while at soil/sediment pH > 6 129I was mostly found to be bound to fulvic acid. Anoxic conditions seem to increase the mobility and availability of iodine compared to oxic, while subaerial conditions (soils) reduces the availability of water soluble fraction compared to subaqueous (marine) conditions.  相似文献   
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