New Isotopic Techniques for Geoscience

放射性核素浓度的测定对于从人类健康风险评估到重建气候记录所需的地质年代学等许多科学领域都至关重要。这项发现资助研究计划的全球目标是开发用于放射性核素测量的新的加速器质谱（AMS）技术，并将这些方法应用于研究重要的环境和地球科学问题。 我们工作的一个重点是开发和应用在线AMS反应池技术来分离同量异位素干扰（与稀有放射性同位素质量相同的同位素），这些干扰通常会妨碍稀有放射性核素的准确测量。例如，在大多数环境样品中，Ba-135的丰度是Cs-135的1010至1015倍。Ba-135可以通过严格的痕量化学萃取和通过使Cs和Ba离子的AMS阴离子束通过充气反应池的组合从样品中去除。这种在线反应将Ba-135浓度降低了约10，000倍。我们的工作将解决剩余的干扰问题，并完成测量环境样品中各种基质和浓度的Cs-135的技术。 我们将使用我们从Cs-135干扰去除研究中获得的知识来研究几种以前没有在环境样品中测量过的新同位素系统。我们将研究Se-79/Br-79、Zr-73/Nb-73、Pb-107/Ag-107和Sn-126/Te-126之间的干扰。这些稀有的放射性同位素中的每一种都存在于环境中，作为核武器试验沉降物的结果，以及来自U-238自发裂变的旧样本。然而，由于它们的弱β发射和长的放射性半衰期，使用放射性衰变技术测量它们是不可能的。迄今为止，放射性β衰变产生的大量同量异位素的干扰阻碍了AMS的测量。我们假设使用阴离子反应池的同量异位素分离将消除这种干扰。* 我们将把这些新的分析技术应用于一些关键的科学问题。这项工作还将开辟在许多系统中大规模追踪Cs和其他长寿命同位素的可能性，因为同位素比率在不同的源材料中不同。举例来说：海洋系统中有来自武器试验沉降物和燃料后处理设施的Cs-137和Cs-135，我们将检验使用我们的分析技术可以区分这些来源的假设。 在放射化学、地球化学和同位素技术方面培训HQP是这项工作的一个非常重要的目标。本提案中所述的跨学科方法为HQP提供了地球科学、放射化学、生态毒理学和实验物理学方面的一系列极好的培训机会。

The determination of radionuclide concentrations is fundamental to many areas of science ranging from risk assessments for human health to the geochronologies needed to reconstruct records of climate. The global objectives of this Discovery Grant research program are to develop new accelerator mass spectrometry (AMS) techniques for radionuclide measurement and to apply these methods to study important environmental and geoscience issues.**** One key focus of our work is the development and application of on-line AMS reaction cell techniques to separate isobaric interferences (isotopes with the same mass as the rare radioisotope) that often prevent the accurate measurement of rare radionuclides. For example, Ba-135 is 1010 to 1015 times more abundant than Cs-135 in most environmental samples. The Ba-135 can be removed from the sample by a combination of rigorous trace chemical extraction and by passing the AMS anion beam of Cs and Ba ions through a gas filled reaction cell. This on-line reaction reduces the Ba-135 concentration by about 10,000 fold. Our work will resolve the remaining interference issues and complete the techniques to measure Cs-135 in a wide variety of matrices and concentrations found in environmental samples.**** We will use the knowledge that we gained from the studies of interference removal for Cs-135 to study several new isotope systems that have not previously been measured in environmental samples. We will investigate the interferences between Se-79/Br-79, Zr-73/Nb-73, Pb-107/Ag-107, and Sn-126/Te-126. Each of these rare radioisotopes is present in the environment as a result of nuclear weapon's test fallout and in older samples from the spontaneous fission of U-238. However their measurement using radioactive decay techniques has been impossible due to their weak beta emissions and their long radioactive half-life. The interference from the abundant isobar produced by the radioactive beta decay has, to date, prevented their measurement by AMS. We hypothesize that the isobar separation using an anion reaction cell will eliminate this interference.**** We will apply these new analytical techniques to a number of key scientific issues. This work also will open up possibilities to trace Cs and other long-lived isotopes on a large scale in many systems since the isotope ratio is different in different source material. For example: Oceanic systems have Cs-137 and Cs-135 from weapons' test fallout and from fuel reprocessing facilities and we will test the hypothesis that these sources can be distinguished using our analytical techniques.**** Training HQP in radiochemical, geochemical and isotopic techniques, is a very important objective of this work. The interdisciplinary approaches described in this proposal offer an excellent range of training opportunities for HQP in geoscience, radiochemistry, ecotoxicology and experimental physics.***