International Research Fellowship Program: Search for Isotopes from Recent Nearby Supernova with Nearby Accelerator Mass

国际研究奖学金计划使美国科学家和工程师能够在国外进行三到二十四个月的研究。该计划的奖项提供了联合研究的机会，并利用国外独特或互补的设施、专业知识和实验条件。该奖项将支持Jonathan Levine博士与阿根廷布宜诺斯艾利斯国家能源原子物理委员会的Jorge O.Fernandez-Niello博士和Andres Arazi博士在阿根廷布宜诺斯艾利斯的实验室合作进行为期三个月的研究。大多数到达地球的陨石在被侵蚀和风化破坏之前最多存活数千年。根据测得的放射性同位素丰度，可以计算出特定陨石的所谓“地球年龄”，也就是陨石落到地球后的持续时间。碳-14被广泛用于这一目的。然而，一些陨石的年龄已经足够大，以至于没有可检测到的碳14残留物。这些稀有的陨石对于不同类型陨石的下落速度在过去数万年里是如何变化的问题，以及对它们被发现的缓慢侵蚀地区的地质研究特别感兴趣。研究人员正试图从放射性镍-59的丰度(半衰期为76,000年)来确定这些古老陨石的地球年龄。他们通过加速器质谱仪寻找镍-59，这使他们能够检测到低于样本镍总储量的万亿分之一的镍-59丰度。他们正在努力通过改进化学分离、质量分辨率和离子检测技术来进一步提高灵敏度。镍-59为测定陨石的年代提供了最大的希望，这些陨石是从保存异常完好的地质环境中收集的，比如南极洲，那里的陨石被侵蚀的速度比其他地方慢得多，因为那里的气候干燥。

0502034LevineThe International Research Fellowship Program enables U.S. scientists and engineers to conduct three to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.This award will support a three-month research fellowship by Dr. Jonathan Levine to work with Drs. Jorge O. Fernandez-Niello and Andres Arazi at Laboratorio TANDAR, Comision Nacional de Energia Atomica Phycics in Buenos Aires, Argentina.Most meteorites that reach the Earth survive for a few thousands years, at most, before they are destroyed by erosion and weathering. The so-called "terrestrial ages" of particular meteorites, or the duration of time since a meteorite has fallen to Earth, can be calculated from the measured abundance of radioactive isotopes. Carbon-14 is used extensively for this purpose. However, some meteorites are old enough that no detectable carbon-14 remains. These rare meteorites are especially interesting for questions about how the fall-rate of different types of meteorites has changed over the last several tens of thousands of years, as well as for geological studies of the slowly-eroding regions where they are found. The investigators are attempting to determine the terrestrial ages of such old meteorites from the abundance of radioactive nickel-59 (half-life 76,000 years). They search for nickel-59 by accelerator mass spectrometry, which allows them to detect nickel-59 abundances lower than one part per trillion of the total nickel endowment of a specimen. They are working to further improve the sensitivity, by improving chemical separation, mass resolution, and ionic detection techniques. Nickel-59 offers greatest promise for dating meteorites collected from geological settings of extraordinary preservation, such as Antarctica, where meteorites are eroded much more slowly than elsewhere because of the dry climate.