Development of Technique: Systematically measuring the cosmogenic 26Al/10Be production ratio at a variety of altitudes and latitudes

地质学家使用不同元素的许多稀有同位素来确定过去事件的日期，包括自然事件和与人类有关的事件。 一个特别广泛应用的系统比较了暴露在地表然后被掩埋的样品中26 Al与10 Be的比率。 为了从测量的26 Al/10 Be的比率中创建年龄，研究人员需要知道暴露后但埋葬前的26 Al/10 Be比率。 虽然这一比率以前曾被估计过，但其数值并不为人所知，而且似乎在世界各地各不相同。该项目将首次测量已经收集的150多个不同样品中的26 Al/10 Be比率，从而为各个领域（地质学，冰川学，考古学）的许多研究人员提供所需的信息，以产生更准确的26 Al/10 Be埋葬年龄。新的数据也将使我们更好地了解这些年龄的不确定性。这项工作将培养一名科学研究生，并将改进古代人类遗骸的日期以及地球气候过去的变化，知道26 Al/10 Be的表面产生比对于计算两种同位素埋藏年龄是至关重要的，因为测量的26 Al/10 Be的表面产生比是26 Al/10 Be的表面产生比。~（10）Be比值小于产率可定量解释为样品暴露后埋藏的时间。虽然26 Al/10 Be测年法已被广泛应用（许多应用得到了NSF的支持），但生产中的26 Al/10 Be比率并没有受到数据的很好约束。最近的测量表明，格陵兰岛的这一比例至少比标准值6.75高出8%，标准值主要来自20世纪90年代初在中纬度高海拔地区进行的一系列测量。基于物理的模型和其他一些新的数据表明，26 Al/10 Be的表面生产率应随纬度和高度系统地变化。在这里，该项目将测试空间差异，并根据经验确定26 Al/10 Be表面生产率作为纬度（两个半球5-45°）和海拔（海拔0至5000米）的函数。该团队将通过对已经准备好的存档样品进行150次高精度的26 Al分析来实现这一目标，并且之前已经分析了10 Be。该团队将比较这种数据驱动的26 Al/10 Be表面生产率的确定与使用核素生产数值模型的预测。该项目将通过在会议上和至少在一份同行审查的出版物上传播成果，扩大这项工作的广泛影响。这将确保社区了解并能够轻松使用所生成的数据，以提高26 Al/10 Be双同位素测年的准确性。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Geologists use many rare isotopes of different elements to date events in the past, both natural and those related to humans. One particularly widely applied system compares the ratio of 26Al to 10Be in samples that have been exposed at the surface of the earth and then buried. To create ages from a measured ratio of 26Al/10Be, researchers need to know the ratio of 26Al/10Be after exposure but before burial. While this ratio has been estimated before, its value is not well known and appears to vary around the world. This project will be the first to measure the 26Al/10Be ratio in over 150 different samples that have already been collected and will thus provide the information needed for many researchers in a variety of fields (geology, glaciology, archeology) to generate more accurate 26Al/10Be burial ages. The new data will also allow much better understanding of the uncertainty of these ages. This work will train a graduate student in science and will improve dates of ancient human remains as well as past changes in Earth's climate, including the coming and going of glaciers.Knowing the surface production ratio of 26Al/10Be is critical for the calculation of two-isotope burial ages because a measured 26Al/10Be ratio less than the production ratio can be interpreted quantitatively as the duration of burial after surface exposure of a sample. Although 26Al/10Be dating has been widely applied (and many of the applications have been supported by NSF), the 26Al/10Be ratio at production is not well constrained by data. Recent measurements suggest that the ratio is at least 8% higher in Greenland than the canonical value of 6.75, which is derived primarily from one series of early 1990s measurements made at high elevation in the mid latitudes. Physics-based models and some other new data suggest that the 26Al/10Be surface production ratio should vary systematically with latitude and altitude. Here, this project will test for spatial variance and determine the 26Al/10Be surface production ratio empirically as a function of latitude (5-45° in both hemispheres) and altitude (0 to 5000 meters above sea level.). The team will do this by making 150 high-precision 26Al analyses of archived samples already prepared and previously analyzed for 10Be. The team will compare this data-driven determination of the 26Al/10Be surface production ratio with predictions made using numerical models of nuclide production. The project will increase the broader impact of this work by disseminating the results both at meetings and in at least one peer-reviewed publication. This will ensure that the community is aware of and can easily use the data that are generated to improve the accuracy of 26Al/10Be two-isotope dating. Additional broader impacts include training a student who will do much of the research and writing.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.