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发生的事件的年代，包括自然事件和与人类有关的事件。一种特别广泛应用的系统比较了暴露在地球表面然后掩埋的样品中26Al与10Be的比例。为了根据测定的26Al/10Be的比值来确定年龄，研究人员需要知道暴露后和埋葬前26Al/10Be的比值。虽然这一比例之前已经估计过，但其值并不为人所知，而且似乎在世界各地有所不同。该项目将是第一个测量已经收集的150多个不同样本的26Al/10Be比率的项目，因此将为各种领域（地质学，冰河学，考古学）的许多研究人员提供所需的信息，以产生更准确的26Al/10Be埋葬年龄。新的数据也将有助于更好地理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，以及过去地球气候的变化，包括冰川的到来和消失。了解26Al/10Be的表面生成比对于计算双同位素埋藏年龄至关重要，因为测量到的26Al/10Be比小于生成比可以定量地解释为样品表面暴露后的埋藏持续时间。虽然26Al/10Be定年已经得到了广泛的应用（许多应用都得到了NSF的支持），但26Al/10Be在生产中的比值并没有很好地受到数据的限制。最近的测量表明，格陵兰岛的这一比率比标准值6.75至少高出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数据表明，26Al/10Be的地表生成比应随着纬度和海拔而系统变化。在这里，该项目将测试空间方差，并根据纬度（南北半球5-45°）和海拔（海拔0 - 5000米）的函数来确定26Al/10Be地表产量比。该团队将通过对已经准备好的存档样本进行150次高精度26Al分析来实现这一目标。该团队将比较26Al/10Be表面生成比的数据驱动测定结果与核素生成数值模型的预测结果。该项目将通过在会议和至少一份同行评议出版物上传播结果，扩大这项工作的广泛影响。这将确保社会意识到并可以很容易地使用生成的数据来提高26Al/10Be双同位素定年的准确性。其他更广泛的影响包括训练学生做大量的研究和写作。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识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.