Cosmogenic Isotopes Produced In Situ in Terrestrial Rocks: Quantifying the Effect of Elevation on the Production Rates

该提案的目标是确定原地宇宙成因同位素的生产率如何随海拔变化。这一目标将通过测量宇宙成因的36 Cl和/或3 He从熔岩流，在垂直方向上延伸了很长的距离样品。夏威夷是这个项目的理想地点，因为：（1）许多非常长的熔岩流已经被绘制出来（有些垂直延伸超过2公里）;（2）熔岩流的地层学已经确定;（3）可以在实地追踪各个熔岩流，从而可以确保从同一熔岩流中采集样本;（4）许多熔岩流的年代测定是准确的，因此有可能将两个或多个熔岩流的衰减长度联合收割机组合成一个复合记录。在每个熔岩流中将测量至少10个来自不同海拔的样品，并且累积的宇宙成因同位素的浓度将被表示为海拔的函数。然后将合并各个熔岩流的数据，并开发描述生产率对海拔的依赖性的复合函数。将该函数与实测中子强度进行比较，并对实测中子衰减长度在地质时间尺度上的适用性进行评估。最后，本文还提出了一个改进的宇宙生成产率的高度标度公式，这将对改进各种宇宙生成测年方法作出重要贡献。

EAR-0001191ZredaThe goal of this proposal is to determine how production rates of in-situ cosmogenic isotopes change with elevation. This goal will be achieved by measuring cosmogenic 36Cl and/or 3He in samples from lava flows that extend over long distances in the vertical. Hawaii is the ideal location for this project because: (1) many very long lava flows have been mapped (some extend over 2 km in the vertical); (2) the stratigraphy of lava flows is well established; (3) individual flows can be traced in the field, thus making it possible to ensure that samples are collected from the same lava flow; and (4) many flows are well dated, thus making it possible to combine attenuation lengths from two or more lava flows into a composite record. At least ten samples from different elevations will be measured in each lava flow, and the concentration of accumulated cosmogenic isotopes will be expressed as a func-tion of elevation. Data from individual lava flows will then be combined and a composite function describing the dependence of production rates on elevation will be developed. This function will be compared with the measured neutron intensity, and the applicability of the measured neutron atten-uation length over geological time scales will be assessed. Finally, improved altitudinal scaling for-mulation for cosmogenic production rates will be constructed, which should be an important contribution to the improvement of all cosmogenic dating methods.