Global Change: Geologic Records Inferred from Cosmic Ray Produced Neon at the Surface of the Earth

最近几年，在地球表面物质中发现了几种宇宙射线产生的放射性核素(10Be、14C、26Al、36Cl)以及稳定的3He、21Ne和22Ne。其中一些核素已被用作地球物理和地质现象研究的示踪剂，开辟了一个新的研究领域，可望提供有关全球变化研究变化率的基本数据。这类研究需要准确了解目前无法获得的现在和过去的生产率。我们正在使用一种直接方法来确定目前的一些生产率，方法是在山区暴露相关的目标。上一个太阳周期的平均生产率可以通过将生产率与中子监测数据进行比较来获得。我们目前正在通过测量石英样品中Ne的同位素来评估宇宙线产生的核素21Ne和26Al的相关生产比P21/P26。我们的初步实验数据与理论预测不太相符。104-105年的平均生产率可以通过测量已知年龄的样品来获得。~3He/~(21)Ne比值测量表明，~3He常不完全保留在石英岩中。因此，21Ne产出率和21Ne/10Be和21Ne/26Al比值提供了必要的信息，这是评估侵蚀速率和确定地质过程(抬升、冰盖变化等)所必需的。

In the last few years, several cosmic-ray-produced radionuclides (10Be, 14C, 26Al, 36Cl), as well as stable 3He, 21Ne and 22Ne have been discovered in terrestrial surface materials. Some of these nuclides are already employed as tracers in studies of geophysical and geological phenomena and open up a new field of study and are expected to provide essential data on rates of change in global change research. Such studies require an accurate knowledge of of the production rates, present and past, which are not currently available. We are using a direct method for the determination of some of present production rates, by exposing relevant targets at mountain altitudes. Production rates averaged over the last solar cycles can be obtained by comparing production rates with neutron monitor data. We are currently evaluating the relevant production ratio P21/P26 of the cosmic-ray-produced nuclides 21Ne and 26Al by isotopic measurements of Ne in quartz samples. Our preliminary experimental data do not agree well with theoretical predictions. Average production rates over 104-105years can be obtained from measurements of samples of known age. Measurements of the 3He/21Ne ratio show that 3He is often incompletely retained in quartzites. Therefore, 21Ne production rates and 21Ne/10Be and 21Ne/26Al ratios provide essential information, which is required to evaluate erosion rates and to define geological processes (uplift, variations in ice cover etc).