Collaborative Research: A Proposal for the Cosmic-Ray prOduced NUclide Systematics on Earth (CRONUS-Earth) Project

1986年首次展示了用于地表暴露、测年和其他地球科学应用的陆地-原位-宇宙成因核素(TCN)方法。在接下来的17年里，这些方法已经发展成为现代地球科学许多领域的通用和不可或缺的工具，包括古气候学、地貌学、构造学、水文学和火山学。已被证明具有广泛应用价值的TCN有：~3H、10Be、14C、21Ne、26Al和36Cl。这一快速发展得益于方法学上的进步，包括在采样战略、样品制备程序和宇宙源核素分析(通过加速器质谱仪和惰性气体质谱仪)方面的改进。为了保持在地球科学的前沿，TCN方法的准确性必须得到显着提高。然而，这是该领域从业者的共识，即进一步的发展正走向僵局。这一限制不是由于方法论上的考虑，而是由于对基本物理过程的不完全理解，以及不同研究者和方法之间缺乏严格的相互可比性。宇宙成因核素产量的全球分布取决于许多相互关联的因素，必须同时控制这些因素，以得出准确定义所有时间点和地质时间的产量的方程和参数。这项任务远远超出了任何一名研究人员的能力。为了实现这一下一步，也是必要的，克罗诺斯-地球计划应运而生。该项目的目标如下：(1)为不同核素的测量和不同研究人员之间的相互比较建立严格的基础；(2)在宇宙线物理学和宇宙射线产生的TCN的系统学之间建立牢固的联系；以及(3)产生被普遍接受的用于计算TCN产生的公式和参数。最终目标是将所有TCN方法的精密度和准确度从目前的约10%到20%提高到5%的水平。这个项目被设想为一项国际性的合作努力。克罗诺斯-地球系统由六个主要部分组成：(1)方法学比较，包括样品制备和分析测量。(2)通过“挖掘”现有的中子监测仪数据集、对中子监测仪的反应进行建模以及现场测量饱和的14C高度/纬度剖面，研究宇宙射线通量的空间/时间分布。(3)安置用于生产3He、21Ne、10Be、32P和36Cl的人造靶标，将当代宇宙射线通量与生产率和比例系数联系起来。(4)使用实验室中子束测量生产截面。(5)综合观测数据并计算过去地磁和古气候变化对宇宙成因核素生产的影响的数值模拟工作。(6)根据世界各地独立测年的表面，对核素产生率进行地质校准。这些将按质量分类为主要校准地点和将用于测试整体生产率模型的次要或“验证”地点。这六个组成部分构成了对一个显然超出个人和小型研究小组范围的问题采取协同和协调的办法。我们建议以联合体的方式管理该项目，包括多名调查人员、每年举行会议以监测进展情况、汇编数据并与社区交流、快速以电子方式分发结果，以及通过负责向社区传播结果的项目办公室整合最终产品。克罗诺斯-欧洲项目已经提交给欧盟，并将与克罗诺斯-地球项目密切协调。克罗诺斯-地球项目将通过建立一个改进的、定量的、基于物理的、对TCN生产和积累的理解来解决NSF的智力功绩审查标准，这些TCN生产和积累可用于解决地球科学中的各种问题。该项目将通过提供公式、参数和计算机代码来处理更广泛的影响标准，这些公式、参数和计算机代码将构成一个智力基础设施，使TCN方法能够在地球科学中得到更一致、准确和广泛的应用。此外，该项目将为今后采取更正式、更有条理的方法来促进TCN方法应用的一致性奠定基础，例如成立委员会提供参数值建议值。最后，它将包括一个内容，让本科生，特别是少数族裔学生，直接参与与克罗诺斯有关的地球科学方面的研究。

Terrestrial- in situ- cosmogenic nuclide (TCN) methods for surface exposure dating and otherearth-science applications were first demonstrated in 1986. During the subsequent 17 years these methods have developed into versatile and indispensable tools in many fields of modern Earth Sciences, including paleoclimatology, geomorphology, tectonics, hydrology, and volcanology. The TCN that have been demonstrated to be widely applicable are 3H, 10Be, 14C, 21Ne, 26Al, and 36Cl. This rapid development has been facilitated by methodological progress, including improvements in sampling strategies, sample preparation procedures and analyses of cosmogenic nuclides (by accelerator mass spectrometry (AMS) and noble gas mass spectrometry). In order to remain at the cutting edge of the earth sciences the accuracy of TCN methods must be significantly improved. However, it is the consensus of practitioners in the field that further developments are instead moving toward an impasse. This limitation is imposed, not by methodological considerations, but rather by incomplete understanding of the fundamental physical processes, and by lack of rigorous intercomparability between different investigators and methods. The global distribution of cosmogenic nuclide production depends on a number of interrelated factors, and thesefactors must be simultaneously controlled in order to arrive at the equations and parameters that accurately define production rates at all points, and over geological time. This task is far beyond the capability of any individual investigator.In order to achieve this next, necessary, step the CRONUS-Earth Project is proposed. The projecthas the following goals: (i) to establish a rigorous basis for intercomparison between measurement of different nuclides and by different investigators, (ii) to provide a firm linkage between cosmic-ray physics and the systematics of the TCN produced by the cosmic rays, and (iii) to produce generally-accepted formulations and parameters for calculation of TCN production. The ultimate goal is to advance the precision and accuracy of all TCN methods from its current range of ~10% to 20% toward a 5% level. This project is envisioned as an international, collaborative effort. CRONUS-Earth consists of six major components: (i) A methodological intercomparison, including sample preparation as well as analytical measurement. (ii) Spatial/temporal distribution of cosmic-ray fluxes, through "mining" existing neutron monitor datasets, modeling of neutron monitor responses, and measurement of saturated in situ 14C altitude/latitude profiles. (iii) Emplacement of artificial targets for 3He, 21Ne, 10Be, 32P and 36Cl production, to link contemporary cosmic-ray fluxes to production rates and scaling factors. (iv) Measurement of production cross-sections using laboratory neutron beams. (v) A numerical modeling effort to integrate the observations and to calculate the effects of past geomagnetic and paleoclimatic changes on cosmogenicnuclide production. (vi) Geological calibration of nuclide production rates, based on independently-dated surfaces worldwide. These will be classified by quality into primary calibration sites and secondary, or "verification", sites that will be used to test the overall production-rate model. These six components comprise a synergistic and coordinated approach to a problem that is clearly beyond the scope of individuals and small research teams. We propose a consortium approach to managing the project, involving multiple investigators, annual meetings to monitor progress, compile data, and exchange with the community, rapid electronic distribution of results, and integration of the final products through a project office charged with disseminating the results to the community. A linked CRONUS-Europe proposal has been submitted to the EU and will be closely coordinated with CRONUS-Earth.The CRONUS-Earth Project will address the NSF intellectual merit review criterion throughestablishing an improved, quantitative, physically-based, understanding of TCN production andaccumulation that can be applied to solve a wide variety of problems in the earth sciences. The Project will address the broader impacts criterion by providing formulations, parameters, and computer codes that will constitute an intellectual infrastructure enabling more consistent, accurate, and widespread application of TCN methods in the earth sciences. Furthermore, the Project will provide a basis for a more formal and organized future approach to promoting consistency in application of TCN methods, such as committees to provide recommended values for parameters. Finally, it will include a component to directly involve undergraduates, and especially minority students, in research in aspects of earth science related to CRONUS.