Continuing Studies of in Situ Cosmogenic 14C in Terrestrial Materials

亚利桑那大学的原位宇宙成因14 C研究小组经过多年开发可靠的提取技术和设备，现在准备将原位14 C与10 Be、26 Al、36 Cl、3 He和21 Ne一起纳入宇宙成因核素surgery过程研究的主流。目前的提取设备和程序将空白水平降低到（2.4 0.1）× 105 14 C原子，并允许在较低的温度（1200 ℃）下可靠的原位14 C提取，并且比以前的方法时间更短。实验表明，该方法能有效地分离原位14 C组分，重复分析精度接近2%（n = 5），同时与早期结果保持一致。这是一个精确度和准确度的水平，相当于或超过目前在现场宇宙成因10 Be，26 Al，3 He，21 Ne和36 Cl。电流测量的精度将允许在约400年的暴露（海平面，高纬度）后，在5克石英样品中原位测量14 C。在NSF的资助下，实现了可行的提取技术，本提案将原位14 C的研究重点放在它非常适合的关键应用上。建议的调查，结合广泛的现场和实验室分析计划，将建立在原位14 C研究的进展，通过（1）限制高能中子散射在海平面和高纬度原位14 C产生机制的相对幅度（散裂14 C）和缓慢的负μ子捕获（mugogenic 14C），（2）独立估计浅层地下（20米深度）和大气衰减长度的散裂和mugogenic原位14 C生产，和（3）经验检验理论模型的散裂和mugogenic生产率随海拔和纬度的变化。这种生产率的变化可以测量现场14 C的程度比目前使用的其他宇宙成因核素可能的更大，利用其快速（~20 kyr）达到长期平衡和不敏感的低和中等（1厘米/kyr）侵蚀率。这些进展将使其他研究人员能够定期使用原位14 C，以逐点确定一系列宇宙成因核素的生产率，从而可能不需要使用比例模型。本研究中使用的样本将来自美国西部的海拔和纬度横断面，智利、澳大利亚和南极洲。最后，这项研究的结果将被完全公布，使广泛应用的原位14 C的表面处理研究。

he in situ cosmogenic 14C (in situ 14C) research group at the University of Arizona, after a number of years developing reliable extraction techniques and equipment, is now prepared to bring in situ 14C into the mainstream of cosmogenic nuclide surficial process studies, alongside 10Be, 26Al, 36Cl, 3He, and 21Ne. Current extraction equipment and procedures reduce blank levels to (2.4 0.1) x 105 14C atoms, and allow reliable in situ 14C extraction at lower temperatures ( 1200C) and in less time than the previous method. Experiments have shown that this new procedure can effectively isolate the in situ 14C fraction with replicate analytical precision approaching 2% (n = 5), while maintaining consistency with earlier results. This is a level of precision and accuracy comparable to or exceeding those currently obtainable with in situ cosmogenic 10Be, 26Al, 3He, 21Ne, and 36Cl. The precision on current measurements will allow measurement of in situ 14C in a 5 g quartz sample after about 400 years of exposure (sea level, high latitude).Having achieved a viable extraction technique with NSF funding, this proposal focuses study of in situ 14C on key applications to which it is uniquely well suited. The proposed investigation, incorporating an extensive field and laboratory analytical program, will build on advances in in situ 14C research by (1) constraining the relative magnitudes of in situ 14C production mechanisms at sea level and high latitude by high-energy neutron spallation (spallogenic 14C) and slow, negative muon capture (muogenic 14C), (2) independently estimating shallow subsurface ( 20 m depth) and atmospheric attenuation lengths for spallogenic and muogenic in situ 14C production, and (3) empirically testing theoretical models of spallogenic and muogenic production rate variation with altitude and latitude. Such production rate variations can be measured with in situ 14C to a much greater extent than is possible with other currently used cosmogenic nuclides, by taking advantage of its rapid (~20 kyr) attainment of secular equilibrium and insensitivity to low and moderate ( 1 cm/kyr) erosion rates. These advances will allow other researchers to use in situ 14C routinely to determine production rates for a range of cosmogenic nuclides on a site-by-site basis, potentially making the use of scaling models unnecessary. Samples used in this study will come from altitude and latitude transects in the western U.S., Chile, Australia, and Antarctica. Finally, results of this research will be fully published to enable widespread application of in situ 14C to surficial process studies.