Continued Development and Application of 40Ar/39Ar Dating for Archaeometric Research

氩定年法对古人类学家来说极其重要，因为它几乎可以用于过去的整个600万年；这是原始人出现和发展的时期。许多重要的考古和古生物遗址位于火山地区，如东非，其中包含可以用这种技术确定年代的地层。在美国国家科学基金会的支持下，伯克利地质年代学中心（BGC）将继续发展40Ar/39Ar定年技术，并将该技术应用于一系列重要的古人类遗址。BGC与非洲、欧洲和亚洲的许多研究人员合作，在美国国家科学基金会的支持下，这些项目将继续和扩大。40Ar/39Ar定年法是基于地质材料中一小部分天然钾随时间的放射性衰变。衰变的产物包括40Ar，它仍然被困在某些类型的地质物质中，比如火山岩中的晶体。测量岩石或矿物中积累的40Ar的量，结合材料中钾的含量，就可以得出结晶的年龄。在40Ar/39Ar年代测定法中，要测定年代的材料在核反应堆的核心处照射几分钟到几天，以便将一些钾转化为人工氩的同位素。然后，人工同位素（代表钾）和放射性产生的氩可以在高灵敏度和精确的质谱仪中同时测量。BGC的设备包括三个全自动测年系统，每个系统都能够通过40Ar/39Ar法测定任何地方的地质物质，从重量不到1毫克的单个小晶体到数百毫克。与过去一样，考古测量的支持对于维持考古和古人类社区的40Ar/39Ar测年的常规可用性以及推进40Ar/39Ar测年方法的能力至关重要。虽然在许多方面是常规的，但不断发展的技术允许该方法的功能不断改进。这些改进扩大了可解决问题的范围，从而带来了巨大的科学红利。这项开发工作的主要动机是：1)维持对全球考古和古人类学研究的高质量40Ar/39Ar数据的常规访问；2)继续改进40Ar/39Ar方法，以提高精度和准确性，特别是在测定更年轻、更小或钾含量更低的材料时；3)更换或增加旧设备，以保持高水平的生产率和科学成就。赠款资金将主要集中在三个方面：1)用CO2激光器替换Nd-YAG，用于加热我们的氩气提取线上的地质材料；2)安装一个强大的UPS电源，以便在日益频繁的停电情况下允许实验室不间断运行；3)自动化提取线/质谱仪组合上的计算机控制系统现代化。转换为基于二氧化碳激光的加热系统的好处主要来自于能够使用均匀能量分布的宽激光束逐步加热大量长石，同时获得提取在线毛坯的好处，其成本比目前使用的传统电阻炉加热设备低许多倍。使实验室能够经受短期停电（持续时间为1小时）将提供三条提取线的持续有效运行，同时保护设备免受偶尔突然断电的破坏性影响。由于软件和硬件组件的过时，计算机控制系统的现代化是必要的，如果要继续创新，这是必不可少的。

Argon dating is extremely important to paleoanthropologists because it can be used over almost the entire last 6 million years; this is the period when hominids emerged and developed. Many significant archaeological and paleontological sites are located in volcanic regions such as Eastern Africa and contain strata which can be dated by this technique. With National Science Foundation support the Berkeley Geochronology Center (BGC) will continue to develop the technique of 40Ar/39Ar dating and apply this technique to a series of significant paleoanthropological sites. The BGC has collaborated with researchers at a number of sites in Africa, Europe and Asia, and with NSF support such projects will be continued and expanded.The 40Ar/39Ar dating method is based on the radiometric decay of a fraction of natural potassium in geologic materials over time. The products of the decay include 40Ar, which remains trapped in certain types of geologic materials, such as crystals within volcanic rocks. Measurement of the amount of 40Ar that has accumulated in a rock or mineral, combined with knowledge of the material's potassium content, yields the age of crystallization. In 40Ar/39Ar dating, the material to be dated is irradiated in the core of a nuclear reactor for minutes to days, in order to transmute some of the potassium to an artificial isotope of argon. Then, both the artificial isotope, which stands in for potassium, and the radiogenically produced argon, can be measured at the same time in a highly sensitive and accurate mass spectrometer.The facilities at BGC include three fully automated dating systems, each of which is capable of dating anywhere from a single small crystal of geological material weighing less than a milligram, to hundreds of milligrams, by the 40Ar/39Ar method.As in the past, Archaeometry support will be vital both to maintaining routine availability of 40Ar/39Ar dating for the archeological and paleoanthropological communities, as well as advancing the capabilities of 40Ar/39Ar dating methods. Though routine in many regards, evolving technology permits continued improvements in the method's capabilities,. Such improvements pay large scientific dividends by expanding the scope of problems that can be solved. The principal motivations for this development effort are to: 1) sustain routine access to high-quality 40Ar/39Ar data for archeological and paleoanthropological research worldwide; 2) continue refinement of 40Ar/39Ar methods to improve precision and accuracy, particularly in dating younger, smaller, or less potassic materials, and 3) replace or augment old equipment to maintain high levels of productivity and scientific excellence.Grant funding will be focused primarily in three areas: 1) replacement of a Nd-YAG with a CO2 laser for heating geological materials on one of our Argon extraction lines, 2) installation of a robust UPS power supply that will permit uninterrupted lab operation in the face of increasingly frequent power outages, and 3) modernization of the computer control systems on our automated extraction line/mass spectrometer combinations. The benefits of converting to a CO2-laser based heating system are derived primarily from an ability to incrementally heat large amounts of feldspar with a broad laser beam with uniform energy profile, while accruing the benefits of extraction-line blanks that are many times lower than the conventional resistance-furnace heating device currently in use. Enabling the laboratory to weather short power outages ( 1hr in duration) will provide for continued efficient operation of three extraction lines while protecting equipment from the occasionally devastating effects of sudden power loss. Modernization of the computer control systems is necessitated by obsolescence of software and hardware components, and is essential if innovation is to continue.