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600万年的整个时期;这是原始人类出现和发展的时期。许多重要的考古和古生物遗址位于火山地区，如东非，并含有可以通过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40 Ar/39 Ar定年技术，并将该技术应用于一系列重要的古人类遗址。BGC已经与非洲、欧洲和亚洲的一些地点的研究人员合作，在NSF的支持下，这些项目将继续并扩大。40 Ar/39 Ar定年方法是基于地质材料中一部分天然钾随时间的放射性衰变。衰变的产物包括40 Ar，它仍然被困在某些类型的地质材料中，例如火山岩中的晶体。测量岩石或矿物中积累的40 Ar的量，结合材料的钾含量，得出结晶的年龄。在40 Ar/39 Ar定年中，要定年的材料在核反应堆的核心中被照射几分钟到几天，以便将一些钾转化为氩的人工同位素。然后，人工同位素（代表钾）和放射性产生的氩都可以在高度灵敏和精确的质谱仪中同时测量。BGC的设施包括三个全自动测年系统，每个系统都能够测年任何地方，从重量不到一毫克的地质物质的单个小晶体到数百毫克，与过去一样，考古学的支持对于维持考古和古人类学社区的40 Ar/39 Ar定年的常规可用性以及提高40 Ar/39 Ar定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能力不断改进。 这些改进通过扩大可以解决的问题的范围而带来巨大的科学红利。其主要目的是：1）为世界各地的考古和古人类学研究提供高质量的40 Ar/39 Ar数据; 2）继续改进40 Ar/39 Ar方法，以提高精确度和准确度，特别是在测定更年轻、更小或更少钾质物质的年代时，以及3）更换或增加旧设备，以保持高水平的生产力和卓越的科学水平。拨款主要集中在三个方面：1）用CO2激光器取代Nd-YAG激光器，用于加热我们的一条氩提取线上的地质材料，2）安装强大的UPS电源，在停电日益频繁的情况下，允许实验室不间断运行，以及3）我们的自动提取线/质谱仪组合的计算机控制系统的现代化。转换为基于CO2激光器的加热系统的好处主要来自于用具有均匀能量分布的宽激光束递增加热大量长石的能力，同时获得比目前使用的传统电阻炉加热装置低许多倍的提取线坯料的好处。使实验室能够经受住短暂的停电（持续时间为1小时），将为三条抽气管线提供持续有效的操作，同时保护设备免受突然停电的偶尔破坏性影响。计算机控制系统的现代化是由于软件和硬件组件的过时而必需的，并且如果要继续创新，则是必不可少的。

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.