Isotope reference standards developed. (General Developments).The dating of important minerals and geologic materials depends upon accurate determinations of potassium (K) and argon (Ar) isotopic ratios, but significant interlaboratory disagreements (1 % to 2 %) exceed intra-laboratory uncertainties by an order of magnitude A change in quantity or volume as measured by the decimal point. For example, from tens to hundreds is one order of magnitude. Tens to thousands is two orders of magnitude; tens to millions is three orders of magnitude, etc. , hampering comparability of results. In response, and under contract to the U.S. Geological Survey (USGS USGS United States Geological Survey (US Department of the Interior) ), NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. developed several all-metal argon isotope spike systems, each consisting of a reservoir and a Dorflinger pipette pipette /pi·pette/ (pi-pet´) [Fr.] 1. a glass or transparent plastic tube used in measuring or transferring small quantities of liquid or gas. 2. to dispense by means of a pipette. capable of delivering the required (2 x [10.sup.-10] to 4 x [10.sup.-10]) mol per aliquot aliquot (al-ee-kwoh) adj. a definite fractional share, usually applied when dividing and distributing a dead person's estate or trust assets. (See: share) . The ultra-low fill pressures ([approximately equal to] 10 Pa) proved to be the major challenge in calibrating the spike systems with requisite uncertainty. Two spike systems deliver pure [Ar.40] and three deliver artificial mixtures of [Ar.sup.40]/[Ar.sup.38] with uncertainties of approximately 0.1 % to 0.2 % for both amount of gas delivered and for isotopic ratios of the mixtures. The Ar spike systems will be used by the USGS to calibrate To adjust or bring into balance. Scanners, CRTs and similar peripherals may require periodic adjustment. Unlike digital devices, the electronic components within these analog devices may change from their original specification. See color calibration and tweak. their mass spectrometric techniques and ultimately measure the Ar concentration in a new preparation of their monitor mineral MMhb-2, which is a reference standard used for calibration and inter-laboratory comparisons. The data, when combined with K concentration data from NIST, will enable the K/Ar age for MMhb-2 to be determined with a 10-fold improvement in uncertainty over existing methods, significantly surpassing USGS expectations. The MMhb-2 will also be certified by NIST for potassium and argon concentrations and distributed as an SRM (1) (Storage Resource Management) The management of the storage resources in an organization in order to avoid duplication of files and to determine space utilization across all servers. that will be used by major argon dating laboratories along with the spike systems to resolve longstanding differences among laboratories, both in the United States and abroad. As an ancillary benefit, the spike systems also will enable the USGS to re-measure the isotopic composition of atmospheric argon and calculate a new atomic weight for argon. CONTACT: Archie Muller, (301) 975-5932; archie.miller@nist.gov. |
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