HR: 1340h
AN: U33A-0002    [Abstracts]
TI: Artificial Targets to Refine Production Rate Scaling Factors for Surface Exposure Dating
AU: * Strasky, S
EM: strasky@erdw.ethz.ch
AF: Institute for Isotope Geology and Mineral Resources, ETH Zentrum, Sonneggstr. 5, Zurich, 8092 Switzerland
AU: Vermeesch, P
EM: vermeesch@erdw.ethz.ch
AF: Institute for Isotope Geology and Mineral Resources, ETH Zentrum, Sonneggstr. 5, Zurich, 8092 Switzerland
AU: Baur, H
EM: baur@erdw.ethz.ch
AF: Institute for Isotope Geology and Mineral Resources, ETH Zentrum, Sonneggstr. 5, Zurich, 8092 Switzerland
AU: Kober, F
EM: kober@erdw.ethz.ch
AF: Geological Institute, ETH Zentrum, Sonneggstr. 5, Zurich, 8092 Switzerland
AU: Schlüchter, C
EM: schluechter@geo.unibe.ch
AF: Institute of Geological Sciences, University of Bern, Baltzerstr. 1-3, Bern, 3012 Switzerland
AU: Wieler, R
EM: wieler@erdw.ethz.ch
AF: Institute for Isotope Geology and Mineral Resources, ETH Zentrum, Sonneggstr. 5, Zurich, 8092 Switzerland
AB: To determine surface exposure ages, an obviously crucial parameter is the production rate of a nuclide of interest at the site of exposure of a given sample. As the cosmic ray intensity depends on the exact location within the troposphere, also the cosmogenic nuclide production rates vary with the geographical position. Accurate scaling of cosmogenic nuclide production rates from a calibration site to another with different geomagnetic latitude and altitude is therefore required. The international community initiated the CRONUS (Cosmic-Ray-Originated NUclide Systematics) project to improve the knowledge on production systematics of cosmogenic nuclides on earth. In our project we approach the "scaling problem'' by measuring the variability of production rates of cosmogenic noble gases (³He and ²¹Ne) as a function of the geographical position in artificial targets. The idea is to expose artificial targets along altitude and latitude transects during 1-2 years and subsequently measure the cosmic-ray produced ³He and ²¹Ne concentrations. The vacuum containers built for the experiment are inconel stainless steel tubes. The main target material is quartz, as quartz is the most commonly used mineral for exposure dating and both, cosmogenic helium and neon are produced and retained in the target container. Each target contains 1 kg of artificial quartz sand, and is degassed in vacuum prior to exposure. Blank measurements are carried out after degassing. So far, four artificial targets have been exposed in Antarctica and Tibet. Further targets will be exposed along an altitude transect between sea level and about 4500 m altitude and a latitude transect between 20-50 degrees. Blank measurements for the first exposed targets revealed ²¹Ne- and ³He-concentrations of about 5·10⁵ and 5·10⁴ atoms per container, respectively. After 1-2 years of exposure we should be able to measure the cosmogenic excess over blank with sufficient accuracy.
DE: 1150 Cosmogenic-nuclide exposure dating (4918)
DE: 4918 Cosmogenic isotopes (1150)
SC: Union [U]
MN: Fall Meeting 2005