A metrological approach to measuring ⁴⁰Ar* concentrations in K-Ar and ⁴⁰Ar/³⁹Ar in mineral standards

Morgan, L.E., Postma, O., Kuiper, K.F., Mark, D.F. , Van der Plas, W., Davidson, S., Perkin, M., Villa, I.M. and Wijbrans, J. (2011) A metrological approach to measuring ⁴⁰Ar* concentrations in K-Ar and ⁴⁰Ar/³⁹Ar in mineral standards. Geochemistry, Geophysics, Geosystems, 12, A0AA20. (doi: 10.1029/2011GC003719)

Abstract

In geochronology, isotopic ages are determined from the ratio of parent and daughter nuclide concentrations in minerals. For dating of geological material using the K-Ar system, the simultaneous determination of ⁴⁰Ar and ⁴⁰K concentrations on the same aliquot is not possible. Therefore, a widely used variant, the ⁴⁰Ar/³⁹Ar technique, involves the production of ³⁹Ar from ³⁹K by neutron bombardment and the reliance on indirect natural calibrators of the neutron flux, referred to as 1Cmineral standards. 1D Many mineral standards still in use rely on decades-old determinations of ⁴⁰Ar concentrations; resulting uncertainties, both systematic and analytical, impede the determination of higher accuracy ages using the K-Ar decay system. We discuss the theoretical approach and technical design of a gas delivery system which emits metrologically traceable amounts of ⁴⁰Ar and will allow for the sensitivity calibration of noble gas mass spectrometers. The design of this system is based on a rigorous assessment of the uncertainty budget and detailed tests of a prototype system. A number of obstacles and proposed resolutions are discussed along with the selection of components and their integration into a pipette system.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Morgan, Dr Leah and Mark, Professor Darren
• Authors: Morgan, L.E., Postma, O., Kuiper, K.F., Mark, D.F., Van der Plas, W., Davidson, S., Perkin, M., Villa, I.M., and Wijbrans, J.
• College/School: College of Science and Engineering > Scottish Universities Environmental Research Centre
• Journal Name: Geochemistry, Geophysics, Geosystems
• Publisher: American Geophysical Union
• ISSN: 1525-2027
• ISSN (Online): 1525-2027
• Published Online: 07 October 2011