Open AccessA metrological approach to measuring 40 Ar* concentrations in K‐Ar and 40 Ar/ 39 Ar mineral standards
Author(s) -
Morgan Leah E.,
Postma Onno,
Kuiper Klaudia F.,
Mark Darren F.,
van der Plas Wim,
Davidson Stuart,
Perkin Michael,
Villa Igor M.,
Wijbrans Jan R.
Publication year - 2011
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2011gc003719
Subject(s) - geochronology , nuclide , calibration , geology , isotope , mineral , mineralogy , radiochemistry , analytical chemistry (journal) , nuclear physics , chemistry , physics , geochemistry , environmental chemistry , organic chemistry , quantum mechanics
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 40 Ar and 40 K concentrations on the same aliquot is not possible. Therefore, a widely used variant, the 40 Ar/ 39 Ar technique, involves the production of 39 Ar from 39 K by neutron bombardment and the reliance on indirect natural calibrators of the neutron flux, referred to as “mineral standards.” Many mineral standards still in use rely on decades‐old determinations of 40 Ar 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 40 Ar 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.