High precision determination of the terrestrial 40K abundance

Naumenko, Mariia Oleksiivna; Mezger, Klaus; Nägler, Thomas; Villa, Igor Maria (2013). High precision determination of the terrestrial 40K abundance. Geochimica et cosmochimica acta, 122, pp. 353-362. Elsevier Science 10.1016/j.gca.2013.08.019

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Recent improvements in the precision of mass spectrometric measurements have reduced the uncertainty of K-Ar and 39Ar-40Ar ages measured on geological materials. Now the major sources of uncertainty are the uncertainties on the 40K decay constant and the absolute abundance of 40K. In order to improve on this situation we determined the abundance of the 40K isotope in terrestrial standards. A ThermoFischer Triton+ thermal ionization mass spectrometer was used for K isotope ratio measurements of the NIST K standard reference materials SRM 918b and SRM 985. Ion beams were measured in Faraday cups with amplifiers equipped with 1E10, 1E11 and 1E12 Ω resistors. Three measurement protocols were used: (A) dynamic measurement with in-run fractionation correction by normalization to the IUPAC recommended isotope ratio 41K/39K = 0.0721677; (B) total evaporation; (C) a modified total evaporation with interblock baseline measurements. Different measurement protocols were combined with different loading procedures. The best results were obtained by loading samples on single tantalum filaments with 0.1M H3PO4. The total ion yields (ionization + transmission) were tested for the evaporation procedures (B) and (C) and ranged up to 48 %. The resulting best estimate for the 40K/39K ratio is 0.000 125 116 ± 57 (2σ), corresponding to 40K/K = (1.1668 ± 8; 2σ) x 10-4.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Institute of Geological Sciences
08 Faculty of Science > Institute of Geological Sciences > Isotope Geology

UniBE Contributor:

Naumenko, Mariia Oleksiivna; Mezger, Klaus; Nägler, Thomas and Villa, Igor Maria

Subjects:

500 Science > 550 Earth sciences & geology

ISSN:

0016-7037

Publisher:

Elsevier Science

Language:

English

Submitter:

Igor Maria Villa-Toscani

Date Deposited:

21 Mar 2014 11:56

Last Modified:

27 Jan 2015 20:31

Publisher DOI:

10.1016/j.gca.2013.08.019

BORIS DOI:

10.7892/boris.46899

URI:

https://boris.unibe.ch/id/eprint/46899

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