Preprints
https://doi.org/10.5194/gchron-2021-42
https://doi.org/10.5194/gchron-2021-42
 
11 Jan 2022
11 Jan 2022
Status: this preprint was under review for the journal GChron. A revision for further review has not been submitted.

Short Communication: Mechanism and Prevention of Irreversible Trapping of Atmospheric He During Mineral Crushing

Stephen Ellis Cox1,a, Hayden Bryce Dutcher Miller1,b, Florian Hofmann1,c, and Kenneth Anthony Farley1 Stephen Ellis Cox et al.
  • 1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
  • acurrent address: Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA
  • bcurrent address: Earth and Environmental Science Division, Los Alamos National Laboratory, Los Alamos, NM, 87545 USA
  • ccurrent address: Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089, USA

Abstract. A pervasive challenge in noble gas geochemistry is to ensure that analytical techniques do not modify the composition of the noble gases in the samples. Noble gases are present in the atmosphere and are used in a number of manufacturing procedures and by laboratory equipment. Of particular concern is the introduction of atmospheric or laboratory noble gases to samples during preparation before samples are placed in a vacuum chamber for analysis. Recent work has shown the potential for contamination of crushed samples with air-derived He that is not released by placing the samples under vacuum at low temperature. Using pure He gas as a tracer, we show that the act of crushing samples to a fine powder itself can introduce He contamination, but that this is easily avoided by crushing under liquid or in an inert atmosphere. Because the He is trapped during crushing, the same concern does not extend to samples that are naturally fine-grained when collected. The degree of He contamination even from crushing samples to sizes smaller than typically used for geochronology is insignificant for samples at least 1 Ma and with more than 1 ppm U when the guidelines outlined here are followed.

Stephen Ellis Cox et al.

Status: closed (peer review stopped)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gchron-2021-42', Jonathan Tucker, 24 Feb 2022
    • AC1: 'Reply on RC1', Stephen Cox, 03 May 2022
  • RC2: 'Comment on gchron-2021-42', Pierre-Henri Blard, 18 Mar 2022
    • AC2: 'Reply on RC2', Stephen Cox, 03 May 2022

Status: closed (peer review stopped)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gchron-2021-42', Jonathan Tucker, 24 Feb 2022
    • AC1: 'Reply on RC1', Stephen Cox, 03 May 2022
  • RC2: 'Comment on gchron-2021-42', Pierre-Henri Blard, 18 Mar 2022
    • AC2: 'Reply on RC2', Stephen Cox, 03 May 2022

Stephen Ellis Cox et al.

Stephen Ellis Cox et al.

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Short summary
Noble gases are largely excluded from minerals during rock formation, but they are produced by certain radioactive decay schemes and trapped in mineral lattices. However, they are present in the atmosphere, which means that they can be adsorbed or trapped by physical processes. We present details of a troublesome trapping mechanism for helium during sample crushing and show when it can be ignored and how it can be easily avoided during common laboratory procedures.