07 Jun 2023
 | 07 Jun 2023
Status: this preprint is currently under review for the journal GChron.

Short communication: Synchrotron-based elemental mapping of single grains to investigate variable infrared-radiofluorescence emissions for luminescence dating

Mariana Sontag-González, Raju Kumar, Jean-Luc Schwenninger, Juergen Thieme, Sebastian Kreutzer, and Marine Frouin

Abstract. During ionising irradiation, potassium (K)-rich feldspar grains emit infrared (IR) light, which is used for infrared-radiofluorescence (IR-RF) dating. The late-saturating IR-RF emission centred at ~880 nm represents a promising tool to date Quaternary sediments. However, in the present work, we report the presence of individual grains of K-feldspar displaying an aberrant IR-RF signal shape, whose combined intensity contaminates the sum signal of an aliquot composed of dozens of grains. Our experiments were carried out at the National Synchrotron Light Source (NSLS-II) on coarse (> 90 µm) K-feldspar grains of five samples of different ages, nature and origin in order to characterise the composition of grains yielding the desired or contaminated IR-RF emission. Using micro-X-ray-fluorescence (µXRF), we successfully acquired element distribution maps of fifteen elements (<1 µm resolution) of the surface of grains previously used for luminescence dating. In keeping with current theories of IR-RF signal production, we observed a correlation between the relative proportions of Pb and Fe and the shape of the luminescence signal: most grains with the desired IR-RF signal shape had high Pb and low Fe contents. Interestingly, these grains were also defined by high Ba and low Ca contents. Additionally, this study represents a proof-of-concept for mapping the oxidation states of Fe-ions using micro-X-ray absorption near-edge structure spectroscopy (µXANES) on individual grains. The high spatial resolution enabled by synchrotron spectroscopy makes it a powerful tool for future experiments to elucidate long-standing issues concerning the nature and type of defect(s) associated with the main dosimetric trap in feldspar.

Mariana Sontag-González et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gchron-2023-14', Svenja Riedesel, 24 Jul 2023
    • AC1: 'Reply on RC1', Mariana Sontag-González, 25 Aug 2023
  • RC2: 'Comment on gchron-2023-14', Anonymous Referee #2, 25 Jul 2023
    • AC2: 'Reply on RC2', Mariana Sontag-González, 25 Aug 2023

Mariana Sontag-González et al.

Data sets

Short communication: Synchrotron-based elemental mapping of single grains to investigate variable infrared-radiofluorescence emissions [Dataset] (v.1.0.0) M. Sontag-González, R. Kumar, J.-L. Schwenninger, J. Thieme, S. Kreutzer, and M. Frouin

Mariana Sontag-González et al.


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Short summary
We conducted a preliminary study using a synchrotron light source to produce elemental maps, including oxidation states, with spatial resolution <1 µm of individual K-feldspar grains previously used in luminescence dating. The elemental fingerprint that characterised grains with a signal suitable for infrared-radiofluorescence dating had high concentrations of K, Pb and Ba and low proportions of Fe and Ca. In contrast, grains with high Fe and Ca levels yielded an unexpected curve shape.