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

• Verfasst von: Sontag-González, Mariana [VerfasserIn]
• Verfasst von: Kumar, Raju [VerfasserIn]
• Verfasst von: Schwenninger, Jean-Luc [VerfasserIn]
• Verfasst von: Thieme, Juergen [VerfasserIn]
• Verfasst von: Kreutzer, Sebastian [VerfasserIn]
• Verfasst von: Frouin, Marine [VerfasserIn]
• Titel: Synchrotron-based elemental mapping of single grains to investigate variable infrared-radiofluorescence emissions for luminescence dating
• Titelzusatz: short communicatio
• Verf.angabe: Mariana Sontag-González, Raju Kumar, Jean-Luc Schwenninger, Juergen Thieme, Sebastian Kreutzer, Marine Frouin
• E-Jahr: 2024
• Jahr: 05 Mar 2024
• Umfang: 12 S.
• Fussnoten: Gesehen am 04.06.2024
• Titel Quelle: Enthalten in: Geochronology
• Ort Quelle: Göttingen : Copernicus Publications, 2019
• Jahr Quelle: 2024
• Band/Heft Quelle: 6(2024), 1, Seite 77-88
• ISSN Quelle: 2628-3719
• DOI: doi:10.5194/gchron-6-77-2024
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 189059055X

Abstract

During ionizing 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. In the present work, we report the presence of individual grains in the K-feldspar density fraction 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) at the submicron-resolution X-ray spectroscopy (SRX) beamline. We analysed coarse (>90 µm) K-feldspar-bearing grains of five samples of different ages and origin in order to characterize the composition of grains yielding the desired or contaminated IR-RF emission. Using micro-X-ray fluorescence (μ-XRF), we successfully acquired element distribution maps of up to 15 elements (<1 µm resolution) of sections of full grains previously used for IR-RF dating. In keeping with current theories of IR-RF signal production, we observed a trend between the relative proportions of Pb and Fe and the shape of the IR-RF signal, namely that 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. Our study also represents a proof of concept for mapping the oxidation states of Fe using micro-X-ray absorption near-edge structure spectroscopy (μ-XANES) on individual grains. The high spatial resolution enabled by synchrotron X-ray 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.