Publication Date:
2023-10-24
Description:
〈p xmlns:mml="http://www.w3.org/1998/Math/MathML" xml:lang="en"〉In a reconnaissance study, we investigated the potential of γ‐ray induced production of 〈sup〉38〈/sup〉Ar〈sub〉K〈/sub〉 from 〈sup〉39〈/sup〉K for geochronological applications. For this purpose, various age monitors commonly in use for the established 〈sup〉40〈/sup〉Ar/〈sup〉39〈/sup〉Ar‐method were co‐irradiated for 60 h at 17.6 MeV maximum energy in the ELBE facility, Dresden‐Rossendorf, Germany. Because the available energy was low, total production of 〈sup〉38〈/sup〉Ar〈sub〉K〈/sub〉 was depressed, leading to low 〈italic toggle="no"〉J〈/italic〉〈sub〉38〈/sub〉‐values of (2.1–4.1) × 10〈sup〉‐6〈/sup〉 and hence resulted in only minor 〈sup〉38〈/sup〉Ar excess when compared with atmospheric 〈sup〉38〈/sup〉Ar〈sub〉/〈/sub〉〈sup〉36〈/sup〉Ar ratios. In spite of these restrictions, ages of younger monitors could be reproduced within error, whereas older age reference materials showed discrepancies due to the low production rate. We observed Ca‐derived contributions on 〈sup〉36〈/sup〉Ar in analysed CaF〈sub〉2〈/sub〉 reference materials, and calculated a limit for Ca‐interference on 〈sup〉38〈/sup〉Ar〈sub〉Ca〈/sub〉 of (〈sup〉38〈/sup〉Ar/〈sup〉36〈/sup〉Ar)〈sub〉Ca〈/sub〉 = 0.07 ± 0.03 (1〈italic toggle="no"〉s〈/italic〉). In addition, we investigated a potential recoil redistribution of 〈sup〉38〈/sup〉Ar by stepwise heating experiments, but could not quantify this further because of concurring processes. More work at higher photon energies is necessary to resolve other open issues, in particular the potential of utilising 〈sup〉40〈/sup〉Ar/〈sup〉37〈/sup〉Ar ratios for age determination and the possibility of 〈sup〉42〈/sup〉Ar production from 〈sup〉44〈/sup〉Ca, which would allow correction for Ca‐interference reactions on other Ar isotopes. This would be a pre‐requisite for dating extra‐terrestrial rocks.〈/p〉
Description:
Klaus‐Tschira‐Stiftung gGmbH
Keywords:
ddc:550.724
;
geochronology
;
γ‐irradiation
;
40Ar/39Ar dating
;
age spectra
;
isochrons
Language:
English
Type:
doc-type:article
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