First principles calibration of 40Ar abundances  in 40Ar/39Ar mineral neutron fluence monitors: Methodology and preliminary results

Leah E. Morgan; Brett Davidheiser-Kroll; Klaudia F. Kuiper; Darren F. Mark; Noah M. McLean; Jan Wijbrans

doi:10.1111/ggr.12464

First principles calibration of ⁴⁰Ar abundances in ⁴⁰Ar/³⁹Ar mineral neutron fluence monitors: Methodology and preliminary results

Geostandards and Geoanalytical Research

By: Leah E. Morgan, Brett Davidheiser-Kroll, Klaudia F. Kuiper, Darren F. Mark, Noah M. McLean, and Jan Wijbrans

https://doi.org/10.1111/ggr.12464

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Abstract

The accuracy and traceability of geochronometers are of vital importance to questions asked by many Earth scientists. The widely applied ⁴⁰Ar/³⁹Ar geochronometer relies on the co-irradiation of samples with neutron fluence monitors (reference materials) of known ages; the ages and uncertainties of these monitors are critical to our ability to apply this chronometer. Previously, first principles, astronomical and optimisation calibrations have been made. The first principles method for determining the age of monitor minerals is the K-Ar method, which involves measurement of their ⁴⁰K and ⁴⁰Ar* abundances. The AQuA (Absolute Quantities of Argon) pipette system, which emits calibrated quantities of ⁴⁰Ar* via the ideal gas law, was used to calibrate the sensitivity of the system across a range of source pressures and estimate ⁴⁰Ar* abundances in neutron fluence monitors. These ⁴⁰Ar abundances were combined with existing ⁴⁰K abundance data for these monitors. Ages for HD-B1 and MD2 (GA1550) biotite fluence monitors were calculated and combined with intercalibration data for HD-B1 and Fish Canyon sanidine (FCs) to determine ages for FCs. Current results do not have the targeted accuracy when compared with previous calibrations; however, we show how the extensive methodology development presented here can be used towards making reliable future measurements.

Additional publication details
Publication type	Article
Publication Subtype	Journal Article
Title	First principles calibration of 40Ar abundances in 40Ar/39Ar mineral neutron fluence monitors: Methodology and preliminary results
Series title	Geostandards and Geoanalytical Research
DOI	10.1111/ggr.12464
Volume	47
Issue	1
Year Published	2023
Language	English
Publisher	Wiley
Contributing office(s)	Geology, Geophysics, and Geochemistry Science Center
Description	14 p.
First page	91
Last page	104
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