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Robust Radiocarbon Dating of Wood Samples by High-Sensitivity Liquid Scintillation Spectroscopy in the 50–70 kyr Age Range

Published online by Cambridge University Press:  18 July 2016

Alan G Hogg ,
L Keith Fifield ,
Jonathan G Palmer ,
Chris S M Turney  and
Rex Galbraith
Alan G Hogg*
Affiliation:
Radiocarbon Laboratory, University of Waikato, Private Bag, Hamilton, New Zealand
L Keith Fifield
Affiliation:
Department of Nuclear Physics, Research School of Physical Sciences and Engineering, Australian National University, Canberra ACT 0200, Australia
Jonathan G Palmer
Affiliation:
Gondwana Tree Ring Laboratory, P.O. Box 64, Tai Tapu, Canterbury 8150, New Zealand
Chris S M Turney
Affiliation:
GeoQuEST Research Centre, School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW 2522, Australia
Rex Galbraith
Affiliation:
Department of Statistical Science, University College London, Gower Street, London WC1E 6BT, United Kingdom
*
Corresponding author. Email: [email protected]
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Abstract

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Although high-sensitivity liquid scintillation (LS) spectroscopy is theoretically capable of producing finite radiocarbon ages in the 50,000- to 70,000-yr range, there is little evidence in the literature that meaningful dates in this time period have been obtained. The pressing need to undertake calibration beyond 26 kyr has resulted in the regular publication of 14C results in excess of 50 kyr, yet very little effort has been made to demonstrate their accuracy or precision. There is a paucity of systematic studies of the techniques required to produce reliable dates close to background and the methods needed to assess contamination from either in situ sources or laboratory handling and processing. We have studied the requirements for producing accurate and reliable dates beyond 50 kyr. Laboratory procedures include optimization of LS spectrometers to obtain low and stable non-14C background count rates, use of low-background counting vials, large benzene volumes, long counting times, and preconditioning of vacuum lines. We also discuss the need for multiple analyses of a suitable material containing no original 14C (background blank) and the application of an appropriate statistical model to compensate for variability in background contamination beyond counting statistics. Accurate and reproducible finite ages >60 kyr are indeed possible by high-sensitivity LS spectroscopy, but require corroborating background blank data to be defensible.

Type
Articles
Information
Radiocarbon , Volume 49 , Issue 2 , 2007 , pp. 379 - 391
Copyright
Copyright © 2007 by the Arizona Board of Regents on behalf of the University of Arizona 

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