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Radon Elimination During Benzene Preparation for Radiocarbon Dating by Liquid Scintillation Spectrometry

Published online by Cambridge University Press:  18 July 2016

Darden Hood
Affiliation:
Beta Analytic Inc, Coral Gables, Florida 33124
Ronald Hatfield
Affiliation:
Beta Analytic Inc, Coral Gables, Florida 33124
Christopher Patrick
Affiliation:
Beta Analytic Inc, Coral Gables, Florida 33124
Jerry Stipp
Affiliation:
Beta Analytic Inc, Coral Gables, Florida 33124
Murry Tamers
Affiliation:
Beta Analytic Inc, Coral Gables, Florida 33124
Robert Leidl
Affiliation:
Radiocarbon Dating Research, Australian National University Canberra 2601, Australia
Barbara Lyons
Affiliation:
Radiocarbon Dating Research, Australian National University Canberra 2601, Australia
Henry Polach
Affiliation:
Radiocarbon Dating Research, Australian National University Canberra 2601, Australia
Steve Robertson
Affiliation:
Radiocarbon Dating Research, Australian National University Canberra 2601, Australia
Weijian Zhou
Affiliation:
Radiocarbon Dating Research, Australian National University Canberra 2601, Australia
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Abstract

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Radon gas is a serious contaminant in radiocarbon dating by radiometry. The low specific ionizations associated with the α-particle emitting radon and its β-particle emitting daughters overlap within the 14C counting window. Elimination of radon is therefore imperative for precise 14C age determinations. This paper deals with the sources and mechanism of incorporation of radon affecting 14C dating by liquid scintillation (LS) counting, and reviews conventional radon elimination practices in 14C laboratories. It demonstrates, based on rigorous multichannel and multiparameter α- and β-particle spectral analyses of some 1000 benzene samples, that parent radium is not present and that its daughter radon is quantitatively eliminated during dynamic vacuum recovery of benzene at −78°C. However, the radon-free benzene can be recontaminated by exposure to air containing traces of radon, such as is common in concrete or low-lying laboratories. The use of radon-free air, when exposing the benzene to the atmosphere, and the monitoring of radon counts from the environment and sample benzene in a fixed ‘radon window', are essential prerequisites to the quality control of 14C age determinations in very low background systems.

Type
I. Sample Preparation and Measurement Techniques
Copyright
Copyright © The American Journal of Science 

References

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