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Simultaneously Measuring 14C and Radon in Benzene Dating Samples

Published online by Cambridge University Press:  18 July 2016

Pall Theodórsson
Pall Theodórsson*
Affiliation:
Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavik, Iceland. Email: [email protected]
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Abstract

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After benzene synthesis, radiocarbon dating samples are usually stored for 3–4 weeks before counting to allow an eventual radon contamination to decay to a negligible level. This paper presents a technique that can minimize, and often eliminate, this delay by using a simple single-phototube liquid scintillation counting system, specifically designed for 14C dating. Radon contamination is assessed by pulses of 214Po (a 222Rn decay product, half-life 0.16 μs), identified through pulse-time analysis. For each 214Po pulse, 0.49 beta particle pulses of 214Pb and 214Bi fall in the 14C counting window, and the 214Po pulses are used to correct the 14C count rate. A 14C sample (count rate 11.6 cpm) was measured continuously for 16 days. It was then doped with radon, which increased the first 24-hr count rate in the 14C channel by 3.8 cpm, and the sample was measured for 27 more days. Radon did not measurably affect the 14C-corrected count rate. Counting a sample for 2 min reveals whether it needs storing. If the radon concentration is low, the sample can be measured immediately without degrading accuracy.

Type
Articles
Information
Radiocarbon , Volume 47 , Issue 2 , 2005 , pp. 231 - 234
Copyright
Copyright © 2005 by the Arizona Board of Regents on behalf of the University of Arizona 

References

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