The efficiency of charcoal decontamination for radiocarbon dating by three pre-treatments: ABOX, ABA and hypy

Bird, Michael I., Levchenko, Vladimir, Ascough, Philippa L., Meredith, Will, Wurster, Christopher M., Williams, Alan, Tilston, Emma L., Snape, Colin E., and Apperley, David C. (2014) The efficiency of charcoal decontamination for radiocarbon dating by three pre-treatments: ABOX, ABA and hypy. Quaternary Geochronology, 22. pp. 25-32.

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Abstract

Here we report results of a direct inter-comparison of the ability of three radiocarbon pre-treatment techniques to remove radiocarbon contamination introduced by exposing known-radiocarbon-free charcoal made at three different temperatures (300, 400 and 500 °C) to environmental contamination on a rainforest floor for one to three years. The initial charcoal had no measureable radiocarbon, but 14C activity increased after environmental exposure to ~1 pMC after one year (apparent age of ~40,000 yrs BP) and ~5 pMC after three years (apparent age of ~25,000 years). For the 400 and 500 °C samples, all techniques were able to reduce contamination by >90%. Acid–base oxidation (ABOX) provided the most reliable decontamination, reducing the radiocarbon activity of the one year samples to background, and reducing the radiocarbon activity of the three year samples to 0.04 ± 0.02 pMC or less (apparent age >56,900 yrs BP). The performance of ABOX was superior to that of both acid–base–acid (ABA) and hydrogen pyrolysis (hypy) treatments, with ABA performing better than hypy in most cases. No technique was able to fully remove decontamination from the 300 °C charcoal (although ABOX again removed the most contamination), likely due to the incompletely pyrolized nature of the charcoal which is dominated by aromatic clusters of small ring size. All the techniques rely on removing contaminant carbon faster than indigenous carbon and this condition is not met in the case of charcoal produced at temperatures below ~350 °C. While all pre-treatments are useful for routine sample processing, the results suggest that ABOX is the only technique that can provide reliable decontamination of charcoal of an age close to the dating limit of the radiocarbon dating technique.

Item ID: 36238
Item Type: Article (Research - C1)
ISSN: 1878-0350
Keywords: Radiocarbon dating, charcoal, biochar, ABOX, ABA, hydrogen pyrolysis, pre-treatment
Funders: Australian Research Council (ARC), Australian Institute of Nuclear Science and Engineering (AINSE), Natural Environment Research Council (UK) (NERC)
Projects and Grants: ARC Federation Fellowship (FF0883221), AINSE grant ALNGRA10061 , NERC standard grant no. NE/F017456/1
Date Deposited: 12 Nov 2014 12:04
FoR Codes: 04 EARTH SCIENCES > 0402 Geochemistry > 040203 Isotope Geochemistry @ 40%
04 EARTH SCIENCES > 0402 Geochemistry > 040204 Organic Geochemistry @ 30%
21 HISTORY AND ARCHAEOLOGY > 2101 Archaeology > 210102 Archaeological Science @ 30%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970104 Expanding Knowledge in the Earth Sciences @ 50%
95 CULTURAL UNDERSTANDING > 9505 Understanding Past Societies > 950599 Understanding Past Societies not elsewhere classified @ 50%
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