Graphitisation & measurement of microgram radiocarbon samples at ANSTO

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dc.contributor.authorSmith, AMen_AU
dc.contributor.authorHua, Qen_AU
dc.contributor.authorVarley, Sen_AU
dc.contributor.authorWilliams, AAen_AU
dc.contributor.authorYang, Ben_AU
dc.date.accessioned2023-01-20T03:36:43Zen_AU
dc.date.available2023-01-20T03:36:43Zen_AU
dc.date.issued2021-11-17en_AU
dc.date.statistics2022-07-01en_AU
dc.description.abstractThe Centre for Accelerator Science (CAS) at ANSTO has been providing radiocarbon analyses for the user community and internal projects for two and a half decades. Early on, there was a need to develop the measurement capability for samples containing just tens of micrograms of carbon [1, 2]. We have continued to develop this capability since. At first effort was directed at optimising our ‘conventional’ graphitisation furnaces [3]. These have a minimum reaction volume of ~ 2.5 mL and reduce CO₂ to graphite over an Fe catalyst at 600 °C in an excess of hydrogen. CAS operates a bank of 24 conventional furnaces which provide for the bulk of our sample graphitisation for samples containing > 5 μg of carbon. In 2003 we began developing a novel, miniaturised graphitisation furnace which used a focused infrared laser to heat the Fe catalyst in a quartz crucible, with the temperature measured indirectly by infrared thermometry [4]. The prototype unit had an internal reaction volume of ~0.5 mL including pressure transducer and the two subsequent furnaces ~ 0.3 mL. These small volumes allow a higher initial pressure for small amounts of CO₂ , improving the efficiency of conversion to graphite. Efficient trapping of the water vapour produced during the reaction and careful selection of the catalyst are also key to optimising graphitisation of small samples [5, 6]. By localising the heated region within the reaction volume, the addition of extraneous carbon is minimised in these furnaces and samples containing just 1-2 μg of carbon are routinely prepared. The laser heated furnaces (LHF) are preferred for processing the very small samples derived from our ¹⁴ C in situ program [7]. The fabrication approach developed for the LHF was adapted to a new type of miniaturised furnace we call micro-conventional furnaces (MCF) [8]. These furnaces have a minimum reaction volume of ~ 0.9 mL with a small tube furnace to heat the catalyst. Variable temperature cold traps have been developed to optimise sample processing with samples as small as 5 μg of carbon routinely prepared. The MCF are used extensively in conjunction with ¹⁴ C measurements of CO, CO₂ and CH₄ derived from ice core and firn air samples. We present an overview of micro-sample graphitisation and measurement at CAS.en_AU
dc.identifier.citationSmith, A., Hua, Q., Varley, S., Williams, A., & Yang, B. (2021). Graphitisation & measurement of microgram radiocarbon samples at ANSTO. Poster plus presentation to the 15th International Conference on Accelerator Mass Spectrometry. ANSTO Sydney, Australia. November 15th – 19th, 2021. (pp. 248). Retrieved from: https://ams15sydney.com/wp-content/uploads/2021/11/AMS-15-Full-Program-and-Abstract-Book-R-1.pdfen_AU
dc.identifier.conferenceenddate19 November 2021en_AU
dc.identifier.conferencename15th International Conference on Accelerator Mass Spectrometryen_AU
dc.identifier.conferenceplaceSydney, Australiaen_AU
dc.identifier.conferencestartdate15 November 2021en_AU
dc.identifier.pagination248en_AU
dc.identifier.urihttps://ams15sydney.com/wp-content/uploads/2021/11/AMS-15-Full-Program-and-Abstract-Book-R-1.pdfen_AU
dc.identifier.urihttps://apo.ansto.gov.au/dspace/handle/10238/14448en_AU
dc.language.isoenen_AU
dc.publisherAustralian Nuclear Science and Technology Organisationen_AU
dc.subjectGraphitizationen_AU
dc.subjectCarbon 14en_AU
dc.subjectANSTOen_AU
dc.subjectAcceleratorsen_AU
dc.subjectMeasuring instrumentsen_AU
dc.subjectFurnacesen_AU
dc.subjectWater vaporen_AU
dc.titleGraphitisation & measurement of microgram radiocarbon samples at ANSTOen_AU
dc.typeConference Abstracten_AU
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