Significant loss of 10Be from quartz previously treated for in-situ 14C extraction

Dr Marcus Christl1, Dr Olivia Steinemann1, Prof Susan Ivy-Ochs1

1ETH Zurich, Laboratory of Ion Beam Physics, Zurich, Switzerland

For the extraction of in-situ produced cosmogenic 14C from quartz with the ETH Zurich extraction line about 5 g of sample material are heated to 1650°C in an atmosphere of 200 mbar He (with 10% O2 and a defined amount of CO2 carrier gas) for three hours [1]. During routine operation of the in-situ 14C line the CRONUS A intercomparison material (ICM) is regularly processed and analyzed for 14C for quality control.

In this study we tested whether the residual quartz, i.e. the quartz sample after being processed in the in-situ 14C extraction line, still can be reliably analyzed for its 10Be content. Visual inspection of quartz samples after in situ 14C extraction indicates they are not fully melted. In our experiment, we extracted 10Be from two CRONUS A samples after they had been processed in the in-situ 14C extraction line, and from one untreated CRONUS A sample applying standard 10Be preparation methods. While the 10Be concentration measured in the untreated CRONUS A ICM agreed very well with the reported value of (3.42±0.10)x107 at/g [2] the two samples that had previously been processed in the in situ 14C extraction line yielded (1.22±0.20) x107 at/g and (2.95±0.40)x107 at/g, respectively.

Our results clearly indicate that some 10Be is lost during sample processing in the in-situ 14C extraction line. The variability of 10Be losses (14% and 65%) indicates that they do not occur under reproducible conditions. Attempts to find the missing 10Be in one of the cleaning columns further downstream in the in-situ 14C extraction line were not successful so far. We currently do not have a robust explanation for the observed behavior. We assume that not all Be is transferred to BeO (melting point >2500°C) while heating but some stays present as Be (melting point: 1287°C). Beryllium may escape as volatile compounds or as stray atoms that are volatilized coincidentally with other elements or compounds.

Further investigations are still ongoing but our results provide strong evidence that quartz samples previously processed for in-situ 14C extraction cannot be used for 10Be analysis any more due to an uncontrolled loss of 10Be before a 9Be carrier can be added. We note that this probably has a negligible effect on routine 10Be-target preparation procedures which involve a heating step to much lower temperatures (600-1000°C) when converting the Be-hydroxide into its oxide form. At this stage the samples are spiked with a 9Be carrier and their isotopic ratios would not be affected by any loss of Be.

[1] M. Lupker et al., NIM B, 457 (2019) 30-36
[2] F.M. Phillips et al., Quat. Geochron., 31 (2016) 119-154


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Date

Nov 08 - 19 2021