¹⁰Be from commercial ⁹Be and ²⁷Al carrier solution – Some measurements
Silke Merchel1,2, Régis Braucher3, Johannes Lachner1,2, Georg Rugel2
1University of Vienna, Faculty of Physics, Isotope Physics, Vienna, Austria, 2Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany, 3CEREGE, Aix Marseille Univ., CNRS, Collège de France, IRD, INRAE, Aix en Provence, France
In the DREsden Acclerator Mass Spectrometry (DREAMS) chemistry laboratory, we see elevated but constant ¹⁰Be/⁹Be levels (1.2-2.0×10⁻¹⁵) when using a customised ⁹Be carrier . In satellite and DREAMS laboratories unexperienced researchers and students are performing their own chemical separation, but the “human influence” is unlikely the sole explanation. Different levels of processing blanks as a function of the preparation laboratory are well-known also at other AMS facilities . In our constant approach lowering processing blank levels for ¹⁰Be/⁹Be we have investigated two potential ¹⁰Be sources: ⁹Be and ²⁷Al carrier solutions.
Beryllium-9 carrier solutions are obvious ¹⁰Be sources and commercial and customised ones from minerals were already investigated earlier . Inspired by numerous users asking for ⁹Be carrier analysis, we have compiled all (new) results from different AMS facilities. Remarkably, ¹⁰Be/⁹Be varies in the range of 1-10×10⁻¹⁵ from batch to batch (LOT) of the same company, very likely related to production date . Currently, Australian Chemical Reagents and LGC provide carriers with the lowest intrinsic ¹⁰Be/⁹Be. For AMS users not affording a customised ⁹Be carrier, we advise buying larger quantities of commercial carriers to guarantee long-time low ¹⁰Be/⁹Be and saving precious AMS time from analysing new batches.
Another potential source for elevated and varying ¹⁰Be/⁹Be in processing blanks are Al carrier solutions (added to processing blanks) when performing ¹⁰Be/²⁶Al projects. According to  commercial aluminium contained ¹⁰Be in the range of 4-10×10⁷ ¹⁰Be atoms/g(Al). Nowadays, laboratories use 0.5-3.0 mg Al for processing blanks, which would yield into 4-10×10⁵ ¹⁰Be atoms/blank increasing the ¹⁰Be/⁹Be ratio to 6-10×10⁻¹⁵.
We asked in-situ dating researchers to provide their Al solutions. To differentiate between ¹⁰Be from Al and other sources (contamination in the chemistry laboratory or the ion source) we used a “basic standard-addition approach”: For each Al solution, two AMS targets containing ~300 µg ⁹Be and either 1 mg ²⁷Al or 3 mg ²⁷Al were prepared. After minimal chemistry (hydroxide precipitation, cation exchange, Be(OH)₂ precipitation, washing, drying, ignition, mixing with Nb) samples were measured at DREAMS.
Todays’ Al solutions are lower in ¹⁰Be compared to the Al investigated by . None of our results is higher than 3.55×10⁻¹⁵, however, the two processing blanks without any Al have ¹⁰Be/⁹Be ratios of 1.2-1.7×10⁻¹⁵, which is in the same range as 12 out of 14 samples from ACROS, MERCK, ROTH and Traceselect, but 2-3 times higher than the machine blank. This means ~5×10⁴ ¹⁰Be atoms/sample are added from chemicals-consumables-materials or laboratory air-dust.
For more quantitative results about the ¹⁰Be concentration of Al carriers and to identify the main sources of the ¹⁰Be contribution for the processing blanks, additional experiments with larger amounts of Al (10-50 mg) and chemicals are needed.
Acknowledgments: Thanks to ASTER, DREAMS, Trondheim, VERA colleagues for ¹⁰Be data, and ANU, AWI, BOKU, CENIEH, CSFK, U Bratislava, U Jerusalem, U Potsdam colleagues for carrier solutions.
References:  Merchel et al., JRNCh (2013).  Wilcken et al., NIMB (2019).  Merchel et al., NIMB (2008).  Merchel et al., MethodsX (2021).  Middleton et al., NIMB (1994).
Silke Merchel received her diploma and PhD at the University of Cologne. After Post-Doc positions at the Max-Planck-Institute for Chemistry in Mainz and the Federal Institute for Materials Research and Testing in Berlin, she was a Marie Curie Fellow at CEREGE, Aix-en-Provence. In 2008, Silke initiated the DREAMS (DREsden Accelerator Mass Spectrometry) facility at the HZDR, Dresden. Currently, she is helping at the Vienna Environmental Research Accelerator (VERA) to use ILIAMS and the 3 MV to determine (non-routine) radionuclides. Her scientific interests are improving chemical separation and AMS measurements for Earth and Planetary Research such as astrophysics, cosmochemistry and geomorphology.