¹⁰Be/⁹Be ratios of phenakite and beryl measured via direct Cs sputtering: Implications for selecting suitable Be carrier minerals for the measurement of low-level ¹⁰Be

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Preparing Be carrier solutions with low ¹⁰Be/⁹Be ratios is essential for the applications of in-situ-produced cosmogenic ¹⁰Be in geochronology. This is because commercially available Be carriers are non-negligibly contaminated by ¹⁰Be. Recently, in-house Be carriers have been successfully applied to samples that contain small amounts of in-situ-produced ¹⁰Be. The first step in preparing in-house Be carriers is selecting suitable Be-bearing minerals that contain less ¹⁰Be. Here, we present a simple method for selecting appropriate raw minerals for in-house Be carriers. That is, measuring the ¹⁰Be/⁹Be ratios of Be-bearing minerals by direct Cs sputtering. Analyses of the ¹⁰Be/⁹Be ratios of phenakite (Be₂SiO₄) and beryl (Be₃Al₂Si₆O₁₈) obtained from a mineral collection at the Geological Survey of Japan indicate that phenakite generally contains more ¹⁰B, interfering isobar of ¹⁰Be, than beryl. In addition to the necessity of finding raw materials that contain low ¹⁰Be, our results indicate that it is preferable to select a starting material with a low B concentration. Fragments of Be-bearing minerals from target samples were directly packed, and showed effective beam currents. Therefore, we anticipate that the direct packing method can also potentially be used to measure ¹⁰Be in Be-bearing minerals for geological applications. The measurement background of accelerator mass spectrometry was evaluated using a B-removed Be carrier solution. While B is partly adhered to hydroxide gel, we demonstrate that the hydroxide gel wash reduces B in a Be carrier solution. To highlight the ¹⁰Be/⁹Be ratios of Be-bearing minerals against commercially available Be solutions, we also investigated the ¹⁰Be/⁹Be ratios of commercially available Be solutions.