GEOCHEMICAL JOURNAL
Online ISSN : 1880-5973
Print ISSN : 0016-7002
ISSN-L : 0016-7002
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
Atsunori Nakamura Atsuyuki OhtaHiroyuki MatsuzakiTakashi Okai
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JOURNAL OPEN ACCESS

2021 Volume 55 Issue 4 Pages 209-222

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Abstract

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.

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© 2021 by The Geochemical Society of Japan
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