ベンゼン－液体シンチレーション法における<sup>14</sup>C計数効率の経時変化

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  • 堀 真子
    広島大学大学院理学研究科地球惑星システム学専攻
  • 近藤 久雄
    産業技術総合研究所活断層研究センター
  • 奥村 晃史
    広島大学大学院文学研究科地理学専攻

書誌事項

タイトル別名
  • Temporal reduction in radiocarbon counting efficiency evaluated by a Benzene-liquid scintillation method
  • ベンゼン-液体シンチレーション法における14C計数効率の経時変化
  • ベンゼン エキタイ シンチレーションホウ ニ オケル 14C ケイスウ コウリツ ノ ケイジ ヘンカ

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説明

To assess the reliability of the Liquid Scintillation Counting method, we monitored the weight and counting ratio of a benzene sample (STD059) prepared in 2000. Both benzene weight and the counting ratio generally decreased during the 2 years of analysis, at rates of 7 mg/yr and 0.073 cpm/gC/yr, respectively. The total decrease in the counting ratio was 97% of the initial value, as calculated using a linear approximation. The counting efficiency of STD059 was 71–73%, less than that for IAEA standards prepared in 2006–2007 (74.3–78.5%). Spectral quenching parameters (SQP) and Channel ratios (R) were similar between the STD059 and IAEA standards (C-1 to C-5), suggesting insignificant quenching of STD059. The temporal reduction in counting efficiency was possibly caused by density quenching, although the scintillator concentration of the solvent was lower than 15.9 g/L during the study period. According to the counting efficiency of STD059, we determined that the 14C activities of the IAEA standards were within 0.10-1.81 pMC of the values recommended by Rozanski et al. (1992), while the C-1 and C-4 samples showed~2% of modern carbon contamination, which resulted in a +1.0 pMC excess.

収録刊行物

  • 地質学雑誌

    地質学雑誌 115 (11), 614-619, 2009

    一般社団法人 日本地質学会

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