ルテチウム-ハフニウム時計の校正
まとめ
新しい測定により,ルテシウム-176の崩壊定数 (λ176Lu) が精製され,地質年代学に影響を与えています. この修正された定数は,地球が地球であることを示唆しています.
科学分野:
- 地質化学 地質化学
- ジオクロノロジー (Geochronology) について
- 同位体地質学とは,同位体地質学である.
背景:
- 放射性崩壊定数は,地球年代論と惑星の分化を理解する上で極めて重要です.
- 古代の岩石や鉱物の年代測定には,正確な崩壊定数が不可欠です.
研究 の 目的:
- 精密にルテシウム-176の崩壊定数 (λ176Lu) を,ウラン-鉛の崩壊計画による校正によって決定する.
- ルーテシウム-ハフニウム (Lu-Hf) の年齢と最初のハフニウム同位体組成を,新しい崩壊定数を使用して再評価する.
主な方法:
- ルテシウム-176の崩壊定数 (λ176Lu) の4つの新しい決定が行われました.
- カリブレーションは,既定のウラン-鉛の崩壊計画に対して行われました.
- 新しい崩壊定数は,Lu-Hf年齢と初期Hf同位体組成を計算するために適用されました.
主要な成果:
- ルテシウム-176の崩壊定数 (λ176Lu) の新しい平均値は1.865 ± 0.015 x 10−11年−1.1と決定されました.
- この値は,最近の崩壊計算実験と一致していますが,以前に使用された値とは異なります.
- 古い定数で計算したLu-Hf年齢は,新しい定数から得られたものより約4%若い.
結論:
- 以前計算されたLu-Hf年齢は,体系的に若すぎます.
- 古代の地上の物質の初期ハフニウム同位体組成は,これまで考えられていたよりも放射性性が低い.
- ハーデア紀と初期のアルケア紀のジルコンに非放射性ハフニウムの存在は,43億年前の早期の地殻の分化を示し,初期の地球分化モデルを改訂する必要がありました.
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