高温の205T1崩壊は,太陽系初期にPbが存在していたことを明らかにする
Guy Leckenby1,2, Ragandeep Singh Sidhu3,4,5, Rui Jiu Chen6,7,8
1TRIUMF, Vancouver, British Columbia, Canada. guy.leckenby@gmail.com.
Nature
|November 13, 2024
まとめ
鉛205 (Pb-205) を使用した隕石の放射性年代測定は,太陽の誕生環境を決定するのに役立ちます. 稀な核崩壊の新しい測定は,正確なPb-205の生産速度を提供し,太陽物質の隔離時間を明らかにします.
科学分野:
- 核天体物理学
- 宇宙化学
- 恒星核合成
背景:
- 隕石の長寿放射性核は 太陽の形成と核合成の洞察力を与えてくれます
- 鉛-205 (Pb-205) はアシンプトティック・ジャイアント・ブランチ (AGB) の恒星でゆっくりとした中性子捕獲 (s-プロセス) により合成されるが,その豊富さの予測は不確実な崩壊率によって制限されている.
- Pb-205とタリウム-205 (Tl-205) の正確な崩壊率は,初期の太陽系年代表を理解するために重要である.
研究 の 目的:
- 実験的にPb-205とTl-205の崩壊速度を制限する.
- その親分子雲の内にある太陽物質の隔離時間を決定する.
- Pb-205/Tl-205の崩壊システムを 初期太陽系のクロノメーターとして検証する
主な方法:
- 完全にイオン化されたTl-205 (Tl-205^81+) の結合状態ベータマイナス崩壊を初めて測定した.
- 実験的に制限された衰退率を持つAGB恒星モデルを使用して,Pb-205の収量を計算した.
- 集積された銀河化学進化 (GCE) モデルで,計算された収量と隕石同位体比 (Pb-205/Pb-204) を用いて,分離時間を決定する.
主要な成果:
- Tl-205^81+の測定半減期は理論的な推定値の4. 7倍で,実験上の不確実性は10%であった.
- 新しいPb-205の産量は,実験的に検証された衰退率を用いて計算された.
- 陽性分離時間は,初期の太陽系の他の短命放射性核と一致しています.
結論:
- この研究は,Pb-205の豊富さを予測する核物理学の主要な制限を解決します.
- この発見は 太陽が長生きした 巨大な分子雲の中で生まれたことを 裏付けています
- Pb-205/Tl-205崩壊系は,初期の太陽系にとって貴重なクロノメーターであると確認されています.
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