熱い濃い鉄の音速: ビーチの法則が再考された
Jung-Fu Lin1, Wolfgang Sturhahn, Jiyong Zhao
1Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, N.W., Washington, DC 20015, USA. j.lin@gl.ciw.edu
まとめ
六角形の密集鉄 (hcp-Fe) の音速は温度とともに低下し,バーチ法に異議を唱える. これは,地球の中核に,これまで推測されたよりも多くの軽い元素があることを示唆している.
科学分野:
- 地質物理学 地質物理学とは地質物理学です.
- マテリアルサイエンス 材料科学
- 高圧物理 高圧物理
背景:
- 地球の核の組成を理解することは,地球物理学にとって極めて重要です.
- 以前のモデルは,鉄の性質を推論するために,ビーチの法則に頼っていた.
- 鉄の高圧および高温の振る舞いは,完全に理解されていません.
研究 の 目的:
- 極端な条件下で六角形の密封鉄 (hcp-Fe) の音速を測定するために.
- hcp-Fe音速の温度依存性を調査する.
- 地球のコアモデリングにおけるビーチの法則の妥当性を評価する.
主な方法:
- 核不弾性X線散射 (NIXS) が採用されました.
- 実験は,レーザーで加熱されたダイヤモンド・アンビル・セルで実施された.
- 測定対象は,最大73GPaの圧力,最大1700Kの温度でした.
主要な成果:
- hcp-Feの圧縮波 (VP) と切断波 (VS) の速度を決定した.
- VPとVSの両方が,温度の上昇とともに,適度な圧力で有意に減少した.
- 線形関係 (Birch's law) は,高圧と高温でデータを記述できませんでした.
結論:
- hcp-Fe音速の温度依存は,線形抽出モデルから逸脱する.
- ビーチの法則は,音速を地球の中核条件に推論するには不十分である.
- この発見は,地球の中核の軽い元素の豊富性が,これまで考えられていたよりも高いことを示唆している.
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