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Atomic Nuclei: Nuclear Spin01:08

Atomic Nuclei: Nuclear Spin

5.1K
All atomic particles possess an intrinsic angular momentum, or 'spin'. Electrons, protons, and neutrons each have a spin value of ½, although protons and neutrons in nuclei may have higher half-integer spins owing to energetic factors.
Atomic nuclei have a net nuclear spin, , which can have an integer or half-integer value. In atomic nuclei, the spins of protons are paired against each other but not with neutrons, and vice versa. Consequently, an even number of protons does not contribute...
5.1K
Atomic Nuclei: Nuclear Magnetic Moment00:59

Atomic Nuclei: Nuclear Magnetic Moment

3.0K
All atomic nuclei are positively charged. When they have a nonzero spin, they behave like rotating charges. As a consequence of their charge and spin, these nuclei generate a magnetic field (B). This, in turn, gives rise to a magnetic moment (μ), which is randomly oriented in the absence of an external magnetic field. When an external magnetic field (B0) is applied, the magnetic moment vectors can align with the field or against it in 2 + 1 orientations. A hydrogen nucleus, which is just a...
3.0K
Atomic Nuclei: Nuclear Spin State Overview01:03

Atomic Nuclei: Nuclear Spin State Overview

1.9K
NMR-active nuclei have energy levels called 'spin states' that are associated with the orientations of their nuclear magnetic moments. In the absence of a magnetic field, the nuclear magnetic moments are randomly oriented, and the spin states are degenerate. When an external magnetic field is applied, the spin states have only 2 + 1 orientations available to them. A proton with = ½ has two available orientations. Similarly, for a quadrupolar nucleus with a nuclear spin value of one, the...
1.9K
Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

1.7K
Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.
1.7K
Atomic Nuclei: Larmor Precession Frequency01:11

Atomic Nuclei: Larmor Precession Frequency

3.5K
The earth's gravitational field produces a 'twisting force' perpendicular to the angular momentum of a spinning mass (such as a spinning top) that causes the mass to 'wobble' around the gravitational field axis in a phenomenon called precession. Similarly, the magnetic moment (μ) of a spinning nucleus precesses due to an external magnetic field directed along the z-axis. The precession of the magnetic moment vector about the magnetic field is called Larmor precession,...
3.5K
Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

1.1K
In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis.
1.1K

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Dual DNA Rulers to Study the Mechanism of Ribosome Translocation with Single-Nucleotide Resolution
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時間解像度の高い原子内殻スペクトロスコピー

M Drescher1, M Hentschel, R Kienberger

  • 1Institut für Photonik, Technische Universität Wien, Gusshausstrasse 27, A-1040 Wien, Austria. drescher@physik.uni-bielefeld.de

Nature
|October 25, 2002
PubMed
まとめ
この要約は機械生成です。

研究者は,アット秒解像度を使用して,原子のリラックスダイナミクスを直接測定しました. 新しいポンプ・プローブ実験により,クリプトンのM殻空白の寿命は7.9フェムト秒であると決定されました.

さらに関連する動画

Neutron Spin Echo Spectroscopy as a Unique Probe for Lipid Membrane Dynamics and Membrane-Protein Interactions
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Dual DNA Rulers to Study the Mechanism of Ribosome Translocation with Single-Nucleotide Resolution
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Neutron Spin Echo Spectroscopy as a Unique Probe for Lipid Membrane Dynamics and Membrane-Protein Interactions
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High-Resolution Neutron Spectroscopy to Study Picosecond-Nanosecond Dynamics of Proteins and Hydration Water
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科学分野:

  • 原子物理 原子物理学
  • 超高速スペクトル顕微鏡
  • 量子ダイナミクスは,量子力学である.

背景:

  • 伝統的に,原子のリラクゼーション時間は,スペクトル線幅から間接的に推論されます.
  • 以前の方法では,超高速原子動態を直接観察する時的解像度が不足していた.

研究 の 目的:

  • 原子核で興奮した原子のリラックスダイナミクスの時間定数を直接測定する.
  • 1秒分解像度の新しいポンプ探査スペクトロスコピーの技術を開発し,適用する.

主な方法:

  • 数フェムト秒の可視パルスと,同期したサブフェムト秒の柔らかいX線パルスを持つレーザーベースのサンプリングシステムを使用しました.
  • タイム・ドメイン測定のためのポンプ・プローブ実験装置を使用しました.
  • 核を刺激したクリプトン原子を研究した.

主要な成果:

  • 原子のリラックスダイナミクスをアット秒解像度でタイムドメインで直接追跡することができました.
  • クリプトンのMシェル空白の寿命は,7.9{\ -0.9}{\ +1.0}フェムト秒であると測定しました.

結論:

  • 開発されたポンプ・プローブ・テクニックは,超高速原子動力の直接観測を可能にします.
  • M-シェルの空白寿命の正確な測定を提供し,原子のリラックスプロセスに関する理解を深める.