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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Bargmann–Michel–Telegdi equation ： ウィキペディア英語版 Larmor precession In physics, Larmor precession (named after Joseph Larmor) is the precession of the magnetic moment of any object with a magnetic moment about an external magnetic field. Objects with magnetic moments have angular momentum and internal currents of electric charge related to their angular momentum; these include electrons, protons, other fermions, many atomic and nuclear systems, as well as classical macroscopic systems. The magnetic field exerts a torque on the magnetic moment, :$\backslash vec\; =$ \vec\times\vec= \gamma\vec\times\vec where $\backslash vec$ is the torque, $\backslash vec$ is the magnetic dipole moment, $\backslash vec$ is the angular momentum vector, $\backslash vec$ is the external magnetic field, $\backslash times$ symbolizes the cross product, and $\backslash \; \backslash gamma$ is the gyromagnetic ratio which gives the proportionality constant between the magnetic moment and the angular momentum. The phenomenon is similar to the precession of a tilted classical gyroscope in an external gravitational field. ==Larmor frequency== The angular momentum vector $\backslash vec$ precesses about the external field axis with an angular frequency known as the Larmor frequency, :$\backslash omega\; =\; -\backslash gamma\; B$ where $\backslash omega$ is the angular frequency,〔Spin Dynamics, Malcolm H. Levitt, Wiley, 2001〕 and $B$ is the magnitude of the applied magnetic field. $\backslash gamma$ is (for a particle of charge $-e$) the gyromagnetic ratio, equal to $-\backslash frac$, where $m$ is the mass of the precessing system, while $g$ is the g-factor of the system. The g-factor is the unit-less proportionality factor relating the system's angular momentum to the intrinsic magnetic moment; in classical physics it is just 1. In nuclear physics the g-factor of a given system includes the effect of the nucleon spins, their orbital angular momenta, and their couplings. Generally, the g-factors are very difficult to calculate for such many-body systems, but they have been measured to high precision for most nuclei. The Larmor frequency is important in NMR spectroscopy. The gyromagnetic ratios, which give the Larmor frequencies at a given magnetic field strength, have been measured and tabulated (here ). Crucially, the Larmor frequency is independent of the polar angle between the applied magnetic field and the magnetic moment direction. This is what makes it a key concept in fields such as nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR), since the precession rate does not depend on the spatial orientation of the spins. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Larmor precession」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.