Larmor precession magnetic field

LARMOR PRECESSION MAGNETICALLY ANISOTROPIC GROUP MAGNETOTACTIC Magnetic field strength,... 

Following Figure 11, we now analyze in detailed the NSE instmment and the connection of measured intensities with the neutron scattering function. The precession angle before and after, the sample and the -flipper, respectively, is proportional to the time the neutron stays in the precession magnetic field. Each infinitesimal section of the path Af hosts the neutron during At = Af/v with the neutron velocity v = (hjm X and thereby contributes AT = y B(l) At with the Larmor constant y = 2 r X 2913.06598 X lO rads f and B(() the local magnetic field (induction). The full path (1=1, 2) then contrihutes... 

Figure 1.1. Nuclear precession nuclear charge and nuclear spin give rise to a magnetic moment of nuclei such as protons and carbon-13. The vector n of the magnetic moment precesses in a static magnetic field with the Larmor frequency vo about the direction of the magnetic flux density vector Bo...

The quantitative formulation of chemical exchange involves modification of the Bloch equations making use of Eq. (4-67). We will merely develop a qualitative view of the result." We adopt a coordinate system that is rotating about the applied field Hq in the same direction as the precessing magnetization vector. Let and Vb be the Larmor precessional frequencies of the nucleus in sites A and B. Eor simplicity we set ta = tb- As the frequency Vq of the rotating frame of reference we choose the average of Va and Vb, thus. 

The frequency with which a nucleus precesses around the applied magnetic field is called its Larmor frequency or Larmor processional... 

In order for relaxation to occur through Wj, the magnetic field fluctuations need to correspond to the Larmor precession frequency of the nuclei, while relaxation via requires field fluctuations at double the Larmor frequency. To produce such field fluctuations, the tumbling rate should be the reciprocal of the molecular correlation time, i.e., f), so most efficient relaxation occurs only when voT, approaches 1. In very small, rapidly tumbling molecules, such as methanol, the concentration of the fluctuating magnetic fields spectral density) at the Larmor frequency is very low, so the relaxation processes Wj and do not occur efficiently and the nuclei of such molecules can accordingly relax very slowly. Such molecules have... 

Precession A characteristic rotation of the nuclear magnetic moments about the axis of the applied magnetic field Bo at the Larmor frequencies. Preparation period The first segment of the pulse sequence, consisting of an equilibration delay. It is followed by one or more pulses applied at the beginning of the subsequent evolution period. 

Unlike these conventional techniques, NSE measures the neutron velocities of the incident and scattered neutrons using the Larmor precession of the neutron spin in an external magnetic field, whereby, the neutron spin vector acts like the hand of an internal clock, which is linked to each neutron and stores the result of the velocity measurement at the neutron itself. The velocity measurement is thus performed individually for each neutron. For this reason, the... 

Larmor frequency The exact frequency at which nuclear magnetic resonance occurs. At this frequency, the exciting frequency matches that of the precession of the axis of the spin of the nucleus about the applied magnetic field. 

Larmor precession The motion describing the rotation of the axis of the spin of a nucleus in a magnetic field. 

Fig. 2. Illustration of the Larmor precession of a magnetic moment m in a field H with the rf field Hi perpendicular to H as in magnetic resonance.

The precession observed in a plane of an electron orbit of an atom when that atom hes within a uniform magnetic field. The plane will precess about the direction of the field such that a cone is traced out having an axis normal to the direction of the field. The frequency of this precession is usually symbolized by j l and is equal to eBI (Aimtc) where e is the electron charge, B is the field strength, m is the mass, and c is the velocity of the electron. Larmor precession is also important in NMR studies of enzymes. 

When exposed to a static magnetic field B0, a spinning nucleus behaves like a gyroscope in a gravitational field. As illustrated by Fig. 1.2, the spin axis - which coincides with the magnetic moment vector p - precesses about B0. The frequency of precession, v0, is known as the Larmor frequency of the observed nucleus. 

Fig. 1.2. Larmor precession of a spinning nucleus in a static magnetic field.

In contrast to bar magnets, the magnetic moments of spinning nuclei do not align in the direction of B0, no matter how strong this field is. Instead, the Larmor precession is accelerated by increasing the strength B0 of the field vector B0 ... 

An alternating magnetic field Bl with frequency irradiating an ensemble of nuclear spins precessing in the static field B0 may overcome the energy difference AE if it meets two conditions The vector of the alternating field B1 must rotate in the plane of precession with the Larmor frequency v0 of the nuclei to be observed (Fig. 1.4(a)). 

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