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Spin waves
Published in A.G. Gurevich, G.A. Melkov, and Waves, 2020
where z0 is a unit vector in the direction of M0. Magnons being the elementary excitations of the electronic magnetic system, we can believe that the magnetomechanical ratio γ of magnons should be the same as for electrons. It follows, then, from (7.74) that magnons are quasiparticles with the moment of momentum (spin) equal to unity. The particles with an integer spin obey the Bose–Einstein statistics (e.g., [244]). If the total number of particles (or quasiparticles) in the system is not fixed, which is the case for magnons, the chemical potential for the system is to be set to zero. Then, the number of particles in a state with energy ε (the distribution function) is [244] () n¯=1exp(ε/κT)−1.
Magnetic Resonance Imaging
Published in Suzanne Amador Kane, Boris A. Gelman, Introduction to Physics in Modern Medicine, 2020
Suzanne Amador Kane, Boris A. Gelman
When a system responds preferentially to one characteristic frequency, we say it exhibits a resonance. Consequently, the preferential absorption or emission of photons of only certain frequency waves by nuclear magnetic dipoles is called nuclear magnetic resonance (NMR). The resonance frequency for nuclear dipole transitions between spin-up and spin-down energy states is given by, fres=ΔEh=2μphB where we use the energy difference between the proton spin-up and spin-down states in an external magnetic field given in Equation 8.2. Transitions between the spin-up and spin-down states are often referred to as spin flips.
The Theory of Atom of Hydrogen
Published in Mikhail G. Brik, Chong-Geng Ma, Theoretical Spectroscopy of Transition Metal and Rare Earth Ions, 2019
Mikhail G. Brik, Chong-Geng Ma
By spin in quantum mechanics is meant an angular momentum, which is an intrinsic property of an object (it should be distinguished from the orbital angular momentum related to the motion of its center of mass about some point which does not coincide with the center of mass). The concept of the electron spin was introduced in 1925 by two Dutch physicists S. A. Goudsmit* and G. E. Uhlenbeck. Figure 3.5 shows a schematic picture (though not completely physically correct!), which may help to illustrate the concept of spin. If a particle simultaneously with the rotation about a point O rotates about its own axis (as shown in the figure), then the angular momentum associated with such a rotation can be thought of as some analogy of spin in quantum mechanics.
Effects of quantum mechanical identity in particle scattering: experimental observations (and lack thereof)
Published in Journal of the Royal Society of New Zealand, 2021
In the quantum description of systems of particles two categories are encountered: particles with half-integer spin, called fermions, and particles with integer spin, called bosons. The quantum mechanical wave function for a system of identical bosons is required to be symmetric under the permutations of two particles. In contrast, the quantum mechanical wave function for a system of identical fermions is required to be antisymmetric under the permutations of two particles. This is the basis of the Pauli exclusion principle which forbids two identical fermions to occupy the same quantum state and for example accounts for the ordering of electrons into shells in atoms: the electron has spin 1/2 (and is consequently a fermion) with the two possible spin projections (spin-up) and (spin-down) – hence there can be exactly two in the innermost shell.