R. V. Pound

Bio: R. V. Pound is an academic researcher from Harvard University. The author has contributed to research in topics: Relaxation (NMR) & Quadrupole. The author has an hindex of 11, co-authored 16 publications receiving 2048 citations.

Influence of electric and magnetic fields on angular correlations

Abstract: The theory of the influence on angular correlations of perturbing interactions in the intermediate state is reformulated to allow the description of the effects of time-dependent as well as of static perturbations. For static interactions of the nuclear electric quadrupole moment with crystalline fields of axial symmetry in polycrystalline sources, attenuation factors are calculated for the coefficients of the various terms in the expansion of the correlation function in Legendre polynomials. No matter how strong the quadrupole interaction, some anisotropy must remain for polycrystalline sources but, for the same interaction in simple single crystals, the anisotropy can be either undisturbed or completely destroyed, depending on the orientation of the crystal. Fields of lower symmetry are shown also to leave, for polycrystalline sources, some anisotropy. Expressions for the influence of randomly fluctuating interactions, such as must exist in liquid sources, are calculated and these predict arbitrarily complete destruction of the correlation under certain conditions, but explain the more nearly unperturbed results usually found with such sources. For electronic shells having magnetic moments, the influences of electronic paramagnetic relaxation and of anisotropy of the hyperfine structure interaction are examined. An applied static magnetic field in the presence of static quadrupole interactions in polycrystalline sources is shown to have differing effects depending on the relative strengths of the two interactions. Application of a magnetic field directed toward a counter cannot reduce the disturbance of the intermediate state in liquid sources, except under special circumstances. The influences of an applied field in the presence of time dependent anisotropic hyperfine structure interactions are discussed. Finally, the feasibility of resonance experiments, for the precise determination of nuclear moments in the intermediate state, is explored.

Radiation Damping in Magnetic Resonance Experiments

Abstract: Magnetic resonance experiments can be described by analogy to a coupled pair of circuits, one of which is the ordinary electrical resonant circuit. The other circuit is formed by the rotating magnetization. For transient phenomena, such as occur, e.g., in the pulse techniques of free nuclear induction, the coupling gives rise to a damping of the magnetic resonance by the electric circuit. Such damping can also be considered as spontaneous radiation damping. It is shown that in certain cases of nuclear induction this radiation damping is more important than the damping from the spin-spin and the spin-lattice relaxation mechanisms usually considered. For ferromagnetic materials at microwave frequencies the radiation damping can become very large.

Nuclear Electric Quadrupole Interactions in Crystals

Abstract: A study is made of the effects of the presence of nuclear electric quadrupole moments on the nuclear magnetic resonance absorption in solids. Necessary theoretical background is followed by descriptions of experiments in which the spectra obtained with an r-f spectrograph, described elsewhere, are found to show marked splitting resulting from the quadrupole interaction with the electric field gradient. Both powder patterns and spectra of single crystals are reported, for ${\mathrm{Li}}^{7}$, ${\mathrm{Na}}^{23}$, and ${\mathrm{Al}}^{27}$, with splittings varying from about 20 kc to 718 kc, depending on the crystal and the nucleus. Unambiguous indication of the spin values is obtained. The possibility of the detection of a resonance resulting from the electric quadrupole splittings in the absence of a static magnetic field is discussed and an unsuccessful attempt to find such a resonance in ICl is described and the failure tentatively explained. Available signal-to-noise ratios are calculated for such resonances. A method is described of determining the frequency of a large electric quadrupole splitting, by observation of the dependence of the frequency of the magnetic splitting of the levels $m=\ifmmode\pm\else\textpm\fi{}\frac{1}{2}$, for an odd half-integral spin, on the angle between the direction of a magnetic field and the symmetry axis of the crystalline field. The electric quadrupole moment is shown probably to account for relaxation times of nuclei of spin greater than \textonehalf{} even in cubic crystals and, as evidence, resonances of ${\mathrm{Na}}^{23}$, ${\mathrm{Li}}^{7}$, ${\mathrm{I}}^{127}$, and ${\mathrm{Br}}^{81}$ are reported. Assuming partial saturation and electric quadrupolar relaxation, calculations are made to account for a departure of the intensity ratios of the lines, in the ${\mathrm{Na}}^{23}$ spectrum in NaN${\mathrm{O}}^{3}$, from the ratios of the transition probabilities for magnetic dipole radiation. The possibility of determining nuclear electric quadrupole moments from splittings or relaxation times in ionic crystals is discussed.

Effect of Gravity on Gamma Radiation

Abstract: Recoil-free resonant absorption of the 14.4-keV $\ensuremath{\gamma}$ ray in ${\mathrm{Fe}}^{57}$ has been employed to measure the effect of gravity over a 75-ft vertical path in the Jefferson Laboratory, in an improved version of the experiment of Pound and Rebka. A ${\mathrm{Co}}^{57}$ source, initially 1.25 Ci, large-windowed proportional counters, and an enriched absorber foil 15 in. in diameter permitted a much increased counting rate. The employment of temperature-regulated ovens for source and absorbers and a redesigned monitor system to detect variations in waveform of the source velocity effected a reduction in systematic uncertainties. The result found was (0.9990\ifmmode\pm\else\textpm\fi{}0.0076) times the value ${4.905\ifmmode\times\else\texttimes\fi{}10}^{\ensuremath{-}15}$ of $\frac{2gh}{{c}^{2}}$ predicted from the principle of equivalence. The range given here is the statistical standard deviation set by the number of counts involved. An estimated limit of systematic error is 0.010.

Theory and Experiment in Gravitational Physics

Abstract: New technological advances have made it feasible to conduct measurements with precision levels which are suitable for experimental tests of the theory of general relativity. This book has been designed to fill a new need for a complete treatment of techniques for analyzing gravitation theory and experience. The Einstein equivalence principle and the foundations of gravitation theory are considered, taking into account the Dicke framework, basic criteria for the viability of a gravitation theory, experimental tests of the Einstein equivalence principle, Schiff's conjecture, and a model theory devised by Lightman and Lee (1973). Gravitation as a geometric phenomenon is considered along with the parametrized post-Newtonian formalism, the classical tests, tests of the strong equivalence principle, gravitational radiation as a tool for testing relativistic gravity, the binary pulsar, and cosmological tests.

Proton Relaxation Times in Paramagnetic Solutions. Effects of Electron Spin Relaxation

Abstract: The proton relaxation time in solutions of paramagnetic ions depends, among other factors, on the relaxation time of the electron spins, τs. It is shown that the latter, for ions of the iron group, is determined mostly by the distortion of the hydrated complex by collisions with other water molecules. The theory provides a quantitative explanation for the decrease in T2 in Mn++ (and other) solutions in very high magnetic fields. The experimentally observed field and temperature dependence of the proton relaxation times, T1 and T2, for ions of the iron group is compared with theory and the features which depend on τs are stressed.

Geometrical Representation of the Schrödinger Equation for Solving Maser Problems

Abstract: A simple, rigorous geometrical representation for the Schrodinger equation is developed to describe the behavior of an ensemble of two quantum‐level, noninteracting systems which are under the influence of a perturbation. In this case the Schrodinger equation may be written, after a suitable transformation, in the form of the real three‐dimensional vector equation dr/dt=ω×r, where the components of the vector r uniquely determine ψ of a given system and the components of ω represent the perturbation. When magnetic interaction with a spin ½ system is under consideration, ``r'' space reduces to physical space. By analogy the techniques developed for analyzing the magnetic resonance precession model can be adapted for use in any two‐level problems. The quantum‐mechanical behavior of the state of a system under various different conditions is easily visualized by simply observing how r varies under the action of different types of ω. Such a picture can be used to advantage in analyzing various MASER‐type devi...

Quadrupole Effects in Nuclear Magnetic Resonance Studies of Solids

Abstract: Publisher Summary This chapter discusses quadrupole effects in nuclear magnetic resonance studies of solids. The first evidence that many nuclei possess magnetic moments came from the study of the hyperfine structure of atomic spectra in the visible region. The interaction of the nuclear magnetic moment with the magnetic field produced by the atomic electrons gives rise to a hyperfine spectrum that is relatively simple, being characterized by the well known “interval rule.” Marked departures from this interval rule do occur in a few cases, however, and some of the departures can definitely be attributed to the presence of a nuclear electric quadrupole interaction. The methods of radio-frequency spectroscopy are very well adapted for the investigation of the very small interaction energies to which nuclear moments give rise. They have led not only to much more precise determinations of nuclear magnetic moments, but also to a vastly increased knowledge of nuclear electric quadrupole effects. The first outstanding success along this line was the discovery, by the molecular beam resonance method, of the quadrupole moment of the deuteron. The field of electric quadrupole interactions in nuclear magnetic resonance can be divided roughly into two areas according to the relative magnitude of the nuclear quadrupole interactions.