Kinetics of positron annihilation in ionic crystals

A kinetic scheme of decay of positron and positronium states for the general case — a real ionic crystal with point lattice defects and a developed surface — is examined. The properties of positron and positronium states in the volume of the crystal, positron and positronium color centers, and surface positron and positronium states, are analyzed. It is shown that all the available experimental data qualitatively confirm the conclusion of an annihilation mechanism based on the postulated kinetic scheme of positron annihilation in real ionic crystals.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 50–55, September, 1977.     

Positronium atom in an ionic crystal

The Sommerfeld-Welker model of a hydrogen atom in a spherical, impenetrable force cavity is used to calculate the basic properties of positronium in an ionic crystal. The basic properties of positronium (the lifetime against 2- and 3-annihilation, the count rate of 3 coincidences, and the magnetic-quenching parameter) are found as functions of the radius of the spherical force cavity.Translated from Izvestiya VUZ. Fizika, No. 7, pp. 71–75, July, 1970.     

Bounds on the correlations and analyticity properties of ferromagnetic Ising spin systems

We consider a ferromagnetic Ising spin system isomorphic to a lattice gas with attractive interactions. Using the Fortuin, Kasteleyn and Ginibre (FKG) inequalities we derive bounds on the decay of correlations between two widely separated sets of particles in terms of the decay of the pair correlation. This leads to bounds on the derivatives of various orders of the free energy with respect to the magnetic fieldh, and reciprocal temperature . In particular, if the pair correlation has an upper bound (uniform in the size of the system) which decays exponentially with distance in some neighborhood of (,h) then the thermodynamic free energy density (,h) andall the correlation functions are infinitely differentiable at (,h). We then show that when only pair interactions are present it is sufficient to obtain such a bound only ath=0 (and only in the infinite volume limit) for systems with suitable boundary conditions. This is the case in the two dimensional square lattice with nearest neighbor interactions for 0<₀, where ₀ ^–1 is the Onsager temperature at which (,h=0) has a singularity. For >₀, (,h)/h is discontinuous ath=0, i.e. ₀=_c, where _c ^–1 is the temperature below which there is spontaneous magnetization.Research supported by AFOSR Contract # F 44620-71-C-0013.     

Green's functions for off-shell electromagnetism and spacelike correlations

The requirement of gauge invariance for the Schwinger-DeWitt equations, interpreted as a manifestly covariant quantum theory for the evolution of a system in spacetime, implies the existence of a five-dimensional pre-Maxwell field on the manifold of spacetime and proper time . The Maxwell theory is contained in this theory; integration of the field equations over restores the Maxwell equations with the usual interpretation of the sources. Following Schwinger's techniques, we study the Green's functions for the five-dimensional hyperbolic field equations for both signatures ± [corresponding to O(4, 1) or O(3, 2) symmetry of the field equations] of the proper time derivative. The classification of the Green's functions follows that of the four-dimensional theory for massive fields, for which the mass squared may be positive or negative, respectively. The Green's functions for the five-dimensional field are then given by the Fourier transform over the mass parameter. We derive the Green's functions corresponding to the principal part _P and the homogeneous function ₁ ; all of the Green's functions can be expressed in terms of these, as for the usual field equations with definite mass. In the O(3, 2) case, the principal part function has support for x²², corresponding to spacelike propagation, as well as along the light cone x²=0 (for =0). There can be no transmission ofinformation in spacelike directions, with this propagator, since the Maxwell field, obtained by integration over , does not contain this component of the support. Measurements are characterized by such an integration. The spacelike field therefore can dynamically establish spacelike correlations.     

Quasi-free “second quantization”

Araki and Wyss considered in 1964 a mapAQ(A) of one-particle trace-class observables on a complex Hilbert-space into the fermionC*-algebraU() over . In particular they considered this mapping in a quasi-free representation.We extend the mapAQ(A) in a quasi-free representation labelled byT, 0TI, to allAB()_sa such that tr(T A(1–T)A)< withQ(A) now affiliated with the algebra. This generalizes some well-known results of Cook on the Fock-representationT=0.     

Electric Dipole Moment Function of the OH Molecule

The electric dipole moment function of the OH radical in the ground electronic state is constructed for internuclear distances R [0, ]. The electric dipole moment function is represented as a piecewise continuous function satisfying physically exact asymptotes and experimental values of the electric dipole moment and its derivatives for equilibrium positions of nuclei of the radical. The Padé form for the electric dipole moment function of the OH radical is also approximated. Electric dipole moment functions obtained are compared with the results of ab initio calculations.     

Study of (Al2O3)n(Ox) clusters with n = 16 and x = 0, 1, 2 from first principles calculations

The ionic and electronic structure of (Al₂O₃)_n(O_x) clusters with n 16 and x = 0, 1, 2 is studied by means of first principles density functional calculations, norm-conserving pseudopotentials and a numerical atomic basis set. The equilibrium geometries have been determined by total energy minimization, starting with several initial geometries for each cluster size. The trends obtained for the atomic arrangements (structural isomers, coordination numbers, disordered versus ordered structures, etc.) and the electronic properties (binding energies, Homo-Lumo gap and dipole moments) are discussed. For most of the oxidized clusters studied here we find that the Homo-Lumo gap and the magnitude of dipole moment of isomeric species can vary drastically.     

Crossover to tricritical behavior at the nematic to smecticA transition: An x-ray scattering study

We have carried out a comprehensive x-ray scattering study of the nematic to smecticA transition in the alkylbenzoate (nCB) and thiosulfate series. By changing the aliphatic chain lengthn (C _n H_2n+1) in these series, crossovers from critical to tricritical behavior are induced. We observe a smooth progression of effective exponents from the set,y1.5,v 0.80, andv 0.67 toy=1.1,v =0.6, andv =0.5 for the critical and tricritical regions respectively. In both cases the exponents are close to, but in disagreement with, values expected from current theoretical models. We conclude on an empirical basis that the varied exponents reported in the literature for other systems reflect the critical to tricritical crossover.     

Angular distribution of the soft component of radiation from relativistic electrons near planar orientation in thick single crystals

The Tomsk synchrotron has been used to carry out an experimental study of the soft component (30 MeV) of the radiation from relativistic electrons in diamond, silicon, and tungsten single crystals. It is shown that a component of the radiation associated with channeling emission from electrons trapped inside the crystal can be distinguished because of angular selection. It is found that the linear density of the radiation from the electrons which must be trapped in planar channeling inside the crystal because of multiple scattering is substantially reduced in comparison with the linear density of the radiation from electrons trapped in this regime in the surface layer of the crystal. It is shown that the quasirefraction of an electron beam by the planar potential in thick single crystals leads to effective reflection of electrons.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 70–80, June, 1991.     

Electromagnetic radiation of relativistic electrons in thick crystals

Angular distributions of soft gamma quanta and spectra of electron radiation intensity are compared in diamond crystals of various thickness for axial orientation. Narrow directionality of the soft gamma quanta and a weak dependence of angular width of the distribution on crystal thickness are noted. For axial orientation the angular width of the soft gamma quantum distribution comprises ± 2_L for diamond, silicon, and tungsten crystals. Radiation losses into the collimator _c = 1/ for axial orientation increases with thickness and reach their maximum value at t 0.1 radiation length. It is shown experimentally that maximum values of radiation loss into the cone ^–1 can be achieved in crystals of the light-elements.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 32–38, September, 1986.     

The magnetic dipole moment of the 150 keV state of177Lu

The magnetic dipole interaction of the 150 keV state of¹⁷⁷Lu in an environment of metallic ytterbium has been investigated by time-differential perturbed angular correlation experiments. The measurements were performed in an external magnetic field of 0.4 T at room temperature. Two independent measurements at different - cascades give the same Larmor precession frequency. From the weighted average the magnetic dipole moment of the 150 keV state is derived as =+5.5(3) _K. From the angular correlation coefficient A₂₂=–0.042(7) of the (139–150) keV - cascade the mixing ratio =+0.21(4) is deduced. The coefficient A₂₂=+0.015(7) of the (1080–150) keV - cascade yields the mixing ratio =+0.08(4).     

Propagation and spreading of unstable perturbations in electron-hole plasmas subject to crossed fields

A model is developed for electrostatic drift instabilities which arise in inhomogeneous electron-hole plasmas subject to crossed fieldsE ₀B ₀. The instabilities are initiated by gradients in the equilibrium plasma densityn ₀. Using two-fluid magnetohydrodynamics and linear perturbation theory the dispersion relation of local density oscillations is calculated for arbitrary inhomogeneous equilibrium distributions and plasma densities. For cases wheren ₀B ₀ andn ₀ ⁺ n ₀ ^- it is found that the propagation direction of maximal gain, , is the bisectrix of the angle between (–n ₀) and (E ₀ ×B ₀) and that stable and unstable configurations are distinguished by the angle between ₀ andn ₀. A local density perturbation built by superpositions of the plane waves, and initially chosen radially symmetric, broadens unisotropically. In the direction transverse to the broadening is anomaleously enhanced, as compared to the broadening by diffusion in the stable case. The results are referred to experimental observations of low-frequency instabilities reported in [1].     

Dielectric loss relaxation maxima of undoped and calcium doped NaCl crystals between 20 and 400°C

When studying the dielectric loss dependence of undoped (pure) and CaCl₂ doped NaCl crystals on temperature and frequency, some further maxima were observed apart from the wellknown relaxation maxima of calcium complexes. The temperature of these maxima shifts with rising calcium content to lower temperatures (from 259 to 142°C), whereas the value of the maxima does not change with concentration and remains unchanged even with the purest crystals. It seems probable that the observed maxima are due to the relaxation loss of the crystal lattice itself.     

Temperature measurement using degenerate four-wave mixing with non-saturating laser powers

We report the use of Degenerate Four-Wave Mixing (DFWM) in the OHA ^{2 +} X ² ( = 0 = 0) band for temperature determination in a propane/air flame using laser powers below the saturation level. We show that at these low power levels the dependence of the signal on the dipole moment for the transition has to be established before meaningful temperature data can be obtained. This presents a paradox in that the temperature has to be known before the form of the dependence on the dipole moment can be determined. Solutions to this paradox are presented. We also show that absorption of the laser beams in this OH band system cannot be neglected and that failure to correctly account for the absorption leads to a large over estimate of the flame temperature. Furthermore, we show that the accuracy of the absorption-corrected temperature is critically dependent on the accuracy with which the measurement position within the flame is known. Finally, the temperature calculated from DFWM spectra using the correct dipole moment power and absorption is compared to the temperatures obtained using Laser-Induced Fluorescence (LIF) and Coherent Anti-Stokes Raman Spectroscopy (CARS).     

Stationary non-equilibrium states of infinite harmonic systems

We investigate the existence, properties and approach to stationary non-equilibrium states of infinite harmonic crystals. For classical systems these stationary states are, like the Gibbs states, Gaussian measures on the phase space of the infinite system (analogues results are true for quantum systems). Their ergodic properties are the same as those of the equilibrium states: e.g. for ordered periodic crystals they are Bernoulli. Unlike the equilibrium states however they are not stable towards perturbations in the potential.We are particularly concerned here with states in which there is a non-vanishing steady heat flux passing through every point of the infinite system. Such superheat-conducting states are of course only possible in systems in which Fourier's law does not hold: the perfect harmonic crystal being an example of such a system. For a one dimensional system, we find such states (explicitely) as limits, whent, of time evolved initial states _i in which the left and right parts of the infinite crystal are in equilibrium at different temperatures, _L ^–L _R ^–1 , and the middle part is in an arbitrary state. We also investigate the limit of these stationary (t) states as the coupling strength between the system and the reservoirs goes to zero. In this limit we obtain a product state, where the reservoirs are in equilibrium at temperatures _L ^–1 and _R ^–1 and the system is in the unique stationary state of the reduced dynamics in the weak coupling limit.On leave of absence from the Fachbereich Physik der Universität München. Work supported by a Max Kade Foundation FellowshipResearch supported in part by NSF Grant MPS75-20638     

Maximum mass-particle velocities in Kantor's information mechanics

Kantor's information mechanics links phenomena previously regarded as not treatable by a single theory. It is used here to calculate the maximum velocities _m of single particles. For the electron, _m/c1–1.253814×10^–77. The maximum _m corresponds to _m/c1–1.097864×10^–122 for a single mass particle with a rest mass of 3.078496×10^–5g. This is the fastest that matter can move. Either information mechanics or classical mechanics can be used to show that _m is less for heavier particles. That _m is less for lighter particles can be deduced from an information mechanics argument alone.     

Gamma-ray optics using57Co-doped iron single crystals

We have begun a search for anomalous emission and anomalous temporal decay of nuclear resonant radiation using internal sources located inside thick single crystals. Our samples are two iron single crystals of thicknesses 0.5 and 1.0 mm that have been doped on one side with⁵⁷Co. From ordinary considerations, these samples are much too thick to allow any 14.4-keV radiation to pass through the crystal and out the other side. However, our results suggest that 14.4-keV radiation is able to be transmitted through the crystals. Furthermore, using coincidence techniques we examined the temporal decay of the 14.4-keV nuclear level under these circumstances.     

Laser Raman Spectroscopy of Crystals with the Structure of Sillenite

The experimental data of the past 10–15 years for the vibrational spectra of crystals with the structure of sillenite Bi₁₂M _x O_20± obtained by the methods of laser Raman scattering and infrared (IR) absorption are generalized. Correlations between the chemical composition and crystal structure of the compounds (variations of the cation M) and their vibrational spectra are established. It is shown that the main contribution to formation of the highfrequency part of the spectrum of two, three, and fourphonon absorption is given by phonons related to vibrations of the [MO₄]^n- complexes. On the basis of the analysis of Raman spectra, the effective use of crystals with the structure of sillenite in acoustooptics is justified.     

Line scattering images on admixtures in alkali-halides

Different types of line scattering images in cubic crystals are discussed and a method for finding the distribution of rods in the basic substance by means of the scattering image is demonstrated on NaCl:SrCl₂. It is shown that the rods in NaCl:SrCl₂ are distributed in all equivalent 141 directions with the same probability.     

An analytical study of the dielectric relaxation mechanism in crystals with polar molecules

The kinetic equations for motion of polar vacancies, the dipole moments of which are numerically equal to the moment of a molecule in an electric field, are derived and studied. The polarization process is explained through orientation of the polar vacancies. A formula for the dielectric loss angle as a function of the frequency spectrum of external fields and temperature is derived, and using this formula calculations are performed for crystals.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 3, pp. 51–58, March, 1972.