A very sensitive search has been made for an anisotropy between the 1274-keV γ ray and K-shell x rays from the internal conversion of the 123-keV transition to the ground state. The asymmetry for the sum of K${\alpha }_1$ and K${\alpha }_2$ x rays was found to be 1.002±0.004. Previous measurements in ${}_{}{}^{169}{}_{}{}^{}\mathrm{Tm}$ and ${}_{}{}^{181}{}_{}{}^{}\mathrm{Ta}$ showed effects of about 4% and 3%, respectively. Corrections for detector solid angles and perturbations of the correlation by the extranuclear crystalline fields were made. This null result, in an atom whose nuclear excited states are known to be highly deformed, might be explained by the disappearance of the nuclear deformation, to its final-state value of zero, in times short compared to those of the atomic processes resulting in the K-shell x rays.

We report the measurement of the 1s2s ${}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$–1s2p ${}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$ transition wavelength in heliumlike Ca xix. The result is 466.8±0.1 Å, which is in agreement with the most recent calculated value of 466.90±0.04 Å. This measurement tests total quantum-electrodynamic effects for this transition to about 3% and is sensitive to the purely two-electron QED corrections.

We show how the causal interpretation provides a physical basis for the Wigner phase-space formulation of quantum mechanics by analyzing the case of a relativistic spin-zero particle in an external electromagnetic field. The Wigner function can be interpreted as both a generalized transformation and a field which defines a quantum potential in phase space. We also propose a Lorentz-vector distribution function which always associates positive probability densities with the real motions of particles and antiparticles in phase space.

Properties of energy eigenvalues for the potential V(r)=-2/r+B exp(-r/D)/r with B>2 and large D are discussed. The energy levels with the same radial quantum number k=n-l-1, where n and l are the principal and azimuthal quantum numbers, respectively, become (nearly) degenerate if the screening length D takes on very large values. This accidental degeneracy results from a vanishing centrifugal correction and as well occurs for other potentials with a repulsive core.

In this paper we introduce the Bloch vector of the SU(1,1) space in full analogy with the well-known vector of the two-level systems.

A complex effective charge is used to calculate the first Born electron-impact cross sections of the hydrogen atom. The results are compared with experimental values, and the usefulness of employing an effective charge is discussed.

We show how a method of continued fractions of Horáček and Sasakawa for solving the Lippman-Schwinger equation for a local or nonlocal potential [Phys. Rev. A 30, 2274 (1984)] should be modified for the case of complex potentials. A nonlocal complex potential for the scattering of electrons from the helium atom is used as a numerical example.

As the velocity of a charged particle increases, its electric flux lines become more and more concentrated about the transverse plane, a circumstance that is sometimes construed to imply that the electric field in front of the particle is zero. This is never exactly true, but is often a valid approximation. The range of validity is discussed.

Classical-trajectory Monte Carlo calculations are used to determine the velocity and angular dependence of the electron ionized in the ${\mathrm{H}}^{+}$+H→${\mathrm{H}}^{+}$+${\mathrm{H}}^{+}$+${\mathrm{e}}^{\mathrm{-}}$ collision. The energy range studied is 40–200 keV. At energies E≤60 keV, ionized electrons with velocities that are near one-half (v/2) the relative velocity v of the collision dominate the electron spectra. At higher energies the maximum position of the ionized electrons shifts and is found centered about the target nucleus.

Recent measurements and Hartree-Slater calculations disagree on the photoionization cross sections of excited states of cesium. We report improved Hartree-Slater calculations which also include effects of spin-orbit interaction. Our results are in substantially better accord with the experimental investigations, one of which is also complemented by using an improved lifetime value as input.

The ionization cross section of hydrogen atom from the metastable 2s state has been calculated in the energy range 5.0–30 eV by using different approximations. The distorted-wave Born approximation has been obtained by solving the static-plus-exchange equation. The present results obtained using the double-Coulomb approximation (in which both the scattered and the ejected electrons are considered to be a Coulomb function with unit charge) are more reliable and are in better agreement with the measured values than other theoretical predictions above 15 eV.

Hartree-Fock calculations of the photoionization cross section of the excited Na 4d state have been performed and compared with experiment. The results indicate an experimental confirmation of a zero in an l→l-1 photoionizing transition.

The exact solution for the spontaneous emission from N identical two-level atoms prepared initially to a symmetrical Dicke state with only one atom excited, which was obtained in our previous paper for the case of a perfectly tuned damped cavity, is generalized to the case of a detuned cavity. By using analytic and numerical results the effects of the detuning and the number N of atoms on the spontaneous emission are discussed.

In a simple, linear fluid model we obtain the longitudinal and radial electric field components generated by the propagation of two electromagnetic waves resonantly beating in a plasma, assuming Gaussian profiles for the pump amplitudes.

A study was made of the asymptotic time evolution of a system of diffusing particles and antiparticles which annihilate irreversibly upon contact. For the case in which all of the particles initially exist in the form of particle-antiparticle pairs, a Monte Carlo simulation on a three-dimensional lattice found the asymptotic density to go as ρ(t)=1.50±0.05$t^{\mathrm{-}1}$.

A general method recently developed to establish the conditions for the existence of similarity solutions of the Fokker-Planck-Smoluchowsky equation is applied to the one-dimensional equation ∂P/∂t=(∂/∂x)[R(x)P +D(x)(∂P/∂x)]. The case of power-law behavior of the coefficient functions R(x) and D(x) is investigated in detail, and a few classes of similarity solutions are presented. In addition, a class of functions R(x) and D(x) is identified such that the general method, based on the invariance under a continuous group of transformations, is equivalent to a generalized scale transformation of the space and time variables.

The uncertainty exponent describing the generalized final-state sensitivity of the logistic map at its periodic windows is analyzed numerically. This exponent itself scales with the nonlinearity parameter according to a power law. The universal value of the exponent characterizing this scaling behavior is conjectured. A consequence of the above scaling for dimensions of fractal sets is pointed out.

In a recent article [Phys. Rev. A 30, 703 (1984)] Hardekopf and Sucher solve the relativistic wave equation in momentum space for hydrogenlike systems. They find that by surrounding the hydrogenic Hamiltonian with projection operators for free-particle positive-energy states, the ground-state energy is lowered. In this Comment, we investigate this problem in some detail and conclude that the application of unsuitable projection operators will, in fact, introduce negative-energy states to the Hamiltonian of interest rather than remove them. The general considerations lead to the conclusion that in studying single-particle corrections to the wave function in a perturbation expansion, the correct procedure is to include the negative-energy states of the unperturbed Hamiltonian. It is also noted that the use of relativistic Hartree-Fock wave functions will remove to lowest order of perturbation theory the presence of single virtual electron-positron pairs.

It is shown that the recently published class of Hill equations with exact analytical solutions is in fact an example of a much broader class of second-order differential equations which admit exact WKB-like solutions.

Hong and Mandel have recently suggested a scheme which allows generalization of ‘‘squeezing’’ to higher-order (even) moments of the electromagnetic field. The new criterion for squeezing is that the expectation value of the moment be less than that for the coherent state. In this paper it is explicitly shown that both electric-field quadrature components are squeezed to fourth order in a ‘‘Jackiw state,’’ thus proving that the coherent state does not minimize the fourth-order uncertainty product. The implications of this result for Hong and Mandel’s proposal are briefly considered.