Table of contents

We investigate the conserved quantities for a closed, N-state quantum system. A simple derivation from the equation of motion for the density matrix shows that there is an infinite number of such conserved quantities. However, only the first N of these constants of the motion are independent. These constants uniquely determine the degree of mixing in the system, which is itself conserved. We discuss the relationship between these results, the properties of Hamiltonians under unitary transformation and van Vleck's principle of spectroscopic stability.

A new on-line mass analyzing device consisting of an ion guide connected to a commerical quadrupole mass spectrometer is in preparation at the Department of Physics, in University of Jyväskylä. It differs from our present Ion Guide Isotope Separator On-Line (IGISOL) in three essential ways: (a) a small economical quadrupole spectrometer is used instead of a magnetic separator, (b) the whole device operates at ground potential, and (c) electric voltages lower than 50 V are used in bringing ions through a differential pumping section into a high vacuum. The new spectrometer is expected to have similar properties as the IGISOL: excellent stability, similar separation efficiency for all chemical elements, and short separation time. It is intended to be a multi-purpose instrument useful in many fields of research; a few examples related to our own work are given.

We reexamine the problem of dynamical breaking of chiral symmetry in Quantum Chromodynamics, with the infrared singular gluon propagator, in the ladder approximation. We show that the Dyson-Schwinger equation leads to a singular integral equation which has no nontrivial solutions. It is argued that both ultraviolet and infrared cutoffs must be introduced in order to make the approximate theory viable.

Collective states have been observed in inelastic deuteron scattering on a target of ²²⁶Ra. Spectra were measured at scattering angles of 90°, 125° and 140°. The reaction products were analyzed in a magnetic spectrograph and detected in photographic emulsions. The 2⁺ strength is found to be highly fragmented in ²²⁶Ra. The transition strengths deduced for the assigned 3⁻ states at 320 and 1119 keV are compatible with both a vibrational and static octupole deformed model description for ²²⁶Ra.

Oscillator strengths for transitions among sextet terms of the configurations 3d⁵, 3d⁴4s, 3d⁴4p, 3d⁴4d and 3d⁴5s of singly ionized Chromium have been calculated. Transition wavelengths lie in the range 2050-3100 A. The calculations have been performed in two independent ways: One uses the Multiconfiguration Optimized Potential Model (MCOPM) and the other uses an R-matrix model in which the target wave functions are obtained from the MCOPM. Some difficulties that arise in calculations involving the open 3d shell are detailed. The main purpose is to obtain data of a relatively high degree of reliability. Comparison of the results as well as estimates of numerical cancellation effects in the MCOPM calculation indicate that they should be accurate to 10% or better with some exceptions where relativistic effects not included in the present calculations may be important. The results provide a useful benchmark for comparison with experimental results since, in the present theoretical work, we do not generally encounter the difficulties of near degeneracies among terms with the same L and S that turn up in other symmetries for this ion. Comparison with observations available at present are given.

Electron capture process, in which the projectile charge (q) is lowered by one unit, have been recorded by means of high-resolution energy-gain spectroscopy for 4q keV Xe^q+-Xe (15 ⩽ q ⩽ 35) collisions. The ratios, R, between the cross sections for the transfer ionisation and single-electron capture were extracted from the measured spectra. The quantity R increases slowly for charges up to q = 25 and decreases rapidly for higher q. Relying on the extended classical over-barrier model we relate R to the branching ratio for autoionisation, F, through R = k · F, and estimate the variation in k as a function of q. On the basis of the extended classical over-barrier model we ascribe the decrease in R at high q to an increase in radiative stabilization of double-Rydberg states formed in slow Xe^q+-Xe, q > 25, collisions.

Ion induced Auger emission leading to transfer ionisation (ATI) in high energy ion-atom collisions is computed for Li³⁺ on H₂ and He targets. QED computations for transfer ionisation (TI), charge transfer (CT) and double capture (DC) were recently reported in two papers (Bhattacharyya et al., 1988 [1], Bhattacharyya, 1989 [2]) subsequently referred to as paper I and II, respectively. Double capture of electrons leading to transfer ionisation ATI is here done in a similar technique. The cross section for ATI is found to lie between 0.1% to 0.2% of the sum of the cross sections for TI and ATI events.

The production of low-energy positron beams is described and some motivation for their use in atomic physics scattering experiments is discussed. Selected topics of current interest relating to positron collisions involving positronium formation and ionisation are highlighted.

Lande g values are calculated for the astrophysically abundant ion Fe II. They are compared with published measured values in order to indicate possible errors that can affect calculated oscillator strengths and eigenvectors. Both the computations of Lande g values and previous oscillator strengths calculations were carried out at the Rutherford Appleton Laboratory through the application of optimisation methods involving the adjustment of Slater parameters.

We report on angular distributions of electron emission at 600 eV and 300 eV in 1 MeV proton-He collisions, in coincidence with electron capture by the projectile. The angular distribution of electrons in the vicinity of the beam velocity (600 eV) exhibits peaks at ~ 58° and ~ 90°, while the distribution of 300 eV electrons peaks at ~ 68° and ~ 110°. The forward peaks are due to a process in which the proton interacts with each of the two target electrons leading to capture and ionization. The features of peaks at ~ 90° and ~ 110° are ascribed to a two-step process of proton-electron scattering in the first step and a localized interaction of electron-electron scattering (correlation) in a second step, in which one of the electrons is deflected into a bound state of H° while the other electron is ionized. The magnitudes of our measured absolute cross sections for the proton-electron-electron scattering processes agree within factors of two to eight with recent theoretical predictions.

Experiments on two-electron processes (double excitation, ionization excitation, and double ionization) in collisions with fast projectiles (p⁺, p⁻, e⁻, C^q+) and helium are considered. The role of electron correlation in the collision mechanism is discussed.

The spectrum of singly ionized oxygen, O II, has been observed with a theta-pinch discharge as a light source. About 150 lines have been measured in the wavelength region 1070-2140 Å. Most of the lines are new observations connecting known levels of O II. However, 28 lines are lines to new levels. In the region 1070-2140 Å, calculated wavelengths based on these measurements are suitable as reference lines.

The dynamics of electron correlation processes are discussed for atoms and ion-atom collision systems. These processes are introduced in analogy with stationary electron correlation phenomena which are well known from atomic structure theory. The role of the Hartree-Fock method in finding a solution within the independent-particle model is pointed out. The concept of configuration interaction is discussed in order to clarify the verification of electron correlation processes. Configuration mixing is treated in stationary states involving bound and continuum electrons. It is pointed out that a specific electron correlation effect in a stationary state corresponds to an analogous effect in a state which evolves in time. In separated atoms emphasis is given to the Auger effect. In ion-atom collisions double ionization and double excitation are analyzed as examples for processes involving dynamic electron correlation.

We are concerned with the theory of reactions in ion-atom collisions under conditions where the initial or final state is strongly distorted by the field of the other collision partner, i.e., electron capture in asymmetric collisions, radiative electron capture or excitation of atoms by highly charged ions. The theoretical camp is currently divided in two groups: one group has emphasized the importance of off-energy-shell effects in the description of the propagation of the active electron in intermediate states. Another group has stressed the significance of a proper inclusion of the Coulomb boundary conditions for such collision processes. This paper describes a recent development that examines the two viewpoints to provide a consistent perturbation expansion.

The odd energy levels of Hf II, Ta II and W II have been investigated by means of the Slater-Condon parametric method. This led us to elimination of fortuitous levels reported in earlier analyses, to revision of J-values and the finding of 23 new levels in Ta II. The configuration mixing is very strong in the groups 5d^N−16s6p + 5d^N−26s6p + 5d^N−36s²6p, the latter configuration being generally unrecognizable. Very few low odd levels are still unknown in these spectra.

Results of interferometric investigation of collisional broadening and shift of the 539.4 nm Ar line emitted from a low current glow discharge in pure argon and argon-helium mixutres are reported. Measurements were performed at low gas densities and the values of the Doppler width and the pressure broadening and shift coefficients were determined. The results are interpreted in terms of the impact theory assuming the Fermi pseudopotential and polarisation interaction.

The spectrum of bromine was studied in the region 450-1100 Å, using the beam-foil method with 6 MeV ions from a tandem accelerator. On the basis of isoelectronic extrapolations and theoretical calculations, 32 lines were classified as transitions between the 3p⁶3d⁸4s and 3p⁶3d⁸4p configurations of Co-like Br IX. Of the 16 possible 4s levels 13 have been located, and 11 new 4p levels have been added to the previously known ones. Only 4 of all the 4p levels (45 in total) remain to be found.

An eigenfuction method is used for the determination of the three-dimensional motion of an inviscid heavy liquid in a cylindrical container. The explicit and exact solutions which are derived for the velocity potential and for the elevation of the free surface of the liquid concern two types of initial conditions, imposed on the free surface, and are expressed in terms of double series of the Bessel-Fourier type. The two-dimensional case concerning the fluid motion which is symmetric with respect to the axis of the container, is also examined and some interesting examples are given.

In the present paper the application of a functional formalism to the description of turbulent thermohaline convection in a linearly stratified binary fluid is shown. The mathematical description of this phenomenon is based on the set of Oberbeck-Boussinesq equations. By assuming that the fundamental equations may be linearized in the sense of Oseen, appropriate functional differential equations have been obtained. On the basis of the methods presented in works of Szafirski and Icha, explicit solutions of these equations have been obtained. Some remarks on the possibility of expansion of the characteristic functional in a functional power series, based on the solution presented in this paper, are given.

A nonlocal treatment of the whistler instability excited by an electron component having a temperature anisotropy in a density crest has been developed. Assuming a parabolic density profile, the mode structure equation and expression for the growth rate of the instability have been obtained.

The anomalous heat transfer across the magnetic field in a non-isothermal plasma, with the cyclotron frequencies of the electrons and ions exceeding their effective collision frequencies, is studied. The stationary electron and ion heat fluxes are found and the possible patterns of the thermal losses are discussed. Within time intervals shorter than the ion free path times, but longer than those of the electron in a plasma with developed ion-acoustic turbulence, the heat transfer is caused by electrons. Within times longer both than the ion free path time and that of the electrons, the relation between the electron and ion fluxes depends on the plasma parameters. In a dense plasma, when the ion-ion collision frequency exceeds the turbulent collision frequency no more than by the ratio of the squared Debye lengths of the electrons and ions, the thermal losses are determined by the electrons. For larger ion-ion collision frequencies, the thermal losses are caused by ions. In a low-density plasma, when the usual ion-ion collisions are of no importance, the relation of the particle thermal fluxes is dependent on the value of the turbulent Knudsen number. Within the limit of the small turbulent Knudsen number the electron thermal losses prevail for short time intervals and then after ion turbulent heating the thermal losses determined by the ions. With large Knudsen numbers, the main part of the thermal fluxes is transferred by more effectively heated ions.

The dynamics of virtually (below gap) nonresonantly excited electron-hole pairs in direct semiconductors is considered by a solution of a linearized and collisionless integro-differential equation. It is an extension of the Schmitt-Rink-Chemla theory for shorter laser pulses, where the stationary treatment does not hold. Typical expectation values are numerically calculated for the real system of GaAs.

Single crystals of Bi_2-xIn_xSe₃ (x = 0.0-0.66) were prepared from the elements of 5N purity using the modified Bridgman method. On the samples with a various content of incorporated In-atoms the reflectivity in IR-region and the transport coefficients (electrical conductivity σ_⊥, Hall coefficient R_H (B ∥ c), Seebeck coefficient S_⊥) were measured. The results showed that the In-atoms incorporation to the crystal lattice of Bi₂Se₃ in the region of small concentrations of In-atoms increases the free carriers concentration, in the region of higher concentrations of In-atoms the free carriers concentration is suppressed. On the ground of measured changes in the values of transport coefficients and optical parameters (determined from the interpretation of infrared reflectivity) a model of point defects in the Bi_2-x In_x Se₃ crystal lattice has been suggested. This model takes into account the existence of antisite defects Bi'_Se in the Bi₂Se₃ crystal lattice the concentration of which is suppressed by incorporated In-atoms. The built-in In-atoms form uncharged defects In^x_Bi which are positively polarized.