Table of contents

Qualitative arguments are discussed for the model of gluon dominance (MGD) of the multihadron production process in hadron and relativistic nuclei interactions. Interpretations is given of basic regularities of the multihadron production in hadron collisions in the concrete variant of MGD-model of two-gluon fusion. Requirements are formulated for the behaviour of the cross section of such a fusion following from the analysis of the production process.

Characteristic features of positron creation in collisions of very heavy ions are depicted. First continuum solutions of the two-centre Dirac equation are presented. Calculated e⁺ -production probabilities are compared with experimental data. The observation of puzzling peak structures in positron spectra is illuminated. Their relationship with the spontaneous positron emission in overcritical fields and, especially, with the hypothesis of a "new particle creation" is investigated. The ability of δ-electrons and positrons to carry precise informations on the time-scale of nuclear reactions in deepinelastic and intermediate-energy collisions is demonstrated. As an outlook we discuss positron production in crossed beams of bare uranium nuclei.

Absolute angular differential capture cross sections for Ar^q+ ions, where q = 6, 7, 8, 9 and 11, colliding with Ar at an energy of 1.8q keV are reported. Absolute total cross sections for q = 12 and 13 are also included. Measuring the final projectile charge, the charge of the target ion and the scattering angle in coincidence, reactions where the target lost up to six electrons were observed. Both absolute and differential cross sections are compared with theoretical predictions based on several extensions of the classical over-barrier model.

Many-body perturbation theory is applied to study P-violating and CP-violating matrix elements in the heavy one-valence-electron atoms rubidium, cesium, gold, and thallium. Results of calculations carried out to lowest and to first order starting from various potentials including the Dirac-Fock potential are given for each of the atoms considered. Energies of low-lying atomic states, atomic hyperfine constants, and amplitudes for allowed transitions are also calculated to aid in gauging the reliability of the predicted weak interaction matrix elements. A technique for treating the double sums occurring in relativistic second-order perturbation calculations is described. This technique, which is being used to extend the present calculations to second order, is illustrated in several examples.

The spectrum of neon-like chlorine, Cl VIII, has been investigated in the wavelength region 100-6000 Å using the beam-foil technique and by means of spark and theta pinch measurements. 188 new levels, most of which are ascribed to the hydrogenic part of the term system, have been determined from 314 combinations. The levels belong to 32 configurations ranging from 2s²2p⁶ up to 2s²2p⁵9l. Term structure and coupling conditions have been analyzed.

Interactions between levels of the 2s²2p⁵np, nd, nf and ng series and those of the 2s2p⁶nl configuration are found to be prominent and have been investigated in detail.

The experimental results are compared with isoelectronic analyses and with parametric and ab initio calculations.

By applying the polarization formula to hydrogenic configurations, the centre of gravity ionization energy of the 2s²2p⁵²P limit is determined to 2 813 823 ± 60 cm⁻¹.

Relativistic effects in electron-atom collision cross sections are discussed. According to the results obtained using the relativistic distorted-wave Born approximation, relativistic cross sections for electron-impact excitations of Li-like ions are smaller than corresponding nonrelativistic cross sections. This reduction results mostly relativistic contraction of bound orbitals and from spin-orbit splitting. We also found that electron exchange and orthogonality between bound and continuum orbitals did not significantly alter cross sections for highly charged ions.

The question of the validity of many body perturbation theory (MBPT) calculations that start from the Dirac-Coulomb Hamiltonian is addressed. An extension of the Furry representation of Quantum Electrodynamics (QED) is introduced in which the nuclear Coulomb field is replaced by a potential more relevant to many-electron atoms. QED perturbation theory for energies and matrix elements is set up and evaluated for exchanges of up to two photons. It is shown that in lowest and first order the expressions used in MBPT starting from the Dirac-Coulomb Hamiltonian are reproduced along with additional Lamb shift and Breit interaction contributions. In second order use of QED gives rise to slight differences with MBPT: however, simple rules pertaining to sums over negative energy states are given that eliminate possible difficulties corresponding to continuum dissolution.

The ground state of the orbitally non-degenerate periodic Anderson model is studied variationally. Our Ansatz is the lattice version of the lowest-order Varma-Yafet trial state, with the number of the independent variational parameters being equal to the number of k-states within the Fermi-surface.

We employ a two-band version of the Gutzwiller method. The only approximation we make is the replacement of the determinant expressions in the Gutzwiller expansion by their averages. Apart from this, the optimisation problem is solved exactly, and the results can be interpreted in terms of an effective free-fermion Hamiltonian. The renormalisation factor of the hybridisation is of the Rice-Ueda form. A simple model is introduced to get closed-form results in the limit of small hybridisation, and we find the same Kondo exponent as Rice and Ueda. The spin dependence of the effective hybridisation leads to a spin polarisation instability for sufficiently small hybridisation, even within the mixed valent regime.

Room temperature measurement of ⁵⁷Fe Mössbauer spectra as well as positron lifetime spectra and angular distributions of photons coming from the two-photon annihilation of an electron-positron pair were performed for Fe-Cr alloys containing 1-15 at.% of chromium. The data were analysed in terms of a rearrangement of valence electrons due to alloying of Fe with Cr. It was shown that the data can be used for verification of theoretical computations concerning the influence of the valence electron distribution on the ⁵⁷Fe isomer shift in alloys.

No abstract; see full text