Table of contents

We consider scalar and vectorial non-relativistic bound-free transition form-factors. These integrals are spatial three-dimensional Fourier transforms of the product of the bound and continuum hydrogenlike wavefunctions ϕ_nlm(r)ϕ_K^–(r), weighted with operators 1, r⁻¹, r or ∇. Hamilton gradient operator ∇_r may be applied to either ϕ_nlm(r) or ϕ_K^–(r). The same type of matrix elements is also calculated by using Slater-type orbitals for ϕ_nlm(r). Concise general results are obtained for all the form-factors under study in terms of finite quadruple summations. Quantization axis for ϕ_nlm(r) is held arbitrary and the exact analytical calculations are carried out for any triple nlm of quantum numbers. Vectorial integrals are most elegantly treated by employing circular Cartesian coordinates and the vector spherical harmonics Y_jlm(r).

In this paper we try to give an answer to the question: how a particle tunneling through a classically forbidden region behaves? Working out the quantum mechanical analysis in a particular case first proposed by Stevens, we find that the group velocity plays an important role, so confirming the results previously obtained by some authors.

Empirical evidence indicating modification of gravity inside matter is summarized. It is argued that four independent sets of facts point in the same direction: a weakening of gravity inside matter. Direct evidence comes from measurements of gravity as function of depth in mines and bore holes (Airy experiments). Indirect evidence comes from discrepancies between the theoretical Standard Solar Model (SSM) and the observed neutrino flux, the observed seismic oscillations of the Sun, and geological evidence about the climate on the early Earth.

The possible modifications of standard general relativity that might be compatible with the above and all other known facts are considered. It is argued that the solution to the problem is a term proportional to the scalar curvature R appearing in the matter Lagrangian leading to appearance of the Einstein tensor as part of the matter energy-momentum tensor. There is in fact strong theoretical reasons to have such terms corresponding to a gravitational "polarization" of matter and there does not seem to be any reason why they could not be large enough to give modifications already at the Newtonian level.

The theory of fragmentation of hot nuclei formed due to the fusion of heavy ions at intermediate energies is reconsidered. Statistical and generalized liquid drop models are used to parametrize the fragments with A ⩾ 6. Average physical quantities related to the nuclear system are calculated by averaging over all the partitions. In the sampling process, the difference between the protons and neutrons in the nucleus is considered. Realistic Skyrme force for the nucleon-nucleon interactions is used in the Extended Thomas-Fermi model to evaluate the coefficients of the liquid-drop expansion.

Differential, integral and momentum transfer cross sections are reported for electron-Kr collisions in the range 1-20eV. An optical potential approach is employed; the static potential is included exactly at the Hartree-Fock level, the short-range correlation and long-range polarisation effects are considered in density functional theory. For exchange interection, we tune the free-electron-gas-exchange (FEGE) potential with respect to R-matrix integral cross section at 1 eV. The tuning parameter is the ionization potential of the atom. The tuned FEGE approximation at 1 eV gives very good results on the differential and integral cross sections at all energies between 1-20eV as compared with recent measurements and the R-matrix calculations. We also discuss the range of validity of the present tuned potential.

The problem of double electron capture by fast bare nuclei from heliumlike atoms is considered. The quantum version of the continuum distorted wave approximation is formulated without recourse to the usual independent particle model. The results for double charge exchange in collisions between protons and helium are in good agreement with the existing experimental data.

The effect of core polarization on the oscillator strength for the resonance transition in neutral zinc is investigated using the multiconfiguration Hartree Fock approach. The use of model potentials and corrections to the dipole operator is compared to a method, where the core polarization is represented by including configuration state functions, with one hole in the 3d core subshell in the CI-expansion. The latter, which is labeled explicit CI, gives results in good agreement with experiment. The reason for deviations in earlier calculations is discussed, together with the validity of the comparison of length and velocity forms of oscillator strengths, as a test of accuracy. The dependence of the model potential results on the choice of cut-off radius is investigated.

The thermal cross sections for quenching of the Ne 3s[3/2]₂ metastable level by foreign molecules have been studied by laser induced fluorescence. The effective decay rate of the Ne atoms was determined in relation to the foreign gas densities. The experiment was performed at 443 K and yielded the total quenching cross sections of 9.3 ± 0.4 Ų, 13.4 ± 0.6 Ų and 30.4 ± 1.4 Ų for collisions with CH₄, NH₃ and CO₂ molecules, respectively.

The Floquet method (non-perturbative) is used to investigate the multiphoton vibration-rotation excitation of SH, SH^- and SH⁺ ions in the presence of an intense infrared laser beam. A number of interesting features such as line broadening and the dynamic Stark shift are studied as a function of laser intensity and frequency.

In a situation where an atom is taken out of a small particle, we find a gain in total absorption strength of up to four orders of magnitude for the separated system as compared to the situation when the atom is part of the original particle. We also discuss if this can be a reason for the particular spatial distribution of chlorophyll molecules in the photosynthetic unit in green plants and arrive at a criterion for this to be possible.

La_1-xCa_xFeO_3-y compounds (0 ⩽ x ⩽ 0.50) have been synthesized and investigated by means of X-ray diffraction and Mössbauer spectroscopy. A linear decrease of the lattice constants of the orthorhombic perovskite with increasing x is found and explained as being partially due to the influence of the increasing valence of iron with increasing x on the ion radius of iron and on the cell dimension. The gradual decrease of isomer shift at room temperature with increasing x arises from the gradually increasing average intermediate valence state of iron due likely to electron hopping not necessarily between paired Fe³⁺ and Fe⁴⁺ but among iron ions mixed in any Fe³⁺/Fe⁴⁺ ratio on identical crystal sites. At low temperature, Fe⁴⁺ ions disproportionate into Fe³⁺ and Fe⁵⁺ ions.