Table of contents

The non-unitary model operator approach which has been previously described is applied to the calculation of the ground state energy of the ⁴He neucleus. Extensive computations are performed by using various central nucleon-nucleon potentials with hard or soft core in order to study the behaviour of the matrix elements of the effective interaction appearing in the expression of the energy of ⁴He and also of the normalization and healing integrals. In addition, the ground state energy of ⁴He is computed for various values of ℏω. The results of the computations show that the existence or not of a minimum in the saturation curve depends, apart from the potential assumed, on the version of the variational method by which the relative two-nucleon wave functions are determined. It is found that with the potentials of Kallio-Kolltveit, S1, Ohmura-Morita-Yamada and with the second method we used, the theoretical value of the ground state energy compares rather well with the corresponding experimental one.

Overlapping Regge resonances successfully accounted for the "ALAS" observed in the ²⁸Si (¹⁶O, ¹⁶O) ²⁸Si elastic scattering data of BNL. They are revealed using (very) weak absorptive (imaginary) potential has the same geometry as the WS real nuclear part. Justification for this analysis was introduced using real double folded nuclear potential.

The photoproduction of pions from ¹²C leading to the ground states of ¹²N and ¹²B is studied in the distorted-wave impulse approximation theory using the nuclear wave functions of Hirooka et al. The final state interaction is incorporated by solving the wave equation with a suitable pion-nucleus optical potential. Our calculations are in reasonable agreement with the available experimental data and the existing theoretical calculations.

It is shown that the statistical approach based on the atomic oscillation theory displays systematic trends of the dipole polarizability, α, variation along isoelectronic sequences both for closed and open shell ions. Within the statistical model, it is found that α is related to the ionization potential α ∼ I^-3(Z). This relationship is shown to be valid for real atomic systems.

The exact quantum asymptotic (N ≫ 1)

is found for highly ionized atoms with closed shells.

VUV-spectra of boron like silicon and phosphorus have been obtained by the beam-foil technique. The intensities of spectral lines originating from the decay of the 2p³²P⁰ level have been measured and intercompared via a relative efficiency curve. From the relative intensities branching ratios and, using experimental atomic lifetime values, transition probabilities have been determined. The data are compared with theoretical predictions.

The spectrum of the He-like nitrogen ion, N VI, has been generated in a laser produced plasma and has been recorded in the 100-190 Å region with the 10.7 m grazing incidence spectrograph of the National Bureau of Standards. Few new lines have been measured and others have been more accurately determined. By combining the results with published data of 2s-2p tranistions a complete experimental term system is derived and compared with existing theoretical evaluations.

Screening parametrisations are used to study the fine structure separations of the ns²np²P ground state terms in the Al, Ga, In and Tl isoelectronic sequences, and of the ns²np^{5 2}P ground state terms in the Cl, Br, I and At isoelectronic sequences. Isoelectronic and homologous regularities are exhibited which permit extrapolative predictions of these separations to high states of ionisation.

The relative values of electron transition probabilities for 101 lines of Er II were measured using an argon-erbium arc plasma. The absolute scale was established by using the values of lifetimes measured by S. M. Bentzen, U. Nielsen and O. Poulsen for 3 levels (E = 27 642, 33 105 and 35 671 cm^-1).

The lifetimes of the terms 3p²P, 3d²D, 4s²S, 4p²P, 4d²D, 4f²F, 5g²G, 6g²G, 6h²H, 7h²H, 7i²I and 8k²K in sodiumlike sulfur, S VI, have been determined using the beam-foil excitation technique. Most of the decay curves were analyzed by means of the ANDC method which corrects for cascading in a very detailed way. Accurate results were thereby obtained which show that an excellent agreement exists between experimental and theoretical values. Some previously noted disagreements between the results of beam-foil experiments and theoretical investigations are explained as being due to less accurate analyses of the experimental data.

Core photoelectron and Auger electron energies of alkali metal ions in solution have been measured and related to the corresponding energies in the gas phase. The magnitude of the electronic polarization contribution to the solvation energies of hard ions is discussed on the basis of measured solvation shifts of photo- and Auger electron lines. Through a combined use of the two types of shift an assessment can be made of the numerical value of the electronic solvation energy with Na⁺ and ions of the same radius as an example. The electronic polarization is found to be of major importance in the solvation of hard ions.

Mössbauer investigations of two achondrites, ALHA 77256 and Stannern, are reported. The results are compared to Mössbauer spectra of selected terrestrial and lunar rocks. The work confirms that the mantle of the Earth is highly oxidized compared to: (1) the mantle of the asteroidal bodies, which are believed to be the source of the meteorites called achondrites, and (2) the lunar basalts.

A preliminary discussion of the significance of Mössbauer spectroscopy in the study of the evolution of planets is included.