Table of contents

An analysis of the number of generations, N_g, in superstring-inspired models is given. It is shown that the N_g=2 case is neither excluded by experimental data nor by theoretical consideration.

VP gamma matrix elements have been calculated within the basic premises of the non-relativistic harmonic oscillator quark model (NRQM) incorporating Lorentz contraction of form factors as well as recoil correction. Without using any of the VP gamma decays as input, the authors find an excellent fit to the data. The disagreement in the decays of eta ' suggests a approximately=30% contribution to its wavefunction from outside the valence u, d, s sector. Moreover, the present fit to VP gamma decays favours the usual pseudoscalar mixing angle to be around -16 degrees .

A systematic disagreement has been found between the results of the deformed shell model calculations and the phenomenological Grodzins estimate for nuclear deformations in the even-even rare-earth nuclei. As a rule, the Grodzins formula overpredicts deformations for N>82 and gives too small values for N<82. The authors have shown that these discrepancies can be explained by the N and Z dependence of the pairing field. Assuming the calculated deformations and the microscopic pairing gaps the experimentally observed behaviour of the nuclear moments of inertia is reproduced.

The influence of interactions with the multipolarity lambda =5, 6, 7 and 9 is studied on the mixing of two-quasineutron and two-quasiproton states with large K in doubly-even deformed nuclei. The mixing of two-quasineutron and two-quasiproton states with the same values of K^pi , caused by a high-multipolarity interaction, is shown to be large in the case of proximity of their energies. A qualitatively correct description of experimental data on the mixing of two-quasineutron and two-quasiproton configurations in ^178,176Hf, ¹⁷⁴Yb, ¹⁶⁸Er and ¹⁵⁸Gd is obtained.

Most shell-model calculations of ⁴He require very large basis space for the energy spectrum to stabilise. Coupled cluster methods and an exact treatment of the centre-of-mass motion dramatically reduce the number of configurations. The authors thereby obtain almost exact results with small bases, but which include states of very high excitation energy.

High spin states in ¹⁶¹Er and ¹⁶²Er have been populated using the ¹³⁰Te+³⁶S reaction at a ³⁶S bombarding energy of 170 MeV. In ¹⁶¹Er, three rotational bands were extended from I approximately=35 h(cross) to I approximately=50 h(cross). In ¹⁶²Er the lowest energy positive parity band was observed to I=44 h(cross) and two negative parity bands to I approximately=32 h(cross). The behaviour of these rotational sequences are explained in terms of the expected spectrum of single neutron states in the absence of static neutron pair correlations.

The fission of light nuclei involves their decay into fragments heavier than alpha particles. The authors review the early results from electrofission and describe measurements using breakup reactions. The theoretical understanding of the fission process is reviewed and the link to clustering in nuclei explored.

The author presents results for light-quark current correlators in the general unequal-mass case.

The authors consider the Saviddy vacuum by making use of an auxiliary field for the field strength tensor, in the Minkowski functional integral. They find that the chromomagnetic vacuum is stable for a range of coupling constant excluding the weak coupling region.

The unpolarised differential cross section and deuteron tensor analysing power t₂₀ are estimated for the dp to ³He pi ⁰ reaction in the forward and backward directions within a two-body cluster model for the ³He nucleus. All the qualitative features of the low-energy data, such as the rapid rise in the forward/backward asymmetry and the oscillation in t₂₀ as the energy increases, are well reproduced in terms of amplitudes deduced from pp to d(d*) pi . At higher energies the forward data are still well described although one of the amplitudes in the backward direction is seriously underpredicted.

A conceptional and numerical comparison of the one parameter generator coordinate method (GCM) and the quantised adiabatic time-dependent Hartree-Fock (ATDHF) theory is performed by applying both theories to the ¹²C+²⁰Ne and ¹⁶O+¹⁶O system. Different parametrisations of the Skyrme interaction are used. The single-particle wavefunctions and the operators are represented on a three-dimensional grid in coordinate and momentum space. The collective path is evaluated in the gradient method, corresponding to GDM, and by solving the numerically more involved ATDHF equations.

Considering the equality of the proton and neutron Fermi levels as an indication of a phenomenological interaction between pairs of protons and neutrons, low-energy isovector monopole resonances are proved to appear in the superfluid nuclei. The required phenomenological interaction is presented as an isospin symmetry-breaking mean field for the four-particle interaction.

The authors study the deformation and the spectral structure of low-lying bands in the nuclei ⁸⁰Zr, ^79,81Y and ⁸¹Zr using the deformed-shell model based on Hartree-Fock fields. In their calculation, ⁵⁶Ni is taken as the inert core with the model space consisting of 1p_3/2, 0f_5/2 1p_1/2 and 0g_9/2 states. An effective interaction given by Kuo (1985) and modified by Bhatt (1988) for this configuration space has been used in the calculation. The role of the g_9/2 state in producing large deformations in ⁸⁰Zr is analysed.

A two-level mixing calculation between normal and intruder states is performed for the low-lying 0⁺ and 2⁺ states in ^190-200Pb. Values for the energies and transition probabilities of the unmixed states are deduced.

The local energy-dependent potential for the elastic scattering of ¹⁶O on ²⁸Si, which was obtained by an inversion procedure from elastic scattering phase shifts of the algebraic scattering theory, is shown to be explainable in terms of a non-local potential. The local and non-local potentials get connected by two different methods: by a Taylor expansion of the non-local potential and by a Wigner representation of this potential within the method of effective equivalent wave numbers. Whereas the method using the Taylor expansion yields a useful non-local potential, the method of effective equivalent wave numbers gives unsatisfactory results.

The 4 alpha -cluster structure of the ¹⁶O nucleus was proposed in order to deduce the folded optical potentials of ¹⁶O-projectiles through either the Watanabe superposition or double folding cluster models. The resultant potentials must be renormalised by factors Nr approximately=1.28+or-0.22 to fit the data. The results were compared with the standard double folding model predictions and experimental data. The alpha +¹⁶O data at 48.7 MeV are also analysed.

The description of the quasimolecular states observed in the ¹²C+¹²C collisions, using a Morse-type potential in a di-nuclear picture, yielded the parameters of the bonding potential. The depth of the potential being 7 MeV, all states lying below it are well described as bound states. The calculation of phase shifts and the corresponding cross sections yields fifteen resonances with higher angular momenta, up to L=12, which are close to the energies of the experimentally observed ones. This reaffirms the diatomic-like rotational and vibrational picture of the quasimolecular states proposed earlier.

The study of high-spin states in ⁷⁹Sr is reported. The ⁷⁹Sr nucleus was populated in the ⁵⁸Ni(²⁴Mg, 2pn)⁷⁹Sr reaction at 65-110 MeV and the inverse ²⁴Mg(⁵⁸Ni, 2pn)⁷⁹Sr reaction at 190 MeV bombarding energy. Using gamma - gamma and recoil- gamma - gamma coincidence techniques, the authors were able to extend the level scheme up to spins (37/2⁺) and (33/2^-) in the positive and negative parity bands respectively. These spins are high enough to study the alignment effects due to protons in this mass region.