Table of contents

Monte-Carlo studies of SO(2) lattice gauge theory in four dimensions are presented. The results include Wilson loop expectation values for a 6⁴ lattice, the string tension, plaquette-plaquette and loop-plaquette correlations. The possibility of measuring the glueball mass is also discussed.

The Hartree-Bogoliubov ground-state band obtained by exact angular momentum and particle number projection can reproduce the backbending results for ¹⁵⁸Er. There is a large sudden drop in the neutron pairing gap during backbending.

Ramirez and Thompson's energy-independent nonlocal potential model (1980) is exploited in order to describe the energy behaviour of the nucleon-nucleus spin-orbit potential. The validity of the model is also discussed.

The absorption length of cosmic-ray showers has been measured for vertical sea-level shower sizes approximately 10⁶ particles. The value of 97+or-2 g cm^-2 obtained for this parameter is consistent with results from other workers, but is considerably more precise. This result sets stringent limits on models of shower development.

Studies the reactions ³He(e,e' pi ⁺)³H and ³H(e,e' pi ^-)³He where the dominant pion kinetic energies are in the 20-40 MeV range. The effects of pion momentum-dependent terms in the production amplitude are calculated and found to only marginally improve the agreement with experiment for pi ⁺ production. Differences between the pi ⁺ and pi ^- production mechanisms are discussed.

Consideration is given to the properties of light nuclei in the method of hyperspherical functions with central realistic potentials. In general, the following set of parameters can be described satisfactorily for the nuclei: binding energy, excitation energy of monopole resonance, RMS radius, elastic and inelastic form factors. The detailed reproduction of the relevant data for each nucleus necessitates the solution of the inverse problem and requires that the corresponding nucleon-nucleon potential (which will probably vary from nucleus to nucleus) be found.

The effect of the Pauli principle on the fragmentation of one-quasiparticle states in spherical nuclei is studied within the quasiparticle-phonon nuclear model. It is shown that the Pauli principle influences considerably the position and structure of a few low-lying states. The fragmentation of one-quasiparticle states at intermediate and high excitation energies is slightly affected by the Pauli principle, and the calculations can be performed by taking the Pauli principle into account roughly.

The even parity states arising from 2h(cross) omega excitations in ¹⁶O are investigated using the shell model. As a residual interaction the authors employ the density-dependent version of the Skyrme interaction SIII and treat the density as an input. Apart from states belonging to the K^pi =0⁺ rotational band, which are assumed to be beyond the present model, the results are quite satisfactory and the number of levels below 25 MeV as well as their distribution in energy is in overall agreement with experiment.

Shell-model calculations have been performed for the nuclides ^44,45Sc and ^44,45,47,49Ca. The one-body part of the Hamiltonian was extracted from the experimental spectra of ⁴¹Ca and ⁴¹Sc whilst the two-body part used was a modification KB5 of the interaction constructed by Kuo and Brown (1968) from the Hamada-Johnston nucleon-nucleon potential. The nuclear wavefunctions so produced, and those from earlier calculations employing a different modification KB1 of the Kuo-Brown interaction, were used to calculate spectroscopic factors for single-nucleon pick-up and stripping reactions to these final nuclei. Comparison with experimental data shows that the interaction KB5 is equally successful for level energies and spectroscopic factors. A lack of definite spin and parity assignments for many excited states, however, limits the extent of the comparison.

Energy spectra of ¹⁵⁹Dy and ¹⁶¹Er have been predicted up to J=11/2 using the surface delta plus quadrupole interaction as the effective two-body Hamiltonian. The predicted spectra agree well with the experimental spectra. The calculated M1 transition probability ratios are found to be closer to those of Alaga's rule than the ratios obtained with only the SDI in the two-body part of the Hamiltonian. It is suggested that the success of the Q.Q interaction is restricted only to low spin states and lower multipole effects.

The gamma-ray spectroscopy of sixty excited states in ³⁹K below an excitation energy of 8.4 MeV has been studied. The data were obtained mainly from the ³⁶Ar+ alpha reaction at beam energies between 7.5 and 16.0 MeV, the remaining data coming from the ²⁴Mg+¹⁸O and ²⁸Si+¹⁶O reactions, both at beam energies of 42 MeV. 13 new levels were established in ³⁹K and several previously unobserved branches were revealed between the previously known levels. Spins, parities, mixing ratios and gamma-ray branching ratios were determined from angular distribution and linear polarisation measurements using the ³⁶Ar+ alpha reaction at several different beam energies. Mean lifetimes were deduced using both the Doppler-shift attenuation method (with the ³⁶Ar+ alpha reaction) and the recoil-distance method (with the ²⁸Si+¹⁶O reaction). The results have allowed transition strengths to be calculated for the decays between many of the levels. The results are discussed in terms of both the shell model and the simple weak coupling model.

Gamma-ray transitions in ¹⁴⁷Eu are studied following the ¹⁴⁸Sm(p,2n) reaction. A level scheme is proposed on the basis of excitation functions, of angular distributions and of prompt and delayed coincidence measurements. Some of the proposed states have not been previously identified. Data for ¹⁴⁷Eu and ¹⁵¹Eu have been analysed in terms of the interacting boson-fermion model.

A study has been made of excited states in ¹⁷²Yb populated in the ¹⁷⁰Er( alpha ,2n)¹⁷²Yb reaction using a bombarding energy of 19 MeV. The experimental information has been derived from gamma-ray singles, coincidence, angular distribution and conversion electron singles measurements. A Coulomb excitation experiment using alphas at projectile energies of 12 and 14 MeV produced measurements of six B(E2)'s and three B(E3)'s to excited 2⁺ and 3^- states respectively. The properties of ¹⁷²Yb have been examined with particular attention being paid to departures from adiabatic rotational behaviour of the excited K^pi =0⁺ band at 1043 keV and the K^pi =1^- octupole band at 1155 keV. M1 admixtures to the Delta I=0 transitions between the band at 1043 keV and the ground-state band have been examined in an attempt to determine their source. E0 strengths have also been measured for these transitions.