Table of contents

The evolution of the shape degrees of freedom, namely necking and deformation, has been studied in a classical dynamical model using the proximity nuclear interaction and the Coulomb interaction for the conservative forces and with wall and window frictions as the dissipative forces. The systems ²³⁸U+²³⁸U at 700 and 800 MeV and ²⁰⁸Pb+²⁰⁸Pb at 650 MeV centre-of-mass energies have been considered. Though the total interaction energy has pockets for certain shapes of the dinuclear complex, the dynamically evolved shapes do not have such pockets and the reaction time is typically approximately 10^-21 s as in deep inelastic collisions.

It is demonstrated that in the stochastic nucleon exchange model the accumulated spins of the reacting nuclei are nearly parallel for peripheral collisions in the absence of the internuclear barrier; the barrier destroys this strong correlation between the spin orientations. The individual spin directions are, however, insensitive to the barrier.

Three rotational bands have been observed up to spin I approximately=50 h(cross) in ¹⁶⁰Er. The band sequences exhibit regular energy spacings between levels characteristic of prolate collective rotation except for certain states near 50 h(cross) where there is evidence for near-yrast aligned single-particle states. The phase boundary between prolate collective and oblate non-collective rotation in the light Er isotopes is summarised.

The high-spin states of even Pt isotopes are described within the conventional interacting boson approximation and the two-quasiparticle model. It was found that the first backbendings of the yrast levels of ¹⁹²Pt and ¹⁹⁰Pt can be reproduced reasonably. The main features of the calculated B(E2) values for ¹⁸⁴Pt yrast band against the spin of the depopulating states are also in agreement with the observed values.

The consequences of applying the local age parameter to individual showers are discussed. It is shown that the local age parameter in individual showers does not behave according to the predictions given by Capdevielle and Gawin (1982). It is also shown that the local age parameter can become negative and that the probability for such events is so large that it cannot be ignored. The results indicate that the local age parameter cannot be used to calculate the age of individual showers according to the procedure given by Capdevielle and Gawin.

The effective potential for spontaneous breaking of chiral symmetry is calculated for finite temperatures and baryon densities from a Nambu-Jona-Lasinio type of Lagrangian with explicit flavour symmetry breaking by bare quark masses.

The weak flavour mixing matrix, appearing in the left-handed charged weak current, is constructed from the Fritzsch mass matrix as functions of six quark masses and three complex phases. On comparing it with the present experimental data on weak flavour mixing, the two complex phases (one taken as zero) seem to be pi /2, for certain quark masses. On the other hand, however, the assumption that the complex phases in the weak flavour mixing matrix are responsible for the weak CP non-conservation implies that the complex phases should be very small for the same quark masses in order to produce the correct magnitude of weak CP non-conservation observed in the neutral kaon system. The discrepancy would not be compromised by varying the quark masses within allowed ranges or by including the long-range contributions to the K⁰-K⁰ transition amplitude.

Using the electroweak theory of Weinberg and Salam in conjunction with the Bethe-Salpeter formalism, the authors calculate the contribution of the Z⁰, both the exchange and annihilation diagrams, to the hyperfine structure of toponium. As a function of the Higgs mass, they also calculate the contribution of a single Higgs boson to the hyperfine structure. Furthermore, they examine both the electromagnetic and strong contribution to the hyperfine structure.

It is argued that retarded/advanced effects of gluon exchange must be taken into account when mesons consisting of light quarks are calculated within the bag model. Good results are obtained for mesons up to 1800 MeV using the coupling constant and the bag radius as the only two parameters. The Coulomb gauge is used to ensure that only transverse gluons can make a contribution. A significant quark-antiquark-gluon component is found in the meson wavefunctions.

The general structure of the asymmetries of longitudinally polarised electron scattering by deuterons with vector and tensor polarisations has been established for the process e^-+d to e^-+n+p using the structure function formalism and considering the deuteron as an elementary particle with a unit spin and a positive space parity. The analysis has been performed in terms of the one-photon approximation using the conservation of the hadron electromagnetic current and P-invariance of the hadron electromagnetic interaction. The inclusive scattering of longitudinally polarised electrons by a target with a vector polarisation is described by two real structure functions, while the scattering of unpolarised electrons by a target with a tensor polarisation is described by four structure functions. Both the vector and tensor target polarisations allow, in principle, studies of possible T-odd effects in hadron electrodynamics. The sensitivity of inclusive asymmetries to the neutron electric form factor and the spin deuteron wavefunction has also been investigated.

Generalised nuclear collective coordinates are introduced and they are used to construct bosons of different multipolarities. The U(r) group created by them is indicated and a general method of searching its subgroups is proposed. It is illustrated by the example of an spdf IMBM of boson multipolarities 0, 1, 2, 3. The procedure for writing the boson Hamiltonian and transition operators in terms of the group generators is sketched. A concise version of a Hamiltonian of several terms is given. The model possibilities for improving the usual IBM by describing missing states and poorly reproduced transition rates are discussed. Its possible application to the recently observed low-lying negative-parity states in doubly even isotopes of the Ra region is pointed out.

The conditions for shock existence in a relativistic fluid with non-zero baryon number are considered. The authors have found the general stability criterion of relativistic shocks for substances with arbitrary thermodynamic properties.

A simple prescription is given for calculating the effect of the break-up channel in deuteron stripping and pick-up reactions, and it is found to work for a wide range of nuclei.

The authors present an analysis of the effect of the long-range residual interaction (LRRI) on the root mean square radius of charge (RMS radius) over a large range of nuclear masses. They also investigate the implications of a consistent treatment of that effect on single-particle potentials and energies.

An analysis of both positive- and negative-parity states of the odd-neutron Ba and the odd-proton La transitional isotopes (N<82) within the framework of the proton-neutron interacting boson-fermion model (IBFA-2) is presented. Energy spectra, electromagnetic properties, isotope shifts and one-nucleon transfer spectroscopic strengths for odd-mass Ba and La isotopes are compared with experiment. Generally good agreement is obtained with a restricted number of adjusted parameters. Some predictions on the properties mentioned above are presented for nuclei for which no experimental data are available.

The decay energy of ¹³²Cs, as determined from intensity ratios of positron branching, is 2128+or-6 keV.

Neutron spectra following ¹²C+^113,115In and ¹²C+¹⁵⁹Tb reactions at E_lab approximately=100 MeV coincident with gamma rays of energies between 2 and 20 MeV, have been measured. The high-energy slope of these spectra is used to probe the neutron gamma-ray emission sequence. It is concluded that gamma rays with an energy exceeding approximately one neutron binding energy have an enhanced probability, compared with low-energy gamma radiation, emitted early in the decay process.

Measurements of the internal conversion electron spectrum provide additional information about the nature of the excited 0⁺ states in ²⁰⁰Hg. The states were excited following thermal neutron capture and levels at 1029.4, 1515.0, 1856.8 and 2116.9 keV were identified as 0⁺. The last one is a new spin assignment and the authors find no evidence for a previously reported 0⁺ level at 2697.1 keV. Altogether 16 E0 transitions were observed. An IBA-2 analysis provides in general an adequate description of the 0⁺ levels and their E0 decay modes.