Table of contents

The authors have proposed a nonet symmetry breaking model to account for the observed branching ratios B(D_s⁺ to eta pi ⁺) and B(D_s⁺ to eta ' pi ⁺). Other consequences of this model are explored. They find that the branching ratios of (D, D_s⁺) decays into two pseudoscalar mesons, one of which is eta ', are enhanced. In particular, they predict B(D⁰ to K⁰ eta ') approximately=20%, B(D⁺ to eta ' pi ⁺) approximately=3% and B(D_s⁺ to eta 'K⁺) approximately=1%, the last two hardly Cabibbo-angle suppressed.

A measurement of the spin correlation parameters between a polarised proton and a vector polarised deuteron in the deuteron break-up reaction dp to (pp)n can lead to interesting nucleon-nucleon information, providing the two final protons are selected to lie within the peak of the ¹S₀ final state enhancement (the d*). Though such experiments should add little to nucleon-nucleon knowledge below 515 MeV, where the phase shifts are already well determined, some systematic corrections are minimised by using a polarised deuteron to investigate neutron-proton charge exchange.

It is shown that the constituent quark model is capable of giving a consistent description of the integrated spin-dependent structure function of the nucleon. This enables the author to perceive an intrinsic connection between the current and the constituent pictures of the quark.

All eigenvalues and eigenvectors of states which occur in the lowest 20-30 MeV of excitation energy are calculated in the full d₅2/-s_1/2-d_3/2 model space for several sd shell nuclei and are analysed in terms of their statistical features.

Mean lifetimes of high-spin states in ¹²⁶Ba were measured using the recoil distance Doppler-shift method. The effect of different sidefeeding times on the results is shown. The B(E2) values are compared to theoretical predictions of collective models.

New measurements of proton inelastic scattering to a number of low-lying positive-parity states in ⁹⁰Zr are reported. Differential cross section and analysing power angular distributions are presented for the 2₁⁺, 4₁⁺, 2₂⁺, 6₁⁺ and 8₁⁺ states to theta _cm approximately=45 degrees at an incident proton energy of 400 MeV. The data are compared with microscopic distorted-wave Born approximation calculations.

A novel formulation of the dependence of the total cross section for the photon-nucleus interaction on photon energy and target mass number is proposed and used to obtain the photofission channel width Gamma _F for ²³⁸U in the quasideuteron energy range. Comparison with experiments and with different calculations show that the formalism used is quite adequate to explain the generally assumed trend of Gamma _F against energy and mass number in this peculiar energy region.

The author discusses new natural radioactivities with emission of ¹⁴C, ²⁴Ne and ²⁸Mg (cluster radioactivity) in the framework of an open quantum nuclear dynamics (fragmentation theory) which uses few collective modes as open quantum systems. Firstly, by assuming that the dissipation could be neglected, it is shown that on the potential energy surface, in addition to the liquid drop model valley corresponding to normal fission, appear other valleys: Pb valley for cluster radioactivity, Sn valley for the bimodal fission or cold fission and alpha valley for the alpha decay. This leads to a unified description of the above decays as spontaneous fission modes, in which one or both fragments have magic or almost magic numbers, a new form of radioactivity-magic radioactivity. Secondly, it is shown that for processes in which the dissipation could not be neglected, like charge equilibration in deep inelastic collisions, the new quantum nuclear dynamics describes excellently the experimental data. Thirdly, it is shown that the nuclear molecules are strongly correlated with the above decays. The author concludes that all the processes which imply large rearrangements of nucleons could be suitably described as open quantum systems.

The authors use the dimensional regularisation approach to study the axial model exploring the analogy existent with the Schwinger model.

Within a three-phase description of strongly interacting matter, the equation of state for the massive quark matter phase is derived from the string-flip model. Values for the latent heat and the critical temperature of the quark-hadron phase transition are given and the duration of the cosmic hadronisation transition is obtained in accordance with earlier estimates. The relation of the authors' equation of state to the widely used bag model approaches is discussed, and especially near the phase transition a bag model with B_Q=(178 MeV)⁴ is a good fit to their results. Bounds for the possible existence of an intermediate massive quark matter phase are estimated.

In standard QED, particle interactions are evaluated using minimal coupling coupling the particles solely through their (electric monopole) charges. The Dirac Hamiltonian is used to describe the interaction of a single spin-¹/₂ particle with an electromagnetic field. Pauli (1934) suggested the addition of a further gauge-invariant term to the Dirac Hamiltonian where the coupling constant for this extra term should not be directly linked to the particle's electric charge. The authors study some of the effects of this additional term and show that for the scattering of electrons off protons, the first-order Pauli-Dirac analysis has at least as good agreement with experiment as previous analyses based on the Dirac Hamiltonian. They show that Rosenbluth used the incorrect sign on the anomalous magnetic moment of the proton. Using Rosenbluth's prescription of considering only the proton's anomalous magnetic moment but correcting the sign, they find only a negligible difference from a completely Dirac analysis. Any proton form factors, and thus any charge distributions, deduced from the Rosenbluth result will be incorrect.

The x-rescaling approach to the EMC effect is used in the analysis of neutrino deep inelastic scattering and Drell Yan processes off nuclei. The expected probe independence of the EMC effect is supported by the good agreement of the results with the experimental data.

The authors present results of calculations of the magnetic moments of nuclei with a doubly-closed shell plus or minus one nucleon using the relativistic scalar-vector model including configuration mixing. Compared with earlier calculations, the inclusion of configuration mixing within one major shell removes most of the discrepancies of the isovector moments without altering the previous satisfactory results for the isoscalar moments.

The Buck-Dover-Vary cluster model is used to generate several bands of alpha-particle cluster states, labelled by the principal quantum numbers N=12, 13, 14, 15, and 16 in ⁴⁴Ti. Various cluster core effective potentials are considered, and the one based on a realistic folding integral with a finite-range Gaussian interaction is found to be the most satisfactory. It is similar to the unique optical potential, deduced from alpha -⁴⁰Ca elastic scattering over a wide range of energies, and so offers the opportunity of unifying the descriptions of the bound-state and scattering phenomena in this nucleus. The authors calculate excitation energies, alpha decay widths and mean-square radii for the cluster states. They thereby find that the N=15 negative parity band overlaps the N=16 positive parity band, in qualitative agreement with experiment.

A cluster model employing a local, effective cluster-core potential based on a folding procedure is used to investigate exotic and alpha decays from heavy nuclei as a quantum tunnelling phenomenon within a semiclassical approximation. For the exotic decays, excellent agreement with all reported experimental measurements of the partial lifetimes for ¹⁴C and ²⁴Ne emission from heavy nuclei is obtained. Further consideration of the structure of these nuclei indicates preformation or spectroscopic factors generally in the range 0.1-0.5. For alpha decay, a similar cluster-core potential is represented by a simple three-parameter form having a fixed diffuseness, a radius proportional to A^1/3 and a depth which is adjusted to fit the Q value of the particular decay. The calculations yield excellent agreement with the vast majority of the available data for ground state to ground state alpha decays. Some examples are presented.

Nuclear medium modifications to the deuteron-nucleus folded potential are discussed using a density-dependent effective interaction derived from Brueckner-Hartree-Fock calculations of the optical model potential in nuclear matter. The medium effects generate central and T_R type tensor potentials which are found to improve the agreement with differential cross section data for the ²⁰⁸Pb(d, d)²⁰⁸Pb reaction at 56 MeV.

High spin states of ¹⁵⁷Er have been populated using the ¹¹⁴Cd+⁴⁸Ca reaction at a ⁴⁸Ca bombarding energy of 200 MeV. Gamma rays were detected in an array (TESSA2) of six escape-suppressed Ge spectrometers and a 50-element BGO multiplicity and summed energy detector. Decay scheme and angular correlation data were obtained from the gamma - gamma BGO coincidence data The yrast band has been identified up to 65/2⁺ and two negative parity sidebands have been identified (one previously unobserved) up to 69/2^- and 63/2^-. An additional sideband of six transitions was also observed. The band structures are interpreted in terms of quasiparticles in the framework of the cranked shell model.

Multiple electromagnetic excitation of a rotational band coupled to high-lying giant dipole states is studied theoretically. The excitation of the rotational band is treated in the sudden approximation. With the help of rather simple scaling properties one can obtain insight into the physics of the process. The authors give explicit results for ¹⁶O-²³⁸U and ²³⁸U-²³⁸U collisions in the range of E/A approximately=100 MeV up to the ultrarelativistic limit ( gamma to infinity ).

Excited states in the nuclei ^128,130La have been investigated to high spin using gamma -ray spectroscopy techniques. In addition to the main rotational structures based on a prolate collective rotor, and a superdeformed band in ¹³⁰La, two bands are seen with properties similar to the collective oblate structure proposed for ¹³¹La. The experimental evidence for these bands is discussed in terms of the variation in energy-level signature splitting, B(M1)/B(E2) ratios and mixing ratios as a function of rotational frequency and single-particle configuration. These results are interpreted using odd-odd particle-rotor model calculations and self-consistent cranking calculations. They are compared with the proposed 'collective oblate' bands in other nuclei in the A=130 region and possible evidence for collective oblate shape co-existence is presented.