Table of contents

A satisfactory description of available experimental data (1000 points) for the pi ⁺d to pp process was obtained using a model including ³P₁, ¹D₂ and ³F₃ diproton resonances in the I=1 channel.

Coupled-channel calculations for elastic and inelastic scattering of ¹²C by ¹²C at 1016 MeV have been performed within the vibration model.

The possible effect of the recently discovered subshell closure at Z=64 is investigated for ¹⁶⁰Dy. Energy levels and B(E2) ratios are compared with IBM-1 calculations assuming either a single Z=50-82 shell or subshell closure at Z=64. The latter calculation improves agreement with experiment.

An alpha-HI correlation measurement was performed to see whether the ¹²C-¹²C molecular resonance states can be populated in the ¹²C(¹⁶O, alpha ) reaction. The cross sections of such processes were small, if any. Instead, the sequential alpha-decay processes of ²⁰Ne* and ¹⁶O* mainly contribute to the molecular-resonance-like structures in the alpha spectra.

It is shown that the Slavnov-Taylor identity does not put enough constraint on the longitudinal vertex function to allow the unambiguous construction of an approximate Schwinger-Dyson equation for the gluon propagator.

The potential description of a quark-antiquark system seems to work very well in describing a number of hadronic properties. However, the precise form of the potential is unknown. The changes in the low-lying eigenvalues as a result of changes in the long-range part of the potential are investigated in a non-perturbative manner. It is shown by considering a variety of examples that the low-lying eigenvalues are insensitive to the long-range part of the potential.

A rapidly converging expansion method for the Coulomb T operator is applied to relate S-wave strong interaction shifts and widths in the ground state of mesic atoms to the pure hadronic scattering length in the corresponding scattering system. The result improves the accuracy of the Deser formula and, in combination with other methods, allows a determination of Coulomb corrections to S-wave scattering lengths in a model-independent way. In detail, the author discusses various corrections in the ground state of kaonic hydrogen, where a discrepancy between bound-state and scattering data exists which is not yet understood. Further applications are given for heavier pionic atoms and atomic protonium.

The expansions E_rot(I)= Sigma _i=1ⁿ¹A_i(I(I+1))ⁱ and E_rot(I)= Sigma _i=1ⁿ² alpha _i omega _I²ⁱ that describe the energies of the levels in the ground-state rotational bands with K^pi =0⁺ are generally not equivalent unless n₁=n₂=1 or infinity . A method is proposed to characterise this non-equivalency quantitatively. It was found that in some nuclei, like ²⁴⁸Cm and ¹⁷⁶Er, the I(I+1) expansion is better than the omega ² expansion, whereas in the majority of nuclei the omega ² expansion is better. The data demonstrate that the rates of convergence of the I(I+1) and omega ² expansions for E_rot depend on the individual properties of the nuclei.

The notion of a multicluster fractional parentage coefficient (MCFPC) is introduced to study reactions with the emission of several composite particles. A compact formalism has been developed for calculating MCFPC in the harmonic-oscillator translationally invariant shell model (TISM) which is based on the relation between the TISM and the conventional shell model. Tables of MCFPC for the disintegration of ¹⁶O into three fragments of 11, 3 and 2 nucleons are given by way of example.

The ³He-nucleus optical potential has been calculated in an extended folding model in which the first- and second-order terms are calculated separately, the internal motion of the ³He nucleons is included, the break-up of the projectile is simulated and the target excited states are coupled to the imaginary potential. An improved version of the Kuo effective interaction including odd-state forces and the projectile energy in the second order terms is used in this model. The data analysis indicates that, in this model, the second-order potential must be calculated more accurately if agreement with experiment is to be obtained and that the backward-angle data are sensitive to the imaginary potential. A comparison has been made with previous analyses.

The modified BCS approach for rotating nuclei is extended in order to include thermal excitations. The formalism is developed to take into account both high-spin and temperature-dependent effects. The method seems to be appropriate for the microscopic description of the pairing correlations at excitation energies above the yrast line.

Strutinsky calculations are used to investigate the shape and fission stability of rotating nuclei. A cranked Woods-Saxon single-particle Hamiltonian is provided to describe triaxial and dumb-bell shapes. Since the cranking term violates time-reversal symmetry the convenient BCS method cannot be applied. On the other hand, the consideration of pairing by the solution of HFB equations is possible for a few selected nuclei only. As demonstrated recently, pairing influences the shape of fission barriers up to very high angular momenta and should not be neglected. Thus, modifications of the BCS equations are desirable. Such methods are discussed and their results are compared with the HFB results.

The thermodynamic properties of a system of Dirac particles interacting through classical fields are studied within the interaction models proposed recently. The theoretical formalism is based on the variational ansatz of the Gibbs free energy. The binding energy per nucleon, pressure and specific entropy are calculated from the low-temperature expansion in the range of densities and temperatures of interest to heavy-ion reactions. The calculated value of specific entropy produced in heavy-ion collisions is found to be much less than that obtained from the measured value of the deuteron to proton ratio. The model of Boguta and Bodmer (1977) predicts larger values of the specific entropy as compared with those of the Walecka model. It is pointed out that the difficulty of understanding the nuclear level density data may be related to that of the entropy production in heavy-ion reactions. A relativistic generalisation of Bethe's level density parameter and the average thermal energy, useful in hydrodynamic calculations, are derived.

Using the liquid-drop model, the authors have performed a systematic study of symmetrical fusion with a neck degree of freedom and tunnelling effects, the nuclear potential being calculated with the proximity approach. Barrier heights and positions are in very good agreement with experimental data when they are known (light-medium systems); the recent experimental data for the reactions ⁵⁸Ni+⁵⁸Ni and ⁶⁴Ni+⁶⁴Ni are investigated particularly. For heavier systems double-humped fusion barriers and isomeric states are predicted which strongly limit the complete fusion probability.

A study of inelastic neutron scattering by the nucleus ¹⁸⁶W at an incident energy of 2.75 MeV using the coupled-channel method has been made. Consideration is made of the 2⁺(0.122 MeV), 4⁺(0.3966 MeV), 2⁺(0.7375 MeV), 3⁺(0.8618 MeV) and 4⁺(1.031 MeV) excited states. It is shown that in this energy range the process may be described satisfactorily by the Davydov-Filippov model, considering ¹⁸⁶W as a deformed nucleus with non-axial symmetry, given the quadrupole and hexadecapole deformations. The scattering process through the compound nucleus is calculated according t the Hauser-Feshbach formula. It is shown that the presence of direct excitation processes may be partly due to the non-axiality of ¹⁸⁶W.

Angular distributions of gamma transitions between the levels in ¹⁹⁰Os fed in the decay of ¹⁹⁰Ir aligned in a rhenium single crystal have been measured at temperatures down to 2 mK. Multipole mixing ratios in both gamma and electron-capture transitions are deduced and compared with various nuclear models. The angular distribution coefficients are applied to interpret very small anisotropies observed when ¹⁹⁰Ir is polarised in an iron host matrix, cooled to 2.5 mK. The deduced magnetic dipole moment of the 4⁺ ground state of ¹⁹⁰Ir is mod mu (¹⁹⁰Ir; GS) mod =0.04(1) mu _N. Possible single-particle descriptions compatible with this result are suggested.

An old model for the origin of cosmic rays is reinvestigated. It is shown that under the assumption of repeated explosions in the galactic centre separated in time by 10⁷ yr, the last one being 10⁶ yr ago, a number of observed cosmic-ray properties can be reproduced. Acceptable fits appear for the form of the energy spectrum of protons from 1-10⁸ GeV and the mean grammage. The long-term near-constancy of the intensity is understandable. However, the observed anisotropy and the grammage distribution can be accounted for only if the diffusion in the disc is much smaller than that in the halo.

In a previous paper Protheroe et al. (1980) used the Uhuru X-ray data of Schwartz (1979) to show that the anisotropy in the diffuse background for the energy range 2-7 keV was not inconsistent with that observed in the 2.7K relict radiation. The authors take more recent and extended data by Iwan et al. (1982) for the range 2-60 keV to make a new determination of the X-ray anisotropy. After eliminating the possibility that galactic effects are responsible or that the anisotropy is due to discrete extragalactic sources it is again found that there is no inconsistency with the 2.7K results, although the X-ray data are still not sufficiently accurate to enable a statement of clear consistency to be made.