Table of contents

Within the framework of the interacting boson model, the authors consider a boson system in which all bosons interact through a surface-delta interaction which spans several single-boson states. The model is tested with medium or heavy two-boson nuclei. Energy levels and relative B(E2) values are reproduced well in some sample calculations.

Ground-state potential energy surfaces for ^176,178,180Pt have been calculated by using the Woods-Saxon single-particle potential and the Strutinsky renormalisation procedure. These potential energy surfaces predict a ground-state shape change from a large prolate deformation for ^178,180Pt ( beta ₂ approximately=0.24) to a smaller triaxial deformation for ¹⁷⁶Pt with a second minimum developing at large prolate deformation ( beta approximately=0.23) above the 4⁺ state. There is excellent agreement between these independent calculations and recent measurements of the yrast bands in ^176,178Pt.

The exotic radioactive emission of heavy ions from very heavy nuclei is studied with regard to transitions into excited states of the daughter nucleus. The influence of these transitions on the total decay rates and branching ratios is discussed.

The consequences for nucleus-nucleus collisions of the invariance (tidal symmetry) of arbitrary but momentum-independent interactions under rotations about the relative coordinate of the interacting nuclei are examined. In conjunction with an approximate treatment of the centrifugal barrier this symmetry leads to a partial diagonalisation of the coupled-channels description of the scattering of the two nuclei. This approximation is found to give an accurate description of the tensor polarisation observables in a specific heavy-ion elastic scattering case. A consequence of the treatment given here is that the so-called 'shape effect' relations can be satisfied in strong-coupling situations.

Based on a supersymmetric subalgebra involving only the Hamiltonian, the lattice N=2 Wess-Zumino model in 1+1 dimensions is formulated so that it can be investigated within the local Hamiltonian Monte-Carlo method. The authors find evidence for the existence of topological excitations in the model, but no evidence for the breaking of supersymmetry within the numerical accuracy.

Positivity and unimodality of an unknown function, chi ₁(x), related to the imaginary part of the forward elastic K^-p amplitude on the unphysical cut, allow one, through a dispersion relation, to obtain upper and lower moment sequences of that function. The inversion of the moment sequences using a Stieltjes-Chebyshev technique allows the calculation of the scattering amplitude on the unphysical cut, so completing the map obtained in a previous work. A range of values is obtained for the K^-p elastic threshold real part between -1.075 and -0.865 fm, in agreement with recent determinations by low-energy parametrisation. A corridor for the real parts of the amplitude has been determined in the unphysical region using (two) upper and lower error sequences.

The equations of multi-step escape width ( Gamma _i up arrow ), damping width ( Gamma _i down arrow ) and the interaction-induced transition from ith stage to the (i+l)th stage (V_i) are formulated. On the basis of these equations, the total number of stages before equilibrium and the Fermi energy of the nucleus are discussed.

Natural samples of In, Sn, Te, I and Hg have been used in a study of the scattering of 2.5 MeV neutrons. The scattered-neutron energy spectra were determined by unfolding the proton-recoil pulse-height spectra from NE 213 scintillation spectrometers. The parameters of the spherical optical model which gave the best fit to the elastic differential cross sections were found and used in Hauser-Feshbach calculations of the inelastic differential cross sections. Calculated inelastic cross sections were combined, with gaussian energy smearing to match the energy resolution of the detectors, for comparison with the measured data. Generally good agreement was obtained. Calculations were also based on 'global' and 'regional' optical-model parameter sets with results that are better in some cases than in others.

36 MeV triton elastic scattering data have been obtained for targets of ³⁰Si, ²⁸Si, ²⁶Mg, ¹⁶O and ¹²C. These data are analysed in terms of a conventional phenomenological optical model and double-folding optical model.

States in ¹⁷O have been populated using the ¹²C(⁶Li,p)¹⁷O reaction at 28 MeV. Some levels are strongly excited and it is suggested that they may contain substantial 5p-4h configurations. Angular distributions show characteristics of both compound nucleus and direct processes and although the overall magnitude of the cross section for most levels is well reproduced by Hauser-Feshbach calculations the forward angle data for the ground state have been fitted assuming a direct transfer of five nucleons as a ⁵He cluster.

The differential cross section and analysing powers iT₁₁, ^TT₂₀, T₂₀, T₂₁ and ^TT₃₀ have been measured for both the elastic scattering of 44 MeV polarised ⁷Li from ¹²⁰Sn and for projectile excitation to the 1/2 state at 478 keV. The data have bee fitted with coupled-channels calculations which include ground-state reorientation of the ⁷Li and coupling to excited states of ⁷Li. The sensitivity of the different observables to a number of coupling schemes is discussed. The potentials were derived from a double folding model which explicitly includes the ⁷Li deformation.

Gamma-ray data from ^74,76Ge+¹⁸O fusion-evaporation reactions are analysed to provide data on yrast decay schemes in ^87,89Zr, ^87,88,89,90Y and ⁸⁶Sr. The data include excitation functions, angular distributions, gamma - gamma coincidences, linear polarisation measurements and lifetimes deduced from both Doppler shift attenuation and recoil distance measurements. Shell-model calculations are presented for ^88,90Y and ⁸⁶Sr.

The E0 and E2 transitions depopulating the O₂⁺ and O₃⁺ states in the N=88-90 nuclei ^150,152Sm have been studied using conversion-electron and gamma -ray spectroscopy. The level energies and the B(E2), rho ²(E0) and X_ijk (E0/E2) values have been calculated on the IBA-1 model and compared with the experimental data and the PPQM results of Kumar (1974). The present data qualitatively agree with the suggested shape-coexistence interpretation of the even-mass Sm isotopes.

The gamma decay of ²³²U has been investigated following the ²³²Th( alpha ,4n) reaction. An experimental technique has been used to suppress fission background. Levels up to 20⁺ in the yrast band in even-even uranium nuclei are compared and their systematic behaviour discussed.

The idea of Bhat et al. (1985) that the bulk of cosmic rays below 10 GeV are accelerated in supernova remnants suggests that cosmic rays should also exhibit intensity variations on a scale comparable with the linear size of a representative remnant. Following the general spirit of shock-wave acceleration models. The authors carry out Monte Carlo simulations to predict what this scale should be and then proceed to present corroborative evidence from an autocorrelation analysis of the COS B and SAS II gamma -ray data for the latitude range mod b mod =10-20 degrees ('near Galaxy') and mod b mod <or approximately=5 degrees ('far Galaxy').

For pt.I see ibid., vol.12, p.1067-86, 1986. Bhat et al. have previously argued that the bulk of the cosmic rays below about 10 GeV are accelerated in supernova remnants. Here the authors search for support amongst results from gamma -ray astronomy on the large-scale distribution of cosmic rays. They conclude that there is support for this idea: the average intensity as a function of Galactocentric distance, the ratio between the average intensity in the second and third quadrants and the reduction in intensity in the interarm region centred on l approximately=65 degrees are all consistent with the SNR model.

The authors examine some properties of 10⁹-10¹⁰ GeV extensive air showers (EAS), such as the electron and the muon lateral distribution, the ratio of muon electron density, the shower front structure and the transition effects in a scintillator, with the new Akeno 20 km² giant air showers (GAS) array at core distances between 100 and 3000 m. At large core distances the lateral distributions of both electrons and muons become steeper than extrapolations of the formulae so far reported. The thickness of shower fronts agrees well with Linsley's formula up to 3 km, to the extent that the authors pulses delayed by more than R/c (R is the core distance).