Table of contents

With the introduction of a transition potential v( gamma N to pi N) and a gamma N to or from Delta interaction, a Hamiltonian is constructed for gamma , pi , N and Delta as a unified theoretical framework for pi -nucleus reactions and photopion processes. Good fits to pi N scatterings and gamma N to pi N are obtained. Unitarity is included in the theory. It enables the author to obtain consistency in two- and many-body problems for both pi -nucleus and photopion reactions. It is proposed that photopion reactions be used to help determine pi -nucleus interactions.

The two-deuteron-alpha-particle overlap, including its D-wave component, is evaluated in the case of realistic two- and four-body wavefunctions. The deduced theoretical D₂(d, alpha ) value is compared with improved empirical estimates of D₂(d, alpha ) based upon DWBA analyses of (d, alpha ) reactions in the sd shell and which incorporate the best available shell-model information for the nuclear states involved. The theoretical and empirical values of this analysis are in agreement and yield a value D₂(d, alpha ) approximately=-0.1 fm². This value differs substantially from other recent empirical estimates, D₂(d, alpha )=-0.3 fm², obtained from (d, alpha ) reactions upon heavier target nuclei and from simple theoretical estimates which make use of a point-deuteron approximation.

The correlations observed recently in high-resolution proton resonance data on medium-mass targets for resonances distant from analogue states are traced back to the modification of nuclear wavefunctions by the continuum. The modifying part of the wavefunction is excited by a 'direct' reaction mechanism. The correlations are shown to be of the same type as those between resonances in the vicinity of analogue states.

A search for monoenergetic positron emission following the decay of the isomer ^152mEu(t₁2/=9.32 h) has been performed using a double-focusing iron-core electron spectrometer. No line was observed at the appropriate point of the spectrum and a consequent branching ratio for this process was determined to be (3.4*10^-7 positrons per gamma transition. From this result it was deduced that the lifetime of the 1511 keV level in ¹⁵²Sm is greater than 3.5*10^-15 s.

New empirical two-body matrix elements derived from the spectra of 1s-0d shell nuclei are compared with previous empirical results and with the G-matrix elements obtained from the Reid soft-core and Paris potentials. A spin-tensor decomposition of the matrix elements is made and comparisons are presented for the separated central, tensor, spin-orbit and antisymmetric spin-orbit components.

Finite-range DWBA analyses have been performed for (⁷Li,t) reactions with the use of a microscopic potential overlap for the alpha +t system. The use of the microscopic potential overlap improves the agreement between the spectroscopic factors extracted and those taken from theoretical calculations.

It is shown that the configuration-mixed shell model predicts alpha branching ratios from high-spin ²⁴Mg states that are in good agreement with the average experimental results whereas the statistical model gives poor agreement. It is concluded that the configuration-mixed shell model is appropriate for considering ²⁴Mg states above 15 MeV.

Inner bremsstrahlung accompanying the first-forbidden beta decay of ⁸⁶Rb was measured using the magnetic defection technique with a 4.5*5.1 cm² NaI(Tl) crystal in the energy range 200-1660 keV. The raw spectrum was unfolded using the step-by-step process of Starfelt and Liden and compared with KUB, LF and FM theories. The measured spectrum is found to show fairly good agreement with LF theory in the energy range 200-1500 keV and it is found to deviate thereafter from all three theories.

Root-mean-square radii of neutron orbits and reduced normalisations of, 1⁺/2 3⁺/2, 5⁺/2, and 7⁺/2 low-lying states in ⁹⁹Mo have been determined from an analysis of angular distributions and absolute cross sections of the ⁹⁸Mo(d,p)⁹⁹Mo reaction. The data were taken at the sub-Coulomb deuteron energy of 4.5 MeV. The systematics of RMS radii of neutron orbits for nuclei with A=89-125 are discussed.

The ¹⁰⁷Ag(n, gamma )¹⁰⁸Ag reaction has been studied using a variety of techniques: (i) thermal neutron capture-primary gamma rays measured with a pencil-shaped Ge(Li) detector; 45-1200 keV gamma rays measured with a bent-crystal spectrometer; 10-80 keV gamma rays measured with a Si(Li) detector; conversion electrons measured with a magnetic spectrometer; gamma-gamma coincidences studied with Ge(Li) detectors; (ii) resonance neutron capture-low-energy gamma rays following both single-resonance (16 eV) and average-resonance (2 and 24 keV) neutron capture have been analysed. The data obtained from these measurements have enabled the construction of a level scheme of ¹⁰⁸Ag containing 65 excited states with precisely determined energies. Spin and parity assignments have been made for most of the levels. The neutron binding energy in ¹⁰⁸Ag has been determined as 7269.6+or-0.6 keV.

The odd-proton nuclei ¹²⁷La and ¹²⁹La have been investigated to high spin using gamma -ray spectroscopy. Seven new states have been found in ¹²⁷La, while in ¹²⁹La six new states were seen. In both nuclei, the yrast band has been extended to J^pi =47^-/2 allowing a band crossing to be found at a rotational frequency near 0.5 MeV/h(cross). Angular correlation and linear polarisation measurements have shown that the positive-parity side-band has a spin sequence 21/2, 25/2, 29/2, etc., i.e. positive signature. In ¹²⁷La a band crossing is also present in the side-band near h(cross) omega =0.5 MeV. The results can be explained in terms of the cranked shell model by assuming an axially symmetric prolate shape with epsilon ₂ approximately 0.25. No evidence is found for triaxial shapes. Mean lifetimes were measured for the yrast states in ¹²⁷La using both the recoil-distance method and the Doppler-shift attenuation method. The results show a marked drop in collectivity which is not understood.