Table of contents

A recently discussed class of gauge models of weak and electromagnetic interactions allows the possibility of a light neutral gauge boson, with mass in the PETRA-PEP energy range. The consequences of such a light gauge boson are investigated for the reactions e⁺e^- to mu ⁺ mu ^-(e⁺e^-). Predictions for the total cross sections and charge asymmetries are presented, covering the energy ranges of DORIS-SPEAR and PETRA-PEP. Curves are also presented for massive muon pair production cross sections in proton-proton and proton-antiproton collisions at centre-of-mass energies of 60 GeV and 200 GeV.

It is shown that a cancellation causes the contribution from certain exchange currents to the pion+deuteron scattering length to be much smaller than previously estimated.

Recent experimental results on beta -decay energies of neutron-rich nuclei indicate the existence of subshell-closure effects of nuclear binding energies for the neutron number N=56 and the proton number Z=38.

A method of lowest-order constrained variation previously applied by the authors to asymmetric nuclear matter is extended to include electrons and muons making the nucleon fluid electrically neutral and stable against beta decay. The equilibrium composition of a nucleon fluid is calculated as a function of baryon number density and an equation of state for beta-stable matter is deduced for the Reid soft-core interaction.

The binding energy shifts arising from the explicit inclusion of intermediate states involving a N*(1234) are calculated for the light nuclei ⁴He, ¹²C and ¹⁶O. An oscillator approximation is made for the single-nucleon wavefunctions and the two-body correlations are taken from an LOCV calculation. It is observed that the Pauli effect per nucleon is essentially the same in all three nuclei and is similar to that found in the nucleon fluids. The dispersion effect in the light nuclei is smaller than in the nucleon fluids. It is concluded that these contributions will have a large effect on the saturation of finite nuclei.

Evidence is given that there is a positive imaginary spin-orbit potential in the proton optical potential for ⁴⁰Ca at around 30 MeV, dropping with energy and apparently becoming negative at high energies. This is consistent with probable phonon-coupling effects but inconsistent at lower energies with ab initio OM calculations. Similar behaviour is found for ¹⁶O but with generally much smaller values of the imaginary potential. The authors comment on the need for suitable data to enable them to establish the general properties of W_so, the imaginary spin-orbit strength. The determination of an imaginary spin-orbit potential is made possible since the l-dependent potential used permits unprecedented quality of fit for angular distributions for these nuclei.

A fourth-power momentum term is added to a simplified form of Skyrme interaction and the resulting two-body force is used to study the real part of the optical-model potential for the elastic scattering process n+⁴⁰Ca at energies of 10 MeV and 50 MeV. It is found that the k⁴ term affects the shape, the magnitude and the energy variation of the optical-model real well.

The unexpectedly large cross section reported by Wolynec et al. (1976) for the ²³⁸U(e, alpha )e'²³⁴Th reaction has been investigated. Using an activation method the cross section is found to be lower by a factor of at least 6 and the results of a direct alpha-particle counting experiment suggest a factor of at least 20. It is concluded that the alpha-decay mode can, at most, exhaust only a few per cent of the isoscalar energy-weighted sum rule for the giant quadrupole resonance.

Angular distributions obtained between 16 degrees and 108 degrees for the ¹⁶O( alpha ,d)¹⁸F reaction leading to the lowest J^pi =5⁺ excited state in the residual nucleus show a drastic variation in the degree of forward peaking over the incident energy range 28.0 MeV to 33.6 MeV. This phenomenon is demonstrated to be correlated with the anomalous large-angle elastic scattering effect in ¹⁶O( alpha , alpha )¹⁶O. The results allow certain conclusions regarding the optical potential of the incident channel.

It is pointed out that a negative slope for the form factor in pseudoscalar Dalitz decays can be explained by vector-meson dominance with a subtracted dispersion relation. Calculations are made for the pi ⁰ and eta using the experimental omega to pi ⁰ gamma , phi to pi ⁰ gamma and phi to eta gamma decay rates and SU(3) symmetry. An incidental consequence of these calculations is that excitable colour gluons do not significantly affect eta Dalitz decay.

Dispersion relations for the real part of the antisymmetric amplitude of the pi ^+or-3He scattering have been used in order to determine the pi ³He³H coupling constant. The coupling constant value determined by this method is larger than the elementary pion-nucleon coupling constant, but is in good agreement with the value obtained by the method of Mach and Nichitiu (1976). The value obtained is f_x²=0.12+or-0.01 (x= pi ³He³H).

The data on multiplicity and one-particle distributions in high-energy hadron-nucleus interactions are reported and discussed in detail. It is shown that these data contradict the recent models proposed for nuclear production, such as the energy flux cascade model, the coherent tube and fragmentation models. It is also shown that in the framework of Reggeon calculus for actual nuclei and at energies presently available, the fan-type diagrams cannot play the dominant role. The bimodal structure in pseudorapidity distributions observed recently in pion-nucleus collisions is discussed. Correlations in hadron-nucleus interactions are found to have a long-range nature with an admixture of the short-range component in the central region. It is shown that only a small amount of short-range correlations can probably be attributed to the action of dynamical reasons.

The authors analyse some aspects of the numerically well-behaved Lanczos method of tri-diagonalising a matrix and the mathematically equivalent but numerically disastrous method of moments. It is shown how the elements of the Lanczos tri-diagonal matrix depend only on certain identifiable contributions to the moments, these contributions being those that do not duplicate any information about the matrix already contained in lower moments, all other contributions cancelling exactly.

The form factors for the two-nucleon transfer reaction are studied, in zero-range DWBA, using five different types of Skyrme nucleon-nucleon potential. The results are compared with those using an interaction potential between two free nucleons. The results are independent of the incident triton energy, the state of the residual nucleus and the method used to calculate the form factor.

The dynamic deformation theory is modified and employed to calculate the spectra of ^70,72,74Ge. The lowering of the lowest excited O'⁺ states is attributed to shape coexistence induced by pair fluctuations, while the extra lowering at ⁷²Ge is attributed to a spherical-oblate shape transition.

A simple phenomenological two-fluid model of nuclear collective motion previously used by the authors to discuss rotations is extended to include surface vibrations. The model is applied to a study of the rare-earth nuclei ¹⁵⁴Gd, ¹⁶⁴Er and ¹⁶⁸Yb in an investigation of the rotation-vibration coupling in the presence of Coriolis antipairing effects and of the effects of Coriolis antipairing in the beta bands.

The possibility of different deformations for the protons and neutrons in ¹⁵⁴Sm, suggested by analyses of (p,p') data, is examined by means of Skyrme-HF calculations in the Sm and Er isotopes. Two different versions of the Skyrme force give essentially identical results, in spite of markedly different surface asymmetry and nuclear compressibility characteristics. Constrained calculations, with either a single constraint on the matter density (quadrupole moment) or separate constraints on the protons and neutrons, illustrate a very strong coupling between proton and neutron deformations. Indeed, proton and neutron deformations are found to follow each other very closely even when the relative strengths of the proton and neutron spin-orbit potentials are altered in opposite senses, or when the proton and neutron pairing interaction strengths are varied separately. Generally the protons have larger quadrupole moments per particle, while for the hexadecapole mode the neutron deformation per particle is greater-contrary to the conclusions drawn from analysis of (p,p') data.

A least-squares fit calculation has been performed on the low-lying spectra of ^{206,204,202,200,198}Pb in a restricted neutron model space. The best-fit two-body interactions were then employed in a weak-coupling calculation to obtain the high-spin states in ^{203,201,199,197,195}Pb considering hole-core coupling. Experimental single-particle energies and excitation energies of the core states were used. Although some difficulties showed up in fitting the even-mass spectra, the weak-coupling structures expected from data were reproduced reasonably well.

Cross sections for production of _Lambda ⁷Li* and _Lambda ⁷He* states in the strangeness-exchange reactions K^- to pi ^- and K^- to pi ⁰ on ⁷Li are calculated from the shell-model theory of their structure, with discussion of the physical factors relevant for the total rates. The gamma -ray spectrum following these production processes is discussed (a) for the best shell-model fit to the present p-shell Lambda -hypernuclear data and (b) for other conceivable energy level patterns. Possible interpretations for the gamma ray observed by Herrera et al. (1978)-if confirmed to be hypernuclear-are considered in relation to knowledge of the Lambda N and Lambda NN interactions, and the possibility of distinguishing between them by measuring its angular distribution is briefly discussed.

The reaction ³⁸Ar( alpha ,p gamma )⁴¹K was used to populate levels up to 3.3 MeV excitation in ⁴¹K. Solid ³⁸Ar targets were used. Gamma-ray angular distributions and linear polarisations were measured at alpha-particle energies of 9.50 and 10.75 MeV. Analysis of these data yielded spin and parity assignments of J^pi =³/₂⁺, ³/₂^-, ⁷/₂⁺, ⁵/₂⁺, ⁵/₂^-, ⁹/₂⁺, ⁷/₂⁺, ¹¹/₂⁺, ¹¹/₂^- and ¹³/₂⁺ for levels at 1560, 1582, 1677, 1698, 2317, 2495, 2509, 2528, 2761 and 2774 keV. Gamma-ray multipole mixing ratios were deduced for many transitions and several branching ratios were measured. A simple shell-model calculation was carried out in an attempt to clarify the structure of positive-parity states.

For pt.I see ibid., vol.4, p.755 (1978). The techniques of gamma -ray spectroscopy have been employed to investigate the structure of levels below 2.0 MeV in excitation energy in ⁶⁷Zn populated in the ⁶⁴Ni( alpha ,n)⁶⁷Zn reaction. Gamma-gamma coincidences have been recorded at several alpha -particle beam energies. Gamma-ray angular distributions and linear polarisations have been measured using an escape-suppressed spectrometer and a three-Ge(Li) Compton polarimeter respectively. The gamma -ray decay modes of the levels have been deduced. Spin and parity assignments have been made. Multipole mixing ratios have been obtained for many of the transitions. The lifetimes of 11 levels have been measured using the Doppler-shift attenuation method. The electromagnetic multipole transition strengths deduced show moderate E2 enhancements. The results have been compared with the particle-vibration coupling model, the Alaga model and the shell model with reasonable agreement in each case.

The ^104,105Cd nuclei have been investigated in the ¹⁰²Pd( alpha ,2n gamma )¹⁰⁴Cd, ¹⁰²Pd( alpha ,n gamma )¹⁰⁵Cd and ¹⁰⁴Pd( alpha ,3n gamma )¹⁰⁵Cd reactions. The proposed level schemes including states up to 4817.7 keV and 3342.9 keV for ¹⁰⁴Cd and ¹⁰⁵Cd respectively are based on results obtained from direct and delayed gamma -ray spectra, excitation functions gamma - gamma coincidences and gamma -ray angular distributions. Intense E2 cascades have been observed in the nucleus ¹⁰⁴Cd. Decoupled bands built on the nu h_11/2 and on nu g_7/2 are populated in ¹⁰⁵Cd.

The elastic electron-scattering form factor, and inelastic form factors for the 2₁⁺ (0.434 MeV), 2₂⁺ (0.931 MeV) and 3^- (2.046 MeV) states in ¹⁰⁸Pd were measured. The ground-state charge distribution parameters were obtained from a phase-shifted analysis of the elastic form factor. Analysis of the 2₁⁺ and 2₂⁺ form factors in the anharmonic vibrator model yields the reduced transition probabilities and the 2₁⁺ quadrupole moment (Q_x, x=2₁⁺) which is in excellent agreement with recent Coulomb reorientation measurements. The 3^- form factor is well described by the assumption that this state is a pure octupole vibration.

The authors have carried out a high-precision test for a time-violating asymmetry in the directional correlation pattern of the 0.342-1.381 MeV gamma gamma cascade in ⁴⁹Ti. Polarised ⁴⁹Ti was prepared following the capture of polarised neutrons. The correlation at fixed angles of 45 degrees and 135 degrees was compared in a multidetector configuration for alternate directions of the neutron (titanium-49) spin. A precision of three parts in 10⁵ in the asymmetry was achieved and indicates that the phase difference between the E2 and M1 components in the 342 keV transition is 180.52+or-0.40 and is consistent with T invariance. The overall precision of the system is of the order of a few parts in 10⁵ and is the greatest so far achieved in this type of measurement.