Table of contents

Presents the results of calculations of effective weak non-leptonic Hamiltonians for s, c, b and t decay. It covers all aspects of the flavour-changing sector of weak non-leptonics mediated by W exchange in the standard model with n quark generations.

An imaginary potential for the ¹²C-¹²C system is proposed; it is derived using a statistical nuclear model. In order to reproduce that elastic cross section one is led to a specific angular momentum dependency of the imaginary potential which gives weak absorption for the molecular resonances observed, reflecting the molecular window close to the yrast band.

It is shown that confining potentials lead to exponential fall-off of the wavefunction at large distance with an exponent that increases faster than r. Matrix elements involving these wavefunctions are shown to be entire functions of momentum.

Studies angular distributions of the hadronic energy released in muon (electron)-nucleon deep inelastic scattering, to the first order in perturbative QCD, over a conveniently extended phase-space region, namely from SPS accelerator energies where the quark content of the target dominates, to the expected HERA regime where the gluonic component is proved the most important.

In an experiment on K^--proton interactions in a hydrogen bubble chamber, the cross sections and angular distributions have been studied for elastic and charge-exchange scattering, and charged sigma hyperon production in the momentum range 90-300 MeV/c. Good agreement is found with previous cross sections except for the charge-exchange channel where the new values are 60% larger. The production distributions of the charged sigma hyperons and the polarisation of the Sigma ⁺ hyperon clearly indicate that P waves are present down to about 150 MeV/c, much lower than previously reported.

It is shown that it is possible to reproduce the structure observed in pp elastic polarisation in the region with rho _lab>or=45 GeV/c and mod t mod <or approximately=1 (GeV/c)² using a pomeron-flip contribution without neglecting the pomeron-flip phase provided one uses alpha _p(t) approximately=1.07+0.1t.

Total reaction cross sections are calculated for light composite projectiles (d, t, ³He and alpha ) incident on a wide range of targets (¹²C-²⁰⁸Pb) at medium energy (150<or approximately=E_CM/A<or approximately=350 MeV). The internal motion of the nucleons in the projectile is taken into account adiabatically. The calculated results reproduce the experimental deuteron and alpha -particle reaction cross sections. The adiabatic effect predicts a reduced dependence of reaction cross sections on projectile size compared with simple geometrical predictions. For small projectiles it is found that in the adiabatic approximation the geometrical reaction cross section reduces to a quadratic function of the target radius, with coefficients which allow a simple physical interpretation.

Several authors have discussed the problems one confronts in attempting to obtain linked-graph energy expansions in a finite-dimensional model space including 2 h(cross) omega excitations (in all oscillator basis), and have indicated that unlinked graphs arise in energy diagonalisations in such spaces. The authors look at a situation somewhat more complicated in form, namely the case when two excitation spaces are included in addition to the unperturbed model state. One conclusion from this work is that unlinked graphs become more important in enlarged mixed-space diagonalisations selective in the type of high-lying excitations one includes.

The dependence of the magnetic moment of ¹¹B on the characteristics of the nucleon-nucleon interaction is investigated in the framework of the shell model. This leads to the construction of a new central two-body interaction for use in variational calculations for nuclei in the second half of the p shell. An intermediate-coupling calculation in a projected Hartree-Fock basis for the ground state of ¹¹B is carried out using the new interaction.

The ground state of the hypertriton (_Lambda ³H) is investigated using a realistic super-soft-core N-N interaction with non-central terms and Lambda -N potentials of Volkov form fitted to the meson-theoretic (model-B) values of the scattering lengths and effective ranges of Nagels et al. (1972). The Lambda separation energy B_Lambda is obtained using the method of hyperspherical harmonics, retaining harmonics up to hyperangular momentum K=18. It is observed that inclusion of non-central terms in the n-p interaction leads to a reduction in B_Lambda . The B_Lambda values (in MeV) found for three different sets of Lambda -N interaction parameters are 0.14, 0.18 and 0.04, respectively, compared with the experimental value of 0.13+or-0.05. The results are discussed in the light of other works.

The multi-step reaction theory of Tamura and Udagawa (1977), which views (p, alpha ) reactions in terms of triton pick-up, is studied numerically, but in more detail with allowance made for improvements in the basic theory. Reactions induced on A approximately 90 nuclei by 40-70 MeV protons are considered. Either the predicted absolute magnitude or the energy and angular dependence of the calculated cross sections change considerably when the alpha -particle optical-model parameters and the geometrical factors of the bound triton well are varied. Calculations based on the knock-on mechanism and the parameters suggested by Gadioli et al. (1980) are found to reproduce the experimental data satisfactorily. It is suggested that this last approach may allow a more reliable a priori prediction of the energy and angular distribution of the alpha particles emitted.

Mean lifetimes and decay-scheme measurements have been made for levels in ⁴⁶Ti up to an excitation energy of about 10 MeV. The states were populated using the ⁴⁰Ar(⁹Be,3n)⁴⁶Ti reaction using a solid argon target at a beam energy of 30 MeV and the ⁴³Ca( alpha ,n)⁴⁶Ti reaction at beam energies between 12 and 17 MeV. Mean lifetimes have been measured for states in the ground-state band up to J^pi =14⁺ and for states in a negative-parity band on a J^pi =3^- level. New results are E_x(keV), probable J^pi , tau (ps): 6151, 8^-, 0.66+or-0.17; 6198, 9⁺, 4.8+or-1.2; 6830, 9^-, 0.75+or-0.12; 7942, 11⁺, 0.45+or-0.12; 8219, 12⁺, 0.82+or-0.09; 10 041, 14⁺, 0.8+or-0.3. The properties of the states in the ground-state band are discussed in terms of the predictions of the (f₇2/)⁶ model. The properties of the negative states are compared with those expected for a K^pi =3^- rotational band.

The levels populated in ^142,144Ce and the gamma -ray transitions between these levels have been studied by the gamma gamma directional correlation method following the beta decay of ^142,144La. The lanthanum activities were produced by the decay of the corresponding caesium fission products. These were selected by the on-line mass separator OSTIS and the measurements were made in an off-line position. Coincidences were recorded in the event-by-event mode by a pair of Ge(Li) detectors and the correlations were measured at six angles. The coincidence data were analysed for a selection of gates to produce extensive decay schemes and transition intensities were also determined. The correlation data provide firm spin assignments to most levels and yielded multipole mixing ratios for many transitions in each isotope. Parity assignments to levels were made on the basis of dominant multipolarities. The experimental results provide extensive data on these transitional nuclei.

Activation techniques have been used to measure the neutron cross sections for ²⁷Al(n,p)²⁷Mg, ⁵⁸Ni(n,2n)⁵⁷Ni, ⁹³Nb(n,2n)^92mNb, ⁹³Nb(n, alpha )^90mY and ¹⁹⁷Au(n,2n)^196mAu at a neutron energy of 14.2+or-0.1 MeV. The absolute cross sections were measured using the associated-particle technique to determine the neutron flux from the ³H(d,n)⁴He reaction and a Ge(Li) gamma-ray spectrometer to determine the activity of the neutron-irradiated samples. These experimental cross sections are compared with theoretical calculations based on the statistical model with corrections for pre-equilibrium and direct-reaction effects.