Table of contents

It is found that classical Yang-Mills equations with external four-vector current densities are equivalent, under a particular ansatz, to the equation Square Operator phi + mu ² phi ³e^K=0 with mu an arbitrary constant and K an arbitrary differentiable function. Kink, sine-Gordon and Liouville equations for radially (spherically) symmetric ansatz functions are obtained with different parametrisations of K.

The microscopic scalar operator measuring the nuclear surface area is identified. Under the assumption that nuclear moments beyond the quadrupole are negligible, the continuum limit of this microscopic observable gives the surface area of the Bohr-Mottelson liquid drop.

The contributions of the convection and spin components of the 2^- state current transition densities to the (e,e') cross section at transferred momentum values q_eff in the range 0 to 2.5 fm^-1 are analysed in the DWBA for ⁹⁰Zr and ²⁰⁸Pb. It is found that the convection component gives the main contribution to the cross section in the region q_eff=0.8^-1 for ⁹⁰Zr and q_eff=0.6 fm^-1 for ²⁰⁸Pb. Thus it is concluded that fragments of the 'nuclear twist' formed by the convection component were detected at Darmstadt in the (e,e') reaction on ²⁰⁸Pb.

The lifetimes of some heavy nuclei relative to the spontaneous emission of various clusters heavier than the alpha particle are estimated with a model extended from the fission theory of alpha decay, showing that this phenomenon is a new manifestation of the nuclear shell structure. A greater probability is obtained for parent-heavy-cluster combinations leading to a magic or almost magic daughter nucleus. The analytical formula obtained allows one to handle a large number of cases to search for new kinds of radioactivities.

Some signals produced by air showers of energy greater than 10¹⁹ eV in scintillators at impact parameters greater than 1 km possess a distinctive feature, a 'sub-luminal pulse' (SLP) following the normal one with a time delay of approximately 1.5 r/c. The average amplitude of the SLP corresponds to an energy deposit of about 50 MeV, three times as much as is deposited by a vertical minimum ionising muon. The SLP account for approximately 5% of the energy deposited in the atmosphere by such air showers at these distances.

Bound heavy-quark systems are treated within the framework of a relativistic quasipotential approach. In the cases of 'charmonium' and 'bottomium' systems the inverse problem of determining the quark mass and potential parameters is formulated and solved numerically. The relativistic character of the cc system is clearly indicated, while the bb system can be still treated as non-relativistic. Some conclusions about the flavour dependence of the potential are presented.

It is shown that the mass-difference effects of the difference between the pp and nn scattering lengths can become anomalously large by off-shell effects. The author's result shows clearly how this mass-difference correction depends on the off-shell behaviour of an interaction model. A comparison of theoretical results and experimental data gives a constraint on the half-shell function at the threshold. Charge-symmetry-breaking effects play an important role in the description of the data by realistic NN potentials such as the Paris potential.

A separable potential with tensor plus central terms is introduced to describe the low-energy neutron-proton final-state interaction in the break-up reaction pd to ppn. The inclusion of the D-wave terms improves significantly the agreement with data at 1 GeV on the cross section and asymmetry at high spectator momenta. The spectator momentum distribution for fixed momentum transfer also provides a strong signal of the importance of the final-state interaction which is confirmed experimentally.

The author presents results for the strong interaction effect in the atomic ground state of kaonic hydrogen. The calculations are based on a phenomenological separable potential model which describes low-energy KN data. It was found that the theoretical results do not agree with the experimental data and the author also finds disagreement with the results of previous calculations. He also applies a model-independent formalism and concludes that the discrepancy with experiment cannot be cured by Coulomb corrections. Coulomb and mass-difference corrections are discussed for low-energy scattering data.

From a chi ² fit to the Lambda binding energy data of p-shell hypernuclei the authors have identified that a zero-range three-body Lambda NN force plays a crucial role in reducing the spin-state dependence of the central charge-independent two-body effective Lambda N potential of Skyrme-type, gaussian, Yukawa and exponential shapes. The exchange contribution of the three-body Lambda NN force to the interaction energy, either ignored altogether or not treated adequately in earlier analyses, has been shown to play an important role. For a Skyrme-type Lambda N potential found from the analysis of p-shell hypernuclei, the authors get a value of 28.52 MeV for Lambda binding to infinite nuclear matter and also Lambda binding in _Lambda ⁵He turns out to be in good agreement with experiment. But the other shapes with reasonable values of the range parameter fail to account for Lambda binding to infinite nuclear matter and B_Lambda of _Lambda ⁵He even qualitatively. The non-central Lambda N potentials (spin-orbit and tensor force) along with the low spin-state dependence of central two-body charge-independent Lambda N potentials fail to account for the data even qualitatively.

Using a one-parameter family of compact and creviced shapes the authors have calculated the deformation energy of the liquid-drop model and included the nuclear proximity energy. The introduction of the proximity forces on such a shape sequence leads to the identification of fission and scission barriers since the rupture of the neck between the fragments is assumed before the barrier is crossed. The fission barrier heights are well reproduced and are much lower than those given by the liquid-drop model (without proximity) for the medium systems. The authors show that these low barriers are compatible with a strong enhancement of the critical angular momentum for cold fission. The translational kinetic energy of the fragments agrees with experimental data. Double-humped barriers are predicted for actinides; the inner barrier has essentially a microscopic origin while the outer one (which plays the role of a scission barrier) is governed mostly by the balance between coulomb and nuclear forces.

Shell-model nuclear densities have been obtained for 17 medium and heavy nuclei (A>34). By folding pairs of them with the effective nucleon-nucleon interaction M3Y an analytical approximation of the folding optical potential has been created for 14 systems with strong Coulomb repulsion (1000<Z₁Z₂<3000) and the fusion barrier has been computed. The predicted fusion cross sections agree well with some experimental data (for Z₁Z₂ approximately=1000) but tend to overestimate others, especially those related to the heaviest systems.

The g factor of the 6.13 MeV 3^- state in ¹⁶O has been remeasured by observing the hyperfine frequency in the one-electron atomic ground state of ions formed by recoil into vacuum at high velocity from the reaction ¹H(¹⁹F, alpha )¹⁶O*. The value of the g factor was deduced to be mod g mod =0.556(4). The significance of this precision value as a critical test of the shell-model description is discussed. An independent test of the accuracy of the method, involving observation of the same hyperfine interaction in the 197 keV ⁵/₂⁺ state of ¹⁹F is also described.

Conversion-electron spectra from the decay of ¹²⁸Cs have been measured using a Si(Li) detector. Internal conversion coefficients of 11 gamma transitions were obtained. Spins and parities determined for the first six excited states are discussed in connection with gamma deformation and related nuclear properties of the gamma -soft ¹²⁸Xe.

The low-lying states of ¹³⁵Ba and ¹³⁷Ba have been studied by means of Coulomb excitation with ¹⁴N, ¹⁶O and alpha particles. Angular distribution measurements were carried out for some transitions in both nuclei with 11.2 MeV alpha particles. Level energies, decay schemes, branching ratios, B(E2) to values and some spin assignments have been established. For the first time the authors have measured B(E2) to values in ¹³⁷Ba and a new level at 1252.5 MeV with spin ⁷/₂⁺ was observed. ¹³⁷B and ¹³⁵Ba have been described theoretically by coupling one and three holes, respectively, to the quadrupole vibrations, and rather good agreement with experiment was obtained.

Angular distribution of 64 gamma rays in ¹⁷²Yb have been measured from the decay of ¹⁷²Lu polarised at low temperatures in gadolinium and iron hosts. Multipole mixing ratios, delta , of 60 transitions have been deduced, 51 of them uniquely. From the experimental values of K conversion coefficients and E2/M1 mixing ratios the authors have determined E0/E2 mixing ratios, mod q mod , for four transitions and deduced the corresponding X(E0/E2) and mod rho (E0) mod values. Energy levels and B(E2), X(E0/E2), mod rho (E0) mod and delta (E2/M1) values have been calculated using the IBA-1 model.

²⁰²Au and ²⁰⁴Au were produced through the reactions ²⁰²Hg(n,p)²⁰²Au and ²⁰⁴Hg(n,p)²⁰⁴Au. The half-lives were determined to be 28.8+or-1.9 s and 39.8+or-0.9 s, respectively. Gamma-ray spectroscopy and gamma - gamma coincidence measurements using Ge and Ge-Ge(Li) detectors have revealed the presence of three new gamma transitions accompanying the decay of ²⁰²Au and 11 new transitions accompanying the decay of ²⁰⁴Au. The energy of the second excited state in ²⁰⁴Hg has been established as 1128.30+or-0.16 keV. Inconsistencies regarding the proposed existence of a 4.0+or-1.0 s activity in ²⁰⁴Au are discussed.

A detailed analysis of the intensity of cosmic gamma rays at intermediate latitudes, mod b mod =11 degrees -10 degrees , given by Strong et al. (1982). has enabled a component to be isolated which the authors identify with the inverse Compton interactions of cosmic-ray electrons with interstellar photons. An approximate analysis of SAS II data at higher latitudes adds weight to the identification.