Table of contents

Excitation energies in rare-earth nuclei belonging to F-spin multiplets are found to be nearly constant for the ground and gamma bands, whereas they vary for the quasi beta band. Implications for the IMB-2 Hamiltonian are discussed.

A restricted Hartree-Fock-Bogoliubov method is developed with a restriction on the angular momenta of the Cooper pairs that conform the vacuum (SD or SDG). The method is applied to ¹⁷⁶Yb. The quadrupole moment in the SD subspace is found to be 80% for neutrons and 91% for protons of its value in the full space. The inclusion of the G part of the Cooper pairs improves that agreement. The descriptions in terms of boson condensate and coherent states are discussed.

The partial neutron strength functions are calculated for ^204,208Pb+n resonances within the quasiparticle-phonon model. Their energy dependence is studied. It is shown that the neutron strength functions of ²⁰⁹Pb have substructures. In ²⁰⁵Pb these substructures are smeared. A comparison with experimental data is performed.

The muon content of gamma-ray-initiated extensive air showers is of considerable importance following the recent detection of excess showers, attributed to ultrahigh energy gamma rays from Cygnus X-3, Vela X-1 and the Crab Nebula. In two of these observations the muon content of the showers have been measured and found to be only marginally less than in cosmic-ray-initiated showers. The authors report the result of a calculation of the expected number of muons in gamma-ray-initiated and cosmic-ray-initiated air showers using a realistic model of hadronic collisions. The model is used to assess the feasibility of using the muon content of showers as a veto to reject cosmic-ray-initiated showers in gamma ray astronomy.

Nucleon electromagnetic form factors are studied invoking the QCD-inspired mixing of states and relativistic boosting of the rest-frame wavefunctions. The authors find that relativistically corrected minimal non-trivial mixing ((70, 0⁺) only) yields the best fit.

The author calculates the strong interaction effect in atomic bound states of various antiprotonic atoms and compares the results with experimental data and with theoretical results from the usual optical potential approach. The agreement with experiment is improved without any free parameters. The basic pN interaction is described by meson-theoretical elastic and phenomenological inelastic contributions. The dependence of the results on the model for the annihilation is discussed.

The authors derive the expression of a model many-body one-point function, which appears in effective many body Hamiltonians, in the framework of a loop expansion by using the replica variable technique. They show the specific properties of the effective Lagrangian appearing in the integral expression of the propagator. They analyse the properties of the lowest-lower expansion terms in the conventional saddle-point approach and discuss other possible developments.

A particular mapping is established which directly connects GCM energy kernels to Weyl-Wigner Hamiltonians under the assumption of a gaussian overlap kernel. As an application of this mapping scheme the author derives the collective Hamiltonians for some giant resonances.

An ansatz is proposed for the master equation controlling the time evolution of the occupation indices in a TDHF study of nuclear collective motion. The model is applied to the study of nuclear vibrations and fission. Thermal equilibrium is established only if the relaxation time in the ansatz is of the order of the mean time between two-body collisions in the nucleus.

Deformed Hartree-Fock calculations are carried out for ⁸¹Sr in the 2p_3/2, 2p_1/2, 1f_5/2 and 1g_9/2 valence space with the nucleus ⁵⁶Ni as the core. Kuo's (1969) effective interaction and an interaction obtained from it by modification of some of the matrix elements are used. Bands of states of definite angular momenta projected from highly deformed intrinsic states with K=⁵/₂^- and ¹/₂^- are obtained. The calculated energy spectra and the B(E2) values for transitions within the bands are in fair agreement with the experimental ones. A positive parity band with K=⁵/₂⁺ and a small deformation has spectral features similar to those observed for the band having the J=⁷/₂⁺ state as the band head. Finally an alternative suggestion is made for the possible structure of the observed K=¹/₂⁺ band with a large deformation.

The scattering problem is solved using a harmonic-oscillator (HO) basis, which is smoothly truncated. As opposed to the usual sharp cut-off of the HO expansion, the introduction of smoothing factors makes the convergence much faster. In combination with the Lippmann-Schwinger formulation and a separable approximation for potentials, the model yields phase shifts and mixing parameters very efficiently for both single and coupled channels.

Proton-nucleus elastic scattering at 800 MeV is calculated in the Glauber model for ¹⁶O, ⁴⁰Ca, ⁴⁸Ca and ²⁰⁸Pb. Nuclear densities are taken from Hartree-Fock-BCS calculations. For the nucleon-nucleon amplitudes, use is made of two recent phase-shift analyses. The effects of intermediate isobars are included by means of a simple model. The results show that the experimental data are qualitatively understood. The polarisation turns out to be quite sensitive to the intermediate isobar effects, which consequently need to be calculated more carefully.

A complex effective interaction calculated from the Reid soft-core potential by solving the Bethe-Goldstone equation for two colliding pieces of nuclear matter is used to calculate the volume part of the ion-ion optical potential for several pairs of nuclei. The contributions from collective surface vibrations are taken into account by eliminating them according to the Feshbach prescription. The optical potentials together with the total reaction cross sections are calculated for energies up to about 90 MeV per nucleon in the laboratory frame. The systematics of the potentials are studied by approximating the potentials with a Woods-Saxon shape. The role of surface excitations in the reaction mechanism is further studied by performing coupled-channel calculations.