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Realistic microscopic RPA calculations forGd with a deformed Woods-Saxon mean field, quadrupole-quadrupole, spin-spin and symmetry-restoring residual interactions show that the purely collective scissors mode of the two-rotor model is fragmented over orbital isovector 1 states, lying at 2-7 MeV. The strongest experimentally observed magnetic dipole state is interpreted as performing a low-collective scissors-type of geometrical motion. This conclusion evolves from the identification of the above state with the strongest RPA excitation, which reproduces well the experimental energy, B(M1) value and ( e, e′) form factor, has the largest overlap with the scissors state and can be represented as a low-collective scissors type vibration. [ABSTRACT FROM AUTHOR]

Within a realistic effective nucleon-nucleon interaction, derived from the Reid soft-core potential at zero temperature by solving the Bethe-Goldstone equation and by renormalizing for the finite model space, the dependence on temperature and angular momentum of fission barriers is investigated for the nucleiCe andDy. The nuclear densities at given values of temperature, angular momentum and quadrupole moment are selfconsistently generated using a Thomas-Fermi model. [ABSTRACT FROM AUTHOR]

The effect of nuclear and Coulomb interactions on the shapes of two collidingPb nuclei at finite temperature is investigated. The complex potential energy density derived by Faessler and collaborators and the kinetic energy density and entropy density for two Fermi spheres at finite temperature are used to calculate the free energy of thePb +Pb system in the energy density formalism. Shell corrections are added to the free energy in the framework of the Strutinsky method. The total free energy is minimized with respect to the quadrupole deformation and the diffuseness to determine the density distribution ofPb nucleus at certain distance R and temperature T assuming the deformed Woods-Saxon shape for each nucleus. It is found that the nucleus acquires larger deformation and diffuseness as the temperature increases. The interaction potential between twoPb nuclei is calculated from the minimized free energy. The total (nuclear + Coulomb) potential is found to decrease with increasing temperature, whereas the real part of the nuclear potential becomes more repulsive as the temperature increases. [ABSTRACT FROM AUTHOR]

A theoretical study of the β- and β-decays of theAs nucleus is performed. Both non-relativistic and relativistic formfactor coefficients are calculated in the framework of the asymmetric rotor model with admixtures of two quasiparticles for transitional nuclei. The induced interactions are shown to have small contributions to the values of the formfactor coefficients in this case. The theoretical results for the principal observables are in good agreement with the experimental data in the case of the beta decays to the 2 final states. The failure in describing the beta observables corresponding to the transitions to the ground states points to the existence of a more complex structure of the 0-states in the daughter nucleiSe andGe. [ABSTRACT FROM AUTHOR]

Using a complex energy density functional derived from the Reid soft-core potential, the changes in nuclear shapes of two collidingPb are investigated. At each separation distance R, the total binding energy of the Pb + Pb system is minimized w.r.t. the quadrupole deformation and diffuseness parameters of nuclear densities. It is found that the nuclear shapes are strongly affected by the nuclear and Coulomb interactions. A sudden transition occurs from oblate to prolate shapes around R16.8fm and a smooth one from prolate to oblate shapes around R≃11.76 fm. [ABSTRACT FROM AUTHOR]

An energy dependent complex optical potential between two nuclei is calculated from the potential energy density for two colliding nuclear matters generated by solving the Bethe-Goldstone equation in which NΔ and ΔΔ channels are explicitly coupled to the NN channel. By adding the contributions from the third and fourth order ring diagrams and the relativistic correction to the calculated potential energy density, the saturation property of a nuclear matter is reasonably well reproduced. This is used together with the kinetic energy density to calculate the optical potential for theC+C system in the energy density formalism with the local density approximation. The surface correction term and the symmetry energy term in the energy density functional are determined to reproduce the observed binding energy and the rms radius ofC. Using this potential, the differential cross sections for elasticC-C scattering at E=1440 and 2400 MeV are calculated and compared with recent experimental data. [ABSTRACT FROM AUTHOR]

A recent approach for calculating both the real and imaginary parts of the ion-ion potential has been modified to produce the ground state properties of separate nuclei. This approach is used to study both the energy and orientation dependence of the optical potential between two U nuclei adopting the sudden and adiabatic approximations. [ABSTRACT FROM AUTHOR]

Two different polarization mechanisms, relevant to the description of nucleon-nucleon (NN) interaction, are investigated within the framework of the Skyrme model. First a 'dynamical' polarization is considered, allowing the excitation of the interacting nucleons to the Δ resonance. This yields attractive components in the central NN interaction, in agreement with corresponding extensions of the One Boson Exchange model. Beside that, geometrical deformations of the chiral fields are considered. The calculations show the inadequacy of the semiclassical approximation and the pure Skyrme model to go beyond a 20-30% accuracy. [ABSTRACT FROM AUTHOR]

The properties of nucleon-nucleon (NN) potentials derived from the Skyrme model are investigated compared to those of typical One-Boson-Exchange (OBE) models, For that purpose the NN as well as the nucleon-antinucleon (N¯N) potentials are evaluated for the isoscalar central channel, the isovector spin channel, and the isovector tensor channel. A comparison of NN and N¯N interactions allows a separation into terms with positive and negative G-parity and therefore a detailed comparison with the properties of the OBE model. This analysis is performed using the classical Lagrangian of the Skyrme model and considering an extension of this Lagrangian by a term of sixth order, which has recently been proposed. The results indicate that the extended Lagrangian yields an interaction which is quite consistent with the OBE picture. The extended model, however, is much more sensitive to the values of the parameters and the approximations being used for the evaluation of the field for two baryons. [ABSTRACT FROM AUTHOR]

Inelastic αα and dd collisions were studied at a centre-of-mass energy √ S=31.2 GeV per nucleon-nucleon collision, using the Split-Field Magnet (SFM) detector at the CERN ISR. In this paper we show the inclusive and semi-inclusive rapidity distributions of protons, compare them with predictions of the Lund model, and calculate the average rapidity loss for participant protons. From the negative particles we calculate the inelasticity of the interaction, the average energy per particle, and the degree of isotropy of the produced hadrons. [ABSTRACT FROM AUTHOR]

The restoring force for scissor isovector vibrations is calculated microscopically with the wave functions of an axially symmetric Woods-Saxon potential from a density-dependent symmetry energy. The experimental energies of the low-lying magnetic dipole states in rare-earth nuclei are well reproduced. It is found that only outer particles, which contribute to the nuclear moment of inertia, take part in this collective vibration. They are about half of the total number of nucleons. [ABSTRACT FROM AUTHOR]

A microscopic calculation of the restoring force for isovector scissor vibrations using the wave functions of a triaxial Woods-Saxon potential shows that the experimentally observed splitting of the isovector M1 state inDy(50keV),Er(70keV) andYb(200keV) could be attributed to the presence of a possible small non-axially symmetric deformation ( γ=0.8°, 1° and 3° respectively). [ABSTRACT FROM AUTHOR]

We have investigated kinematical correlations between the outgoing beam proton and the proton emerging from the fragmenting α-particle in pα collisions at $$\sqrt {s_{p\alpha } } = 88GeV$$ . Strong correlations are seen, indicating the dominance of quasi-elastic pp scattering in the fragmentation channel p+α→ p+pX, for the ¦ t¦ range 0.05-1.00 (GeV/c). A Monte Carlo simulation of this process can explain the observed correlation spectra assuming an admixture of about 16% spectator protons. [ABSTRACT FROM AUTHOR]

A recently derived nucleon-nucleon interaction has been used to calculate both the real and imaginary parts of the optical-model potential for the two nuclear pairs Pb+U and U+U. Three different bombarding energies per projectile nucléon (6 MeV, 11.8 MeV and 20.9 MeV) have been considered. We found a dramatic dependence of both the real and imaginary parts of the optical-model potential on relative orientation of the colliding nuclei. For the two considered pairs we predicted pockets whose depths depend strongly on orientation. [ABSTRACT FROM AUTHOR]

The effect of quark exchange between different nucleons on the one pion exchange potential is studied in the framework of the resonating group method. The calculated phase shifts including the one pion exchange potential with quark exchange in addition to the one gluon plus σ meson exchange are shown to be consistent with experiments. Especially the p-wave phase shifts are improved by taking into account the quark exchange on the one pion exchange potential. [ABSTRACT FROM AUTHOR]

The real and imaginary parts of the optical model potential for several pairs of magic nuclei have been calculated by a double folding procedure. The complex effective interaction is calculated from the Reid soft core potential by solving the Bethe-Goldstone equation in two colliding nuclear matters. The calculated potentials were approximated with a Woods-Saxon shape. We studied the dependence of the parameters of these Woods-Saxon forms on the masses of the interacting nuclei. [ABSTRACT FROM AUTHOR]

An attempt is made to take into account single particle degrees of freedom in angular momentum projected HFB-calculations via the explicit inclusion of two quasiparticle states. For this purpose a formalism is used which, though being rather general, nevertheless is rather suitable for numerical applications even in realistic model spaces. As a first test the method is applied in the i-shell, where exact shell model solutions are available. Though using only a rather truncated quasiparticle space we obtain almost perfect agreement with these exact solutions. [ABSTRACT FROM AUTHOR]

Competition of strong and decoupling is studied systematically for odd-odd mass nuclei as a function of the position of the Fermi surfaces ε( π) and ε( υ) and the deformations β and γ. As an example we useBr. For a prolate deformation the odd proton likes to decouple while the odd neutron couples strongly. This favours a ground state angular momentum of 5 to 6. The strong coupling is described by the admixture of a d nucleon. Only for the neutrons the admixture is so appreciably that it affects the spectrum and improves the agreement between theory and experiment forBr. [ABSTRACT FROM AUTHOR]

Asymmetric nuclear matter is studied, within the Hartree-Fock approach, employing the Skyrme force. It is seen that the asymmetry ratio can be considered to be an order parameter for phase transitions between a solid and a fluid phase. [ABSTRACT FROM AUTHOR]

The high spin states and of those especially the yrast isomers are studied in the region near the rare earth nuclei. The deformation energy surface is calculated with a method modelled in principle according to a shape constrained cranked HF theory (CHF). In practice, the expectation value of the many-body Hamiltonian is calculated with cranked Nilsson functions. One finds rotation around a slightly deformed oblate or prolate symmetry axis in front or behind the rare earth region, respectively. Near the Hf isotopes strongly prolate deformed nuclei rotating around the symmetry axis are found in agreement with the known K isomers in this region. These results are explained also qualitatively with the help of the MONA ( Maximisation of the Overlap of Nucleonic wave functions by Alignment of single particle angular momenta) effect. In the second part high spin states and yrast isomers in the N=82 region are caluclated in the cranked Hartree-Fock-Bogoliubov approach with four and six quasi-particle excitations. For the excitation energies inGd andDy and a measured g factor one finds satisfactory agreement. [ABSTRACT FROM AUTHOR]

Excited states of finite nuclei are described in a selfconsistent Random Phase Approximation (RPA) starting from a realistic NN interaction like the Hamada-Johnston or Reid soft core potential. The expressions for the single particle Hamiltonian and the residual particle-hole interaction to be used in the RPA equations, are derived applying the Landau prescription to the Brueckner-Hartree-Fock (BHF) approximation for the total energy, considered as a functional of density. This Brueckner RPA is used for a description of the collective 3 and the giant multipole states inO. The importance of the renormalisation of the p-h interaction and of the BHF selfconsistency due to rearrangement terms is investigated. [ABSTRACT FROM AUTHOR]

The consequences of the variational definition of the self-consistent potential in Brueckner-Hartree-Fock theory are explored to higher orders even summing up some classes of diagrams to infinity. The consistency of this definition with a diagrammatic expansion are checked. Overcounting terms in the variational approach are pointed out and their numerical influence on the ground state properties of nuclei is checked at the example ofO. Ambiguities of the potential defined by the variational procedure stemming from the property of the Pauli-operator Q = Q are studied diagrammatically and numerically. The application toO shows that the influence of the Pauli rearrangement term is partially cancelled by the higher order starting energy rearrangement terms discussed in this work. [ABSTRACT FROM AUTHOR]

The low lying high spin states in the transitional odd-odd mass nuclei are studied systematically in the framework of gamma deformed rotor model. The two odd particles, a proton and a neutron, are treated as the BCS quasi particles moving in a triaxially deformed field. The calculations are confined to small β-deformation which is typical of the transitional nuclei. Moreover, we consider only the case where two odd particles are in single j-shells. Results for the excitation energy covering the various physical situations are presented as a function of the β-deformation, the asymmetry γ, and the Fermi energies λ and λ. Electromagnetic transitions and moments are also calculated. Certain features well known in the odd mass nuclei are shown to persist also in the odd-odd mass system. Trends in the level systematics and the electromagnetic properties are predicted for the case where both particles decouple or remain strongly coupled, and for the case where one decouples and the other couples strongly with the core. Measurements which are getting now available show encouraging agreement with the theoretical results. [ABSTRACT FROM AUTHOR]

The most general Hartree-Fock orbitals of the so-called lattice-density-wave character are introduced and its properties studied. Application to the nuclear matter problem is made by employing a density dependent interaction of the Skyrme type, α-clustering effects are predicted at low densities. [ABSTRACT FROM AUTHOR]