Ael Dieperink

DESCRIPTION OF THE Pt AND Os ISOTOPES IN THE INTERACTING BOSON MODEL

Received 10 April 1980 Abstract: Properties of the even-even Pt and Os isotopes are investigated in the framework of the inter- acting boson approximation, including the neutron-proton degree of freedom. It is shown that the transition between the gamma unstable region of the heavier Pt isotopes towards the more axially symmetric deformed features of the lighter Os and Pt isotopes can be described very well by the IBA hamiltonian ; qualitatively the properties of the transitional region are reproduced by the smooth change of one parameter, Zv, which determines the character of the quadrupole-quadrupole inter- action. Calculated excitation energies and electromagnetic properties are compared with experiment.

A dynamic algebra for rotation-vibration spectra of complex molecules

Abstract An algebraic approach to tri- and poly-atomic molecules is presented. This approach is applied to the study of linear triatomic molecules. It is suggested that these techniques may be useful in the description of complex molecular rotation-vibration spectra.

On shapes and shape phase transitions in the interacting boson model

Abstract The algorithm developed by Gilmore and Feng for the construction of classical limits of quantum operators belonging to a compact Lie algebra is applied to the SU(6) hamiltonian of the interacting boson model for the description of collective nuclear properties. It is shown that the three limiting cases (dynamical symmetries) that appear in the IBA model correspond to different shape phases. The study of the shape phase transitions between the extreme cases shows that the nature of the phase transition is different for each of the three transitional regions.

ON MAGNETIC DIPOLE PROPERTIES IN THE NEUTRON PROTON IBA MODEL

Abstract Magnetic dipole properties of even-even nuclei with 54 ⩽ Z ⩽ 78 are described in terms of the neutron-proton interacting boson model (IBA-2). A phenomenological analysis of the g-factors of the 21+ states in terms of two parameters, gp and gn, is presented. The values of these parameters as a function of N, Z are compared to the results of a microscopic calculation. In addition, some properties of collective M1 transitions are discussed; in particular, the possible existence of a low-lying 1+ state in deformed nuclei carrying appreciable orbital M1 strength is pointed out.

The geometrical-classical limit of algebraic Hamiltonians for molecular vibrotational spectra

Abstract A classical limit, which is amenable to a geometrical interpretation, is discussed for the vibron model of molecular vibrotational spectra. Both diatomic and triatomic molecules are considered. An example of a coupling between the two stretching modes of a linear triatomic is examined in detail.

On triaxial features in the neutron-proton IBA

We show that the neutron-proton IBA model contains a dynamical symmetry that can be interpreted as a tdaxial rotor in a geometrical approach. It is suggested that the energy spectrum and electric quadrupole matrix elements of the nucleus l°4Ru can be described by a situation intermediate between the triaxial and the -t-unstable limit. It has been known for a long time that in certain regions of the periodic system nuclei with static deformation show deviations from a rigid axially symmetric rotor picture. In the geometrical approach these nuclear properties are usually interpreted in terms of either a T.unstable rotor model [1 ], or a rigid triaxial rotor (with 0 ° < Y < 60 °) model [2]. Since most experimentally observable quantities are rather insensitive to the difference between these two shape parametrizations it has been difficult to really judge the validity of either approach. More recently data from Coulomb excitation measurements [3,4] that seem to suggest a more complex and possibly intermediate situation between T-rigid and T-unstable properties, have stimulated renewed interest in the nature of the T-potential. In this note we address the question of the description of nonaxially symmetric features in terms of the neutronproton IBA model [5]. We show that two of the dynamical symmetries occurring in this model can be interpreted as T-unstable and triaxial rotors, respec

Nuclear symmetry energy and the neutron skin in neutron-rich nuclei

The symmetry energy for nuclear matter and its relation to the neutron. skin in finite nuclei is discussed. The symmetry energy as a function of density obtained in a self-consistent Green function approach is presented and compared to the results of other recent theoretical approaches. A partial explanation of the linear relation between the symmetry energy and the neutron skin is proposed. The potential of several experimental methods to extract the neutron skin is examined.

G-FACTORS IN THE NEUTRON-PROTON INTERACTING BOSON APPROXIMATION

Abstract Recent accurate measurements of g -factors of the first excited 2 + states in collective even-even nuclei show substantial deviations from the value Z ∣ A . We investigate the implications that these deviations have for our understanding of collective states in nuclei.

PROPERTIES OF A GENERALIZED PSEUDO-SPIN SYSTEM - APPLICATION OF THE TIME-DEPENDENT MEAN FIELD METHOD TO AN SU(4) INVARIANT HAMILTONIAN

Abstract Properties of an SU (4) invariant generalized pseudospin hamiltonian are studied using a functional integral representation of the time evolution operator. In the transitional region between the U (3) and O (4) dynamical symmetries the energy levels are calculated in the time dependent mean field approximation and compared to the exact energies. The possible relevance of this hamiltonian for the description of diatomic molecules is discussed.

Description of odd-A nuclei in the Pt region in the interacting boson-fermion model

Abstract Properties of unique parity states in odd-proton (77Ir, 79Au) and odd-neutron nuclei (78Pt) are investigated in the framework of the interacting boson-fermion approximation model. The core (boson)-particle (fermion) interaction is represented by a quadrupole-quadrupole interaction and an exchange term, which takes into account the effects of the Pauli exclusion principle. The even-even core nucleus is described in terms of the IBA-1 hamiltonian. The change in the properties of the corresponding odd-A nuclei can be interpreted in terms of a transition of the core hamiltonian between the O(6) and SU(3) limiting cases.