Description of the Pt and Os isotopes in the interacting boson model

Properties of the even-even Pt and Os isotopes are investigated in the framework of the interacting 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 festures 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, χ_ν, which determines the character of the quadrupole-quadrupole interaction. Calculated excitation energies and electromagnetic properties are compared with experiment.     

Study of Pt isotopes in the core excited interacting boson model 1

The core exited IBM model was applied to the Pt isotopes. It was found that the energy spectra of the high-spin states as well as those of the low-spin states can be reproduced quite well. Also, it was found that there is a structure transition between ¹⁸⁶Pt and ¹⁸⁸Pt. The B(E2) values of ¹⁸⁴Pt were calculated and compared with recent experimental data. It was found that the general features of the B(E2) values can be reproduced qualitatively. The need of more boson core excitations is also discussed.     

The interacting boson model: Microscopic calculations for the mercury isotopes

Microscopic calculations of the parameters of the proton-neutron interacting boson model (IBM-2) appropriate to the even Hg isotopes are reported. The calculations are based on the Otsuka-Armia-Iachello boson mapping procedure, which is briefly reviewed. Renormalization of the parameters due to exclusion of the l=4 g boson is treated perturbatively. The calculations employ a semi-realistic shell-model Hamiltonian with no adjustable parameters. The calculated parameters of the IBM-2 Hamiltonian are used to generate energy spectra and electromagnetic transition probabilities, which are compared with experimental data and with the result of phenomenological fits. The overall agreement is reasonable with some notable exceptions, which are discussed. Particular attention is focused on the parameters of the Majorana interaction and on the F-spin character of low-lying levels.     

Symmetries of the interacting boson model

This contribution reviews the symmetry properties of the interacting boson model of Arima and Iachello. While the concept of a dynamical symmetry is by now a familiar one, this is not necessarily so for the extended notions of partial dynamical symmetry and quasi dynamical symmetry, which can be beautifully illustrated in the context of the interacting boson model. The main conclusion of the analysis is that dynamical symmetries are scarce while their partial and quasi extensions are ubiquitous.     

A study of Cd and Te isotopes in the interacting boson approximation

An investigation of the properties of the Cd and Te isotopes is performed in the framework of the interacting boson approximation. Particular attention is paid to the presence of “intruder” 0⁺ and 2⁺ states at the energy of the two-phonon triplet in the middle-shell Cd isotopes. It is suggested that these states originate from two-particle two-hole proton excitations across the shell gap at Z = 50. The behaviour of these states is studied as a function of the neutron number. No clear evidence of similar phenomena is observed in the Te isotopes. The collectives features of these nuclei are found to be in satisfactory agreement with the predictions of the neutron-proton interacting boson model.     

Charge and transition densities of samarium isotopes in the interacting boson modei

The interacting boson approximation (IBA) model has been used to interpret the ground-state charge distributions and lowest 2⁺ transition charge densities of the even samarium isotopes for A = 144–154. Phenomenological boson transition densities associated with the nucleons comprising the s- and d-bosons of the IBA were determined via a least squares fit analysis of charge and transition densities in the Sm isotopes. The application of these boson transition densities to higher excited 0⁺ and 2⁺ states of Sm, and to 0⁺ and 2⁺ transitions in neighboring nuclei, such as Nd and Gd, is described. IBA predictions for the transition densities of the three lowest 2⁺ levels of ¹⁵⁴Gd are given and compared to theoretical transition densities based on Hartree-Fock calculations. The deduced quadrupole boson transition densities are in fair agreement with densities derived previously from ¹⁵⁰Nd data. It is also shown how certain moments of the best fit boson transition densities can simply and successfully describe rms radii, isomer shifts, B(E2) strengths, and transition radii for the Sm isotopes.     

Electron scattering in the interacting boson model

It is suggested that the interacting boson model be used in the analysis of electron scattering data. Qualitative features of the expected behavior of the inelastic excitation of some 2⁺ states in the transitional SmNd region are discussed.     

g-boson excitations in the interacting boson model

We have extended the interacting boson model (IBM) by including the g-boson degree of freedom. Schematic model calculations have been carried out in the two different limits: SU(5) and O(6). Particular applications have been carried out for ¹⁰⁴Ru, a nucleus intermediate between SU(5) and O(6). In all cases, energy spectra, E2 and E4 transition rates have been studied in detail and compared with the most recent experimental data for ¹⁰⁴Ru.     

Order and chaos in the interacting boson model

We investigate both quantum and classical signatures of order/chaos interplay within the symmetry triangle of the interacting boson model. Special attention is devoted to the increased regularity in the Alhassid-Whelan semiregular arc inside the symmetry triangle. Significant changes in properties of classical trajectories therein are found to accompany the strong bunching of levels in the 0⁺ spectrum. The text was submitted by the authors in English.     

Decay properties of neutron deficient Kr isotopes

The decay properties of the neutron deficient isotopes^73–77Kr and^73–76Br have been studied at the ISOLDE facility at CERN. The total decay energiesQ, as determined fromβ ⁺ singles orβ ⁺ -γ coincidence measurements, are compared with mass formulae.     

Electric monopole transitions and isotope shift of nuclear radii of even Sm isotopes in the interacting boson model

The interacting boson model has been used to calculate the isotope shift in^146–154Sm isotopes. Fitted model parameters have been used for calculation of the monopole strength parameters (EO) and the branching ratios X(EO/E2) for^150–154Sm. Consideration of the effective proton boson number as it reflects the Z=64 subshell closure, is shown to be insignificant in the present calculation.     

Mixed-symmetry states in the neutron-proton interacting boson model

States of mixed proton-neutron symmetry are investigated in different dynamical symmetries of the interacting boson model. We discuss in each of the limits the energy spectrum, the wave functions and the B(M1; 0₁⁺ → 1 _1⁺) values. We also study three classes of transitional nuclei namely the Pd nuclei [U(5) → O(6)], the Sm nuclei [U(5) → SU(3)] and the Pt nuclei [O(6) → SU(3)] with respect to the energy of the lowest non-symmetric J^π = 1⁺, 3⁺ levels as well as the M1 and M3 strengths for exciting these levels from the ground state. For ⁹⁸Pd we compare this calculation with a shell-model calculation. Finally, we adress the problem of the mixing of the non-symmetric J^π = 1⁺ state with nearby hexadecapole (g-boson) configurations.