P. Van Isacker

The F-spin symmetric limits of the neutron-proton interacting boson model

Abstract The F -spin symmetric limits U (5), SU (3), and O (6) of the neutron-proton interacting boson model are studied. The conditions for and consequences of F -spin symmetry are investigated. In each of the three limits closed expressions for the following properties are given: the excitation energies; the M 1, E 2, and M 3 excitation strengths from the ground state to all 1 + , 2 + , and 3 + states; the M 1 and E 2 decay of the nonsymmetric 1 + and 2 + states; and the dipole and quadrupole moments of maximal F -spin states and of the nonsymmetric 1 + and 2 + states. The predictions for these properties are compared with the experimental data.

Quadrupole moments and E2 transitions with Δτ = 0, ±2 in the γ-unstable O(6) limit of the interacting boson model

Abstract Closed expressions are derived for quadrupole moments and Δτ = 0, ±2 E2 transitions in the γ-unstable O(6) limit of the interacting boson model with a general quadrupole operator of the form (s + d +d † s) (2) +χ(d † d ) (2) . The possible use of these expressions for the identification of O(6)-like nuclei is illustrated by comparing electric quadrupole properties of 104Ru, 134Ba, and 196Pt with the predictions of the γ-unstable O(6) limit.

IBM-2 description of M1 properties in deformed nuclei

Abstract Results of schematic calculations are presented in which various terms breaking F -spin symmetry are considered in the hamiltonian of the neutron-proton interacting boson model (IBM-2). Specific attention is paid to the effect of F -spin symmetry breaking on γ → ground and γ → γ M1 transitions in deformed nuclei. A comparison with available M1 data in the rare-earth nuclei is presented. The constraints implied by these data on the form of the IBM-2 hamiltonian in well-deformed nuclei are discussed.

M1 transitions from the gamma band and F-spin mixing in 168Er

Abstract The M1 strength in a number of γ → g transitions in 168Er have been determined from high-precision L-subshell conversion electron intensity measurements. The results are combined with earlier data for transitions within the γ-band and compared with the predictions of an IBA-2 calculation. It is shown that a satisfactory description of both E2 and M1 properties can be obtained with the appropriate degree of F-spin symmetry breaking in the hamiltonian, which in turn relates to the degree of neutron-proton symmetry in the collective wavefunction.

A U(620) supersymmetry for the A ≅ 130 mass region

Abstract A new dynamical symmetry appropriate for the single-particle orbits j = 1 2 , 3 2 , 5 2 and 7 2 coupled to the O(6) symmetry of the interacting boson model is constructed. For this symmetry we calculate energy spectra, wave functions, electromagnetic transitions rates and single-particle transfer amplitudes. This limit is applied to the A ≅ 130 mass region. We discuss possible evidence for the existence of a U( 12 20 ) supersymmetry in this region.

Description of vibrational odd-odd nuclei with the interacting boson-fermion-fermion model

Abstract The vibrational symmetry limits of the interacting boson-fermion-fermion model (IBFFM) for odd-odd nuclei are studied when neutrons and protons occupy orbits with j = 1/2, 3/2 and 5/2. Three essentially different situations occur depending on whether the fermions are particles or holes. Applications are presented for the odd-odd nuclei 76 As and 80 Br.

Supersymmetry in transitional nuclei and its application to the Ru and Rh isotopes

Abstract We present an application of nuclear supersymmetry in transitional nuclei by establishing a connection between the spectroscopic properties of the even-mass ruthenium and the odd-mass rhodium isotopes.

Gamma-ray scattering by deformed nuclei

Abstract Simple analytic formulae are used to describe gamma-ray absorption and scattering in the SU(3) (axial) and SU ∗ (3) (triaxial) limits of the interacting boson model.

In-beam spectroscopy of 120Xe☆

Abstract Excited states of 120 Xe have been studied by in-beam γ-ray spectroscopy using the 110 Cd( 13 C, 3n) and 111 Cd( 12 C, 3n) reactions. The yrast band was observed up to the 14 + level, showing backbending at the 12 + state. A γ-band and two new negative-parity bands were found. The low-lying levels of 120 Xe could be described by the IBA-1 hamiltonian plus a triaxial degree of freedom.

An isospin invariant form of the interacting boson model for odd nuclei (IBFM-3)

Abstract The interacting boson-fermion model IBFM for odd nuclei is extended to incorporate isospin symmetry in nuclei where valence neutrons and protons occupy the same orbits. A mapping is established with shell-model states. A boson-fermion hamiltonian is derived for the special case of charge-independent pairing forces and is found to reproduce the shell-model energies exactly. A comparison of the extension (IBFM-3) with the earlier version IBFM-2 shows that the latter omits some low-lying shell-model states.