[en] As an alternative to Wigner's spin-isospin symmetry, known to be broken in heavier nuclei, a pseudo SU(4) symmetry is proposed which follows from the combined invariance in pseudo spin and isospin. Its consequences with regard to Gamow-Teller β decay are pointed out

[en] An isopin-invariant boson-fermion model is proposed for odd-mass nuclei and its connection with the shell model is investigated in the case of neutrons and protons in the f_7/2 shell. (author)

No abstract available

[en] Isospin invariant boson models, IBM-3 and IBM-4, applicable in nuclei with neutrons and protons in the same valence shell, are reviewed. Some basic results related to these models are discussed: the mapping onto the shell model, the relation to Wigner's supermultiplet scheme, the boson-number and isospin dependence of parameters, etc. These results are examined for simple single-j shell situations (e.g. f_7/2) and their extension to the fp shell is investigated. Other extensions discussed here concern the treatment of odd-mass nuclei and the classification of particle-hole excitations in light nuclei. The possibility of a pseudo-SU(4) supermultiplet scheme in fp-shell nuclei is discussed. (orig.)

[en] In the mass regions near single-closed shell configurations such as Tl(Z=81), Sb(Z=51), In(Z=49) and N=81, N=83 isotones; deformed Nilsson orbitals can give rise to minima in the total potential energy of the nucleus. Thus low-lying, deformed states can occur whereas the ground state in these nuclei is spherical. Comparison with the existing experimental data is made in all cases. (Auth.)

[en] The ideas of Wigner continue to inspire present-day research in nuclear physics. Two examples are discussed in this contribution: the supermultiplet model and random matrix theory. (author)

[en] The electromagnetic properties of low-excitation states in ¹⁹¹Ir and ¹⁹³Ir have been studied following Coulomb excitation. Gyromagnetic ratios were measured by the transient-field technique and level lifetimes were measured by the Doppler-shift recoil distance method. Multipolarity mixing ratios were determined from measured particle-γ angular correlations. The present lifetime and g-factor results extend the data available for comparison with theory and help discriminate between disparate experimental values reported previously in the literature. We compare the experimental data with particle-triaxial-rotor model calculations and with the predictions of the U(6/4) and U(6/20) supersymmetry models based on the interacting-boson-fermion model

[en] Magnetic dipole moments for low-lying collective quadrupole excitations are studied in heavy and medium-heavy nuclei within the framework of the interacting boson model (IBM-2). In the present study, the authors concentrate mainly on the fully symmetric representations of the U(6) group and their magnetic dipole moments. They shortly discuss the lowest non-symmetric 1⁺ level. Comparison with other collective model calculations of gsub(R) and microscopic studies as well as with experimental data is performed. (Auth.)

[en] The extended Skyrme force has been used to calculate self-consistently ground-state properties, pairing correlations and properties of excited states of spherical nuclei throughout the whole mass region. The shell-model matrix elements exhibit the same behaviour as the bare reaction matrix elements of realistic interactions, and have to be renormalized due to core polarization effects (3p-1h, 4p-2h), to generate good effective interactions. A numerical application on ⁴²Ca is presented. (Auth.)

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