arXiv subjects

Stefan Frauendorf

Publications and source records attributed to Stefan Frauendorf.

8 recordsLinked to original sources

arXiv2026

Development of the γ strength function with the neutron number

The M1 and E2 γ strength functions (γsf) have been calculated for extended series of the Mo, Fe, Sn, Ge and Gd isotopes using the conventional spherical shell model (SSM) and, as a new tool, the triaxial projected shell model (TPSM). For almost all cases the strong enhancement of the M1 γsf (low energy magnetic radiation-LEMAR) is found. In the mid-shell region, a bimodal structure of the LEMAR spike and a bump around 3 MeV, interpreted as the scissors resonance (SR), develops. The combination of LEMAR and the SR is generated by the splitting of the spherical single particle multiplets of given j caused by deformation and their fragmentation over nearby quasiparticle configurations.

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arXiv2026

Systematic study of E2 matrix elements in the framework of the Triaxial Projected Shell Model

Nuclides for which extended sets of E2 matrix elements have been measured by means of COULEX experiments are studied in the framework of the triaxial projected shell model (TPSM). The studies encompass: 70,72,74,76Ge, 76,78,80,82Se, 100Mo, 104Ru, 110Pd, 168Er, 186,188,190Os, 184Pt. The experimental energies of the ground band, of the quasi gamma band and of some excited 0+ bands as well as their individual intra and inter band matrix E2 matrix elements are systematically accounted for by the microscopic TPSM calculations.

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arXiv2024

Wobbling motion in triaxial nuclei

The experimental evidence for the collective wobbling motion of triaxial nuclei is reviewed. The classification into transverse and longitudinal in the presence of quasiparticle excitations is discussed. The description by means of the quasiparticle+triaxial rotor model is discussed in detail. The structure of the states is analyzed using the spin-coherent-state and spin-squeezed-state representations of the reduced density matrices of the total and particle angular momenta, which distill the corresponding classical precessional motions. Various approximate solutions of the quasiparticle+triaxial rotor model are evaluated. The microscopic studies of wobbling in the small-amplitude random phase approximation are discussed. Selected studies of wobbling by means of the triaxial projected shell model are presented, which focus on how this microscopic approach removes certain deficiencies of the semi-microscopic quasiparticle+triaxial rotor model.

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arXiv2023

Microscopic aspects of gamma softness in atomic nuclei

It is demonstrated that the Triaxial Projected Shell Model reproduces the energies and transition probabilities of the nucleus 104Ru and the rigid triaxial nucleus 112Ru. An interpretation in terms of band mixing is provided.

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arXiv2022

Triaxiality explored by an odd quasi-particle

The triaxiality of odd-mass nuclei is investigated by coupling a quasiparticle to an even-even core through the core-quasiparticle coupling model. Both soft and rigid triaxial cores are considered. The "soft core" is described by the collective model with rotation-vibrational motion, while the "rigid core" is described by the triaxial rotor model, which is a limiting case of the collective model with only rotational motion. We show that the presence of the odd quasiparticle modifies the collective quadrupole dynamics of the core to appear more "rigid".

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arXiv2017

Beyond the Unified Model

The key elements of the Unified Model are reviewed and checked against modern experimental data. For medium-mass or heavy nuclei it is found that separation between collective and intrinsic degrees freedom becomes invalid for after exciting five to ten collective quanta along the yrast line and two quanta above it. The microscopic derivation of the Bohr Hamiltonian by means of adiabatic time-dependent mean field theory is presented and results compared with experiment. The description of the strong coupling between the rotational and intrinsic degrees of freedom in framework of the rotating mean field is described from a conceptual point of view. The classification of rotational bands as configurations of rotating quasiparticles is introduced. Using the concept of spontaneous symmetry breaking the microscopic underpinning of the rotational degrees is refined. Resulting phenomena, as tilted-axis rotation, transverse wobbling, chirality, magnetic rotation, and band termination are discussed.

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arXiv2014

Overview of Neutron-Proton Pairing

The role of neutron-proton pairing correlations on the structure of nuclei along the $N=Z$ line is reviewed. Particular emphasis is placed on the competition between isovector ($T=1$) and isoscalar $(T=0$) pair fields. The expected properties of these systems, in terms of pairing collective motion, are assessed by different theoretical frameworks including schematic models, realistic Shell Model and mean field approaches. The results are contrasted with experimental data with the goal of establishing clear signals for the existence of neutron-proton ($np$) condensates. We will show that there is clear evidence for an isovector $np$ condensate as expected from isospin invariance. However, and contrary to early expectations, a condensate of deuteron-like pairs appears quite elusive and pairing collectivity in the $T=0$ channel may only show in the form of a phonon. Arguments are presented for the use of direct reactions, adding or removing an $np$ pair, as the most promising tool to provide a definite answer to this intriguing question.

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arXiv2011

Chiral vibrations in the A=135 region

Chiral vibrations are studied with the RPA plus self-consistent tilted axis cranking formalism in the A=135 region. In this method chiral vibrations appear as a precursor to the static chiral regime. The properties of the RPA phonons are discussed and compared to experimental data. We discuss the limits the chiral region and the transition to the non harmonic regime.

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