arXiv subjects

S. Frauendorf

Publications and source records attributed to S. Frauendorf.

87 records · Page 5Linked to original sources

arXiv2001

Quadrupole moments of high-spin isomers: test of the tilted-axis cranking model

We report the results of recent measurements of the spectroscopic quadrupole moments of high-spin isomers. For the K=35/2- five-quasiparticle isomer in 179W we measured Q_s=4.00(+0.83)(-1.06)eb. It corresponds to a smaller deformation compared to the ground states of the W isotopes and is in disagreement with the current theoretical predictions. We also measured the quadrupole moment of the I=11- isomer in 196Pb, Q_s=(-)3.41(66)eb. It has the same proton s(-2)1/2 h9/2 i13/2 configuration as the one suggested for the I=16- magnetic bandhead which allows to deduce the quadrupole moment of the 16- state as Q_s=-0.316(97)eb. This small value proves the near sphericity of the bandhead.

nucl-ex↗

arXiv2000

Pair correlations in high-K bands

The tilted axis cranking model is used in combination with the random phase approximation and particle number projection to analyze the influence of dynamical pair correlations in the high-K bands of 178-W and their effect on relative energy and angular momentum. The calculations show the importance of dynamical pair correlations to describe the experiment as well as advantages and problems with the different models in the superfluid and normal state regions.

nucl-th↗

arXiv2000

Incipient magnetic rotation? A magnetic dipole band in 104Cd

High spin states of the nucleus 104Cd have been studied using the Gammapshere array. The level scheme for 104Cd has been revised and evidence for a structure consisting of magnetic dipole transitions is presented. Shell model calculations, published previously, are invoked to support an interpretation of this structure as an incpient case of magnetic rotation where the transversal magnetic dipole moment is not strong enough to break the signature symmetry.

nucl-ex↗

arXiv2000

Description of Multi Quasi Particle Bands by the Tilted Axis Cranking Model

The selfconsistent cranking approach is extended to the case of rotation about an axis which is tilted with respect to the principal axes of the deformed potential (Tilted Axis Cranking). Expressions for the energies and the intra bands electromagnetic transition probabilities are given. The mean field solutions are interpreted in terms of quantal rotational states. The construction of the quasiparticle configurations and the elimination of spurious states is discussed. The application of the theory to high spin data is demonstrated by analyzing the multi quasiparticle bands in the nuclide-s with $N=102,103$ and $Z=71,72,73$.

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arXiv2000

Chirality of nuclear rotation

It is shown that the rotating mean field of triaxial nuclei can break the chiral symmetry. Two nearly degenerate $ΔI =1 $ rotational bands originate from the left-handed and right-handed solution.

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arXiv2000

Moments of inertia for multi-quasiparticle configurations

Tilted-axis cranking calculations have been performed for multi-quasiparticle states in well deformed A$\approx$180 nuclei. In the limit of zero pairing, not only are the calculated moments of inertia substantially smaller than for rigid rotation, but also they are close to the experimental values. The moments of inertia are found to be insensitive to dynamic pair correlations.

nucl-th↗

arXiv2000

Very high rotational frequencies and band termination in 73Br

Rotational bands in 73Br have been investigated up to spins of 65/2 using the EUROBALL III spectrometer. One of the negative-parity bands displays the highest rotational frequency 1.85 MeV reported to date in nuclei with mass number greater than 25. At high frequencies, the experimental dynamic moment of inertia for all bands decrease to very low values, indicating a loss of collectivity. The bands are described in the configuration-dependent cranked Nilsson-Strutinsky model. The calculations indicate that one of the negative-parity bands is observed up to its terminating single-particle state at spin 63/2. This result establishes the first band termination case in the A = 70 mass region.

nucl-ex↗

arXiv2000

A hybrid version of the tilted axis cranking model and its application to ^{128}Ba

A hybrid version the deformed nuclear potential is suggested, which combines a spherical Woods Saxon potential with a deformed Nilsson potential. It removes the problems of the conventional Nilsson potential in the mass 130 region. Based on the hybrid potential, tilted axis cranking calculations are carried out for the magnetic dipole band in ^{128}Ba.

nucl-th↗

arXiv2000

Step wise destruction of the pair correlations in micro clusters by a magnetic field

The response of $nm$-size spherical superconducting clusters to a magnetic field is studied for the canonical ensemble of electrons in a single degenerate shell. For temperatures close to zero, the discreteness of the electronic states causes a step like destruction of the pair correlations with increasing field strength, which shows up as peaks in the susceptibility and heat capacity. At higher temperatures the transition becomes smoothed out and extends to field strengths where the pair correlations are destroyed at zero temperature.

cond-mat.mes-hall↗

arXiv2000

Symmetry Breaking by Proton-Neutron Pairing

The symmetries of the $t=1$ and $t=0$ pair-fields are different. The consequences for rotational spectra are discussed. For $t=1$, the concept of spontaneous breaking and subsequent restoration of the isospin symmetry turns out to be important. It permits us to describe the proton-neutron pair-correlation within the conventional frame of pairing between like particles. The experimental data are consistent with the presence of a $t=1$ field at low spin in $N\approx Z$ nuclei. For a substantial $t=0$ field, the spectra of even-even and odd-odd $N\approx Z$ nuclei become similar. The possibility of a rotationally induced $ J=1$ pair-field at high spin is considered.

nucl-th↗

arXiv1998

Rotational alignment near N=Z and proton-neutron correlations

The effects of the residual proton-neutron interactions on bandcrossing features are studied by means of shell model calculations for nucleons in a high-j intruder orbital. The presence of an odd-nucleon shifts the frequency of the alignment of two nucleons of the other kind along the axis of rotation. It is shown that the anomalous delayed crossing observed in nuclei with aligning neutrons and protons occupying the same intruder subshell can be partly attributed to these residual interactions.

nucl-th↗

arXiv1998

Pair-correlations and magnetic susceptibility of small Al-grains

Paircorrelations and the magnetic susceptibility of electrons in a spherical cavity are studied both for grand canonical and the canonical ensemble. The coupling constant of the $BCS$ Hamiltonian is adjusted to experimental values of the gap parameter. The gap parameter is found to increase for small grains as a consequence of the pronounced shell structure in the spectrum of the spherical cavity. The sharp phase transition at $T_c$ is smeared out for the canonical ensemble. The strong paramagnetic susceptibility of the normal electrons in the cavity is reduced by the superconductivity, but it remains positive.

cond-mat.mes-hall↗

arXiv1998

Super Shell Structure of the Magnetic Susceptibility

The magnetic susceptibility of electrons confined to a spherical cavity or a circular billiard shows slow oscillations as a function of the number of electrons, which are a new manifestation of the Super Shell Structure found in the free energy of metal clusters. The relationship of the oscillations of the two different quantities is analyzed by means of semiclassical calculations, which are in quantitative agreement with quantal results.

physics.atm-clus↗

arXiv1992

Chaotic Behavior in Warm Deformed Nuclei Induced by Residual Two-Body Interactions

Band mixing calculations in rapidly rotating well-deformed nuclei are presented, investigating the properties of energy levels and rotational transitions as a function of excitation energy. Substantial fragmentation of E2 transitions is found for $E_x \gsim$ 800 keV above yrast, which represents the onset of rotational damping. Above $E_x \approx $ 2 MeV, energy levels and E2 strengths display fluctuations typical of quantum chaotic systems, which are determined by the high multipole components of the two-body residual interaction.

nucl-th↗

arXiv1992

Poisson and Porter-Thomas Fluctuations in off-Yrast Rotational Transitions

Fluctuations associated with stretched E2 transitions from high spin levels in nuclei around $^{168}$Yb are investigated by a cranked shell model extended to include residual two-body interactions. It is found that the gamma-ray energies behave like random variables and the energy spectra show the Poisson fluctuation, in the cranked mean field model without the residual interaction. With two-body residual interaction included, discrete transition pattern with unmixed rotational bands is still valid up to around 600 keV above yrast, in good agreement with experiments. At higher excitation energy, a gradual onset of rotational damping emerges. At 1.8 MeV above yrast, complete damping is observed with GOE type fluctuations for both energy levels and transition strengths(Porter-Thomas fluctuations).

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