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Rotational bands in Ru-108,Ru-110,Ru-112 have been investigated by means of gamma-gamma-gamma and gamma-gamma(theta) coincidences of prompt gamma rays emitted in the spontaneous fission of Cf-252. The positive parity bands are described by different versions of IBA, where Ru-108 is best described as a gamma-soft nucleus whereas Ru-110,Ru-112 these are more like rigid triaxial rotors. New Delta I = 1 negative parity doublet bands are found. In case of Ru-110,Ru-112, these are interpreted as soft chiral vibrations. Many of the experimental findings can be explained by microscopic calculations that combine the TAC mean-field with random phase approximation but a simple geometrical explanation is not apparent. ispartof: Physics letters b vol:670 issue:4 pages:307-312 status: published

Lifetimes have been measured for transitions in the two multiquasiparticle rotational bands in the nucleus Nd136. The extracted transition probabilities are compared with results of tilted-axis cranking and random-phase approximation calculations. The bands are identified as being built on two distinct quasiparticle configurations, with very different associated transition rates. These findings are contrary to an earlier suggestion that the bands form a chiral-band pair in this even-even nucleus.

Electromagnetic transition probabilities have been measured for the intraband and interband transitions in the two sequences in the nucleus Nd135 that were previously identified as a composite chiral pair of rotational bands. The chiral character of the bands is affirmed and it is shown that their behavior is associated with a transition from a vibrational into a static chiral regime.

Using a microscopic self-consistent model, we analyse the excitation built upon the rotational band in Lu-163, which has been identified as a wobbling excitation on top of the rotation of a triaxial, trongly deformed shape. We find that the presence of pairing correlations substantially affects the energy of the excitation. Our calculations predict the onset of tilted rotation at a critical rotational requency where the energy of the excitation approaches zero.

The tilted axis cranking model is used in combination with the random phase approximation and particle number projection to analyze the influence of dynamical pairing 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 pairing correlations to describe the experiment as well as advantages and problems with the different models in the superfluid and normal state regions.

Physical Review Letters

This thesis is focused on quantum fluctuations in rotating nuclei and on the effect they have on observables such as relative energy and angular momentum. The study of the nucleus under extreme conditions has been one of the main sources of information about nuclear structure over the last decades. Nuclei at high angular momenta are studied by means of modern gamma-detector arrays. Among the phenomena studied in such experiments are the phase transition from superfluid to normal phase, orientation changes in rotating nuclei, shape changes in rotating nuclei, super deformation etc. The most powerful method to calculate nuclear properties is the mean field approach known as Hartree-Fock or Hartree-Fock-Bogoliubov method. Within this method the two-body interaction is replaced by a selfconsistent one-body potential which is calculated in an iterative way. The nuclear mean field breaks a series of symmetries present in any realistic two-body Hamiltonian. One motivation to include effects that go beyond the mean field is to restore these symmetries. Two methods of restoring symmetries are used in this thesis, namely, the projection method and the random phase approximation (RPA). An advanced quantum mechanical description of a nuclei should take into account quantum fluctuations around the mean field minimum. The quantal fluctuations do not only lead to a series of collective excitations like vibrations and rotations but also add correlations to the mean field ground state. The correlation energy gained by these quantum fluctuations is, in general, state dependent and is important when describing observables like the moment of inertia, the ordering and relative energies between states.

The spectroscopic quadrupole moment of the high-spin, high-K five-quasiparticle isomer (Kπ=[(35-)/2],T1/2=750(80) ns, Ei = 3349 keV) in 179W has been determined using the level mixing spectroscopy method. A value Qs = 4.00([(+0.83) || (-1.06)])e b was derived, which corresponds to an intrinsic quadrupole moment Q0 = 4.73([(+0.98) || (-1.25)])e b and to a quadrupole deformation β2 = 0.185([(+0.038) || (-0.049)]). These values differ significantly from the deduced ground-state quadrupole moments and are in disagreement with the current theoretical predictions in this mass region.

Using the spectral function F'(z)/F(z) the RPA correlation energy and other properties of a finite system can be written as a contour integral in a compact way. This yields a transparent expression and reduces drastically the numerical efforts for obtaining reliable values. The method applied to pairing vibrations in rotating nuclei as an illustrative example., Comment: 9 pages, 2 figures (eps files)

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., Comment: Contributed paper at "High Spin Physics 2001", see http://www.fuw.edu.pl/~hs2001/, to be published in Acta Physica Polonica B

Rotational bands in 110,112Ru and 108Mo have been investigated by means of γ-γ-γ and γ-γ(θ) coincidences of prompt γ rays emitted in the spontaneous fission of 252Cf. New δI = 1 negative parity doublet bands are found. These bands in 110,112Ru and 108Mo have all the properties expected for chiral vibrations. Microscopic calculations that combine the TAC meanfield with random phase approximation support this interpretation.