Filetype
Extreme nuclear shapes are considered from the clustering point of view. General aspects of light nuclei which possess very exotic, elongated shapes ("α-strings") are given. The relation between superdeformation and di-molecules is considered, and it is shown that nuclear di-molecules have the same magic numbers and orbits filled as the ellipsoidal superdeformations for light nuclei, while for hea
The structure of superdeformed (SD) nuclei is discussed, and some open questions are raised. Octupole vibrations built on SD and hyperdeformed (HD) shapes are described in an analytically solvable model, and structure effects on low-lying vibrational states, as well as the deformation splitting of the giant resonance states are discussed. From cranked Nilsson-Strutinsky calculations it is predicte
Using γ-γ correlation techniques, unresolved γ radiation associated with superdeformed (SD) excited states has been investigated for the nucleus 149Gd populated via the 124Sn(30Si, xn) reaction at 155 MeV bombarding energy. the intensity distrib ution has been measured as a function of rotational frequency. A "quasi-damped" region of excitation energy where the identity of individual SD bands melt
The octupole vibrational mode is studied in the deformed harmonic oscillator model. A residual octupole-octupole interaction for K=0,1,2 and 3, and the corresponding coupling constants, are included by a self-consistent approach. Analytical solutions of the RPA equations are obtained for the excitation energies of all possible octupole vibrations at closed spherical (1:1), superdeformed (2:1) and
The appearence of quantum chaos in the excited rapidly rotating nucleus is studied in a simple nuclear model, consisting of the cranked Nilsson model with a schematic two-body interaction added. Chaos is found to smoothly set in at a much lower excitation energy in normal-deformed 168Yb than in superdeformed 152Dy. A dynamical sign of chaos is a saturation of the standard deviation of the E2-stren
Two excited superdeformed bands in Gd149 have been observed in -ray spectroscopy. Based on the behavior of the dynamical moments of inertia, we assign one band to a neutron excitation and the other to a proton excitation. The proton-excited-band -ray energies are nearly identical to those already known in Tb150. In addition, two new members of the Gd149 yrast cascade have been observed, extending
Some recent theoretical achievements on superdeformed nuclei are discussed. A theoretical search for superdeformations in all even-even nuclei between 3466Se32 and 84218Po134 is presented, and new favourable cases are discussed. The unique role of high-N orbits, and also the effect of a static pairing gap on particularly the J(2) moment of inertia is briefly reviewed. Observed single-particle cros
A general survey of the octupole instability of high spin superdeformed (2:1) and hyperdeformed (3:1) nuclei has been performed in the cranked Nilsson-Strutinsky model. The octupole degree of freedom is predicted to play an important role in several already observed superdeformed nuclei around152Dy, and in particular in N=114 isotones in the Hg-Pb-region. High spin reflection asymmetric hyperdefor
A discrete superdeformed band is found in 146Gd. Lifetime measurements yield an average quadrupole moment of 12±2 e b. A band crossing corresponding to an alignment of ≈2h{stroke} is observed at a rotational frequency of 0.65 MeV. A theoretical analysis suggests that the band has a π62v71 configuration with odd spins and odd parity. Arguments are given that the [651 1 2] and [642 5 2] single-parti
The experimental energy level spectrum of 24Mg is compared with potential energy surfaces calculated from the Nilsson-Strutinsky cranking formalism. Positive-parity states are also compared with the Glasgow school sd shell-model calculations. Emphasis is placed on the high spin and energy states. The subshell occupancies are used in the investigation of similarities and differences of the two comp
Some recent advances in high-spin physics are reviewed emphasising the role of symmetries in rotating nuclei. Evidence is presented for breaking of the axial symmetry (triaxiality) as well as of the reflection symmetry (octupole deformation). Spectroscopic consequences of shell structure in rapidly rotating nuclei with 2:1 shapes (superdeformations) are discussed.
It is investigated how particles in high-N shells affect the moment of inertia, {A figure is presented}(2), and the quadrupole moment, Q0, of superdeformed high-spin states. The different behaviour of {A figure is presented}(2) versus the rotational frequency observed for superdeformed states in 152Dy and 149Gd is explained in terms of different occupations of a few high-N orbits. Predictions for
Level densities are calculated at high spins in the cranked Nilsson model by a simple counting procedure. At a fixed deformation and angular momentum excited states are created as many-particle many-hole excitations (up to 10p-10h) on the cranked ground state. The method allows for a detailed study of high-spin level densities at low excitation energies, at most about 6 MeV above the yrast state,
Potential-energy surfaces of heavy nuclei in the Ra-Th region are calculated by the macroscopic-microscopic method using the modified oscillator potential. A rather large region of nuclei with a third minimum along the fission trajectory is found. This minimum appears at a very large quadrupole deformation, ε2 ∼ 0.9, and has a stable octupole deformation with ε3 ∼ 0.2. It is found that in addition
Isoscalar and isovector giant monopole and quadrupole resonances built on high-spin states are studied in a simple model. Using the random-phase approximation the giant resonance states at spin zero are calculated in the deformed harmonic oscillator potential. Quadrupole and monopole operators, as well as the corresponding coupling constants, are obtained in a self-consistent way, and the coupling
The differential cross-section of inelastic electron scattering for the excitation of the K = 1+ mode in156Gd is calculated in DWBA by using microscopically calculated transition-densities. Discussions are given in comparison with experimental data, isovector rotational mode and the quasi-DWBA technique.
Effects of quantum fluctuations, like wobbling and γ-fluctuations, are examined in even- as well as in odd-particle systems by making use of a simple model based on the Bohr hamiltonian. The strong signature dependence observed in ΔI = 1 E2 transitions in odd nuclei is studied in the context of an axially asymmetric deformation. We point out the importance of the quantum fluctuations especially at
The shell effects responsible for superdeformation in the 152Dy region are discussed. Why is only one band observed in 152Dy and why is there another coexistent collective band? How does the superdeformed band decay?
High-spin states in 164Yb have been populated in the 152Sm(16O, 4n) and 150Sm(18O, 4n) reactions. From studies of γγ coincidences, γ-ray angular distributions and conversion electron measurements the level scheme has been constructed. The g-band and the S-band have been established to spin and parity 22+ and 26+', respectively, and the rotational sequences (π, α) = (-, 1)1, (-, 0)1 and (-, 0)2 to
Theoretical calculations show that both the deformation and the pair field change considerably with increasing spin in the ground-state band of transitional rare-earth nuclei with neutron number close to 90. As a consequence of these changes the g factor is expected to show a significant spin dependence in the ground band of certain transitional nuclei. It is suggested that g-factor measurements m
