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The possibility that shell structure related to double-spherical shapes may produce new regions of superdeformed or "hyperdeformed" nuclei is discussed. Of special interest is the mass region around 180Hg (90Zr+90Zr) which is studied in detail. Extended cranked Nilsson-Strutinsky calculations are performed with the Woods-Saxon potential and finite-range liquid-drop model, and "hyperdeformations" w
The nearest neighbour level spacing distribution and the Δ3 statistic of level fluctuations associated with very high spin states (I ≳ 30) in rare-earth deformed nuclei are analysed by means of a cranked shell model. The many particle-many hole configurations created in the rotating Nilsson potential are mixed by the surface-delta two-body residual interaction. The levels in the near-yrast region
The dynamics of a classical, heavy system coupled to a quantum mechanical light system is studied in a simple time-dependent random matrix model, where the degree of complexity can be changed by a “chaoticity parameter.” It is shown that the energy of the quantum mechanical system diffuses as it interacts with the classical system, providing it is chaotic, while a ballistic behavior appears in the
Magnetic dipole transition matrix elements are calculated in the particle(s)+rotor model for rotational bands in superdeformed nuclei in the A = 190 region. Several bands are found to have large B(M1) values. Drastically different M1-properties appear for the maximal (K> = K1 + K2) and minimal (K< = K1 - K2) K values in strongly coupled tow-quasiparticle states. The B(M1) values may give informati
A simple model, based on random matrix theory, is utilized for the description of energy levels and level dynamics in mixed regular and chaotic quantum systems. We find that different types of level statistics, such as nearest neighbor distributions, long-range correlations, wave function analysis, curvature distributions, etc., show dramatically different sensitivity to the "chaoticity parameter.
The giant dipole resonance is studied in nuclei with exotic shapes utilizing the Woods-Saxon potential for the single-particle states, and the RPA formalism for the phonon states. Requirements on translational invariance is used to determine the residual interaction including coupling constants. The low-lying resonance component in superdeformed nuclei, which corresponds to vibrations along the lo
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
