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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
We derive quadrupole operators for vibrational excitations in a triaxially deformed potential of harmonic oscillator type. Also the self-consistent coupling constants are derived.
The yrast spectra are investigated for the non-collective nuclei150, 152Dy using the Nilsson-Strutinsky + blocked BCS model. The separate effects from the pairing force and the quadrupole force (deformation changes) are studied. It is found that the pairing force is important in describing the yrast line up to/- 30, while the quadrupole force is important for I ≥ 20. The calculated increase of the
The side-feeding patterns and the spectra of unresolved γ-lines are calculated for Gd, Dy and Er nuclei with neutron numbers from 82 to 86. Energies and configurations for states from the yrast line and approximately 2 MeV higher in energy are calculated as many-quasiparticle configurations in a deformed oblate potential. The γ-cascade is simulated by a Monte Carlo calculation. With a common avera
A recently observed Kπ = 1+ mode in deformed nuclei is studied microscopically. By calculating the energies, the B(M1)-values and the form-factors of inelastic electron scattering for 156Gd, we conclude that the relatively strong M1-strength observed at 3.075 MeV comes predominantly from the convection current of proton excitations in the Oh 1 2-orbit. We suggest a search for the M1-strength aroun
The yrast states of 160Yb are calculated using the cranked HFB model with particle-number projection and assuming diabatic bands. The energy of each state is minimized with respect to the proton and neutron pairing gap parameters and the deformation parameters ε and γ. The deformation of the ground band is found to increase with increasing spin, i.e. ε gets larger. Simultaneously γ gets slightly n
We derive an expansion of integrals containing a general function multiplied by a Fermi function raised to an arbitrary power v. When v is an integer, direct expressions for the expansion coefficients are given. The expansion is found to converge quite rapidly if the diffuseness of the Fermi distribution is small, and when v ≳ 1.
The spectrum of 28Si is investigated within the cranked Nilsson-Strutinsky model with all kinds of many-particle-many-hole excitations accounted for. Calculated excitation energies and quadropole moments are compared with experimental data. The recently observed backbend from 8+ to 10+ is suggested to be caused by the crossing of the oblate ground band with a prolate or slightly triaxial band havi
A microscopic analysis of moments of inertia is performed within the cranked Nilsson model. Special emphasis is put on the second-derivative moment of inertia, J(2). Contributions to this from changes of rotational frequency and deformation are separately discussed. A simple expression for the latter is derived and it is for a studied series of Yb isotopes usually found to contribute with less tha
The cranked Nilsson-Strutinsky formalism is applied to the many-faceted spectrum of 16O. The deformation parameters ε{lunate}, γ and ε4 are varied independently and many-particle-many-hole excitations are considered in the rotating system. Potential-energy surfaces are presented at different values of spin, parity and signature. Surprisingly good agreement is obtained when the different minima are
The interplay between angular momentum and particle number (which is the equivalent to the angular momentum in gauge space) is studied. The same technique that is used in the case of rotations in ordinary space can be used in gauge space for investigating the properties of individual quasiparticle levels and the total angular momentum of a nucleus. We study the isotopes of Dy and W, where a back-
