Sökresultat

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-

A new development within the high spin Nilsson-Strutinsky formalism presented and applied to certain sd-shell nuclei. The previous method of calculating potential-energy surfaces as a function of angular momentum using interpolated spin values is not satisfactory when studying the individual bands for these light nuclei. In the present research, manyparticle many-hole excitations are considered in

The Nilsson model of high-spin states is developed to include particle-hole excitations for rotation around an arbitrary axis. Potential-energy surfaces are calculated with constraints not only on the total spin but also on parity and signature. The method is applied to very light nuclei with A ~ 10. Good agreement for the ground-state bands of 8Be and 12C is obtained and predictions are made for

Nuclear superdeformation is studied theoretically using both simple models and more realistic numerical calculations. From the simple models general rules are formulated about the shell structure of the nucleus at large deformation, its affinity for reflection asymmetric or necked-in distortions and its response to rotation. The numerical calculations are based on realistic single-particle schemes

Collective properties at low and high spin for nuclei with Z ≥ 64 and N ≥ 82 are calculated on the basis o f deformed single-particle potentials. The calculations are confronted with the available experimental data like low-lying octupole bands, rotational bands of transitional nuclei with N ≥ 90 and evidence for collectivity in high-spin single-particle spectra. In the latter collective triaxiali

The Nilsson-Strutinsky approach to the description of yrast properties at very high spins is reviewed. Some recent calculations are presented and discussed with regard to the available experimental data. A nice agreement in the Te-region is pointed out. The aim is however more to describe physical trends than to make detailed predictions for specific nuclei. The general variation of the shell effe

Potential-energy surfaces at high spin are calculated for nuclei in the superheavy region by use of the cranked Nilsson hamiltonian. It is found, that the maximum fission barrier is shifted from the doubly magic 298114 to nuclei with fewer protons and more neutrons, as the spin increases. We also estimate, by use of simple models, the half-lives associated with alpha-decay, gamma-decay and fission

Calculations with the cranking-plus-Strutinsky formalism indicate that some part of the yrast line in almost all the nuclei of the A ∼ 40-80 region may be of non-collective type, corresponding to rotation around a symmetry axis. A numerical study of many such single-particle spectra shows that even at very high spins there is a non-negligible probability for the occurrence of isomers. This conclus

The cranked modified oscillator potential is used to study the nuclei 172-18072Hf at very high angular momenta. All these isotopes are found to "rotate around the prolate symmetry axis" for spin values I= 15-40 h {combining short stroke overlay}. In this region of spin we then look for prolate yrast traps. The pairing interaction with an approximative particle number projection as well as the hexa