K. R. Sandhya Devi

Backbending: Coriolis antipairing or rotational alignment?

Abstract A theoretical description of the ground-state bands m even-mass nuclei is given which includes the possibility of Coriolis antipairing (CAP) and rotational alignment (RAL) in the explanation of backbending. The method is based on a combination of Hartree-Fock- Bogoliubov, cranking model and particle number projection and applied to the high ( ≦ 18 h ) and very high ( ≦ 80 h ) spin states of 162 Er. The results indicate that the nucleus behaves according to a combination of CAP and RAL effects. Pairing for all neutron pairs near the Fermi surface is markedly reduced although the two i 13 2 pairs nearest to the Fermi level are somewhat more affected. However the dominant contribution to the total angular momentum for spins greater than 12 ħ comes from one i 13 2 pair, (with large components Ω = 1 2 3 2 5 2 ). For the very high spin states ( 30 h h ) the nucleus becomes triaxial and well defined shape isomers appear.

Cause of backbending in the Os region

Abstract The cause for backbending in 180–182 Os and 181 Re nuclei is studied using a theoretical description which includes the possibility of Coriolis antipairing (CAP), rotational alignment (RAL) and deformation jumps (DEJ). It is found that the h 9 2 protons play no important role as advocated by Neskakis et al . Practically the total angular momentum of the system is instead found to be due to the RAL of i 13 2 neutron pairs. To produce the backbending one needs a sudden enough RAL of i 13 2 neutron pairs, and this RAL seems to depend on the details of the single particle levels which in turn are influenced strongly by the hexadecapole deformation. Indications are found that the γ-DEJ may also be responsible for backbending in this mass region.

Influence of protons on backbending

Abstract Backbending in (at least the first half of) the rare earth nuclei seems to be determined by the alignment of an i 13 2 neutron pair. This is supported by the disappearance of backbending due to the blocking of an i 13 2 level by an odd neutron for example in 165Yb. Contrary to expectations backbending disappears also by adding an odd h 9 2 ,proton to 70166Yb in 71167Lu for this state (but is present if the odd proton is in the g 7 2 level). A theory is presented which explains the odd neutron and the odd proton nuclei. It turns out that the odd proton in 167Lu serves only as a type of catalyst for the alignment of an i 13 2 neutron pair. The odd proton changes the deformation and moves the Fermi surface nearer ( g 7 2 ) or farther away ( h 9 2 ) from the nearest i 13 2 neutron level. In one case one finds backbending and in the other case no backbending in 167Lu.

Projected Hartree-Fock-Bogolubov calculation for Ti isotopes

Abstract Deformed Hartree-Fock-Bogulubov calculations have been carried out for 46, 48, 50Ti. The angular momentum projected spectra show a great improvement over the projected Hartree-Fock ones and are in very good agreement with the experimental results.

Microscopic determination of energy surfaces at very high spin states

Deformation energy surfaces for very high angular momentum states in the rare earth nuclei are calculated microscopically forβ andγ deformations using a pairing, quadrupole and Coulomb Hamiltonian. The parameters of the Hamiltonian are adjusted to the ground state deformations and the odd-even mass differences. It is found that even with the Nilsson basis one may obtain the correct asymptotic moment of inertia by omitting a few high lying large angular momentum basis states which are depressed too much by thel2 term. Similarities and discrepancies between the proposed microscopic model and the Strutinsky calculations are displayed and discussed. The advantages as well as the limitations of the microscopic description presented here are analysed.

On the Correlations of the Resonance Parameters for the Overlapping Resonances

A statistical study of the correlations of the complex poles of the unitary collision matrix is carried out. It is shown that both for the elastic and the inelastic scattering the correlation coefficient of the two total widths is always very small. A simple relation satisfied by the correlation coefficient of the real parts of the complex poles is given. The distribution of the single width is calculated and compared with the Porter‐Thomas distribution and the one obtained by a numerical calculation. Some other interesting results, like the energy correlation function for the purely elastic scattering cross section and a relation satisfied by the resonance parameters for the fluctuation calculation, are also given.