The Subtleties of Pairing and Collective Structures in Deformed Nuclei

It is well known that simple monopole pairing is a pretty crude approximation. It can account for the observations that the ground states of all even-even nuclei have spinparity 01 and that there is a pairing gap above the ground state in deformed nuclei before particle-hole configurations can be excited. As an approximation it is best for proton and neutron mid-shell nuclei where the available single particle Nilsson wavefunctions have large overlaps. However at the beginning of regions of deformation, where high-K orbitals can be bought to the Fermi surface from a lower shell, simple monopole pairing is inadequate in describing the physics of the observed data. More recently, with a considerable increase in the quantity and quality of experimental data available, configuration dependent pairing has been used to account for the properties of low-lying first excited 02 states in N = 88 and 90 nuclei at the onset of deformation in the rare earths. The properties of 02 states in these and other nuclei at the start of regions of deformation and the effects of blocking of pairing leading to a decrease in the backbending critical frequencies in odd nuclei are presented.