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 70 166Yb in 71 167Lu 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.