The evolution of shapes and collectivity with increasing angular momentum

The light rare-earth nuclei near N = 90, are textbook examples of the evolution of nuclear structure with excitation energy and angular momentum. They display a variety of different phenomena, such as, multiple backbends, dramatic shape changes and band termination. However, it has taken several decades before we were able to observe structures beyond band termination. A spectacular return to collectivity has been found to take place extending discrete gamma-ray spectroscopy into the so-called 'ultrahigh-spin regime' (I = 50-70). These latter sequences, observed initially in ^157,158Er, are interpreted as being associated with a particularly stable and energetically favored strongly deformed triaxial shape minimum. These data have generated a good deal of theoretical discussion. New results on similar evolutionary trends in other neighboring nuclei will be discussed. The latter are beginning to reveal a fascinating spectroscopy in this new exotic shape and spin regime. This document is composed of an abstract and the slides of the presentation. (authors)