Nuclear structure at high spin is influenced by a combination of liquid-drop and shell-structure effects. For N 86 both contribute towards the occurrence along the yrast line of high-spin oblate aligned-particle configurations. Shell effects are mainly responsible for the prolate deformation of nuclei with N 90. The competition between oblate and prolate driving effects leads to a prolate-to-oblate shape transition in 154Dy. The role of rotation-aligned configurations in the shape change is discussed.

Dramatic progress has been made in all branches of physics since the National Research Council's 1986 decadal survey of the field. The Physics in a New Era series explores these advances and looks ahead to future goals. The series includes assessments of the major subfields and reports on several smaller subfields, and preparation has begun on an overview volume on the unity of physics, its relationships to other fields, and its contributions to national needs. Nuclear Physics is the latest volume of the series. The book describes current activity in understanding nuclear structure and symmetries, the behavior of matter at extreme densities, the role of nuclear physics in astrophysics and cosmology, and the instrumentation and facilities used by the field. It makes recommendations on the resources needed for experimental and theoretical advances in the coming decade.

Experimental nuclear moments of inertia at high spins along the yrast line have been determined systematically and found to differ from the rigid-body values. The difference is attributed to shell effect and these have been calculated microscopically. The data and quantal calculations are interpreted by means of the semiclassical Periodic Orbit Theory. From this new perspective, features in the moments of inertia as a function of neutron number and spin, as well as their relation to the shell energies can be understood. Gross shell effects persist up to the highest angular momenta observed.

This volume contains the proceedings of the "International Conference on Spin Excitations in Nuclei" held in Telluride, Colo rado, March 25-27, 1982. The motivation for the conference was, in a large part due to the recent development of new variable energy accelerators which produce high quality beams of electrons, protons, and pions that are providing the first precise information on spin excitations in nuclei over a large range of spin and mass. In the past such data had been restricted primarily to light nuclei and were generally resolution limited. Perhaps, the most exciting new result has been the clear observation of the elusive spin-dipole strength (Gamow Teller and Ml) in medium and heavy mass nuclei through the use of the (p,n) and (p,p') reactions at or near zero degrees with 100-200 MeV incident protons. Energy dependence in the isovector parts of the nucleon-nucleon interaction make the 100-200 MeV energy region particularly appropriate for such studies. The clean data from (e,e'), ('IT,'IT'), (p,p'), and (p,n) on high spin "stretched" states which have particularly simple structure has also been quite impor tant. The recent results contain important new information on the nature of the spin dependent forces in nuclei. These in turn are inherently related to the properties of the nuclear mesonic field and the underlying quantum chromodynamics.