Nuclei at high angular momenta

Two developments that have recently attracted attention to high-spin states in nuclei are described. The first is the discovery (Johnson, Phys. Lett.; B34:605 (1971)) of a pronounced irregularity around spin 16 (h/2)sub(π) in the otherwise very regular behaviour of the rotational energy spacings in some even-even rare earth nuclei; this is referred to as backbending. The second has to do with what are termed the yrast states above the backbend region; this has recently produced the first information about states with spins as high as 50 (h/2)sub(π) (Simon, Phys. Rev. Lett.; 36:359 (1976)). It is stated to be now clear that nuclei respond to increasing angular momentum, and that changes begin to occur from the beginning and some major modifications of structure of most nuclei happen by spin 20 (h/2)sub(π). Calculations have recently suggested dramatic structural changes at higher angular moments, and experimental techniques to identify these seem to be at hand. This promises continued progress in the understanding of this aspect of nuclear matter. (U.K.)