Nuclear Structure at High Spins

Nuclear structure at the highest spins is very likely to involve both collective and single-particle aspects. The liquid-drop model favors shapes that imply combinations of collective (rotational) and rotation-aligned single-particle angular momenta. The detailed band structures for the full range of such mixtures are considered. Nuc le i are composed o f a smal l ( b u t n o t t o o sma l l ) number o f nucleons. As a r e s u l t t hey d i s p l a y bo th c o l l e c t i v e and s i n g l e p a r t i c l e (non -co l l ec t i ve ) f ea tu res . For example, i n t h e ra re -ea r th and a c t i n i d e reg ions, t he lowly ing r o t a t i o n a l bands represent an almost pure c o l l e c t i v e motion, w i t h energ ies f o l l o w i n g t h e 1(1 + 1) r o t o r fo rmula t o w i t h i n a percent o r two, and E2 t r a n s i t i o n p r o b a b i l i t i e s n e a r l y 200 t imes l a r g e r than a s i n g l e p ro ton would have. On t h e o t h e r hand, near t h e c losed s h e l l s , t h e energy l e v e l s are almost comple te ly determined by t h e mot ion of a s i n g l e nucleon. Most nuc lear l e v e l s d i s p l a y both c o l l e c t i v e and non -co l l ec t i ve fea tu res , and h igh-sp in s t a t e s a re no except ion. To approach t h e phys i cs o f these s t a t e s I w i l l f i r s t desc r ibe some p r o p e r t i e s o f a p u r e l y c o l l e c t i v e , c l a s s i c a l r o t o r , and then cons ider t h e e f f e c t s o f c o u p l i n g s i n g l e p a r t i c l e mot ion t o t h i s . The o b j e c t i v e i s t o understand t h e k i n d s o f m ix tu res o f c o l l e c t i v e and s i n g l e p a r t i c l e mot ion t h a t are impor tan t i n n u c l e i a t t he h ighes t sp ins . Chr ideas about such * Presented a t t he I n t e r n a t i o n a l Conference on Nuclear Behavior a t High Angular Momentum, Strasbourg, France, A p r i l 22-24, 1980. s t a t e s have undergone impor tan t developments recen t1 y t h a t now make p o s s i b l e a reasonably s imple d e s c r i p t i o n o f t h i s sub jec t , which I w i l l