PHASE COEXISTENCE IN TRANSITIONAL NUCLEI AND THE INTERACTING-BOSON MODEL

Recent data provide evidence for coexisting phases at low energy in th e spherical-deformed transitional nucleus Sm-152. The nature of the wa ve functions at the spherical-deformed phase transition in nuclei is a nalyzed within the framework of the interacting-boson model. It is sho wn that in the U(5)-SU(3) transition, two phases coexist in a very sma ll region of parameter space around the critical value of the control parameter xi. The coexistence region with two minima in the potential shrinks to zero as one moves to the U(5)-O(6) transition. Implications for other systems are briefly mentioned. [S0031-9007(98)06839-2].