The spherical to asymmetric shape transition in the mass region with 50<(N, Z)<82
Collective potential energy surfaces were determined in the mass region with 50<(N, Z)<82 by fitting experimental level spectra andB(E 2)-values on the basis of the generalized collective model of Gneuss and Greiner. While the nuclides withN=80 and withZ=52 are rather soft vibrators we find an abrupt transition to asymmetric rotators forN=78 and forZ=54 tending to more symmetric shapes further away from the closed shells. The results predict the position of levels not yet observed andB(E 2)-values.