The systematics of the onset of deformation in the $N=88-90\mathrm{}$ region is reexamined in light of the recently discovered shell closure at $Z=64\mathrm{}$. It is shown that the microscopic explanation of the origin of deformation already proposed for the $A\sim 100$ region is equally applicable here and leads to a new interpretation of the $A\sim 150$ region.

• Received 3 August 1981

DOI:https://doi.org/10.1103/PhysRevLett.47.1433