Monopole strength as a measure of nuclear shape mixing

A survey of observed E0 transition strength shows that some of the largest strength occurs for transitional nuclei whenever large mixing between almost spherical and largely deformed shapes results. This leads to the conclusion that large E0 strength is not an indication of coexisting shapes but of strong mixing between nuclear states with largely different radii. In addition, we discuss the variation of E0 transition rates in regions where intruder states become the nuclear ground state. We illustrate this by recent results in the A≃100 region concentrating especially on the anomalously large monopoles strength and its variation in the even-even N=60 isotones as compared with the N=58 isotones.