Discontinuities And Prolate Oblate Competition Near Spin 40 In The N=90 Isotones

The systematics of irregularities in rotational sequences near I=40 are summarised for N=90 isotones. These discontinuities can be understood in terms of competition between prolate collective structures and oblate single-particle states. Such an interpretation implies a sizeable interaction between “prolate collective” states and “oblate single-particle” states which was unexpected.