Rotation-alignment mechanism and the second discontinuity in the yrast level spacing

We report the result of a calculation of the yrast levels for a system of four nucleons in the i/sub 13/2/ shell, interacting via a pairing force, and coupling to a strongly deformed, axially symmetric core. In addition to an initial backbend at I = 12, a second smaller backbend occurs at I = 38. The structure of the wave functions at the second discontinuity indicates that it arises because of the decoupling of all four nucleons and subsequent alignment with the core angular momentum