N=Z Waiting Point Nucleus ⁶⁸Se: Collective Rotation and High-K Isomeric States

The structure of collective states and quasi-particle excitations in $^{68}$Se is analyzed by using the projected shell model. It is found that the $g_{9/2}$ orbitals play a decisive role for the structure of this nucleus. At the prolate minimum, alignment of the low-K states causes the observed first backbending in moment of inertia and we predict a second backbending that has not yet been reported. At the oblate minimum, quasi-particles having high-K can form long-lived isomeric states. The structure of $^{68}$Se is discussed with respect to the isomers and their possible impact on the determination of its nuclear mass.