Persisting α-planar structure in ²⁰Ne

Nine low-lying O_n⁺ states of ²⁰Ne and their possible rotational bands have been studied by employing the isomorphic shell model which is a hybrid between conventional shell model and the liquid drop model in conjunction with the nucleon finite size and which in addition uses no adjustable parameters. The configurations of six out of these nine O_n⁺ states have an α-planar structure when, for each set of four closeby nucleon average positions (two protons and two neutrons), possessing the same principal quantum number n and forming an instant α-like particle, the center of gravity is considered. The novelty of the present study is focused on the fact that the axis of rotation and the number of rotating nucleons inside the same rotational band may change in such a way that the relevant moment of inertia increases monotonically in steps forming for each step a new branch of the band. Up to five such branches have been found and each time the moment of inertia of the last of them approaches the rigid body limit, creating superdeformed bands. The coexistence of a superdeformed band and of lower deformation bands include several states with the same I^π value. Two rotational bands are introduced for the first time and the model predictions of states in all cases are very close to the experimental data. Another important feature of the present study is that two different configurations possess identical binding energy (the maximum among all possible configurations) and are assigned, by 50% each, to the g.s. of ²⁰Ne. This has been verified by successfully employing many observables and results of other models. © 1996 The American Physical Society.