PERSISTING ALPHA-PLANAR STRUCTURE IN NE-20

Nine low-lying O-n(+) states of Ne-20 and their possible rotational ba nds have been studied by employing the isomorphic shell model which is a hybrid between conventional shell model and the liquid drop model i n 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 alpha-planar structure when, for each set of fou r closeby nucleon average positions (two protons and two neutrons), po ssessing the same principal quantum number n and forming an instant al pha-like particle, the center of gravity is considered. The novelty of the present study is focused on the fact that the axis of rotation an d the number of rotating nucleons inside the same rotational band may change in such a way that the relevant moment of inertia increases mon otonically 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 ine rtia of the last of them approaches the rigid body limit, creating sup erdeformed bands. The coexistence of a superdeformed band and of lower deformation bands include several states with the same I-pi value. Tw o rotational bands are introduced for the first time and the model pre dictions of states in all cases are very close to the experimental dat a. Another important feature of the present study is that two differen t configurations possess identical binding energy (the maximum among a ll possible configurations) and are assigned, by 50% each, to the g.s. of Ne-20. This has been verified by successfully employing many obser vables and results of other models.