Study Of Nonlocalized Clustering In Nuclear Cluster Physics

The formation of clusters in nuclei is a fundamental aspect of nuclear many-body dynamics, and the investigation of the nuclear cluster motion and structure becomes one of hot topics in nuclear physics. In this thesis, a new concept, nonlocalized clus-tering, is proposed for understanding the cluster structures in nuclei. In this new pic-ture, the clusters are nonlocalized and move around in the whole nuclear volume, only avoiding mutual overlap due to the Pauli blocking effect, which is completely different from the traditional understanding of the localized clustering in nuclei. The concept of nonlocalized clustering makes us understand deeper the correlations of the clusters, and it also opens a door for exploring more complex cluster structures in nuclei. The new concept in nuclear cluster physics is proposed in two steps.Firstly, the THSR (Tohsaki-Horiuchi-Schuck-Ropke) model has been very suc-cessful in describing the na gas-like states in nuclei, which is based on the concept of nonlocalized clustering. As a natural extension, we propose a generalized THSR wave function, which is applicable to studies of general cluster structures in nuclei. The ground-state band in20Ne is investigated by using this generalized THSR wave function and the energies obtained agree well with the experimental values. Moreover, it is found that the single generalized THSR wave functions almost completely coin-cide with the exact solutions of the α+16O resonating group method (RGM) for the ground-state band in20Ne. For the ground state of20Ne, for instance, the squared over-lap between them is99.3%. Therefore, the THSR model can also be extended to study more compact cluster states in nuclei such as, e.g., the ground-state band in20Ne. And more importantly, in this new picture the a and16O clusters move in a nonlocalized way, rather than localized, rigid-body like clustering with a certain separation distance between the clusters. Thus, we indeed have a new understanding for the ground-state band in20Ne based on the concept of nonlocalized clustering.Secondly, we need to prove whether nonlocalized clustering is the general charac-ter of the cluster structures in nuclei or not. As we know, the existence of the inversion doublet bands has been an important basis of the localized clustering picture which has been the long-standing concept of nuclear cluster physics. The only successful descrip-tion of the ground-state band in20Ne is not enough. To obtain a conclusive answer to the question whether cluster motion in nuclei is localized or nonlocalized, it is neces-sary to study the inversion doublet bands in20Ne, especially the negative-parity band in the THSR framework. Recently, we proposed a Hybrid-Brink-THSR wave func-tion, which includes the THSR wave function and the localized Brink wave function as its two limit cases. After variational calculations, it was found that the hybrid wave function became. THSR-type wave function. We further found the highly surprising fact that those single THSR wave functions at the energy minimum points are nearly100%equivalent to the exact RGM solution of the α+16O system. Thus, we proved that the a and16O clusters make the nonlocalized motion rather than the traditional localized motion in20Ne and based on this result we further proposed the concept of nonlocalized clustering in nuclear cluster physics.