8He and 9Li cluster structures in light nuclei
Abstract
The possibility of the 8He and 9Li clusters in atomic nuclei is discussed. Until now most of the clusters in the conventional models have been limited to the closures of the three-dimensional harmonic oscillators, such as 4He, 16O, and 40Ca. In the neutron-rich nuclei, however, the neutron to proton ratio is not unity, and it is worthwhile to think about more neutron-rich objects with N>Z as the building blocks of cluster structures. Here the nuclei with the neutron number six, which is the subclosure of the p3/2 subshell of the jj-coupling shell model, are assumed to be clusters, and thus we study the 8He and 9Li cluster structures in 16Be (8He+8He), 17B (8He+9Li), 18C (9Li+9Li), and 24C (8He+8He+8He). Recent progress of the antisymmetrized quasi cluster model (AQCM) enables us to utilize jj-coupling shell model wave functions as the clusters rather easily. It is shown that the 8He+9Li and 9Li+9Li cluster configurations cover the lowest shell-model states of 17B and 18C, respectively. To predict the cluster states with large relative distances, we increase the expectation value of the principal quantum numbers by adding the nodes to the lowest states under the condition that the total angular momentum is unchanged (equal to Jπ =0). As a result, developed cluster states are obtained around the corresponding threshold energies. The rotational band structure of 24C, which reflect the symmetry of equilateral triangular configuration (D3h symmetry) of three 8He clusters, also appears around the threshold energy.