Abstract
The structure change of nuclear systems as a function of excitation energy is discussed. In the nuclear systems, protons and neutrons are considered to perform independent particle motion in low-lying states close to the ground state, however α cluster structure appears around the α-threshold energy to decay into subsystems. Until now, such cluster states have been investigated in light stable nuclei with equal numbers of protons and neutrons, and gas-like nature of α cluster structure has been well studied. In the present study, we discuss in neutron-rich nuclei how the gas-like cluster structure changes when excess neutrons are added. We show the appearance of cluster states with geometric shapes due to the "glue effect" of the excess neutrons.
