3-body cluster gas structures in the excited $0^+$ states of $N=6$ nuclei

Abstract

We investigate the cluster structure of $α+{}^2n+{}^2n$ in $^8\mathrm{He}(0_2^+)$ and compare it with those of $2α+{}^2n$ in $^{10}\mathrm{Be}(0_2^+)$ and $3α$ in $^{12}\mathrm{C}(0_2^+)$ to understand the emergence mechanism of the 3-body cluster gas states. We apply an extended cluster model combined with cluster breaking components in a microscopic framework using effective nuclear forces based on nucleon degrees of freedom including the antisymmetrization between nucleons. In detailed analysis of the 3-body cluster structures of excited $0^+$ states, it is shown that $^8\mathrm{He}(0_2^+)$ exhibits 3-body cluster gas feature of $α+{}^2n+{}^2n$ similar to $^{12}\mathrm{C}$ but contains significant mixing of a 2-body-like $(α+{}^2n)+{}^2n$ component. We discuss cluster structures of $^8\mathrm{He}(0_2^+)$ and $^{12}\mathrm{C}(0_2^+)$ from the point of view of inter-cluster energies of ${}^2n \text{-} {}^2n$ and $α\text{-}{}^2n$ in comparison with the $α\text{-} α$ energies and find that the origin for the 2-body-like $(α+{}^2n)+{}^2n$ mixing is the unbalance of the $α\text{-}{}^2n$ and ${}^2n \text{-} {}^2n$ energies, in which Pauli effects play an essential role through the kinetic energy loss and internal potential energy loss of clusters. We clarify the emergence mechanism of the 3-body cluster gas state in excited $0^+$ states of $^8\mathrm{He}$ and $^{12}\mathrm{C}$ systems. The balance of inter-cluster interactions is essential for the appearance of 3-body cluster gas states. Microscopic effects, i.e., the Pauli effects of nucleons between clusters play a crucial role in cluster structures of excited $0^+$ states.