Kosei Nakagawa | Searcharxiv

arXiv2026

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

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.

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arXiv2025

$α+{}^2n+{}^2n$ 3-body cluster structures and dineutron breaking in ${}^8 \mathrm{He}$

The $0_2^+$ state of ${}^8\mathrm{He}$ has been discovered by a recent experiment, which suggested a developed cluster structure of spatially correlated neutron pairs, called "dineutrons" (${}^2n$). We aim to investigate the structure of ${}^8\mathrm{He}(0^+_1)$ and ${}^8\mathrm{He}(0^+_2)$ to clarify the monopole excitation mode in ${}^8\mathrm{He}$ system while focusing on the $α+{}^2n+{}^2n$ cluster structures and the breaking of ${}^2n$ clusters. We apply a microscopic cluster model with the generator coordinate method for the $α+{}^2n+{}^2n$ cluster and ${}^6\mathrm{He}+{}^2n$ cluster dynamics. The $p_{3/2}$-closure component, which is induced by the spin-orbit force, is also incorporated. The present calculation reasonably reproduces the experimental data of the properties of ${}^8\mathrm{He}$, such as $2n$ and $4n$ separation energies, energy spectra, and radii. The spatially developed cluster structure of the $0_2^+$ state is obtained. The $0_1^+$ and $0_2^+$ states have dominant components of $α+{}^2n+{}^2n$ 3-body cluster, but contain significant ${}^2n$ breaking components which contribute to the energy gain and size shrinking of the ${}^8\mathrm{He}$ system. The monopole excitation in ${}^8\mathrm{He}$ is regarded as a radial excitation, which is similar to that in ${}^{12}\mathrm{C}$. The $α+{}^2n+{}^2n$ cluster structures play a dominant role in ${}^8\mathrm{He}(0_{1,2}^+)$, and the mixing of the dineutron breaking contributes to significant structural effects.

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