The antisymmetrized quasi-cluster model (AQCM) is a method to describe a transition from the alpha-cluster wave function to the jj-coupling shell model wave function. In this model, the cluster-shell transition is characterized by only two parameters
; R representing the distance between alpha clusters and Lambda describing the breaking of alpha clusters, and the contribution of the spin-orbit interaction, very important in the jj-coupling shell model, can be taken into account starting with the alpha cluster model wave function. In this article we show the generality of AQCM by extending the application to heavier region; various 4N nuclei from 4He to 52Fe. We show and compare the energy curves for the alpha+40Ca cluster configuration calculated with and without alpha breaking effect in 44Ti.
The low-lying states of the $^{9}$Li nucleus are investigated with a unified framework of microscopic structure and reaction models. In the structure model, the wave function is fully antisymmetrized and the $^{9}$Li nucleus is described as an $alpha
$ + $t$ + $n$ + $n$ four-body system, and low-lying 1/2$^{-}$, 3/2$^{-}$, 5/2$^{-}$, and 7/2$^{-}$ states are obtained by the stochastic multi-configuration mixing method. Using these wave functions, the quasi-elastic cross section at $E/A$ = 60 MeV and the elastic and inelastic cross sections at $E/A$ = 50 MeV on the $^{12}$C target are calculated in the framework of the microscopic coupled channel (MCC) method. The characteristic inelastic angular distribution is seen in the 3/2$_{2}^{-}$ state, whose $alpha+t$ cluster structure and valence neutron configurations are discussed in detail. We find the possibility of triaxial deformation and mixing of di-neutron components in the $^{9}$Li nucleus.
We investigate the possibility of the existence of the exotic torus configuration in the high-spin excited states of $^{40}$Ca. We here consider the spin alignments about the symmetry axis. To this end, we use a three-dimensional cranked Skyrme Hartr
ee-Fock method and search for stable single-particle configurations. We find one stable state with the torus configuration at the total angular momentum $J=$ 60 $hbar$ and an excitation energy of about 170 MeV in all calculations using various Skyrme interactions. The total angular momentum J=60 $hbar$ consists of aligned 12 nucleons with the orbital angular momenta $Lambda=+4$, +5, and +6 for spin up-down neutrons and protons. The obtained results strongly suggest that a macroscopic amount of circulating current breaking the time-reversal symmetry emerges in the high-spin excited state of $^{40}$Ca.
We investigate the existence of weakly coupled gas-like states comprised of three $alpha$ particles around an $^{16}$O core in $^{28}$Si. We calculate the excited states in $^{28}$Si using the multi-configuration mixing method based on the $^{16}$O +
3$alpha$ cluster model. We also include the $^{16}$O + $^{12}$C and $^{24}$Mg + $alpha$ basis wave functions prepared by the generator coordinate method. To identify the gas-like states, we calculate the isoscalar monopole transition strengths and the overlap of the obtained states with the geometrical cluster wave function and the Tohsaki-Horiuchi-Schuck-R{o}pke (THSR) wave function. The results show that the obtained fourth and twelfth states significantly overlap with the THSR wave function. These two states clearly coexist with the $^{16}$O + $^{12}$C cluster states, emerging at similar energies. The calculated isoscalar monopole strengths between those two states are significantly large, indicating that the states are members of the excitation mode. Furthermore, the calculated root-mean-squared (RMS) radii for these states also suggest that a layer of gas-like three $alpha$ particles could exist around the surface of the $^{16}$O core, which can be described as a two-dimensional gas in the intermediate state before the Hoyle-like three $alpha$ states emerge.
We investigate the linear-chain configurations of four-$alpha$ clusters in $^{16}$O using a Skyrme cranked Hartree-Fock method and discuss the relationship between the stability of such states and angular momentum. We show the existence of a region o
f angular momentum (13-18 $hbar$) where the linear chain configuration is stabilized. For the first time we demonstrate that stable exotic states with a large moment of inertia ($hbar^2/2Theta$ $sim$ 0.06-0.08 MeV) can exist.
We have studied gas-like states of $alpha$ clusters around an $^{16}$O core in $^{24}$Mg based on a microscopic $alpha$-cluster model. This study was performed by introducing a Monte Carlo technique for the description of the THSR (Tohsaki Horiuchi S
chuck R{o}pke) wave function, and the coupling effect to other low-lying cluster states was taken into account. A large isoscalar monopole ($E0$) transition strength from the ground to the gas-like state is discussed. The gas-like state of two $alpha$ clusters in $^{24}$Mg around the $^{16}$O core appears slightly below the 2$alpha$-threshold e
