Many-Particle and Many-Hole States in Neutron-Rich Ne Isotopes Related to Broken N=20 Shell Closure

The low-lying level structures of $^{26}{\rm Ne}$, $^{28}{\rm Ne}$ and $^{30}{\rm Ne}$ which are related to the breaking of the N=20 shell closure have been studied by the framework of the deformed-basis antisymmetrized molecular dynamics plus generator coordinate method using Gogny D1S force. The properties of the many-particle and many-hole states are discussed as well as that of the ground band. We predict that the negative-parity states in which neutrons are promoted into $pf$-orbit from $sd$ orbit have the small excitation energy in the cases of $^{28}{\rm Ne}$ and $^{30}{\rm Ne}$ which, we regard, is a typical phenomena accompanying the breaking of N=20 shell closure. It is also found that the neutron $4p4h$ structure of $^{30}{\rm Ne}$ appears in low excitation energy which contains $\alpha + ^{16}{\rm O}$ correlations.Comment: 18 pages, 7 figure

Low-lying 2+^+ states generated by pnpn-quadrupole correlation and N=28N=28 shell quenching

The quadrupole vibrational modes of neutron-rich $N$=28 isotones ($^{48}$Ca, $^{46}$Ar, $^{44}$S and $^{42}$Si) are investigated using the canonical-basis time-dependent Hartree-Fock-Bogoliubov theory with several choice of energy density functionals, including nuclear pairing correlation. It is found that the quenching of $N$=28 shell gap and the proton holes in the $sd$-shell trigger quadrupole correlation and increase the collectivity of the low-lying 2$^+$ state in $^{46}$Ar. It is also found that the pairing correlation plays an important role to increase the collectivity. We also demonstrate that the same mechanism to enhance the low-lying collectivity applies to other $N$=28 isotones $^{44}$S and $^{42}$Si, and it generates a couple of low-lying 2$^+$ states which can be associated with the observed $2^+$ states.Comment: 7 page and 4 figure

Characteristic \alpha and ^{6}He decays of the linear-chains in ^{16}C

The linear-chain states of $^{16}$C and their decay modes are theoretically investigated by using the antisymmetrized molecular dynamics. It is found that the positive-parity linear-chain states have the $(3/2^-_\pi)^2(1/2^-_\sigma)^2$ configuration and primary decay to the $^{12}$Be($2^+_1$) as well as to the $^{12}$Be(g.s.) by the $\alpha$ particle emission. Moreover, we show that they also decay to the $^6{\rm He}+{}^{10}{\rm Be}$ channel. In the negative-parity states, it is found that two types of the linear-chains exist. One has the valence neutrons occupying the molecular-orbits $(3/2^-_\pi)^2(1/2^-_\sigma)(3/2^+_\pi)$, while the other's configuration cannot be explained in terms of the molecular orbits because of the strong parity mixing. Both configurations constitute the rotational bands with large moment of inertia and intra-bands $E2$ transitions. Their $\alpha$ and ${}^{6}{\rm He}$ reduced widths are sufficiently large to be distinguished from other non-cluster states although they are smaller than those of the positive-parity linear-chain.Comment: arXiv admin note: text overlap with arXiv:1605.0556

Laplace expansion method for the calculation of the reduced width amplitudes

We derive the equations to calculate the reduced width amplitudes (RWA) of the different size clusters and deformed clusters without any approximation. These equations named Laplace expansion method are applicable to the nuclear models which uses the Gaussian wave packets. The advantage of the method is demonstrated by the numerical calculations of the ${}^{16}{\rm O}+\alpha$ and ${}^{24}{\rm Mg}+\alpha$ RWAs in $^{20}{\rm Ne}$ and $^{28}{\rm Si}$.Comment: 26 pages, 4 figure

Three-body decay of linear-chain states in 14^{14}C

The decay properties of the linear-chain states in $^{14}$C are investigated by using the antisymmetrized molecular dynamics. The calculation predicts two rotational bands with linear-chain configurations having the $\pi$-bond and $\sigma$-bond valence neutrons. For the $\pi$-bond linear-chain, the calculated excitation energies and the widths of $\alpha$-decay to the ground state of $^{10}{\rm Be}$ reasonably agree with the experimental candidates observed by the $\alpha+{}^{10}{\rm Be}$ resonant scattering. On the other hand, the $\sigma$-bond linear-chain is the candidate of the higher-lying resonant states reported by the break-up reaction. As the evidence of the $\sigma$-bond linear-chain, we discuss its decay pattern. It is found that the $\sigma$-bond linear-chain not only decays to the excited band of $^{10}{\rm Be}$ but also decays to the three-body channel of $^{6}{\rm He}+\alpha+\alpha$, and the branching ratio of these decays are comparable. Hence, we suggest that this characteristic decay pattern is a strong signature of the linear-chain formation and a key observable to distinguish two different linear-chains

Deformation of hypernuclei studied with antisymmetirzed molecular dynamics

An extended version of the antisymmetrized molecular dynamics to study structure of $p$-$sd$ shell hypernuclei is developed. By using an effective $\Lambda N$ interaction, we investigate energy curves of $^9_\Lambda$Be, $^{13}_\Lambda$C and $^{20,21}_\Lambda$Ne as function of nuclear quadrupole deformation. Change of nuclear deformation caused by $\Lambda$ particle is discussed. It is found that the $\Lambda$ in p-wave enhances nuclear deformation, while that in s-wave reduces it. This effect is most prominent in $^{13}_\Lambda$C. The possibility of the parity inversion in $^{20}_\Lambda$Ne is also examined