arXiv subjects

S. Okabe

Publications and source records attributed to S. Okabe.

3 recordsLinked to original sources

arXiv2001

Triaxial deformation in 10Be

The triaxial deformation in $^{10}$Be is investigated using a microscopic $α+α+n+n$ model. The states of two valence neutrons are classified based on the molecular-orbit (MO) model, and the $π$-orbit is introduced about the axis connecting the two $α$-clusters for the description of the rotational bands. There appear two rotational bands comprised mainly of $K^π= 0^+$ and $K^π= 2^+$, respectively, at low excitation energy, where the two valence neutrons occupy $K^π= 3/2^-$ or $K^π= 1/2^-$ orbits. The triaxiality and the $K$-mixing are discussed in connection to the molecular structure, particularly, to the spin-orbit splitting. The extent of the triaxial deformation is evaluated in terms of the electro-magnetic transition matrix elements (Davydov-Filippov model, Q-invariant model), and density distribution in the intrinsic frame. The obtained values turned out to be $γ= 15^o \sim 20^o$.

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arXiv2001

Molecular-orbital structure in neutron-rich C isotopes

The molecule-like structure of the C isotopes (A=12, 14, 16) is investigated using a microscopic $α+α+α+n+n+\cdot \cdot \cdot$ model. The valence neutrons are classified based on the molecular-orbit (MO) model, and both $π$-orbit and $σ$-orbit are introduced around three $α$-clusters. The valence neutrons which occupy the $π$-orbit increase the binding energy and stabilize the linear-chain of 3$α$ against the breathing-like break-up. However, $^{14}$C with the $π$-orbit does not show clear energy minimum against the bending-like path. The combination of the valence neutrons in the $π$- and the $σ$-orbit is promising to stabilize the linear-chain state against the breathing- and bending- modes, and it is found that the excited states of $^{16}$C with the $(3/2^-_π)^2(1/2^-_σ)^2$ configuration for the four valence neutrons is one of the most promising candidates for such structure.

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arXiv2000

Important role of the spin-orbit interaction in forming the 1/2^+ orbital structure in Be isotopes

The structure of the second 0^+ state of ^{10}Be is investigated using a microscopic $α+α+n+n$ model based on the molecular-orbit (MO) model. The second 0^+ state, which has dominantly the (1/2^+)^2 configuration, is shown to have a particularly enlarged $α-α$ structure. The kinetic energy of the two valence neutrons occupying along the $α-α$ axis is reduced remarkably due to the strong $α$ clustering and, simultaneously, the spin-orbit interaction unexpectedly plays important role to make the energy of this state much lower. The mixing of states with different spin structure is shown to be important in negative-parity states. The experimentally observed small-level spacing between 1^- and 2^- (~ 300 keV) is found to be an evidence of this spin-mixing effect. ^{12}{Be} is also investigated using $α+α+4n$ model, in which four valence neutrons are considered to occupy the (3/2^-)^2(1/2^+)^2 configuration. The energy surface of ^{12}Be is shown to exhibit similar characteristics, that the remarkable $α$ clustering and the contribution of the spin-orbit interaction make the binding of the state with (3/2^-)^2(1/2^+)^2 configuration properly stronger in comparison with the closed p-shell (3/2^-)^2(1/2^-)^2 configuration.

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