||Inversion doublets of reflection-asymmetric clustering in Si-28 and their isoscalar monopole and dipole transitions
Chiba, Y. ,
Taniguchi, Y.Kimura, M.
, p.044328 , 2017-04-28 , American Physical Society (APS)
Background: Various cluster states of astrophysical interest are expected to exist in the excited states of Si-28. However, they have not been identified firmly, because of the experimental and theoretical difficulties. Purpose: To establish the Mg-24 + alpha, O-16 + C-12, and Ne-20 + 2 alpha cluster bands, we theoretically search for the negative-parity cluster bands that are paired with the positive-parity bands to constitute the inversion doublets. We also offer the isoscalar monopole and dipole transitions as a promising probe for the clustering. We numerically show that these transition strengths from the ground state to the cluster states are very much enhanced. Method: The antisymmetrized molecular dynamics with GognyD1S effective interaction is employed to calculate the excited states of Si-28. The isoscalar monopole and dipole transition strengths are directly evaluated from wave functions of the ground and excited states. Results: Negative-parity bands having Mg-24 + alpha and O-16 + C-12 cluster configurations are obtained in addition to the newly calculated Ne-20 + 2 alpha cluster bands. All of them are paired with the corresponding positive-parity bands to constitute the inversion doublets with various cluster configurations. The calculation shows that the bandheads of the Mg-24 + alpha and Ne-20 + 2 alpha cluster bands are strongly excited by the isoscalar monopole and dipole transitions. Conclusions: The present calculation suggests the existence of inversion doublets with the Mg-24 + alpha, O-16 + C-12, and Ne-20 + 2 alpha configurations. Because of the enhanced transition strengths, we offer the isoscalar monopole and dipole transitions as good probe for the Mg-24 + alpha and Ne-20 + 2 alpha cluster bands.