Speaker
Prof.
Yoshiko Kanada-En'yo
(Department of Physics, Kyoto University)
Description
Cluster structures have been found in light unstable nuclei as well as stable nuclei. For instance, neutron-rich Be isotopes show remarkable cluster structures of a 2 alpha core with surrounding excess neutrons. For C isotopes, three-body cluster structures in excited states have been suggested and attracting a great interest. How can we experimentally probe such the cluster structures ? For the ground states, it is useful tool to measure charge radii along an isotope chain because they reflect the cluster development though the proton distribution. For excited states, monopole and dipole excitations, which are measured by inelastic scatterings, can be useful approaches.
Low-energy isoscalar(IS) and isovector(IV) strengths separated from the giant resonances appear originating in new collective modes such as cluster modes and valence neutron modes, respectively. Our aim is to clarify the natures of low-energy ISM, ISD, IVD strengths and understand the mechanism of the separation of low-energy strengths from the GR strengths. For this aim, we apply a newly-developed method, the shifted base AMD, and combine it with the cluster GCM. The framework can describe the GR modes given by the coherent 1p-1h excitations as well as the large amplitude cluster modes. Applications to 9Be and 10Be and that to 12C are reported. In 9Be and 10Be, the IVGDR in E > 20 MeV shows a two peak structure because of the dipole excitation in the 2-alpha core with the prolate deformation, whereas the low-energy E1 resonances appear in E < 20 MeV exhausting 20% of the TRK sum rule. The 1- resonance at E~15 MeV in 10Be has a 6He+alpha cluster structure and shows the remarkable E1 strength because of coherent contribution of two valence neutrons. The calculated E1 strengths reasonably describe the experimental photonuclear cross sections. We also investigate the ISM and ISV strengths in 12C and discuss the remarkable low-energy strengths for cluster states separating from the GR strengths. We show that the monopole and dipole excitations are good probes to pin down the cluster structures in the excited states.
Primary author
Prof.
Yoshiko Kanada-En'yo
(Department of Physics, Kyoto University)