Speaker
Dr
Yutaka Utsuno
(Japan Atomic Energy Agency)
Description
The tensor force has been regarded as an importance ingredient that causes the evolution of the shell structure in exotic nuclei. From its point of view, the spin-orbit splitting decreases from the L-S closure to the j-j closure. It is thus predicted that a new N=34 magic number would arise in Ca isotopes according to high location of the f5/2 orbit. In Ca isotopes, while the location of the g9/2 orbit is also of great interest because it can be very close to the pf shell due to the tensor-force-driven shell evolution, it has not been determined yet because of lack of direct experimental evidence. In the present study, performing a large-scale shell model calculation whose model space consists of the full sd-pf shell and part of the sdg shell, we propose some excited states in Ca isotopes are highly influenced by the g9/2 orbit, which carries much information on its location. The position of the gap between the pf and sdg shells can be fixed at 51Ti, Z=22, having a 9/2+ state dominated by the g9/2 orbit. Adopting the Hamiltonian whose single-particle energy of the g9/2 orbit is thus determined, the first 3- states in 50,52Ca become in good agreement with experiment. They comprise of strong admixture of proton excitation from the sd- to pf-shell and neutron excitation from the pf- to sdg-shell. On the other hand, they are located too high without g9/2 in a similar way to other sd-pf shell-model calculations. The strong mixing successfully accounts for a large cross section of the 48Ca(t,p)50Ca(3-) reaction as well as the 3- of 52Ca strongly populated by the two-proton knockout reaction of 54Ti. As a result, the g9/2 is predicted to lie ~1 MeV higher than f5/2 in neutron-rich Ca isotopes.
Primary author
Dr
Yutaka Utsuno
(Japan Atomic Energy Agency)
Co-authors
Prof.
Michio Honma
(University of Aizu)
Prof.
Noritaka Shimizu
(University of Tokyo)
Prof.
Takaharu Otsuka
(University of Tokyo)
Prof.
Takahiro Mizusaki
(Senshu University)
