Skyrme-QRPA calculations for low-lying excitation modes in deformed neutron-rich nuclei

Abstract

Low-frequency modes of excitation in deformed neutron-rich nuclei are studied by means of the quasiparticle random-phase approximation on the Skyrme-Hartree-Fock-Bogoliubov mean field. We investigate the microscopic structure of the soft $K^{\pi }=0^{+}$ modes systematically in neutron-rich Magnesium isotopes with $N=22,24,26$ and 28 close to the drip line, and it is found that the strong collectivity in ${}^{34}$Mg and ${}^{40}$Mg is acquired due to the coherent coupling between the $\beta$ vibration and the pairing vibration of neutrons. Microscopic structure of the $K^{\pi }=2^{+}$ modes changes gradually associated with the location of the Fermi level of neutrons, and it is found that the proton particle-hole excitation generating the $\gamma -$vibrational mode in ${}^{24}$Mg continues to play a key role in the near-drip-line nucleus ${}^{40}$Mg. The low-frequency octupole excitations are also investigated and the microscopic mechanism for the enhancement of transition strengths is discussed.

Comments: Accepted for publication in Eur. Phys. J. A, as a contribution to the ENAM08 conference