Pygmy dipole mode in deformed neutron-rich Mg isotopes close to the drip line

Kenichi Yoshida
Phys. Rev. C 80, 044324 – Published 21 October 2009

Abstract

We investigate the microscopic structure of the low-lying isovector-dipole excitation mode in neutron-rich Mg36,38,40 close to the drip line by means of the deformed quasiparticle random-phase approximation employing the Skyrme and the local pairing energy-density functionals. It is found that the low-lying bump structure above the neutron emission-threshold energy develops when the drip line is approached, and that the isovector dipole strength at Ex<10 MeV exhausts about 6.0% of the classical Thomas-Reiche-Kuhn dipole sum rule in Mg40. We obtained the collective dipole modes at around 810 MeV in Mg isotopes, that consist of many two-quasiparticle excitations of the neutron. The transition density clearly shows an oscillation of the neutron skin against the isoscalar core. We found significant coupling effects between the dipole and octupole excitation modes due to the nuclear deformation. It is also found that the responses for the compressional dipole and isoscalar octupole excitations are much enhanced in the lower energy region.

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  • Received 20 August 2009

DOI:https://doi.org/10.1103/PhysRevC.80.044324

©2009 American Physical Society

Authors & Affiliations

Kenichi Yoshida

  • RIKEN Nishina Center for Accelerator-Based Science, Wako, Saitama 351-0198, Japan

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Issue

Vol. 80, Iss. 4 — October 2009

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