Neutron transition strengths of 21+ states in the neutron-rich oxygen isotopes determined from inelastic proton scattering

A coupled-channel analysis of the O-18,O-20,O-22(p,p(')) data has been performed to determine the neutron transition strengths of the 2(1)(+) states in oxygen targets, using the microscopic optical potential and inelastic form factor calculated in the folding model. A complex density- and isospin-dependent version of the CDM3Y6 interaction was constructed, based on the Brueckner-Hartree-Fock calculation of nuclear matter, for the folding model input. Given an accurate isovector density dependence of the CDM3Y6 interaction, the isoscalar (delta(0)) and isovector (delta(1)) deformation lengths of the 2(1)(+) states in O-18,O-20,O-22 have been extracted from the folding model analysis of the (p,p(')) data. A specific N dependence of delta(0) and delta(1) has been established which can be linked to the neutron shell closure occurring at N approaching 16. The strongest isovector deformation was found for the 2(1)(+) state in O-20, with delta(1) about 2.5 times larger than delta(0), which indicates a strong core polarization by the valence neutrons in O-20. The ratios of the neutron/proton transition matrix elements (M-n/M-p) determined for the 2(1)(+) states in O-18,O-20 have been compared with those deduced from the mirror symmetry, using the measured B(E2) values of the 2(1)(+) states in the proton-rich Ne-18 and Mg-20 nuclei, to discuss the isospin impurity in the 2(1)(+) excitation of the A=18, T=1 and A=20, T=2 isobars.