Large proton contribution to the 2+ excitation in Mg20 studied by intermediate energy inelastic scattering

Coulomb excitation of the proton-rich nucleus {sup 20}Mg was studied using a radioactive {sup 20}Mg beam at 58A MeV impinging on a lead target. The reduced transition probability B(E2;0{sub g.s.}{sup +}{yields}2{sub 1}{sup +}) was extracted to be 177(32) e{sup 2} fm{sup 4}, which agrees with the theoretical predictions by a cluster model assuming {sup 16}O + 2p + 2p structure, a mean-field approach based on the angular momentum projected generator coordinate method, and the USD shell model. The ratio of the neutron-to-proton multipole matrix elements M{sub n}/M{sub p} in the mirror nucleus {sup 20}O was deduced to be 2.51(25) with the M{sub n} value evaluated from the measured B(E2) value for {sup 20}Mg with the help of isospin symmetry. The results confirm the large M{sub n}/M{sub p} value previously reported in {sup 20}O, leading to the dominant role of the four valence nucleons in the 2{sub 1}{sup +} excitation and persistence of the {sup 16}O core in {sup 20}O and {sup 20}Mg.