Collective E2 transitions in 18O

Coulomb form factors for collective E2 transitions in 18O are discussed taking into account core-polarization effects. These effects are taken into account through a microscopic perturbation theory including excitations from the core orbits and the model space valence orbits to all higher allowed orbits with 10ℏω excitations. The two-body Michigan three range Yukawa (M3Y) interaction is used for the core-polarization matrix elements. Two different model spaces with different Hamiltonians are adopted. The calculations include the lowest four excited 2+ states with excitation energies 1.98, 3.92, 5.25 and 8.21 MeV. Comparisons were made with the available experimental data for both the transition strengths and the form factors. The results are quite convincing that one needs to use orbitals from the normally considered inert core of Z and N=8 in order to be able to describe both the correct excitation energy of the third and fourth 2+ levels and the increased E2 collectivity.