Selectivity in heavy ion transfer reactions

One-two-and three-nucleon stripping reactions induced by 480 MeV 12C and by 793 MeV 16O have been studied on 12C, 16O, 28Si, 40Ca, and 54Fe targets. Discrete levels are fed with cross sections up to 1 mb/sr for d-transfer reactions and one and two orders of magnitude less for 2p- and 3He-transfers, respectively. These reactions are governed by two selection rules contained in the semi-classical model of Brink: i) Large orbital final momentum states are selectively populated and ii) The most highly populated states correspond to no-flip transitions. Two-proton transfer reactions induced by 112 MeV 12C on even Ni and Zn isotopes are found to be less selective than two-neutron transfer reactions induced by the same projectile on the same targets in a similar incident energy range. The additional collective aspects observed in the two-proton transfers are examined in view of a semiphenomenological model of two quasi-particles coupled to a triaxial asymmetric rotor. The energy of excited states is well reproduced by simple shell model calculations. Such estimates are useful in proposing spins of newly observed states, especially as the shapes of the measured angular distributions are independant of the final spin of the residual nucleus. The experimental results of two-proton and two-neutron stripping reactions and the simple shell model allow an estimate of two-body matrix elements describing the nucleon-nucleon interaction and of the Coulomb energy