High-lying neutron hole strengths observed in pick-up reactions

Abstract

Neutron-hole states in orbits well below the Fermi surface have been observed in a number of medium-heavy nuclei from A = 90 to 209 using one nucleon pick-up reactions. The excitation energies, angular distributions of such broad and enhanced structures will be discussed. The fragmentation of the neutron-hole strengths as well as the spreading of such simple mode of excitations into more complex states are compared to recent calculations within the quasiparticle-phonon or the single particle-vibration coupling nuclear models. We report on recent measurements of J for inner-hole states in 89Zr and 115, 119Sn using the analyzing power of the ( p -1, d) and ( d -2, t) reactions. Large enhancement of cross-sections are observed at high excitation energy in the study of the (p, t) reactions on Zr, Cd, Sn, Te and Sm isotopes. The systematic features of such high-lying excitation are related to the ones observed in one neutron pick-up experiments. The origin of such concentration of two neutron-hole strengths in Cd and Sn isotopes will be discussed. Preliminary results obtained in the study of the (α, 6 He) reaction at 218 MeV incident energy on 90Zr, 118 Sn and 208pb targets are presented and compared to the (p, t) results. Finally the properties of hole-analog states populated in neutron pick-up reactions (from 90Zr to 208Pb) will be presented.