High-j single-particle neutron states outside the N=82N=82 core

The behaviour of the i13/2i13/2 and h9/2h9/2 single-neutron strength was studied with the (α,He3) reaction on 138Ba, 140Ce, 142Nd and 144Sm targets at a beam energy of 51 MeV. The separation between the single-neutron states i13/2i13/2 and h9/2h9/2 was measured in N=83N=83 nuclei with changing proton number. To this end spectroscopic factors for states populated in high-ℓ   transfer were extracted from the data. Some mixing of ℓ=5ℓ=5 and 6 strength was observed with states that are formed by coupling the f7/2f7/2 state to the 2+2+ and 3−3− vibrational states and the mixing matrix elements were found to be remarkably constant. The centroids of the strength indicate a systematic change in the energies of the i13/2i13/2 and h9/2h9/2 single-neutron states with increasing proton number that is in quantitative agreement with the effects expected from the tensor interaction.