Session I: Theory: Nuclear Structure and Nuclear Astrophysics Session II: Experiment: Nuclear Reactions, Hadrons

δVpn is a particular double difference of nuclear binding energies serving as a filter isolating the valence proton-neutron interaction. δVpn is known to exhibit spikes in light nuclei at N=Z, explained by the SU(4) Wigner supermultiplet. Recently, it has been found that δVpn values in the rare earth region show similar peaks, occurring at Nval~Zval. These peaks, evident for both even and odd Z values, are interpreted in terms of large spatial overlaps of respective proton and neutron wave functions whose Nilsson quantum numbers are related by ∆K[∆N, ∆n_z, ∆Λ] = 0[110], i.e., the wave functions differ only by a single oscillator quantum in the z-direction. The implications of this for the development of collectivity and deformation in heavy nuclei, and the locus of this development, are dicussed. The double difference of binding energies δVpn(Z,N)=[B(Z,N)+B(Z-2,N-2)-B(Z,N-2)-B(Z-2,N)}/4 (1) is known [1] to be a measure of the average interaction between the last two protons with the last two neutrons in a given nucleus having Z protons and N neutrons. δVpn is known [1] to exhibit spikes in light nuclei with N=Z, shown in Fig. 1. These spikes are justified [2] by the existence of the SU(4) Wigner supermultiplet in this region. Recently, it has been shown [1] that δVpn also exhibits similar spikes in rare earth nuclei with equal numbers of valence neutrons and valence protons, Nval=Zval, shown in Fig. 2. Since the SU(4) Wigner supermultiplet is not present in this region, destroyed by the strong spin-orbit interaction, an alternative justification has to be found. A detailed study of the orbitals occupied by the last two neutrons and the last two protons in the rare earths exhibiting the spikes, reveals [1] that they are Nilsson orbitals differing by ∆K[∆N, ∆n_z, ∆Λ] = 0[110], as shown in the upper part of Fig. 3. These orbitals show similar evolution as functions of the nuclear deformation, as shown in the lower part of Fig. 3. They are expected to have maximal spatial overlaps, thus leading to enhanced proton-neutron interactions, in a situation reminiscent of the Federman-Pittel mechanism [3]. A more careful look at these orbitals reveals that they correspond to proton-neutron pairs with S=1, T=0. When plotted in the nuclear chart vs. Z and N, the spike-exhibiting nuclei appear on a straight line bordering the plateau of high deformation.