Proton-neutron interactions in N approx Z nuclei

Proton-neutron (p-n) interactions and its various aspects in $N\approx Z$ nuclei of $g_{9/2}$- and $f_{7/2}$ subshell are studied using a schematic model interaction with four force parameters proposed recently. It is shown that the model interaction well reproduces observed physical quantities: the double differences of binding energies, symmetry energy, Wigner energy, odd-even mass difference and separation energy, which testifies the reliability of the model interaction and its p-n interactions. First of all, the double differences of binding energies are used for probing the p-n interactions. The analysis reveals different contributions of the isoscalar and isovector p-n pairing interactions to two types of double difference of binding energies, and also indicates the importance of a unique form of isoscalar p-n pairing force with all $J$ components. Next, it is shown that this p-n force is closely related to the symmetry energy and the Wigner energy. Other calculations demonstrate significant roles of p-n interactions in the odd-even mass difference and in the separation energy at $N=Z$.