We first consider lead isotopes with valence neutrons in the g 9/2 shell. We especially compare 211 Pb (n=3), 213 Pb (n=5) and 215 Pb (n=7), 213 Pb being at mid-shell. Motivated by the fact the J = 21/2 + and J =3/2 + states are pure seniority v=3 states for both n=3 and n=5, we compare the energy splitting E(J=21/2 + )-E(J=3/2 + ) for various interactions. We then discuss the position of the lowest J=3/2 + state in both n=3 and n=5, although, this state has not been found experimentally. Calculations with configurations beyond g 9/2 are also considered. We next address the fact that the J=21/2 + state is isomeric for both n=3 and n=5.
Zamick et al. (Fri,) studied this question.