Gaps in nuclear spectra as traces of seniority changes in systems of both neutrons and protons

There has been a great deal of attention to the low lying energy spectum in a nucleus because of the abundance of experimetal data. Likewise ,perhaps to a lesser extent but still significant the high end for a given configuration has been examined. Here ,using single j shell calculations as a guide we examine the middle part of the spectum resulting form single j shell calculations. Seniority arguments are used to partially explain the midshell behaviours even though in general seniority is not a good quantum number for mixed systems of neutrons and protons.