Single j-shell studies of cross-conjugate nuclei and isomerism

It is noted that in a calculation with 4 nucleons with isospin 1 in a single j shell (f_{7/2}, g_{9/2}, h_{11/2}) the state with median angular momentum J = (J_{max}+1)/2 lies very low in energy becoming either an isomeric state or a ground state. Also states with J = J_{max} are isomeric for the orbits g_{9/2} and h_{11/2}. Comparisons with experiment are made. A hybrid mixture of shell model and rotational model arguments are used to explain the (J_{max} +1)/2 rule.