Partial conservation of seniority and its unexpected influence on E2 transitions in $g_{9/2}$ nuclei

There exist two uniquely defined $v=4$ states in systems within a $j=9/2$ subshell, which automatically conserve seniority and do not mix with other states. Here I show that the partial conservation of seniority plays an essential role in our understanding of the electric quadrupole transitions of the semimagic nuclei involving $j=9/2$ subshells, including the long-lived $8^{+}$ isomer in $^{94}$Ru. The effects of configuration mixing from neighboring subshells on the structure of those unique states are analysed. It is shown that a sharp transition from pure seniority coupling to a significant mixture between the $v=2$ and $v=4$ states may be induced by the cross-orbital non-diagonal interaction matrix elements. Such strong mixture is essential to explain the observed E2 transition properties of $N=50$ isotones $^{96}$Pd and $^{94}$Ru.