Nucleon pair breaking in fission has been an important topic in nuclear physics for decades.
The most measured quantities in research on nuclear fission are the charge and mass fragments yields for uranium-235 and other fissile nuclides.
[1] The importance of these distributions is because they are the result of rearrangement of nucleons on the fission process due to the interplay between collective variables and individual particle levels; therefore they permit to understand several aspects of dynamics of fission process.
Because, for even Z (proton number) and even N (neutron number) nuclei, there is a gap from ground state to first excited particle state—which is reached by nucleon pair breaking—fragments with even Z is expected to have a higher probability to be produced than those with odd Z.
The preference even Z even N divisions is interpreted as the preservation of superfluidity during the descent from saddle to scission.