Role of isospin and its conservation in neutron-rich fission fragments

Following upon our earlier paper [1] containing some initial results, we present detailed discussion and complete results in this paper, which provide the first direct evidence for the validity of isospin as a nearly good quantum number in neutron-rich systems. The evidence comes from the reproduction of the general features of the partition-wise relative yields of neutron-rich fission fragments produced in two heavy-ion induced fusion fission reactions, namely $^{208}$Pb ($^{18}$O, f) and $^{238}$U ($^{18}$O, f), by using the concept of isospin conservation. To fix the isospin values and use the isospin algebra, we invoke what we term as Kelson's conjectures. We present a consistent scheme for isospin assignments based on these considerations. Our calculated results confirm that isospin behaves as an approximately good quantum number in neutron-rich systems, in this case, the fission fragments.