According to Order-Disorder Model (ODM), in the early stages of fission, the charges in a fissioning nucleus gets polarised into two impending parts along with corresponding most stable neutrons which are calculated from the minimum in isobaric mass parabola. This polarisation into two most stable configuration leaves a small number of neutrons as balance neutrons i.e.N_bal. The distribution of theseN_bal for various polarisation modes, shows a very profound correlation with the yield distribution. Judging from this striking correlation between these two distributions, it can be predicted that the asymmetry in fission decreases gradually and ultimately disappear for nuclei havingZ ⋍ 102 but reappears again for the nuclei in super heavy region.

The order-disorder model has been used to explain asymmetry of mass and charge division and related phenomena in fission. According to this model the fission process involves two steps consisting of charge polarisation into two ‘impending fragment clusters’ with beta stable neutron numbers and subsequent distribution of the balance neutrons between the two. Mode of elemental division of the fissioning nuclei is attributed to the charge polarisation in the first step. Theory of reaction rate has been applied to the system.

The frequency term is obtained by applying the conditional stochastic process under charge polarisation constraint and the energy-dependent term is given by the condition of minimum in free energy of the system. Using this, the relative probability of polarisation into given charge pair is arrived at.

The model uses stable neutron numbers for the charges as the only input. No explicit assumption or quantification on the preference of formation of shell closure species in fission is necessary. The statistics developed on the principle of equala priori probability of all charge polarisation is used. The shell effects come into play only in deciding a stable neutron number for the charges. The total isotopic yield distribution for a number of fission reactions shows asymmetry in the actinide region which reduces with increasing mass/charge of the fissioning nuclide and bunching of the higherz peaks. Although the mass yields obtained therefrom for a number of fission reactions agree with experimental results, the peaks of the distributions are slightly shifted away from the symmetric point and the distributions are somewhat narrower. Charge distribution parameters obtained from these results are also presented.