Fission yield systematics and covariance study for 238U

Mass distribution data measured up to 200 MeV by the kinetic energy method by Zoeller were adjusted for mass resolution and used to study the systematics of the chain yield dependence on incident neutron energy. The energy dependence for each fission fragment mass number was represented by linear and quadric functions. Furthermore, the systematics of the whole mass distribution and representation by a 5 (or 3) Gaussian model as a function of the incident neutron energy was also investigated. A code was developed to deduce the model parameters by a non-linear least squares fit of the experimental data. The mass distributions calculated with these parameters were subsequently compared with the experimental data. However, comparisons with radiochemically measured yields revealed systematic differences between the data obtained by the two methods. The uncertainties and correlations in the systematics were also studied: uncertainties in the mass distributions can be reduced by 20-80% (about 50% on average) when calculated from the systematics, and greater reductions can be achieved when the initial uncertainty is higher. These studies have also shown that there is a strong but rather complicated correlation between the yields calculated from the systematics and the parameters of the systematics. (author)