Isotopic product distributions in the near symmetric mass region in proton induced fission ofU238

We have studied fission product yields using 19.8 MeV proton induced fission of a thin ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ target and the on-line mass separator IGISOL. The nonselectivity of the separation method used with respect to Z has allowed accurate determination of the yields of symmetric fission for the first time. The cumulative yields for the elements from Z=40 (Zr) up to Z=47 (Ag) have been determined from the beta- and gamma-radioactivity measurements. The independent fission product yield distributions for elements Tc, Ru, and Rh are obtained from the experimental data. An improved theoretical model for calculating mass and independent yields is described and applied. It is found that the charge splitting for the primary fragments differs from that obtained with the unchanged charge division model at moderate excitation energies of compound nuclei. A comparison of the calculated and experimental fission product yields shows that the model presented can be applied for predictions of cross sections for very neutron-rich nuclei in the light particle induced fission.