Charge distribution, neutron evaporation, and energy distribution in higher energy binary fission

A computational procedure based on the order-disorder model for predicting independent yields of fission products in higher energy fission is described. Based on the experimental observation that increase in excitation energy of the compound nucleus is used up only in exciting the fragments resulting from fission, a scheme for the distribution of extra excitation between the fragments has been evolved. The extra excitation energy is shown to be shared between the two impending fragments in proportion to the number of neutrons out of the balance number (as per the order-disorder model) going to either of the fragments. The calculational procedure essentially consists of making use of the scheme and obtaining the excitation energy of the fragments for higher energy fission from those for spontaneous fission. Data on neutrons evaporated $\overline{\ensuremath{\nu}}({Z}_{i},{N}_{j})$ from individual fragments for the higher energy fission are calculated from the excitation energy using the cascade evaporation scheme. The product isotopic distributions are calculated from $\overline{\ensuremath{\nu}}({Z}_{i},{N}_{j})$ data and calculated fragment isotopic distributions given by the order-disorder model. The product isotopic distributions thus calculated along with experimental product mass yield data give the independent yields of the products. The results obtained for fission of $^{235}\mathrm{U}$ by fission spectrum neutrons (fast) and 14.7 MeV (high energy) neutrons are discussed in the paper. A comparison of the predicted independent yields with experimental values shows good agreement within reasonable limits. The total isotopic yield versus $Z$ distribution for fast and high energy neutronic fission show as expected a decrease in peak to valley ratio with increasing excitation energy of the compound nucleus. $\overline{\ensuremath{\nu}}({Z}_{i},{N}_{j})$ distributions for both the fission reactions are presented. They show less pronounced shell effects at $N=50 \mathrm{and} 82$ than in the case of thermal fission. The isotopic, isobaric, and isotonic averages of $\overline{\ensuremath{\nu}}({Z}_{i},{N}_{j})$ retain the sawtooth nature as in the case of thermal fission. The Wahl plot shows that $|{Z}_{p}\ensuremath{-}{Z}_{\mathrm{UCD}}|$ decreases with increasing energy of fission. The present study also confirms the experimental observation that ${Z}_{p}$ for higher energy fission lies between the values predicted by the unchanged charge density and equal charge displacement hypotheses.NUCLEAR REACTIONS, FISSION $^{235}\mathrm{U}(n,f)$, $E=2$ MeV, 14.7 MeV; calculated isotopic distributions, charge distributions, independent yields of products and neutron evaporation and energy distribution in individual fragments using order-disorder model.