Nuclear charge dispersion in mass chains 130–135 from the fission of 238U by medium-energy protons

Abstract

Independent formation cross-sections of 131mTe, 131gTe, 130I, 131I, 132I, 133I, 134I and 132Cs, and cumulative formation cross-sections of 131Sb, 132Te, 133mTe, 133gTe, 134Te and 135I resulting from the fission of 238U induced by protons of 30–85 MeV energy have been measured. From these data isobaric charge dispersion curves were constructed for mass chains A = 130–135 and were found to be well represented by Gaussian distributions. Within the mass region 130 < A < 135 and proton energy range 30 < E p < 85 MeV, Z A − Z p values for each mass chain approached stability with increasing energy and were independent of mass number. Values of Z p varied smoothly but nonlinearly with proton energy. The derivative ( ∂Z p / ∂A E was measured to be 0·38 ± 0·02, in good agreement with the assumption Z p parallels Z A . The charge dispersion widths were found to increase slightly with both increasing proton bombarding energy and mass number. Estimates of the number of neutrons emitted in fission as a function of average excitation energy were made using a Monte Carlo cascade model, the unchanged charge distribution (UCD) mechanism and the experimentally determined Z p values from this study.