Analysis of isotopic yield distributions inB−11andNe22-induced fission ofU238

Abstract

First moments and variances of measured rubidium and cesium isotopic distributions in the fission of $^{238}\mathrm{U}$ by $^{11}\mathrm{B}$(${E}_{\mathrm{lab}}=85$ MeV) and $^{22}\mathrm{Ne}$ (${E}_{\mathrm{lab}}=132 \mathrm{and} 162$ MeV) are analyzed in the framework of the statistical model for nuclear fission and of evaporation theory. Excellent agreement with the data is obtained for $^{11}\mathrm{B}$-induced fission, assuming a compound-nuclear mechanism. The comparatively large isotopic variance observed in $^{22}\mathrm{Ne}$-induced fission can be explained if moderate contributions from fission following direct reactions are taken into account.NUCLEAR REACTIONS, FISSION $^{238}\mathrm{U}$ with heavy ions ($^{11}\mathrm{B}$, $^{22}\mathrm{Ne}$); isotopic distributions, calculated first moments, variances. Statistical model theory; good agreement with data; direct reaction contributions important.