Analysis of isotopic yield distributions in B − 11 and Ne 22 -induced fission of U 238

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.