Fission fragment angular distributions inLi6,7+U235,238reactions

Fission fragment (FF) angular distributions for ${}^{6,7}\mathrm{Li}+^{235,238}\mathrm{U}$ reactions have been measured at energies near and above the Coulomb barrier. The angle integrated fission cross sections for $^{6}\mathrm{Li}$ induced reactions at sub-barrier energies are found to be higher than $^{7}\mathrm{Li}$ induced reactions possibly due to a larger contribution of breakup or transfer induced fission in cases of the former compared to the latter. The FF anisotropies for $^{6,7}\mathrm{Li}+^{235}\mathrm{U}$ are found to be slightly smaller than $^{6,7}\mathrm{Li}+^{238}\mathrm{U}$, manifesting the effect of target spin. The statistical saddle point model predictions underestimate the measured FF anisotropy for all four systems at measured energies. Anisotropy calculation by entrance channel dependent $K$-state distribution model and determination of $\ensuremath{\langle}{\ensuremath{\ell}}^{2}\ensuremath{\rangle}$ from continuum discretized coupled channels calculations suggest that the above enhancement in experimental anisotropy is due to a combined effect of entrance channel dependent pre-equilibrium fission and projectile breakup induced fission.