Energy dependence of fission-fragment mass distributions from strongly damped shape evolution

The recently developed treatment of Brownian shape evolution is refined to take account of the gradual decrease in microscopic effects as the nuclear excitation energy is raised. We construct effective potential-energy surfaces by multiplying the shell-plus-pairing correction term by a suppression factor that depends on the local excitation energy. While this approach is equivalent to the modification of the Fermi-gas level density parameter suggested by Ignatyuk et al. [Sov. J. Nucl. Phys. 29, 450 (1979)], we adopt a more general functional form for the suppression factor, which is adjusted to measured charge yields for U-234 (E* approximate to 11 MeV). The resulting model is benchmarked by comparison with 70 measured yields.