  Random walks on five-dimensional potential-energy surfaces were recently
found to yield fission-fragment mass distributions that are in remarkable
agreement with experimental data. Within the framework of the Smoluchowski
equation of motion, which is appropriate for highly dissipative evolutions, we
discuss the physical justification for that treatment and investigate the
sensitivity of the resulting mass yields to a variety of model ingredients,
including in particular the dimensionality and discretization of the shape
space and the structure of the dissipation tensor. The mass yields are found to
be relatively robust, suggesting that the simple random walk presents a useful
calculational tool. Quantitatively refined results can be obtained by including
physically plausible forms of the dissipation, which amounts to simulating the
Brownian shape motion in an anisotropic medium.
