Excitation Energy Dependence of Shell Effects on Nuclear Level Densities and Fission Fragment Anisotropies

It is shown that the nuclear shell effects on the level density disappear even at medium excitation energies of the order of 40 MeV. Fission-fragment anisotropy data for actinide nuclei having double-humped fission barriers are shown to contain evidence for this effect. The implication of this effect on the production of superheavy nuclei is pointed out.