A study of the influence of shell effects in nuclear level densities on the decay of the compound nucleus58Ni

Mass andZ-distributions of fusion products from the reaction 5.8 MeV/u⁴⁶Ti+¹²C were measured in the angular range between?_lab=1.5° and 8° using a time-of-flight?E-E telescope. The results are compared with an earlier measurement of the reaction³²S+²⁶Mg, in which the same compound nucleus was produced at higher excitation energy. The residual nuclide distributions are interpreted with the aid of evaporation calculations and the influence of shell effects in the level densities is discussed. The data are consistent with the assumption that the shell effects vanish above 15 to 20 MeV excitation energy, that is, that they are essentially only important for the last evaporation step.