Alpha particle emission as a probe of the level density in highly excited A~200 nuclei.

Abstract

The alpha particle emission from 90 to 140 MeV $^{19}\mathrm{F}$${+}^{181}$Ta fusion-evaporation reactions has been studied. The comparisons of the experimental spectral shapes and multiplicities with statistical model predictions indicate a need to use an excitation energy dependent level-density parameter a=A/K in which K increases with excitation energy. This increase is more rapid than that in lower mass nuclei. The effect of this change in level density on the prescission multiplicities in fission is significant.