Effect of isospin on the evaporation residue cross section

Based on a Langevin equation coupled with a statistical decay model, we have studied the effect of isospin on the evaporation residue cross section as a probe of nuclear dissipation by calculating the excess of evaporation residues over its standard statistical-model value as a function of viscosity coefficient for ${}^{194}\mathrm{Pb}$, ${}^{200}\mathrm{Pb}$, and ${}^{206}\mathrm{Pb}$ nuclei. Calculations show that a low isospin not only amplifies the dissipation effects on the excess of evaporation residues but also significantly increases the sensitivity of this excess to the nuclear viscosity coefficient. These results suggest that to obtain a more accurate information of viscosity coefficient inside the saddle point by measuring evaporation residue cross sections, it had better choose those compound systems with small isospin.

Figure 1

Excess of the evaporation residue cross section of nuclei ${}^{194}\mathrm{Pb}$, ${}^{200}\mathrm{Pb}$, and ${}^{206}\mathrm{Pb}$ as a function of viscosity coefficient at excitation energy $E^{*}=100$ MeV and critical angular momentum ${\ell }_c=50\hslash$.

Figure 2

Excess of presaddle neutrons of nuclei ${}^{194}\mathrm{Pb}$, ${}^{200}\mathrm{Pb}$, and ${}^{206}\mathrm{Pb}$ as a function of viscosity coefficient at excitation energy $E^{*}=100$ MeV and critical angular momentum ${\ell }_c=50\hslash$.

Figure 3

Fission barrier of nuclei ${}^{194}\mathrm{Pb}$, ${}^{200}\mathrm{Pb}$, and ${}^{206}\mathrm{Pb}$ as a function of angular momentum.