Fusion enhancement in theS38+Pb208reaction

Abstract

The capture-fission cross section was measured for the reaction of $^{38}\mathrm{S}$ with $^{208}\mathrm{Pb}$ for center-of-mass projectile energies ${E}_{\mathrm{cm}}$ of 160--265 MeV. The $^{38}\mathrm{S}$ beam was prepared by projectile fragmentation at the NSCL at higher energies and degraded to 4--7 MeV/nucleon. The time of flight (energy) of each interacting beam particle was measured along with the fission fragments. The data were compared to previous measurements of the capture-fission excitation function for the $^{32}\mathrm{S}+^{208}\mathrm{Pb}$ reaction. The interaction barrier for the $^{38}\mathrm{S}$-induced reaction is $16.1\ifmmode\pm\else\textpm\fi{}10.1$ MeV lower than the $^{32}\mathrm{S}$-induced reaction whereas the reduced excitation functions for the two reactions are similar. A discussion of the systematics of barrier shifts in the fusion of $n$-rich nuclei is given and the implications of this shift for the synthesis of heavy nuclei with radioactive beams are discussed.