Evaporation residue cross sections forS32+Sn112,116,120,124from x-ray and direct recoil-nucleus measurements

Abstract

Evaporation residue cross sections have been measured for the systems $^{32}\mathrm{S}$ + $^{112,116,120,124}\mathrm{Sn}$ at incident energies between 130 MeV and 247 MeV. Total cross sections were measured by direct detection of recoil nuclei in a particle counter telescope. In addition, total and partial cross sections were determined from $K$-vacancy production cross sections and $K$ x-ray multiplicities of the evaporation residues. The x-ray multiplicities are of the order of \ensuremath{\sim} 1 and vary slowly with target mass and incident energy, indicating that x-ray detection can be reliably used to study fusion cross sections induced by heavy projectiles in this mass region. The total evaporation residue cross sections rise with increasing energy, saturate at \ensuremath{\sim} 190-MeV incident energy, and decrease slightly at higher energies. The saturation value shows distinct differences between systems and ranges from \ensuremath{\sim}600 mb for $^{32}\mathrm{S}$ + $^{112}\mathrm{Sn}$ to \ensuremath{\sim}800 mb for $^{32}\mathrm{S}$ + $^{124}\mathrm{Sn}$. The gross behavior of the partial evaporation residue cross sections is in agreement with statistical model calculations, but there remain deviations in the element distribution of the evaporation residues which might be explained by contributions from incomplete fusion reactions. As a byproduct we have measured $K$-vacancy production cross sections for atomic excitation of the target atoms by the projectiles and compared them with theoretical predictions.