Isotopic yields of intermediate-mass fragments emitted inE/A=50 MeVHe4+116,124Sn reactions

Inclusive yields of isotopically resolved intermediate-mass fragments (IMF) with Z=3–6 have been measured for the reaction of E/A=50 MeV ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ with ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$ and ${}_{}{}^{124}{}_{}{}^{}\mathrm{Sn}$ targets. The isotopic yield patterns reflect the N/Z ratio of the target for both equilibriumlike and nonequilibrium components of the spectra. In addition, the IMF elemental cross sections for the ${}_{}{}^{124}{}_{}{}^{}\mathrm{Sn}$ target decrease much more rapidly with Z than for ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$. This effect is presumably due to lower barriers for IMF emission from residues formed with the neutron-deficient ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$ target and increased competition from pre-IMF neutron emission for the neutron-excess ${}_{}{}^{124}{}_{}{}^{}\mathrm{Sn}$ target. The experimental cross sections are compared with statistical and accreting-source calculations.