Electron stripping at MeV/u energies for U $^{28+ }$and Xe$^{18+ }$ ions .

Beam lifetimes were measured for 10 MeV/u to75 MeV/u Xe$^{18+ }$ and 10 MeV/u to 50 MeV/u U $^{28+}$. Lifetimes resulting from interactions with background gases at base pressures in the GSI ESR storage ring and for molecular hydrogen and molecular nitrogen were measured. For H$_{2}$ and N$_{2 }$, ion beams where injected in the ESR and a fast valve was opened to admit the supersonic jet from the ESR gas target. The N$_{2}$ results imply that the stripping cross section has approximately a v$^{-1}$ dependence, whereas the H$_{2 }$results imply nearly a v$^{-2}$ dependence.