Measurement of cross sections for electron capture and stripping by highly relativistic ions

We have made the first measurements of the equilibrium charge state and cross sections for orbital electron capture and stripping of ions with Lorentz factor {γ}>10. We used gold ions from the AGS at Brookhaven with a mean kinetic energy of 10.8A GeV. The measurement of the cross section for electron capture is consistent with the prediction of radiative capture of Anholt and Becker, and with the Weizs\"acker-Williams calculations of the vacuum capture cross section. The measurement of the cross section for stripping differs from the prediction of Anholt and Becker by a factor of 2.0. We set an upper limit for vacuum capture which constrains recent nonperturbative calculations.