Coulomb explosion of 173-MeV HeH⁺ ions traversing carbon foils

The Coulomb explosion of 173-MeV HeH⁺ molecular ions traversing thin carbon foils has been measured for foil thicknesses ranging from 2 to 200 μg/cm². In contrast with measurements at lower energies, the energy spectra for protons observed emerging in the incident beam direction show distinct components that correspond to the partner helium ions being in charge states 0, 1, and 2. From an analysis of the variation of the yields of these components as functions of the target thickness, we extract electron-loss cross sections that are in good agreement with theoretical estimates. ``Wake effects'' that increase with increasing target thickness are observed as asymmetries in the yields and energy shifts for ``backward-going'' as compared to ``forward-going'' protons.