ENERGY-LOSS OF CARBON-TRANSMITTED 1-MEV H2+ IONS

Energy losses of 1-MeV H-2+ ions passing through carbon foils of 2-8 m ug/cm2 thickness have been measured. The observed energy loss increase s linearly with the target thickness and shows an offset, 0.4 keV, at zero thickness. The stopping power derived from the observed energy lo sses is 1.15 times as large as the sum of the stopping powers for two single H+ of the same velocity. Stopping powers for H-2+ ions and dipr otons are calculated with the first Born approximation. The calculated stopping power for the diproton agrees quite well with the one observ ed. This indicates that the observed H-2+ ions traverse the target as diprotons after the loss of the binding electrons upon entrance into t he foil and recapture target electrons at the exit surface. The observ ed energy-loss offset at zero thickness also supports this scenario.