Emergent-angle-dependent charge-state distributions of 2-MeV ⁴He transmitted through a thin carbon foil

The emergent-angle-dependent charge-state fractions of 2-MeV ⁴He transmitted in a carbon foil of 2.5 μg/cm² in thickness have been measured in the range from 0 to 8 mrad. The angular distribution due to multiple scattering has been also obtained for each outgoing charge state. Up to the angle of ∼4 mrad, both the neutral and singly charged fractions increase with increasing the emergent angle. This trend is more remarkable in the neutral fraction. At the larger angles, these fractions reach saturated values. The observed behavior can be explained qualitatively by the impact parameter dependence of the charge-exchange probabilities. Although a Monte Carlo simulation can reproduce the obtained angle-dependent charge-state fractions, it gives a slightly narrower angular distribution due to multiple scattering for each outgoing charge state.