Angular and energy dependences of the scattered ion yield in low-energyHe+4-Bi scattering

Measurements of the scattered ion yield $Y$ vs primary energy $E$ and scattering angle $\theta$ on a set of bismuth surfaces are reported. The $Y\left(E\right)\mathrm{}$ curve exhibits a shift of the maxima to lower energies with decreasing $\theta$ and a steep rise at low energy in the low-$\theta$ range. In addition to this rise, the $Y\left(\theta \right)$ curve displays an unexpected maximum. The results are tentatively interpreted in terms of a combination of quasiresonant and Auger-type neutralization processes.