The width of an RBS spectrum revisited: Influence of multiple scattering

P. Bauer, E. Steinbauer, and J.P. Biersack calculated with Monte Carlo the RBS spectrum of 100 keV protons backscattered from a 100 nm thick Au foil . They stated in the caption of that a fairly large area, located to the left of the single scattering signal, "corresponds to the contribution due to multiple scattering". This led to the widespread belief amongst code developers that "multiple scattering manifests itself mostly as an additional contribution to the energy spread and as small low energy tails on signal edges arising from non-Gaussian wings in the energy distribution (…). The small tails have not, so far, been modeled analytically". A new analytical calculation is now presented, showing that an extra yield due to multiple scattering indeed exists, but it is much smaller than the hatched area in of Bauer et al. That area is not an additional contribution of multiple scattering, it is simply the width of the low energy edge of the single scattering signal, which is broader due to the extra energy spread coming from multiple scattering.