Small-angle multiple scattering and spatial resolution in charged particle tomography

The formulae for the RMS scattering angle given by small-angle multiple-scattering theory are discussed and a correction to the standard Rossi formula is derived. Values of the correction factor are calculated for protons, alpha-particles and heavy ions; these results show that the correction is important for protons and alpha-particles but negligible for heavy ions with mass number 12-40. The values of the RMS scattering angle and the RMS lateral displacement are calculated for a proton beam passing through water. For protons the correction for energy loss in thick targets is even more important.