Determination of the difference between the mean and the most probable energy loss of low-energy proton beams traversing thin solid foils

Abstract Precise determinations of the energy loss of ion beams in solid targets in the low-energy range (typically a few keV/u) using the transmission technique, require, among other things, a fine analysis of the energy distributions of the transmitted ion beams. In particular, it is known that possible asymmetries in the energy distributions – and related differences between the mean and the most probable energy loss – may be a source of discrepancies or uncertainties in stopping power determinations. We have performed detailed analyses of the energy-loss distributions of proton beams traversing various thin foils (12–24 nm) of metallic elements (Al, Au and Bi) including mono and polycrystalline foils. The differences between the mean and the most probable energy losses in these conditions were analyzed. The analysis has been extended to the first three moments of the energy loss spectra and the results have been compared with theoretical predictions. The magnitude of the differences so obtained were in all cases very small and give good support to the use of the transmission method for precise energy loss determinations in the few-keV region.