  The normalized differential mean free path for volume scattering and the
differential surface excitation probability for medium energy electrons
travelling in Fe, Pd and Pt are extracted from Reflection Electron Energy Loss
Spectra (REELS). This was achieved by means of a recently introduced procedure
in which two REELS spectra taken under different experimental conditions are
simultaneously deconvoluted. In this way, it is possible to obtain the unique
reconstruction for the surface and volume single scattering loss distribution.
The employed method is compared with a procedure that is frequently used for
this purpose [Tougaard and Chorkendorff, Phys. Rev. B 35(1987)6570]. It is
shown, both theoretically and through analysis of model spectra as well as
experimental data that this method does not result in a {\em single} scattering
loss distribution. Rather, it gives a mixture of surface, bulk and mixed
scattering of any order.
