[en] This article reviews the problem of whether it is necessary to compute backscattering of MeV ions using quantum mechanics. Arguments are given that support the need to include quantum Fresnel diffraction in backscattering by adequately thin single crystals. The particle-scattering problem is investigated using a many-body approximate wave function, defined by a generalised product of two-body scattering wave function. To apply such a wave function to realistic systems, the inclusion of screened Coulomb wave functions and of lattice correlations is proposed and discussed. Examples of computed axial backscattered angular scans are given for 2 MeV proton scattering by strings of 50-atom-layer Cu and Au, and some unexpected interference effects found