Deviations from Rutherford Formula

If the projectile energy is chosen properly (below Coulomb barrier and above electronic screening - see Sect. 2.5.2 for shielded Rutherford cross-sections), the scattering yield follows the Rutherford cross-section which is basically proportional to the square of the atomic number of the element and inversely proportional to the square of the projectile energy (Fig. 2.11). If the energy is higher than the upper value, the backscattering cross-section shows deviation from Rutherford formula as discussed in Sect. 2.5. 

Huan-Sheng et al. (1991) measured Rutherford cross-sections for 165° backscattering of He from sodium and aluminum for He energy between 2.0 and 6.0 MeV. Their experimental results show that for sodium and aluminum, the upper energies are 3.0 and 3.5 MeV, respectively, at which the backscattering cross-section can still be predicted by the Rutherford scattering formula, 

When the energy is higher than the upper value, the backscattering cross-section shows deviation from Rutherford formula. 

A database of non-Rutherford scattering cross-sections of H, He, and several other light elements, is also included in the available computer simulation codes (listed at page 362) for RBS analysis. 

---