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Ernest Rutherford's 1911 calculation explained rare large-angle alpha particle scattering by concentrating an atom's central electric charge into a region small compared with the atom. In the single-Rutherford scattering approximation, the predicted differential scattering cross-section varies as ${\sin }^{-4}(\theta /2)$ and as the inverse square of the incident kinetic energy. These dependencies make the model testable through angular counts and controlled changes of beam energy, beyond merely observing that occasional particles turn backward.^[ref]

A physicist.^[ref]

The Rutherford scattering model connects large-angle deflections to concentrated electric charge. The Geiger-Marsden experiment supplies the experimental context; a predicted angular distribution needs comparison with detector geometry and background counts.