Solution (source code)

= Solution

For $V(r)\sim r^{-n}$, the small-$q$ transform scales as $q^{n-3}$. Since $d\Omega$ contributes $q\,dq$ near forward scattering, the total Born cross section behaves as $\int_0 q^{2n-5}\,dq$, finite exactly for $n>2$. Coulomb decay $n=1$ gives the familiar divergent forward Rutherford cross section and requires long-range treatment.