Hello.

b = \frac{k_{e}zZe^{2}}{2K} \frac{1}{tan(\frac{1}{2}θ)}

N(θ) = \frac{nt}{4r^{2}} (\frac{zZ}{2K} )^{2}(\frac{e^{2}}{4πϵ_{0}} )^{2} \frac{1}{sin^{4}(\frac{1}{2}θ)}

impulse ∼  F  t

∼ \frac{k(2e)(Ne)}{R^{2}} \frac{L}{v}

∼ \frac{k(2e)(Ne)}{R^{2}} \frac{2R}{v}

∝  \frac{1}{R^{2}}  R