In Geiger Marsden alpha scattering experiments , a beam of alpha particles emitted from $Bi_{83}^{214}$ were directed to strike a gold foil and various observations were made. Now answer the following questions.

In Geiger Marsden experiments , If an alpha particle of energy 5MeV hits a nucleus of z = 80 , the distance of closest approach is :

46fm

$\text{Distance of closest approach is } r = \frac{2ze^2}{4\pi\epsilon_0 (K.E)} = 46fm$