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.

An alpha particle of energy 5MeV is scattered through $180^o$ by a fixed Uranium Nucleus. The distance of closest approach is of the order of :

$10^{-12} cm$

$\text{The distance of closest approach is of the order of fermi meter } $