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

The trajectory of alpha particles depends on the impact parameter of the collision.The impact parameter was found to be minimum for the alpha particles, the scattering angle (nearly) is:

$\pi$

For minimum impact parameter the particle will rebound and hence scattering angle $\theta = \pi$