In Rutherford's alpha scattering experiment, what is the impact parameter for an $\alpha$-particle t

Question

In Rutherford's alpha scattering experiment, what is the impact parameter for an $\alpha$-particle that rebounds back with a scattering angle of $180^\circ$?

Professor PC Thomas Classes · Answer

For a head-on collision, the alpha particle is aimed directly at the center of the nucleus, making the impact parameter $b$ minimum (zero) and resulting in a $180^\circ$ deflection.