Assertion(A): The trajectory traced by an incident particle depends on the impact parameter of collision.
Reason(R): The impact parameter is perpendicular distance of the initial velocity vector of the incident particle from the center of the target nucleus.

If the impact parameter is zero, the scattering angle is 180⁰ and the particle will retrace its path.

The impact parameter is defined as the perpendicular distance of the velocity of the α-particle from the center of the nucleus when it is far away from the nucleus.

$\mathrm{b}=\frac{{\mathrm{Ze}}^2\cot (\mathrm{\theta }/2)}{4{\mathrm{\pi \epsilon }}_0\left(1/2{\mathrm{mv}}^2\right)}$