Impact Parameter, Scattering Angle, and Distance of Closest Approach

1 Impact Parameter, Scattering Angle, and Distance of Closest Approach 

The distance of closest approach or collision diameter d of the incoming particle, for head-on collision with the target nucleus is given by 

For backscattering to occur, the projectile and target must get close enough together such that the distance of closest approach is within the K-shell radius, and that is why we can ignore the electrons. 

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