Density Effect in Ionization Energy Loss of Charged Particles

A more rigorous justification is given for the statement made by Aage Bohr that for an incident particle of relativistic velocity, the electrostatic effect of the surrounding electrons is negligible and the main factor in the screening is due to the electromagnetic interactions which limit the impact parameter to a value $\frac{c}{\Omega }$, where $\Omega ={\left(\frac{4\pi n{e}^2}{m}\right)}^{\frac{1}{2}}$ and $n$ is the electron density in the medium.