Collision stopping power ($S_{\mathrm{col}}=-dT/dx$)

The positive mean loss of projectile kinetic energy per path length through electronic excitation and ionization, conventionally $S_{\mathrm{col}}=-dT/dx$. Dividing by absorber density gives mass stopping power.

A high-speed approximation for electronic stopping power of charged particles. Its leading heavy-projectile dependence is $z^2{\beta }^{-2}[\ln (2m_e{c}^2{\beta }^2{\Gamma }^2/I)-{\beta }^2]$; low-speed charge exchange and binding effects require corrections.