Stopping Power

Stopping power is defined as the rate of energy loss per unit path length as a charged particle travels through a material.

The total energy loss of the particle can be separated into collisional and radiative components:
S/dtot= (S/d) collision+(S/d) radiative
Where d is the density of the material transversed and S/d represents the mass stopping power.

Stopping power is greater for low Z material than for High Z because High Z materials have fewer electrons per gram and have more tightly bound inner electrons.