Abstract
An expression for the energy transfer between two particles moving with relativistic velocities has been given on the basis of a binary-encounter description of elastic scattering. By means of a Lorentz transformation of the differential scattering cross section in the center-of-mass system the differential cross section and the total cross section have been established for relativistic particle velocities. Expressions have been derived that relate stopping power and straggling for a projectile penetrating a medium in internal motion to the stopping parameters of a medium at rest. These expressions contain the velocity distribution of target particles, kinematic factors and the Moller speed.