1.1. Process of absorption of ionizing radiation energy

The electron states of atoms and molecules are explained with regard to material media close to human tissue. The transfer of ionizing radiation energy to electrons bound in molecules takes place by inelastic collisions of charged particles. The definition of excitation potential is given. The process of absorption of ionizing radiation energy in material media is divided into successive phases: the physical, physico-chemical, chemical and biological phase. The absorption is affected by the charged particle track. The character of the track is discussed separately for low, intermediate and high stopping power of the medium. (M.D.)