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Air Kerma

Energy transfer by photon radiation to the medium of air takes place indirectly, in two steps: First, charge carriers (electrons) are released through interactions between photons and the atoms of the air (with the photoelectric effect and the Compton effect dominating in the case of X-radiation). Along their paths, electrons transfer energy to the air. A fraction of the initial kinetic energy of the electrons is transformed into bremsstrahlung and is not deposited in the vicinity of the electron paths. In terms of physics, the first step is described by the measurand  air kerma (kinetic energy released per unit mass), the second step by the absorbed dose in air:

1st stepKERMA

2st step:   ABSORBED DOSE