KERMA

Kerma is an acronym for kinetic energy released per unit mass. It is a nonstochastic quantity applicable to indirectly ionizing radiations such as photons and neutrons. It quantifies the average amount of energy transferred from indirectly ionizing radiation to directly ionizing radiation without concern as to The energy of photons is imparted to matter in a two stage process

In the first stage, the photon radiation transfers energy to the secondary charged particles (electrons) through various photon interactions (the photoelectric effect, the Compton effect, pair production, etc.). In the second stage, the charged particle transfers energy to the medium through atomic excitations and ionizations

The unit of kerma is joule per kilogram (J/kg). The name for the unit of kerma

is the gray (Gy), where 1 Gy = 1 J/kg

Radiation Oncology Physics A Handbook for Teachers And Students