In radiation physics, kerma is an acronym for "kinetic energy released per unit mass" (alternately, "kinetic energy released in matter", "kinetic energy released in material", or "kinetic energy released in materials"), defined as the sum of the initial kinetic energies of all the charged particles liberated by uncharged ionizing radiation (i.e., indirectly ionizing radiation such as photons and neutrons) in a sample of matter, divided by the mass of the sample. It is defined by the quotient