Kinetic Energy Released per Unit Mass. Kerma is a dose variable. Kerma K is the quotient of dEtr and dm; whereby dEtr is the sum of the starting values of kinetic energies of all charged particles released by indirectly ionizing radiation from the material in a volume element dV, and dm is the mass of the material in this volume element. All indications for a Kerma must mention the reference material (i.e. the material dm). The SI unit of the kerma is gray (Gy).