text: The  value is defined as the total energy released in a given nuclear decay. In beta decay,  is therefore also the sum of the kinetic energies of the emitted beta particle, neutrino, and recoiling nucleus. (Because of the large mass of the nucleus compared to that of the beta particle and neutrino, the kinetic energy of the recoiling nucleus can generally be neglected.) Beta particles can therefore be emitted with any kinetic energy ranging from 0 to . A typical  is around 1 MeV, but can range from a few keV to a few tens of MeV.
  Since the rest mass of the electron is 511 keV, the most energetic beta particles are ultrarelativistic, with speeds very close to the speed of light.
  In the case of Re, the maximum speed of the beta particle is only 9.8% of the speed of light.
  The following table gives some examples: