Decay energy (also decay heat ) is the energy that is released during the radioactive decay of an unstable atomic nucleus . It is transferred as kinetic energy to the decay products and the daughter nucleus , emitted in the form of radiation or stored as excitation energy in the electron shell of the remaining nucleus. The easiest way to measure and usually tabulate the energy of the emitted alpha , beta or gamma radiation . If caloric investigations are carried out, the energy of the recoil nuclei and the energy of any subsequent reactions ( e.g. electron-positron annihilation after β + decay or neutron capture after the emission of neutrons ) must also be taken into account.
Part of the decay energy can be transferred to particles that are difficult to detect. For example, when the beta decays , an electron antineutrino is generated that takes on a variable part of the kinetic energy.
The decay energy is usually measured in megaelectron volts (MeV) or kiloelectron volts (keV). An electron volt (eV) is the energy that an electron absorbs when it passes through an electrical field with a voltage of 1 volt . It corresponds to about 1.6 · 10 −19 J.