CPB Ljubljana 2018 course book

Radioactive Decay

All unstable nuclei spontaneously transform into other nuclear species by means of different decay processes that change the Z and N numbers of nucleus, until stability is reached. Such spontaneous nuclear processes are called radioactive decays .

Among well-known radioactive decays are: • alpha decay

• beta decay (incl. electron capture) • spontaneous fission of heavy nuclei

Excited states of nuclei are also unstable (usually when a nucleus decays by alpha- or beta-emission it is left in an excited state) and eventually decay to the ground state by emission of gamma-radiation (no change of Z or N occurs, isomer ).

Radioactivity is thus a property of the nucleus, according to which the nucleus decays to a more stable state.