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