If the daughter nucleus is formed in an 'excited' state after alpha or beta emission, the nucleus moves to its ground state by emitting gamma radiation.For example, a magnesium-27 (Z=12) decays into aluminium-27 (Z=13) by beta emission. The aluminium is in an excited state and de-excites and falls to ground state by the emission of gamma radiation.Some isotopes remain in an excited state - the metastable state - after alpha or beta emission for long enough to be isolated. Molybdenum-99 (Z=42) decays into the Technetium-99 (Z=43) metastable state which decays into the ground state by gamma emission.