Why do gamma rays accompany other kinds of decay?

[LogicalAcid]

I read that gamma rays are usually emitted by the nucleus of an atom after it emits an alpha particle, but have been wondering: If the alpha particle being emitted was meant to stabilize the atom, and should have, why does the nucleus need to emit such high energy waves?

 

[mathman]

Unless the masses of the daughter particles (alpha + whatever) add up exactly to that of the parent, for conservation the difference will generally end up in the form of energy, usually a gamma ray.

 

[LogicalAcid]

Unless the masses of the daughter particles (alpha + whatever) add up exactly to that of the parent, for conservation the difference will generally end up in the form of energy, usually a gamma ray.

why is this?

 

[lpetrich]

The left-behind nucleus could be in an excited state. It may then emit gamma rays as it decays to its ground state.