= Gamma ray
{wiki}
Most commonly known as a byproduct <radioactive decay>.
A <decay scheme> such as <image caesium-137 decay scheme> illustrates well how gamma radiation happens as a byproduct of <radioactive decay> due to the existence of <nuclear isomer>.
Gamma rays are pretty cool as they give us insight into the energy levels/different configurations of the nucleus.
They have also been used as early sources of high energy particles for <particle physics> experiments before the development of <particle accelerators>, serving a similar purpose to <cosmic rays> in those early days.
But <gamma rays> they were more convenient in some cases because you could more easily manage them inside a <laboratory> rather than have to go climb some bloody mountain or a <balloon>.
The <positron> for example was first observed on <cosmic rays>, but better confirmed in <gamma ray> experiments by <Carl David Anderson>.