Page "Electromagnetic radiation" Paragraph 4

In classical physics, EMR is considered to be produced when charged particles are accelerated by forces acting on them.

Electrons are responsible for emission of most EMR because they have low mass, and therefore are easily accelerated by a variety of mechanisms.

Rapidly moving electrons are most sharply accelerated when they encounter a region of force, so they are responsible for producing much of the highest frequency electromagnetic radiation observed in nature.

Quantum processes can also produce EMR, such as when atomic nuclei undergo gamma decay, and processes such as neutral pion decay.