An evacuated tube used as an oscillator or amplifier at microwave frequencies. In the klystron, an electron beam is velocity modulated (periodically bunched) to produce large amounts of power.
The phenomenon of spontaneous decay is called radioactivity.
Spontaneous emission of radiation, either directly from unstable atomic nuclei or as a consequence of a nuclear reaction.
The radiation, including alpha particles, nucleons, electrons, and gamma rays, emitted by a radioactive substance.
Radioactive decay is the set of various processes by which unstable atomic nucleii emit subatomic particles. Decay is said to occur in the parent nucleus and produce a daughter nucleu to become more stable.