放射線
Typical ionizing subatomic particles include alpha particles, beta particles and neutrons. These are typically created due to radioactive decay, and almost all are energetic enough to be ionizing. Secondary cosmic particles produced after cosmic rays interact with Earth's atmosphere, and include muons, mesons, and positrons. Cosmic rays may also produce radioisotopes on Earth (for example, carbon-14), which in turn decay and emit ionizing radiation. Cosmic rays and the decay of radioactive isotopes are the primary sources of natural ionizing radiation on Earth, contributing to background radiation. Ionizing radiation is also generated artificially by X-ray tubes, particle accelerators, and nuclear fission.