Gamma ray

A gamma ray is a photon of electromagnetic radiation with very high energy and frequency, commonly produced by nuclear transitions or energetic cosmic processes.

Nuclear transition: A change in an atomic nucleus from one energy state to another, often emitting a photon. Excited nuclei emit gamma rays when they fall to lower energy states.
Radioactive decay: The spontaneous transformation of an unstable atomic nucleus into a more stable configuration. Many gamma rays accompany radioactive decay as daughter nuclei shed excess energy.
Gamma-ray astronomy: The study of celestial objects and processes through their gamma-ray emission. Observatories use gamma rays to investigate the most energetic events in the universe.
X-ray: A high-energy photon commonly produced by electron interactions or transitions in atomic electron shells. X-rays and gamma rays overlap in energy; their names usually distinguish production origin.
Pair production: The conversion of a photon into a particle and its antiparticle, usually near a nucleus. A sufficiently energetic gamma ray can create an electron–positron pair in matter.
Gamma decay: A nuclear transition that releases excess energy as a gamma-ray photon without changing the nucleus's composition. This is the direct nuclear emission process behind many gamma rays.
Positron emission tomography: A medical imaging technique that maps radioactive tracer distribution by detecting paired photons. The positron-annihilation photons detected in PET are gamma rays.
Alpha particle: A helium-4 nucleus emitted during some radioactive decays. Unlike a gamma ray, an alpha particle has mass, charge, and a nuclear identity.
Compton scattering: The scattering of a photon by a charged particle, transferring energy and momentum. Gamma rays lose energy through collisions with electrons in detectors and shielding.
Gamma-ray burst: A brief, extraordinarily luminous explosion that emits intense gamma radiation from a distant astrophysical source. These bursts show how violent cosmic events can produce immense gamma-ray output.

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