= Gamma ray
{wiki}
A gamma ray is a high-<energy> <photon>, conventionally associated with a transition of an <atomic nucleus>, <radioactive decay> or a <particle> reaction. <X-rays> and gamma rays are both <electromagnetic radiation>; their <energy> ranges overlap, so the production mechanism can be more informative than an arbitrary <energy> boundary.
A <nuclear energy level> transition emits a gamma ray whose <energy> is approximately the level difference, with a correction for nuclear recoil. Detectors infer the incoming <energy> from interactions such as <photoelectric absorption>, <Compton scattering> and, above threshold, <pair production>. A measured gamma-ray <spectrum> can therefore identify nuclear transitions even when a detector does not absorb the entire <photon energy> in each event.
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