annihilation radiation


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an·ni·hi·la·tion ra·di·a·tion

the radiation resulting when a positron from beta-positive decay comes to rest. It encounters an electron, and the two particles annihilate each other and convert their rest mass into two 0.51-MeV gamma rays emitted in exactly opposite directions. See: pair production.
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Although the source of the annihilation radiation is debatable, there is no dearth of candidates in the crowded environs of the galactic center.