In physics, the antimatter counterpart of a nucleon (proton or neutron), which annihilates when it meets its corresponding nucleon.
From anti- (opposite) + nucleon (a proton or neutron in an atomic nucleus). Nucleon comes from Latin nucleus (kernel). The term emerged in particle physics in the mid-20th century as scientists discovered antimatter particles.
When an antinucleon meets a regular nucleon, both completely vanish in a burst of pure energy—it's the most perfectly efficient energy conversion known to physics, and it's why antimatter is so dangerous and so exciting to scientists!
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