Positron
Definition
The electron's antimatter twin — same mass, opposite charge; when it meets an electron, both vanish into gamma rays.
Symbol: ·
Technical definition
The electron's antiparticle (e⁺), predicted by Dirac in 1928 and discovered in 1932. Annihilation e⁺ + e⁻ → 2γ conserves energy and momentum.
Example
PET scans inject a positron-emitting tracer — each annihilation's twin gamma rays pinpoint exactly where the tracer decayed, mapping brain activity.
Common confusion
Positrons aren't a curiosity — they are genuine antimatter, occurring naturally in beta-plus decay and cosmic rays, not just in laboratories.