Positron
A positron is the antimatter counterpart of the electron. It has an identical mass to the electron (approximately 9.11 × 10⁻³¹ kilograms) but carries a positive electrical charge (+e) rather than the electron’s negative charge (−e). In all other respects, including spin and magnetic moment properties, the positron mirrors the electron’s characteristics.
Discovery and Early Observations
The positron was discovered in 1932 by physicist Carl Anderson while studying cosmic ray interactions using a cloud chamber. Anderson observed tracks of positively charged particles with the mass of an electron, providing the first experimental evidence for antimatter. This discovery confirmed theoretical predictions made by physicist Paul Dirac a few years earlier, who had proposed the existence of such particles through his relativistic quantum mechanics equations.
Annihilation and Practical Applications
When a positron encounters an electron, the two particles annihilate each other, converting their combined mass entirely into energy according to Einstein’s mass-energy equivalence (E=mc²). This process releases energy typically in the form of gamma rays. Positron-electron annihilation has practical applications in positron emission tomography (PET), a medical imaging technique widely used in diagnostics, where positrons emitted by radioactive tracers create detectable signals as they annihilate with electrons in tissue.