Defining an Antiparticle
An antiparticle is a type of subatomic particle that has the same mass as its corresponding particle but carries opposite electrical charge and other quantum numbers. For example, the electron's antiparticle is the positron, which has the same mass as an electron but a positive charge. The existence of antiparticles is predicted by quantum field theory, particularly the Dirac equation, which describes electrons.
Key Properties and Annihilation
Beyond mass and charge, antiparticles also have opposite values for other quantum properties like baryon number, lepton number, and strangeness. A crucial characteristic is that when a particle encounters its antiparticle, they undergo mutual annihilation, converting their combined mass into energy, typically in the form of photons (gamma rays). This process is an important demonstration of Einstein's mass-energy equivalence principle (E=mc²).
The Positron: A Common Example
The most well-known antiparticle is the positron (e+), the antimatter counterpart of the electron (e-). Discovered by Carl Anderson in 1932, positrons possess the same mass as electrons but an elementary positive charge. They are commonly produced in certain types of radioactive decay, known as beta-plus decay, where a proton in an unstable nucleus converts into a neutron, emitting a positron and a neutrino.
Significance in Science and Technology
Antiparticles play a vital role in understanding the fundamental laws of physics, including the Standard Model of particle physics and theories about the early universe's matter-antimatter asymmetry. Practically, positrons are used in Positron Emission Tomography (PET) scans, a medical imaging technique that utilizes the annihilation of positrons with electrons in the body to produce gamma rays, which can be detected to create detailed images of organ function and disease.