Every particle has a corresponding antiparticle. An antiparticle has the same mass (rest mass) as its particle but the opposite charge. If a particle is neutral, its antiparticle is also neutral.Examples:• electron e− and positron e+: the positron has the same mass as the electron but a charge of +e.
• proton p and antiproton p̄: the antiproton has a charge of −e.
• neutron n and antineutron n̄: both have zero charge.
• neutrino ν and antineutrino ν̄: both have zero charge and almost zero mass.Antiparticles are usually written with a bar over the symbol, except the positron, which is written e+.When a particle meets its antiparticle, they annihilate: their mass is converted completely into energy, usually as two gamma-ray photons travelling in opposite directions (so that momentum is conserved).The reverse process is pair production: a high-energy photon can create a particle and its antiparticle together. The photon must have at least enough energy to supply the rest mass energy of both particles.
Positrons are emitted in beta-plus decay. They are used in PET scanners in hospitals, where the gamma-ray photons from annihilation are detected to build up an image of the body.Antimatter is rare in the universe today, because it is annihilated almost as soon as it meets ordinary matter.
• proton p and antiproton p̄: the antiproton has a charge of −e.
• neutron n and antineutron n̄: both have zero charge.
• neutrino ν and antineutrino ν̄: both have zero charge and almost zero mass.Antiparticles are usually written with a bar over the symbol, except the positron, which is written e+.When a particle meets its antiparticle, they annihilate: their mass is converted completely into energy, usually as two gamma-ray photons travelling in opposite directions (so that momentum is conserved).The reverse process is pair production: a high-energy photon can create a particle and its antiparticle together. The photon must have at least enough energy to supply the rest mass energy of both particles.
Positrons are emitted in beta-plus decay. They are used in PET scanners in hospitals, where the gamma-ray photons from annihilation are detected to build up an image of the body.Antimatter is rare in the universe today, because it is annihilated almost as soon as it meets ordinary matter.