IB PHYSICS Topic : Atomic and Nuclear Physics – Antimatter

Every form of matter has an equivalent form of antimatter. If matter and antimatter meet, they annihilate each other to produce energy. Antimatter is rare but can be produced in normal radioactive decay processes. For example, a proton decays into a neutron resulting in an anti – electron or positron ()being produced (along with a neutrino):

Anti - particles can form anti – atoms. An anti - electron or positron and an anti - proton could form an anti - hydrogen atom in the same way that an electron and a proton form a normal matter hydrogen atom.

Every antimatter particle has the same mass but the opposite electric charge to it's matter equivalent. Every particle of matter has an antimatter equivalent, opposite in charge but with the same mass as it's particle equivalent. Matter and antimatter can annihilate to produce photons and conversely, a photon can 'decay' to produce matter and antimatter in equal amounts.For this to happen the energy of the photon must be at least equal towhereis the mass of one of the matter – antimatter pair. The difference between the initial photon energy andgoes into the kinetic energy of the particles. The normal rules of conservation of energy and momentum apply during these processes.

In the diagram above left, a gamma ray decays into an electron and it's antiparticle, the positron. The energy of the gamma ray is at leastAny excess of the gamma ray energy over this may go into the kinetic energy of the electron and proton.
In the diagram above right, an electron and it's antiparticle, the positron meet and annihilate. A gamma ray photon is produced. The energy of the gamma ray is at leastAny excess of the gamma ray energy over this is due to kinetic energy of the electron and proton.