PAIR CREATION & ANNIHILATION - Nuclear Physics

PAIR CREATION & ANNIHILATION

        Relativity and the mass-energy relation,

E = mc²                  . . .(1)

 that came from it has been used to explain some natural phenomena that occur in high energy physics. Observations are made of elementary particle-antiparticle pairs that get created or annihilated.

          Conversion of mass to energy, as taking place with various processes like burning fuels, fission or fusion are low yield processes and not all of the available energy can be converted. Matter – antimatter reactions are the exceptions to such processes.

          In pair production, electron-positron, for instance, a photon transforms to material particles. In any such process, energy, momentum and charge must all be conserved. The minimum energy required for the production of the positron-electron pair would be

2 m_e c² = 1.02 MeV            . . .(2)

where m_e is the rst mass of the electron/positron.

          As a photon’s energy is given by ‘hf’, the minimum energy requirement for the above process(2), would decide the photon’s frequency,

hf_min = 1.02 MeV                . . .(3)

Pair production does not occur in vacuum and takes place only in the presence of a massive particle[like atomic nuclei] to enable simultaneous conservation of energy & momentum.

PAIR ANNIHILATION

            Pair annihilation is the inverse of pair production. An electron & positron, initially at rest, combine and then disappear to create two photons. Two photons are needed as the initial momentum of the source pair is zero. Momentum can be conserved only if two photons of same energy and momentum[magnitude] move of in opposite directions!

--        --        --        --        z

March 2017                                                                                        qed n_ln