What is Pair Production?

     Pair production is a physical process where a photon is turned into an electron-positron pair nearby a nucleus. Pair production is defined to be the conversion of a neutral boson particle into subatomic particles and their antiparticle. 

    For example, when a photon hit a nucleus, the nucleus will give out electron and positron. 

Basically, a positron is a subatomic particle that has the same mass as that of an electron but of the opposite charge. It constitutes the antiparticle of an electron. 

1. Why positron is created? 

Electric charged must be conserved in every physical process. The portion has no charge while the electron on the other hand is negatively charged. After the interaction, the charge must sum up to zero according to the principle of conservation of charges then there should exist a particle that has a charge opposite to the electron and that particle is called a positron. 

2. Can any photon create an electron-positron?

The simple answer is NO. Energy must be conserved. Considered the case of least energy where the electron and position are created at rest that has no kinetic energy. The total energy after the interaction is the sum of the rest of mass-energy which is 2mc^2. so for the interaction to occur, the photon must have enough energy that is to be considered as the threshold.