Pair production is a phenomenon that occurs when a photon interacts with a nucleus, resulting in the creation of a particle-antiparticle pair.

When a high-energy photon, such as a gamma ray, enters the electric field surrounding a nucleus, it can be absorbed by that nucleus. This absorption leads to the excitation of the nucleus, which subsequently releases energy in the form of an electron-positron pair. For this process to take place, the energy of the incoming photon must exceed the rest mass energy of the particle-antiparticle pair.

The electron and positron produced during pair production possess opposite charges and can be detected as they traverse through a material medium. However, they quickly interact with other particles within that medium and annihilate each other, resulting in the emission of two gamma rays. This phenomenon is referred to as annihilation and represents the reverse process of pair production.

Pair production plays a crucial role in high-energy physics, helping to describe the behavior of particles in particle accelerators. Additionally, it is significant in astrophysics, particularly in the vicinity of black holes and other high-energy sources, where it contributes to the formation of electron-positron pairs.

In summary, pair production is the process by which a photon interacts with a nucleus to generate a particle-antiparticle pair. This process is vital in both high-energy physics and astrophysics, and its effects can be observed through the annihilation of the resulting particles.