Positron emission is a form of radioactive decay in which a proton in the nucleus of an atom transforms into a neutron, resulting in the emission of a positron.

Also referred to as beta-plus decay, positron emission is a specific subtype of radioactive decay and falls under the broader category of beta decay. This process occurs when a proton within an unstable atomic nucleus is converted into a neutron. During this transformation, a positron—essentially the antimatter counterpart of an electron—and a neutrino, which is a subatomic particle possessing no charge and having an extremely small mass, are emitted.

The positron emission process can be mathematically represented by the equation:

In this equation, $p$ denotes a proton, $n$ represents a neutron, $e^+$ indicates a positron, and $\nu_e$ stands for a neutrino. This expression illustrates that when a proton ($p$) undergoes positron emission, it is converted into a neutron ($n$) while emitting a positron ($e^+$) and a neutrino ($\nu_e$).

The emitted positron has the same mass as an electron but carries a positive charge. When a positron encounters an electron, the two particles annihilate each other, resulting in the production of two gamma-ray photons. This annihilation process is fundamental to positron emission tomography (PET), a medical imaging technique that utilizes radioactive substances to visualize metabolic activities within the body.

Positron emission is a prevalent decay mechanism for radioisotopes that possess an excess of protons. This decay reduces the atomic number by one unit while leaving the atomic mass number unchanged. This is because the total number of nucleons (the sum of protons and neutrons) in the nucleus remains constant, despite one proton being converted into a neutron.

A comprehensive understanding of positron emission is vital in various disciplines, including nuclear physics, medical imaging, and astrophysics. It offers valuable insights into the nature of antimatter, the behavior of unstable isotopes, and the processes taking place within stars and other celestial bodies.