What is positron emission in radioactivity?

Positron emission is a type of radioactive decay where a proton in the nucleus converts into a neutron, emitting a positron.

Positron emission, also known as beta-plus decay, is a subtype of radioactive decay and a form of beta decay. It occurs when a proton within an unstable atomic nucleus is transformed into a neutron. This process results in the emission of a positron, which is the antimatter counterpart of an electron, and a neutrino, a subatomic particle with no charge and a very small mass.

The process of positron emission can be represented by the equation p → n + e+ + νe. Here, 'p' represents a proton, 'n' a neutron, 'e+' a positron, and 'νe' a neutrino. This equation shows that when a proton (p) undergoes positron emission, it transforms into a neutron (n) and emits a positron (e+) and a neutrino (νe).

The emitted positron is a particle with the same mass as an electron but with a positive charge. When a positron comes into contact with an electron, both particles annihilate each other, resulting in the production of two gamma-ray photons. This annihilation is a key aspect of positron emission tomography (PET), a medical imaging technique that uses radioactive substances to observe metabolic processes in the body.

Positron emission is a common decay mode for radioisotopes that have a surplus of protons. This process decreases the atomic number by one but leaves the atomic mass number unchanged. This is because the total number of nucleons (protons and neutrons) in the nucleus remains the same, even though one proton has been converted into a neutron.

Understanding positron emission is crucial in various fields, including nuclear physics, medical imaging, and astrophysics. It provides insights into the nature of antimatter, the behaviour of unstable isotopes, and the processes occurring within stars and other celestial bodies.