positronemissioa

Positronemissioa refers to a decay process in which a proton-rich nucleus converts a proton into a neutron with the emission of a positron and a neutrino. In nuclear physics it is known as beta-plus decay. The fundamental reaction is p -> n + e+ + νe, and for a nucleus this can be written as (A,Z)X -> (A,Z-1)Y + e+ + νe. The emitted positron subsequently loses energy in matter and may annihilate with an electron to produce two gamma rays.

In medical science, positronemissioa is exploited in positron emission tomography (PET). Radioisotopes that decay by positron emission, such as fluorine-18, carbon-11, nitrogen-13, and oxygen-15, are produced in cyclotrons and incorporated into biologically active molecules. Common radiotracers include fluoro-deoxyglucose (FDG) labeled with fluorine-18. After administration, the emitted positrons travel a short distance before annihilating with electrons, emitting two 511 keV photons in nearly opposite directions. PET scanners detect these coincident photons to localize the radiotracer distribution inside the body, enabling functional imaging.

Key properties of positronemissioa isotopes include their half-life, which ranges from minutes to a few hours, and their production and handling requirements. Modern PET systems often combine PET with CT or MRI to provide both metabolic and anatomical information, and time-of-flight techniques can improve spatial localization.

Applications span oncology, neurology, and cardiology, supporting diagnosis, treatment planning, and research. Safety and regulatory considerations focus on controlling radiation exposure and ensuring appropriate use, storage, and disposal of radioactive tracers. Positronemissioa has been central to advances in molecular imaging since the late 20th century.