What is the energy emitted by Fluorine-18 (F-18)?

Fluorine-18 (F-18) is a radioisotope widely used in positron emission tomography (PET) imaging due to its favorable decay properties. When F-18 decays, it emits positrons, which are the antimatter counterparts of electrons. Upon encountering electrons, these positrons annihilate, resulting in the emission of two gamma photons, each with an energy of 511 keV. This emission of 511 keV photons is pivotal for PET imaging as it enables the detection of gamma rays, thereby allowing for the visualization of metabolic processes in the body.

The other energy levels listed—93 keV, 159 keV, and 140 keV—do not correspond to the primary emissions from F-18. These energies may relate to other radionuclides or specific interactions but are not the characteristic energy associated with the positron annihilation process of F-18. Thus, understanding that F-18 specifically emits 511 keV photons upon annihilation provides clarity on its production of detectable signals in PET scans.