Fluorine-18
The nuclide 18F is the radionuclide of fluorine with the longest half-life, 109.771 minutes, allowing it to serve commercially as an important source of positrons. Its major use is for the production of the radiopharmaceutical fludeoxyglucose for positron emission tomography scanning in medicine.
Like all positron-emissing radioisotopes, 18F also has a probability to decay by electron capture. In this case, 18F decays 96.86 (19)% of the time by beta plus (positron emission), and 3.14 (19)% by electron capture.
Read more about this topic: Isotopes Of Fluorine