= Fluorine-18
{title2=$^{18}\mathrm F$}
<Fluorine-18> is a radioactive <isotope> of <fluorine> with 9 <protons> and 9 <neutrons>. It decays to <oxygen-18>, mainly by emitting a <Positron> and also by <electron capture>. Its approximately 110-minute <half-life> makes its <radioactivity> change appreciably over an ordinary laboratory session. It is used in <positron emission tomography>.https://arxiv.org/abs/1012.3891[Original standardization study, abstract: daughter isotope, competing decay modes, half-life and PET use]{ref}
The <half-life> can be measured by following the falling <radioactivity>, rather than by watching one nucleus wait to decay. A 2010 experiment used <ionization chambers>, <germanium> detectors and <coincidence counting> with fast <scintillators>, following decay for up to nine <half-lives>. The combined result was $1.82871(18)\,\mathrm h$. Comparing different detector systems tests whether the inferred decay rate depends on one measurement technique.<The half-life of 18F by Eduardo García-Toraño and others>[Abstract: apparatus, observation interval and reported result]{ref}
For a closed sample governed only by <radioactive decay>, the surviving parent fraction is $N(t)/N(0)=2^{-t/T_{1/2}}$. Taking 110 minutes as an illustrative rounded <half-life>, 220 minutes leaves one quarter of the original <fluorine-18> nuclei. Four <half-lives> leave $1/16$, not zero. This calculation concerns nuclear survival; movement of a labelled <molecule> into or out of an observed region is an additional process.
Back to article page
