Radiolabeling and Isotopic Markers
All elements can exist as two or more isotopes that differ in the number of neutrons in the nucleus. Some isotopes are stable indefinitely, while others are unstable (radioactive). Radioactive isotopes decay with a defined half-life, and primarily through release of helium nuclei (α particles), electrons or positrons (β particles), and γ radiation. The ready detection of this emitted radiation, even on a very small scale, underlies the utility and high sensitivity of a radioactive label.
This website focuses on the isotopes primarily of interest to organic chemists, which include the non-metal Main Group elements. Once prepared, radiolabeled compounds meet a variety of fates, but the goal is ultimately to detect the labeled molecule, fragment or metabolite: a suitable radiolabel or isotopic marker should allow normal chemical or biochemical processes to be monitored without causing any interference.