Radionuclide

Radioactive isotopeOne of two or more atoms with the same atomic number (Z), but different mass (A). For example, hydrogen has three isotopes: H, H (deuterium), and H (tritium). Different isotopes of a given element have different numbers of neutrons in the nucleus. – Atomic nuclideA nuclear species characterized by Z protons and N neutrons. that decays radioactively .