Each atomic number identifies a specific element, but not the isotope; an atom of a given element may have a wide range in its number of neutrons.
The number of nucleons (both protons and neutrons) in the nucleus is the atom's mass number, and each isotope of a given element has a different mass number.
Over 10,000 hospitals worldwide use radioisotopes in medicine, and about 90% of the procedures are for diagnosis.
The most common radioisotope used in diagnosis is technetium-99 (Tc-99), with some 35 million procedures per year, accounting for about 80% of all nuclear medicine procedures worldwide.
The number of protons within the atom's nucleus is called atomic number and is equal to the number of electrons in the neutral (non-ionized) atom. The term isotope is formed from the Greek roots isos (ἴσος "equal") and topos (τόπος "place"), meaning "the same place"; thus, the meaning behind the name is that different isotopes of a single element occupy the same position on the periodic table. All isotopes of a given element have the same number of protons in each atom.Isotopes of a given element typically behave alike chemically.With the exception of hydrogen, elements found on Earth generally have the same number of protons and neutrons; heavier and lighter isotopes (with more or fewer neutrons) are often unstable and undergo radioactive decay.-suh-tohp)]In physics, different forms of the same element, with nuclei that have the same number of protons but different numbers of neutrons.