Last revised by Daniel J Bell on 21 Feb 2024

A nuclide is a nuclear-centric term describing an atomic species by its nuclear composition and nuclear energy state.

A nuclide has a specific number of protons and neutrons and will additionally have a specific energy state of its nucleus.

Radionuclides are unstable nuclides that undergo radioactive decay.

Types of nuclides are demonstrated below:

  • isotopes: same atomic number (Z)

  • isotones: same neutron number (N)

  • isobars: same mass number (A)

  • isomers: same atomic (Z) and mass (A) numbers, different energy states

History and etymology

Truman Kohman, a 20th century American chemist, proposed the use of the term nuclide in 1947 (and its derivative radionuclide) as a more accurate substitute for the terms isotope and radioisotope. This recommendation was not widely adopted in scientific literature until the 1960s.

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