Nuclide

Lore & Background

The word nuclide was coined by American nuclear physicist Truman P. Kohman defined a nuclide as a 'species of atom characterized by the constitution of its nucleus' containing a certain number of neutrons and protons. The term originally focused on the nucleus, deliberately set apart from 'isotope' to consider nuclear properties independently of chemical properties, though 'isotope' remains in common use in nuclear technology and medicine.

Reader's Guide

Nuclides are fundamental to understanding nuclear properties and stability. Unlike isotopes, which are defined by equal proton number (same element), nuclides encompass all atomic species defined by proton number, neutron number, and nuclear energy state. This includes isobars (equal mass number), isotones (equal neutron number), isodiaphers (equal neutron excess), and nuclear isomers (same isotope but different excitation states). The longest-lived non-ground state nuclear isomer is tantalum-180m, with a half-life exceeding 10^17 years. Natural radionuclides arise from three sources: primordial remnants from stellar nucleosynthesis, radiogenic daughters from decay chains, and cosmogenic or nucleogenic nuclides from natural nuclear reactions. The concept of nuclide is essential for distinguishing between stable and radioactive species, and for understanding the role of neutron number in nuclear behavior, as illustrated by the different quantum statistics of helium-4 and helium-3.

Did You Know?

• The longest-lived non-ground state nuclear isomer is tantalum-180m, with a half-life exceeding 10^17 years.
• Nuclides with equal neutron number but different proton numbers are called isotones.