Nuclide

[1] The word nuclide was coined by the American nuclear physicist Truman P. Kohman in 1947.

[2][3] Kohman defined nuclide as a "species of atom characterized by the constitution of its nucleus" containing a certain number of neutrons and protons.

For hydrogen, the lightest element, the isotope effect is large enough to affect biological systems strongly.

Nuclear isomers are members of a set of nuclides with equal proton number and equal mass number (thus making them by definition the same isotope), but different states of excitation.

The longest-lived non-ground state nuclear isomer is the nuclide tantalum-180m (180m73Ta), which has a half-life in excess of 1,000 trillion years.

(In contrast, the ground state nuclide tantalum-180 does not occur primordially, since it decays with a half life of only 8 hours to 180Hf (86%) or 180W (14%).)

These are remnants of nucleosynthesis that occurred in stars before the formation of the Solar System.

The second group of radionuclides that exist naturally consists of radiogenic nuclides such as 226Ra (t1/2 = 1602 years), an isotope of radium, which are formed by radioactive decay.

The third group consists of nuclides that are continuously being made in another fashion that is not simple spontaneous radioactive decay (i.e., only one atom involved with no incoming particle) but instead involves a natural nuclear reaction.

An example of nuclides made by nuclear reactions, are cosmogenic 14C (radiocarbon) that is made by cosmic ray bombardment of other elements, and nucleogenic 239Pu which is still being created by neutron bombardment of natural 238U as a result of natural fission in uranium ores.

Beyond the naturally occurring nuclides, more than 3000 radionuclides of varying half-lives have been artificially produced and characterized.

Note that numbers are not exact, and may change slightly in the future, if some "stable" nuclides are observed to be radioactive with very long half-lives.

Atomic nuclei other than hydrogen 11H have protons and neutrons bound together by the residual strong force.