Nuclear species

A nuclide, which is also called a nuclear species, is a unique configuration of nucleons (which is the collective term for protons and neutrons) inside of a nucleus.This term allows nuclear scientists to distinguish between nuclei that differ in any way; number of protons, neutrons, or energy configuration of either.

Examples

Changing the number of protons (the atomic number) creates a different nuclear species:

${\phantom{A}}_{\phantom{16}}^{\phantom{36}}{\phantom{A}}_{\phantom{2}16}^{\phantom{2}36}\mathrm{S}$ is a different species than ${\phantom{A}}_{\phantom{17}}^{\phantom{37}}{\phantom{A}}_{\phantom{2}17}^{\phantom{2}37}\mathrm{C}\mathrm{l}$.

Likewise, changing the number of neutrons (the neutron number) changes the nuclear species:

${\phantom{A}}_{\phantom{19}}^{\phantom{39}}{\phantom{A}}_{\phantom{2}19}^{\phantom{2}39}\mathrm{K}$, and ${\phantom{A}}_{\phantom{19}}^{\phantom{40}}{\phantom{A}}_{\phantom{2}19}^{\phantom{2}40}\mathrm{K}$ are two different nuclear species.

Both of the previous examples changed the mass number, but different isobars (same mass number, different number of protons and neutrons individually) would also be different nuclear species:

${\phantom{A}}_{\phantom{20}}^{\phantom{40}}{\phantom{A}}_{\phantom{2}20}^{\phantom{2}40}\mathrm{C}\mathrm{a}$, and ${\phantom{A}}_{\phantom{19}}^{\phantom{40}}{\phantom{A}}_{\phantom{2}19}^{\phantom{2}40}\mathrm{K}$ are different nuclear species.

Slightly abstractly, putting the nucleons into a different configuration (same number of protons, same number of neutrons, but in different energy levels (this is an example of two different nuclear isomers)):

${\phantom{A}}_{\phantom{91}}^{\phantom{234m}}{\phantom{A}}_{\phantom{2}91}^{\phantom{2}234m}\mathrm{P}\mathrm{a}$, and ${\phantom{A}}_{\phantom{91}}^{\phantom{234}}{\phantom{A}}_{\phantom{2}91}^{\phantom{2}234}\mathrm{P}\mathrm{a}$ are different nuclear species.