‘Strong evidence’ unusual nitrogen-9 nucleus exists, scientists say

There are 118 elements. Each element is unique by virtue of the different numbers of electrons, protons, and neutrons its atoms contain.

Isotopes are atoms of a given element that vary only in the number of neutrons. This difference sets apart one isotope from another. Many isotopes are also unstable, especially those whose atoms have too few neutrons for the number of protons.

Unstable isotopes are short-lived, and often decay by releasing some energy to achieve a more stable configuration. Isotopes in nuclear physics constitute an ongoing area of research, with many isotopes not known to physics.