sentence: Many elements have multiple isotopes which are stable for weeks, years, or even billions of years.
sentences_before: If a nucleus has too few or too many neutrons it may be unstable, and will decay after some period of time. In this decay a neutron in the nitrogen nucleus is turned into a proton and an electron by the weak nuclear force.
concept_name: element
headings: Atomic nucleus Modern topics in nuclear physics Spontaneous changes from one nuclide to another: nuclear decay
categories: Nuclear physics Matter