Science / Periodic Table of Elements / Isotope: Atoms of the same element with the same atomic number, but different number of neutrons. Isotope of an element is defined by the sum of the number of protons and neutrons in its nucleus. Elements have more than one isotope with varying numbers of neutrons. For example, there are two common isotopes of carbon, 12C and 13C which have 6 and 7 neutrons respectively. The abundances of different isotopes of elements vary in nature depending on the source of materials. For relative abundances of isotopes in nature see reference on Isotopic Composition of the Elements.
Science / Biology / Radioisotope: Term applied to a radioactive isotope, such as carbon-14 or uranium 238. Radioisotope nuclei are unstable and spontaneously breakdown and emit one of a number of types of radiation. MORE
Science / Geology / Isotope Geology: The study of the relative abundances of isotopes in rocks to determine their ages (see geo-chronology) or conditions of formation. MORE