Of the 26 'monoisotopic' elements that have only a single stable isotope, all but one have an odd atomic number—the single exception being beryllium. In addition, no odd-numbered element has more than two stable isotopes, while every even-numbered element with stable isotopes, except for helium, beryllium, and carbon, has at least three. The partitioning of stable isotopes between two substances A and B can be expressed by use of the isotopic fractionation factor (alpha): A-B = R A /R B where 'R' is the ratio of the heavy to light isotope (e.g., 2 H/ 1 H or 18 O/ 16 O).
Isotopes may be radioactive, or unstable in the natural environment and prone to decay to another state known as a daughter product, or stable. Common stable isotopes include 2 H/H, 18 O/ 16 O, and 13 C/ 12 C. These isotopes occur naturally in the environment, but their natural abundance differs with different environmental conditions.
Stable Isotope Of Carbon
Selected Publications
Stable Isotopes
Joan Brenner Coltrain, Joel C. Janetski, and Shawn W. Carlyle. 2007. The stable and radio-isotope chemistry of Western Baketmaker burials: Implications for early Puebloan diets and origins. American Antiquity 72(2): 301-321.
Joan Brenner Coltrain, M. Geoffrey Hayes, and Dennis H. O'Rourke. 2006. Hrdlicka's Aleutian Population-Replacement Hypothesis: A Radiometric Evaluation. Current Anthropology 47(3): 537-548.
D.G. Williams, J.B. Coltrain, M. Lott, N.B. English, and J.R. Ehleringer. 2005. Oxygen isotopes in cellulose identify source water for archaeological maize in the American Southwest. Journal of Archaeological Science 32: 931-939.
Joan Brenner Coltrain, John M. Harris, Thure E. Cerling, James R. Ehleringer, Maria-Denise Dearing, Joy Ward, and Julie Allen. 2004. Rancho La Brea stable isotope biogeochemicstry and its implication for the palaeoecology of late Pleistocene, coastal southern California. Palaeogeography, Palaeoclimatology, Palaeoecology 205: 199-219.
Joan Brenner Coltrain, M. Geoffrey Hayes, and Dennis H. O'Rourke. 2003. Sealing, whaling, and caribou: the skeletal isotope chemistry of Eastern Arctic foragers. Journal of Archaeological Sciences.
What Makes An Isotope Stable
The nucleus of each atom contains protons and neutrons. While the number of protons defines the element (e.g., hydrogen, carbon, etc.) and the sum of the protons and neutrons gives the atomic mass, the number of neutrons defines the isotope of that element. For example, most carbon (≈ 99 %) has 6 protons and 6 neutrons and is written as 12C to reflect its atomic mass. However, about 1 % of the carbon in the Earth’s biosphere has 6 protons and 7 neutrons (13C) forming the heavy stable isotope of this important element. Stable isotopes do not decay into other elements. In contrast, radioactive isotopes (e.g., 14C) are unstable and will decay into other elements.
The less abundant stable isotope(s) of an element have one or two additional neutrons than protons, and thus are heavier than the more common stable isotope for those elements. Both heavy and light stable isotopes participate freely in chemical reactions and in biological and geochemical processes, but the rate at which heavy and light stable isotopes react during physical or chemical reactions differs. The chemical bonds and attractive forces of atoms with heavy stable isotopes are stronger than those in the more common, lighter isotopes of an element. As a result, the heavier isotopes react more slowly than the lighter isotopes leading to isotopic separation or fractionation between reactant and product in both physical and biological reactions. Fractionation of the heavy and light stable isotopes is important because it a) produces variation in the stable isotope ratio of different element pools and b) establishes an isotope signal that can indicate the existence or magnitude of key processes involved with elemental cycling.