An Introduction to Isotopic Calculations（介绍同位素计算）.pdf

An Introduction to Isotopic Calculations John M. Hayes (jhayes@) Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA, 30 September 2004 Abstract. These notes provide an introduction to: termed isotope effects. As a result of such effects, the • Methods for the expression of isotopic abundances, natural abundances of the stable isotopes of practically • Isotopic mass balances, and all elements involved in low-temperature geochemical • Isotope effects and their consequences in open and ( 200°C) and biological processes are not precisely con- closed systems. stant. Taking carbon as an example, the range of interest is roughly 0.00998 ≤ 13 F ≤ 0.01121. Within that range, Notation. Absolute abundances of isotopes are com- differences as small as 0.00001 can provide information monly reported in terms of atom percent. For example, about the source of the carbon and about processes in atom percent 13C = [13C/(12C + 13C)]100 (1) which the carbon has participated. A closely related term is thefractional abundance The delta notation. Because the interesting isotopic fractional abundance of 13 13 C ≡ F