Stable isotope. Relative atomic mass

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1 Stable isotope Relative atomic mass Mole fraction 130 Ba Ba Ba Ba Ba Ba Ba Radioactive isotope having a relatively long half-life and a characteristic terrestrial isotopic composition that contributes significantly and reproducibly to the determination of the standard atomic weight of the element in normal materials. Half-lives of 130 Ba and 132 Ba are ~10 21 years and years, respectively. Barium isotopes in Earth/planetary science Because molecules, atoms, and ions of the stable isotopes of barium possess slightly different physical, chemical and biological properties, they can be isotopically fractionated during physical, chemical, and biological processes, giving rise to variations in isotopic abundances and in atomic weights. von Allmen et al. [411] observe barium isotopic fractionation in the global barium cycle (Figure 1).

2 High-precision barium isotope measurements reveal differences of up to 25 parts per million in the isotope-amount ratio n( 137 Ba)/n( 136 Ba) and 60 parts per million in the n( 138 Ba)/n( 136 Ba) ratio between chondrites and the Earth. These differences probably arose from incomplete mixing of nucleosynthetic material in the solar nebula. Barium isotopes may be the decay products of now-extinct 135 Cs, which is thought to be a nucleosynthetic component. Chondritic meteorites have a slight excess of supernova-derived material as compared to Earth, demonstrating that the solar nebula was not perfectly homogenized upon formation (Figure 1) [ ]. Fig. 1: Variation in selected barium-bearing substances (modified from [411]).

3 Glossary atomic number (Z) The number of protons in the nucleus of an atom. atomic weight (relative mean atomic mass) the sum of the products of the relative atomic mass and the mole fraction of each stable and long-lived radioactive isotope of that element in the sample. The symbol of the atomic weight of element E is A r (E), and the symbol of the atomic weight of an atom (isotope) of element E having mass number A is A r ( A E). Because relative atomic masses are scaled (expressed relative) to one-twelfth the mass of a carbon-12 atom, atomic weights are dimensionless. [return] chondrites (or chondritic meteorites) non-metallic meteorites which have not undergone compositional change due to melting because they were part of primitive asteroids, and thus reflect the composition of the solar nebula from which our Solar System formed. [return] decay product (daughter product) any nuclide produced by a specified radionuclide (parent) in a decay chain. [return] electron elementary particle of matter with a negative electric charge and a rest mass of about kg. element (chemical element) a species of atoms; all atoms with the same number of protons in the atomic nucleus. A pure chemical substance composed of atoms with the same number of protons in the atomic nucleus [703]. [return] gamma rays (gamma radiation) a stream of high-energy electromagnetic radiation given off by an atomic nucleus undergoing radioactive decay. The energies of gamma rays are higher than those of X-rays; thus, gamma rays have greater penetrating power. half-life (radioactive) the time interval that it takes for the total number of atoms of any radioactive isotope to decay and leave only one-half of the original number of atoms. [return] isotope one of two or more species of atoms of a given element (having the same number of protons in the nucleus) with different atomic masses (different number of neutrons in the nucleus). The atom can either be a stable isotope or a radioactive isotope. isotopic abundance (mole fraction or amount fraction) the amount (symbol n) of a given isotope (atom) in a sample divided by the total amount of all stable and long-lived radioactive isotopes of the chemical element in the sample. [return] isotope-amount ratio (r) amount (symbol n) of an isotope divided by the amount of another isotope of the chemical element in the same system [706]. [return] isotopic composition number and abundance of the isotopes of a chemical element that are naturally occurring [706]. [return]

4 isotopic fractionation (stable-isotope fractionation) preferential enrichment of one isotope of an element over another, owing to slight variations in their physical, chemical, or biological properties [706]. [return] meteorite a meteoroid that has survived atmospheric passage and fallen to the Earth s surface in one or more recoverable fragments. See also chondrites [705]. [return] neutron an elementary particle with no net charge and a rest mass of about kg, slightly more than that of the proton. All atoms contain neutrons in their nucleus except for protium ( 1 H). normal material a reasonably possible source for an element or its compounds in commerce, for industry or science; the material is not itself studied for some extraordinary anomaly and its mole fractions (isotopic abundances) have not been modified significantly in a geologically brief period [4]. [return] nucleosynthesis the production of a chemical element from simpler nuclei (as of hydrogen) especially in a star. See r-process, s-process, and p-process [710]. [return] p-process a nucleosynthesis process responsible for proton-rich nuclei [711]. proton an elementary particle having a rest mass of about kg, slightly less than that of a neutron, and a positive electric charge equal and opposite to that of the electron. The number of protons in the nucleus of an atom is the atomic number. r-process (rapid neutron capture process) nucleosynthesis process that occurs when supernovae collapse, resulting in neutron-rich atomic nuclei heavier than iron. radioactive decay the process by which unstable (or radioactive) isotopes lose energy by emitting alpha particles (helium nuclei), beta particles (positive or negative electrons), gamma radiation, neutrons or protons to reach a final stable energy state. radioactive isotope (radioisotope) an atom for which radioactive decay has been experimentally measured (also see half-life). [return] radionuclide a nuclide that is radioactive [703]. s-process (slow-neutron-capture-process) a nucleosynthesis process that occurs at relatively low neutron density and intermediate temperature conditions in stars, producing isotopes of the elements heavier than iron. The s-process is import in controlling the chemical evolution of the galaxy. solar nebula the cloud of dust and gas from which the solar system is believed to have condensed, mainly by gravitational attraction about 4.5 billion years ago. [return]

5 stable isotope an atom for which no radioactive decay has ever been experimentally measured. [return] standard atomic weight an evaluated quantity assigned by the IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW) to encompass the range of possible atomic weights of a chemical element that might be encountered in all samples of normal terrestrial materials. It is comprised of either an interval (currently for 12 elements) or a value and an uncertainty (a standard Atomic-weight uncertainty), and currently there are 72. A standard atomic weight is determined from an evaluation of peer-reviewed scientific publications. [return] supernova (plural supernovae) a star that suddenly increases greatly in brightness because of a catastrophic explosion that ejects most of its mass [716]. [return] X-rays electromagnetic radiation with a wavelength ranging from 0.01 to 10 nanometers shorter than those of UV rays and typically longer than those of gamma rays. References 4. C. Kendall, and Coplen, T.B. Hydrological Process. 15, 1363 (2011) /hyp M. E. B. K. von Allmen, E. Samankassou, and T. F. Nägler. Chemical Geology. 277, 70 (2010) M. C. Ranen, and Jacobsen, S.B. Science. 314 (5800), 809 (2006) /science H. Hidaka, Ohta, Y., and Yoneda, S. Earth and Planetary Science Letters. 214 (3-4), 455 (2003) /S X(03) S. B. Jacobsen, and Ranen, M.C. Geochimica et Cosmochimica Acta. 70 (18), A286 (2006) /j.gca I. U. o. P. a. A. Chemistry. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Blackwell Scientific Publications, Oxford (1997) American Geological Institute Glossary of Geology. American Geosciences Institute, Alexandria, Virginia (2011) Coplen. Rapid Communications in Mass Spectrometry. 25 (2011) Merriam-Webster. nucleosynthesis. Merriam-Webster M. A. a. S. Goriely. Physics Reports. 384 (2003) Merriam-Webster. supernova. Merriam-Webster June 22.