Isotopic Composition of the Elements

Atomic symbol Name Atomic No. Mass No. Isotopic mass Isotopic comp. Relative a-tomic mass 

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P. DeBievre and I.L. Barnes, Table of the isotopic composition of the elements as determined by mass spectrometry, Int. J. Mass Spectrom. Ion Processes, 65 (1985) 211-230. 

As a concluding remark of this section, the theoretical models of nucleosynthesis within stars show that the isotopic compositions of the elements are highly variable depending on star size, metallicity, companion s presence. From the isotopic data obtained in diverse solar system materials it turns out that most of this material was highly homogenized in the interstellar medium or by the formation of the solar system. The presence of isotopic anomalies preserved in some primitive materials are the last witnesses of the initial diversity of the materials constituting our planetary system. 

Because in nature the ground state of a stable nuclide is often attained by decay chains involving intermediate species decaying at different rates, it is worth evaluating the implications of the relative magnitudes of the various decay constants on the isotopic composition of the element. 

The isotopic composition of the elements (including the exact atomic mass and the abundance of the isotopes), the atomic weights of elements, definitions and abbreviations are summarized in Appendix II. 

Mass spectrometric measurements are based on measuring ion currents of separated ion beams of isotopes. With knowledge of the isotopic composition of the elements investigated (see Table of Isotopic Abundances in Appendix I5), a simple identification of chemical elements using singly... 

I he atomic wcighi varies because of natural variations in the isotopic composition of the element, caused by the various isotopes having different origins - I h is the end product of the thorium decay scries, while Ph and " Pb arise Irom uranium as end products of the actinium and radium series respectively. Lead-204 has no existing natural radioactive precursors. Electronic configuration l.v 2s lfc22/j"3v 3//,3i/l"4v- 4/, 4l/" 4/ IJ5v- 5/ "5t/l"bv />-. Ionic radius Pb I.IX A. Pb 1 0.7(1 A. Metallic radius 1.7502 A. Covalent radius (ip i 1.44 A. First ionization potential 7.415 cV second. 14.17 eV. Oxidation... 

Isotope Ratio Measurements The analysis of milk samples for the accurate determination of its constituent elements has also been done by isotope dilution analysis [34, 102, 103]. For that purpose, an enriched isotope of the element or elements to be determined is spiked to the sample, altering the natural isotopic composition of the element to be analyzed. By measuring the altered... 

If we assume that the isotopic composition of the elements was set by the original processes of nucleosynthesis, deviations from the primordial ratios can originate by ... 

Isotopic Compositions of the Elements 1989, Pure Appl. Chem. 63 (1991) 991-1002. 

The activity of naturally radioactive elements is a measure of their mass. Prerequisites of application of the correlation between mass and activity according to eq. (17.1) are that the isotopic composition of the element to be determined is constant and that interfering radioactive impurities are absent. If the daughter nuelides are also radioactive, radioactive equilibrium must be established or the daughter nuclides must be separated off quantitatively. Interference of radioactive impurities may be avoided by measuring the a or y spectrum of the radionuclide considered. 

The isotopic compositions of the elements are not discussed in this chapter. The compilation by Palme and Beer (1993) contains a list of isotopes and their relative abundances. Lodders (2003) has prepared a new compilation. From... 

Relative Atomic Masses and Natural Isotopic Composition of the Elements... 

The 1981 report on atomic weights includes a complete review of the natural isotopic composition of the elements and also tabulates the relative atomic masses for selected radioisotopes. This information is required for the conversion of spectroscopic data from that corresponding to specific isotopes to the naturally occurring isotopic abundance. 

The measurement of isotopic abundances began early this century following the discovery of neon isotopes by J.J. Thompson in 1912. F.W. Aston developed the mass spectrometer into a quantitative instrument for measuring isotopic abundances and by 1935 the isotopic composition of most elements was known. The first International Table of Stable Isotopes was drawn up in 1936, while the latest table of Isotopic Compositions of the Elements appeared recently (4). Lead is an element for which there was early evidence of natural variations in its isotopic composition (5) these were ultimately used to measure the age of the Earth (6). Natural variations have been reported in 43 other elements although many relate to exceptional samples. There are 18 elements in which variations are not uncommon, although most of these elements have relatively light atoms with atomic numbers less than 16 (4). 

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