Die Häufigkeit der Edelgase Auf Der Erde Und Im Kosmos

The cosmic abundance of the rare gases is now known with sufficient accuracy to allow a quantitative comparison with the corresponding data for the earth's atmosphere. It seems safe to assume that the cosmic abundance of neon is closely approximated by Unsöld's value for the neon content of the Bo star, τ Scorpii. The values for the other rare gases have been determined in a way previously described by the author, viz., by interpolation of the relative values for the different nuclear species in "smoothed" abundance curves. These values, as well as the neon value, may be considered to be correct within a factor of 2. Argon 40 and the two helium isotopes are omitted from consideration because their atmospheric concentration is of radiogenic origin. The comparison of these values with those for the composition of the earth and its atmosphere show that the relative abundance of xenon (the ratio of the number of xenon atoms to the number of silicon atoms) is about 107 times smaller on the earth than in the universe, whereas for neon this figure exceeds 1011. A separation of neon from xenon, shifting the ratio of concentrations by a factor of more than 104, has obviously taken place during the process of the atmosphere's evolution. This cannot be explained by chemical absorption or solution processes but can be understood by assuming selective diffusion from the earth's gravitational field during a limited epoch of evolution. In greater detail, it is found that the ratios of terrestrial and cosmic abundances of Ne, A36 plus A38, Kr, and Xe, plotted against atomic weight, lie close to a curve, which is given by the following equation:\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage{wasysym} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document}$$-{\mathrm{log}}_{10} \frac{N_{ter}}{N_{sol}} = 10 \times e^{-0.045M/m_{1}} + 7.1,$$\end{document} in which Nter = atoms of rare gas present in the earth's atmosphere per 100 atoms of Si present in the earth; Nsol = atoms of rare gas in the universe per 100 atoms of Si; M = atom weight of rare gas; and m1 = atomic mass unit. The form of this function corresponds to what one would expect to result from selective diffusion. Further discussion of the equation shows that the remarkably small value of the exponent makes it impossible to explain the selective escape from the earth's field of gravitation as a consequence of high temperature only, but that the small value can be understood only if the short period of the earth's rotation at the time of evolution is taken into account. The equation indicates that approximately 107 parts to 1 of the rare gases originally present may have escaped from terrestrial matter without undergoing separation, leaving only the small residual fraction to be involved in the separation process. Attention is drawn to the fact that, according to the given equation, a marked difference should exist between the isotopic composition of atmospheric and that of cosmic rare gases. An investigation of the isotopic composition of Ne and Ar obtained from meteorites, rocks, or natural gases containing an excessive amount of neon might lead to a final decision on the correctness of the assumption suggested.