Atomic Number Ratio Research Articles

DETERMINATION OF ð18 IN WATER FROM ð18 IN EOUILIBRATED CO2: INFLUENCE OF CHANGES IN EXPERIMENTAL PARAMETERS ON THE EOUILIBRATION PROCESS

The result of an isotopic exchange reaction is expressed in terms of the isotopic abundance ratios, the fractionation factor and the atom number ratio of the reactants. The general formula is applied to the CO 2 -H 2 O system and simplified by neglecting terms small in relation to the experimental crror. The influence of variations in the experimental parameters on the equilibrium is discussed. It is found that changes in temperature as well as atom number ratio will influence the equilibration process appreciably.

X-Ray-Emission Microanalysis of Rock-Forming Minerals I. Experimental Techniques

In order to provide a basis for calibration of X-ray-emission analyses, existing theories and experimental measurements on the generation, absorption, and fluorescence of X-rays produced by electron bombardment of mixed targets are reviewed and compared with new measurements for a variety of targets, principally common silicates. Theoretically, the efficiency of X-ray generation should depend strongly on the mean atomic number of a mixed target, and its variation is commonly described by a so-called atomic-number factor. Using hard radiation for which the absorption is trivial, measurements have shown that the Philibert factor (1 + h) varies too little with mean atomic number. A new empirical factor, fits the data to within 2 per cent, except for close to (is incident electron accelerating voltage in kilovolts, is ionization voltage for K-electrons, {\langle}Z{\rangle} is mean atomic number of target weighted according to mass concentration, {\langle}Z/A{\rangle} is a similar average for ratio of atomic number to atomic weight, R is Green's backscatter coefficient to express proportion of potential ionization energy retained in target). For soft radiation, empirical absorption curves have been derived for simple and complex oxides on the assumption that the above efficiency-of-generation factor is valid. These curves differ markedly from those suggested by measurements on single-element targets, and it is recommended that the new curves be used for analyses in which the same experimental conditions are used. It is concluded that analyses of major elements in common minerals can be carried out to a relative accuracy of 1-5 per cent by suitable choice of standards and experimental conditions; such conditions are described.