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Isotope Techniques in Flood Analysis
Published in Saeid Eslamian, Faezeh Eslamian, Flood Handbook, 2022
Samir Al-Gamal, Saeid Eslamian
Where R = the ratio of the heavy isotope to the lighter isotope (i.e., D/H, δ 18O/δ 16O, δ 34S/δ 32S) etc. in compounds A and B. The value of such an equilibrium fractionation factor can be calculated based on spectral data of the isotopic molecular species, at least for simple molecules. The values generally differ by only a few percent from the equal-energy value of 1.00, except for exchange reactions involving hydrogen isotopes where a value may be as large as 4 at room temperature (Friedman and O'Neil, 1977). The sign and magnitude of a are dependent on many factors, of which temperature is generally the most important. Other factors include chemical composition, crystal structure, and pressure.
Hydrochemistry and groundwater isotopes
Published in Ian Acworth, Investigating Groundwater, 2019
Fractionation of stable isotopes occurs as a result of different physical processes and because of the mass differences between isotopes of the same element. Two fundamental processes control the fractionation. The first of these, known as equilibrium fractionation, results from chemical bonds of molecules containing the lighter isotope being slightly weaker than those containing the heavier isotope. Molecules containing the lighter isotope therefore react more quickly during phase changes or reversible chemical reactions. For example, the exchange between isotopes of hydrogen and oxygen between liquid water and vapour (evaporation): H2Oliq⇔H2Ovap
Application of Natural and Artificial Isotopes in Groundwater Recharge Estimation
Published in M. Thangarajan, Vijay P. Singh, Groundwater Assessment, Modeling, and Management, 2016
The deuterium excess was also quite different for the two rains. Deuterium excess is defined as the excess deuterium that cannot be accounted by equilibrium fractionation of isotopes between water and vapor (Clark and Fritz, 1997) and is calculated as Deuteriumexcess(%)=δD−8δ18O
Refractive Index Measurements of Solid Hydrogen Isotopologues
Published in Fusion Science and Technology, 2023
Jiaqi Zhang, Akifumi Iwamoto, Keisuke Shigemori, Masanori Hara, Kohei Yamanoi
Isotopologue fractionation has two kinds of processes: equilibrium isotope effects and kinetic isotope effects.15 Equilibrium fractionation means a heavier isotope equilibrates into the compound or phase in which it is most stably bound. Thus, D2 was more inclined to be enriched in the solid phase. For kinetic fractionation, if reaction products become physically isolated from the reactants, this isotopologue fractionation is a unidirectional kinetic reaction. During H-D solidification, as the temperature decreased, D2 solidified first and precipitated at the bottom of the cell. Since heavier isotopologues move more slowly (KE = 1/2 mv2) leading to slower reactions, D2 was covered with new crystals before the exchange reaction with liquid H2 took place in time. Meanwhile, the H composition increased in the residual liquid H2-D2. As crystallization continued, the residual liquid solidified into new crystals with a higher H composition. The diffusion of H2 and D2 in the solid phase was slower, which eventually led to fractional crystallization. Based on isotopic fractionation in the solid H-D, it can be predicted that this phenomenon may also occur in the solid D-T fuel.