Isotopes Have Different Numbers Of

Surface and Ground Water, Weathering, and Soils

C. Kendall , D.H. Doctor , in Treatise on Geochemistry, 2003

five.11.1.2.1. Basic principles

Isotopes are atoms of the same chemical element that have different numbers of neutrons just the same number of protons and electrons. The difference in the number of neutrons between the various isotopes of an element means that the various isotopes have different masses. The superscript number to the left of the element abbreviation indicates the number of protons plus neutrons in the isotope. For example, among the hydrogen isotopes, deuterium (denoted as ⁱⁱH or D) has one neutron and one proton. This is approximately twice the mass of protium (ⁱH), whereas tritium (³H) has approximately iii times the mass of protium.

The stable isotopes have nuclei that exercise non decay to other isotopes on geologic timescales, but may themselves be produced past the decay of radioactive isotopes. Radioactive (unstable) isotopes have nuclei that spontaneously disuse over time to class other isotopes. For example, ¹⁴C, a radioisotope of carbon, is produced in the atmosphere past the interaction of cosmic-ray neutrons with stable ¹⁴Northward. With a half-life of ∼5,730 yr, ¹⁴C decays back to ^xivN by emission of a beta particle. The stable ¹⁴Northward produced past radioactive disuse is called "radiogenic" nitrogen. This chapter focuses on stable, nonradiogenic isotopes. For a more than thorough give-and-take of the fundamentals of isotope geochemistry, come across Clark and Fritz (1997) and Kendall and McDonnell (1998).

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Belittling Geochemistry/Inorganic INSTR. Analysis

A. Stracke , ... B.C. Reynolds , in Treatise on Geochemistry (Second Edition), 2014

15.iv.two.two 'Double Spiking' for IC Measurements

For IC measurements by mass spectrometry, the add-on of ii spike isotopes and analyses of 4 or more than isotopes of an element can help distinguish the isotope fractionation that occurs before the equilibration of the spike-sample mixture from any isotope fractionation that occurs afterwards. This so-called double-spike technique is used to separate natural isotope fractionations from those induced past chemical processing and analytical measurements. Alternatively, the addition of two spike isotopes may enable mass fractionation corrections to be made for elements that do not accept enough stable nonradiogenic isotopes bachelor for internal normalization, such as Pb ( Compston and Oversby, 1969; Galer, 1999). Owing to the increasing impact of natural stable isotope fractionation on world and planetary science research that has been sparked by analytical advances in mass spectrometry, there has been renewed interest in applying this well-established method. Double-fasten techniques are specially useful for correcting for instrumental mass fractionation and for quantifying natural stable isotope variations for elements ranging from Ca to U (due east.g., DePaolo, 2004; Stirling et al., 2007).

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Surface And Groundwater, Weathering and Soils

C. Kendall , ... M.B. Young , in Treatise on Geochemistry (2nd Edition), 2014

7.ix.one.2.one Basic principles

Isotopes are atoms of the aforementioned chemical element that have different numbers of neutrons but the same number of protons and electrons. The departure in the number of neutrons between the diverse isotopes of an element means that the diverse isotopes accept dissimilar masses. The superscript number to the left of the chemical element abbreviation indicates the number of protons plus neutrons in the isotope. For example, amid the hydrogen isotopes, deuterium (denoted equally ²H or D) has one neutron and one proton. This is approximately twice the mass of protium (¹H), whereas tritium (ⁱⁱⁱH) has approximately three times the mass of protium.

The stable isotopes take nuclei that practise not decay to other isotopes on geologic time scales but may themselves be produced by the disuse of radioactive isotopes. Radioactive (unstable) isotopes accept nuclei that spontaneously decay over fourth dimension to form other isotopes. For example, ^fourteenC, a radioisotope of carbon, is produced in the atmosphere past the interaction of cosmic-ray neutrons with stable ¹⁴N. With a one-half-life of about 5730 years, ^fourteenC decays back to ^xivN past emission of a beta particle. The stable ¹⁴N produced by radioactive disuse is chosen 'radiogenic' nitrogen. This chapter not only focuses on stable, nonradiogenic, isotopes of several elements (hydrogen, oxygen, carbon, nitrogen, and sulfur) but also includes brief discussion of radioisotopes of these elements (³H, ¹⁴C, ³⁵S) that are important hydrological tracers. For a more thorough discussion of the fundamentals of isotope geochemistry, see capacity in Clark and Fritz (1997) and the Kendall and Caldwell (1998) affiliate in Kendall and McDonnell (1998).

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Radioactive waste

Paul K. Andersen , ... Majid Ghassemi , in Encyclopedia of Energy, 2004

3.9 Plutonium

Isotopes of plutonium (Pu, diminutive number 94) are generated past neutron capture in uranium-238 or thorium-232. Plutonium-239 (half-life 24,110 years) is of greatest concern because it is fissionable. Other important isotopes are plutonium-238 (half-life 87.7 years), plutonium-240 (half-life 6564 years), plutonium-241 (half-life 13 years), and plutonium-242 (half-life 3.76×x ^five years). All of these isotopes have very loftier radiotoxicity.

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Belittling Geochemistry/Inorganic INSTR. Analysis

J.W. Olesik , in Treatise on Geochemistry (Second Edition), 2014

xv.17.11.4.3 Internal standardization using a pair of isotopes of another element

Isotopes of an element other than the analyte element can exist added to the sample for mass bias correction. Tl isotopes have been used for Pb mass bias correction, Tl for Hg, Zn for Cu, Cu for Zn, Zr for Mo, Ru for Mo, Zr for Sr, and Zr for Rb. In order to right for chemical element-dependent mass bias, the signals for the added isotopes can be calibrated against a certified reference material. In this approach, the concentrations of the analyte element and added element in the sample must be carefully matched to those in the standard.

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Geochemistry of Estuaries and Coasts

M.F. Fitzsimons , ... 1000.E. Millward , in Treatise on Estuarine and Coastal Science, 2011

iv.04.four.6 The Use of Isotopes as Tracers of SPM-Associated Trace Metals

Isotopes take been used as tracers of SPM-associated trace metals, and to identify the export of these metals from estuarine environments ( Bergquist and Boyle, 2006; Ingri et al., 2006; de Jong et al., 2007; Escoube et al., 2009). For case, Atomic number 26 isotopes accept been employed to identify the two major suspended fractions of colloidal Fe in river h2o: the oxyhydroxide phase, which shows positive δ⁵⁶Fe values, and the fulvic fraction, which has a more negative signal (Ingri et al., 2006). River water–seawater mixing experiments past Bergquist and Boyle (2006) have shown that aggregated Fe was enriched in heavy isotopes. Therefore, the aggregation and sedimentation of the oxyhydroxide fraction during estuarine mixing should remove heavy isotopes from surface SPM, resulting in a more negative bespeak in the suspended phase (Breitbarth et al., 2010). A contempo study examined the process of potential fractionation of Fe-isotopes during estuarine mixing and flocculation and found that information technology produced minimal Fe-isotope fractionation suggesting that the δ⁵⁶Iron of the dissolved Fe pools preserved during estuarine mixing (Escoube et al., 2009). Cycling of Fe in coastal areas appears to result in the export of a negative Fe isotope point from benthic sources and slightly positive δ⁵⁶Fe values from rivers in the truly dissolved fraction. Thus, Fe-isotopes can provide valuable tracers to distinguish the various Fe-sources in coastal oceans (Escoube et al., 2009). A similar result was found for δ⁶⁵Cu, where the isotopically heavy dissolved phase of all the rivers originates in an isotopic partitioning of the weathered pool of δ⁶⁵Cu between a calorie-free fraction, adsorbed to particulates, and a heavy, dissolved fraction dominated by δ⁶⁵Cu bound to stiff organic complexes (Vance et al., 2008). Recent advances suggest that Iron and Cu isotope measurements accept the potential to provide important, new information on trace metal cycling and send from coastal areas to the open ocean and their potential impact in marine ecosystems.

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Carbon Isotope Stratigraphy

Darren R. Gröcke , in Stratigraphy & Timescales, 2020

1.two Definition of isotope stratigraphy

Isotope stratigraphy can be broadly defined equally the variation of a stable isotope signature preserved in the sedimentary record through a period of time. Information technology is a sub-discipline of chemostratigraphy that looks at the chemical signature of sediments through fourth dimension; most chemostratigraphic studies, however, apply stratigraphic changes in trace element and rare earth element abundances to define and correlate sedimentary packages (east.g., Hines et al., 2019; LaGrange et al., 2020; Mackey and Stewart, 2019). With respect to the definition of isotope stratigraphy, time can be divers equally anything greater than seasonal, and therefore include research in many other disciplines, such every bit limnology, glaciology, archeology and pedology. Isotope stratigraphy also relies on similar principles in Darwin's theory of development. That is, in order for isotope stratigraphy to work and be informative nigh the history of biogeochemical cycles, it must rely on the fact that the stable isotope ratio (δX, where X is whatsoever isotope organisation of interest, east.m., ¹³C or ¹⁵Northward or ³⁴S) volition evolve/alter through time, and those changes are dictated past climate/ecology changes in that global wheel.

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Physical Properties of H2o

K.1000. Stewart , in Encyclopedia of Inland Waters, 2009

Isotopes

An isotope is one of two or more forms of the same chemical element. Unlike isotopes of an chemical element accept the aforementioned number of protons in the nucleus, giving them the same diminutive number, but a dissimilar number of neutrons giving each elemental isotope a different atomic weight. Isotopes of the same chemical element have different physical properties (melting points, boiling points) and the nuclei of some isotopes are unstable and radioactive. For water (H ₂O), the elements hydrogen (atomic number one) and oxygen (atomic number sixteen) each have three isotopes: ^aneH, ²H, and ³H for hydrogen; ¹⁶O, ¹⁷O, and ¹⁸O for oxygen. In nature, the ¹H and ^xviO (commonly simply given equally O) isotopes are by far the most common. In water, the water molecule may be given equally ¹H₂O or hydrogen oxide, ⁱⁱH₂O or deuterium oxide, and ³H₂O or tritium oxide, the radioactive i. Both of the latter two are sometimes chosen heavy water because of their increased mass. Still, the phrase 'heavy water' gained notoriety primarily because of the clan of ²H₂O or deuterium oxide, also called the deuterated class of h2o, in the evolution of nuclear weapons. Many elements take isotopes, simply the isotopes of hydrogen and oxygen are of particular interest because fractionation occurs in vapor–liquid–solid phase changes. Heavier molecular 'species' tend to exist enriched in the condensation phase and lighter molecular 'species' in the vapor phase. Some isotopes tin be used to bang-up advantage as tracers in understanding water movements and exchanges within atmospheric, oceanic, lake, stream, and ground h2o systems.

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Book 5

Yan Hu , Fang-Zhen Teng , in Encyclopedia of Geology (2nd Edition), 2021

Mass-Independent Isotope Fractionation

Isotope fractionation in most terrestrial and extraterrestrial samples is mass-dependent, i.e., the magnitude of fractionation amongst iii or more isotopes directly depends on their mass differences. For example, mass difference between ¹⁷O and ¹⁶O is almost half of that between ¹⁸O and ^sixteenO, hence the fractionation between ¹⁷O and ¹⁶O is almost half of that of ¹⁸O and ¹⁶O. However, studies of extraterrestrial materials by Clayton et al. (1973) revealed the kickoff mass-independent fractionation of O isotopes, originally interpreted as a event of nucleosynthetic effect and later explained by the involvement of photochemical reactions (Dauphas and Schauble, 2016). Subsequent studies also observed large mass-contained fractionation of S isotopes in geological record (Farquhar and Wing, 2003), which was as well produced primarily by photochemical reactions.

Many non-traditional stable isotopes have loftier atomic numbers with more than two stable isotopes, which allows studies of mass-contained fractionation. Mercury isotopes display the nigh significant mass-independent isotope fractionation amongst both odd and even isotopes, reflecting magnetic isotope effects and nuclear volume effects during photochemical reactions (Blum et al., 2014). Non-traditional stable isotopes of many other heavy elements (e.g., Cr, Ni, Mo, Ba, Nd) also display mass-independent fractionation in meteorites. These isotopic anomalies mainly result from nucleosynthetic effects during formation of the Solar System (Dauphas and Schauble, 2016); chapters dedicated to nucleosynthesis (Yokoyama and Tsujimoto) and nucleosynthetic heterogeneities in meteorites (Steele) tin be found in this Encyclopedia.

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Volume 5

Jennifer C. Stern , Scott T. Wieman , in Encyclopedia of Geology (Second Edition), 2021

Equilibrium and Kinetic Isotope Fractionation

Isotope fractionations are usually discussed in terms of whether they are equilibrium or kinetic processes. These two designations comprehend most fractionations, with kinetic fractionation referring to a broad range of non-equilibrium processes such every bit evaporation and diffusion. Equilibrium isotope fractionation occurs primarily due to differences in vibrational frequencies of isotopologues, and as such is a function of temperature. The consequence of this is that heavier isotopes form stronger bonds than light isotopes, and at equilibrium, the heavier isotope volition partition into the phase with the stronger bail ( White, 2015). Isotope fractionation is large at Globe's surface temperatures and decreases with increasing temperature until α approaches 1 at igneous temperatures. This temperature dependence forms the basis for stable isotope geothermometry and paleothermometry. Equilibrium fractionation factors can be predicted by quantum statistical mechanics (Chacko et al., 2001), although nigh fractionation factors in stable isotope geochemistry have also been adamant experimentally.

Kinetic isotope fractionation is caused by uni-directional reactions such as distillation, evaporation, diffusion, crystallization, and redox reactions. In these reactions, lighter isotopes, because they grade weaker bonds that are more readily broken, react faster than heavier isotopes. Biological reactions in particular tin can showroom large kinetic fractionation effects and these large fractionations tin can be used as tracers of biological action and specific metabolic processes.

Fractionations are likewise dependent on whether the system is open, and product is removed or cannot back-react, or closed, and products may dorsum-react. Rayleigh fractionation or distillation describes open up system equilibrium fractionation and kinetic fractionation by uni-directional reactions with a finite source of reactant, which is functionally analogous to open arrangement equilibrium reactions where products are removed and not allowed to back react . Rayleigh fractionation can be expressed as the equation:

(half-dozen) $R = R_{0} \cdot f^{(α - 1)}$

where R, the isotopic composition of a phase is a part of the initial isotope ratio R₀, the fraction of material f remaining in the reservoir, and the fractionation factor α. Fig. 1 shows Rayleigh fractionation of water during evaporation, a kinetic procedure that can be described past the Rayleigh equation. As water with R₀ = 0‰ evaporates (bend A), the residual water becomes heavier due to the removal of the light isotope, following Eq. six. The δ^xviiiO of instantaneous vapor (curve B) is 10‰ lighter than the residual water, but also becomes heavier as the reaction progresses. The accumulated vapor (bend C) does not exceed the fractionation dictated by the equilibrium fractionation factor between water and water vapor at a given temperature. Closed arrangement equilibrium fractionation is demonstrated by lines D and E.

Near isotope fractionation is mass dependent. When in that location are more than two stable isotopes of an chemical element, such as oxygen or sulfur, isotope fractionations between unlike pairs of isotope ratios (e.g., ¹⁶O/¹⁷O and ¹⁶O/¹⁸O) tin be predicted based on the relative mass difference between the isotopes and are therefore called mass dependent isotope fractionations. When fractionation significantly deviates from this relationship, it is called mass independent fractionation (MIF). For instance, the mass dependent fractionation between the iii isotopes of oxygen can exist predicted by the relationship δ¹⁷O ≈ 0.5 δ^eighteenO, reflecting the relative mass differences betwixt ¹⁶O, ¹⁷O, and ¹⁸O. The line with slope ≈ 0.5 produced by plotting δ¹⁷O vs. δ^eighteenO is referred to as the terrestrial fractionation line. When this slope departs significantly from the prediction, fractionation is caused past something other than, or addition to, mass difference. MIF is reported using Δ or cap delta, which represents the difference between the expected mass-dependent fractionation and the actual fractionation measured.

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