Nuclear Volume Effect Research Articles

Mercury Isotope Fractionation during Dark Abiotic Reduction of Hg(II) by Dissolved, Surface-Bound, and Structural Fe(II).

Stable mercury (Hg) isotope ratios are an emerging tracer for biogeochemical transformations in environmental systems, but their application requires knowledge of isotopic enrichment factors for individual processes. We investigated Hg isotope fractionation during dark, abiotic reduction of Hg(II) by dissolved iron(Fe)(II), magnetite, and Fe(II) sorbed to boehmite or goethite by analyzing both the reactants and products of laboratory experiments. For homogeneous reduction of Hg(II) by dissolved Fe(II) in continuously purged reactors, the results followed a Rayleigh distillation model with enrichment factors of -2.20 ± 0.16‰ (ε202Hg) and 0.21 ± 0.02‰ (E199Hg). In closed system experiments, allowing reequilibration, the initial kinetic fractionation was overprinted by isotope exchange and followed a linear equilibrium model with -2.44 ± 0.17‰ (ε202Hg) and 0.34 ± 0.02‰ (E199Hg). Heterogeneous Hg(II) reduction by magnetite caused a smaller isotopic fractionation (-1.38 ± 0.07 and 0.13 ± 0.01‰), whereas the extent of isotopic fractionation of the sorbed Fe(II) experiments was similar to the kinetic homogeneous case. Small mass-independent fractionation of even-mass Hg isotopes with 0.02 ± 0.003‰ (E200Hg) and ≈ -0.02 ± 0.01‰ (E204Hg) was consistent with theoretical predictions for the nuclear volume effect. This study contributes significantly to the database of Hg isotope enrichment factors for specific processes. Our findings show that Hg(II) reduction by dissolved Fe(II) in open systems results in a kinetic MDF with a larger ε compared to other abiotic reduction pathways, and combining MDF with the observed MIF allows the distinction from photochemical or microbial Hg(II) reduction pathways.

Mass-independent Sn isotope fractionation and radiogenic 115Sn in chondrites and terrestrial rocks

Tin has ten stable isotopes, providing the opportunity to investigate and discriminate nucleosynthetic isotope anomalies from mass-dependent and mass-independent isotope fractionation. Novel protocols for chemical separation (based on TBP-resin) and MC-ICP-MS analyses are reported here for high precision Sn isotope measurements on terrestrial rocks and chondrites. Relative to the Sn reference standard (NIST SRM 3161a), terrestrial basalts and chondrites show isotope patterns that are consistent with mass-dependent and mass-independent isotope fractionation processes as well as with 115Sn radiogenic ingrowth from 115In.Two different mass-independent isotope effects are identified, namely the nuclear volume (or nuclear field shift) and the magnetic isotope effect. The magnetic isotope effect dominates in the two measured ordinary chondrites, while repeated analyses of the carbonaceous chondrite Murchison (CM2) display a pattern consistent with a nuclear volume effect. Terrestrial basalts show patterns that are compatible with a mixture of nuclear volume and magnetic isotope effects. The ultimate origin of the isotope fractionation is unclear but a fractionation induced during sample preparation seems unlikely because different groups of chondrites show distinctly different patterns, hence pointing towards natural geo/cosmochemical processes. Only the carbonaceous chondrite Murchison (CM2) shows a Sn isotope pattern similar to what expected for nucleosynthetic variations. However, this pattern is better reproduced by nuclear volume effects. Thus, after considering mass-independent and mass-dependent effects, we find no evidence of residual nucleosynthetic anomalies, in agreement with observations for most other elements with similar half-mass condensation temperatures.Most chondrites show a deficit in 115Sn/120Sn (typically −150 to −200 ppm) relative to terrestrial samples, with the exception of one ordinary chondrite that displays an excess of about +250 ppm. The 115Sn/120Sn data correlate with In/Sn, being consistent with the β− decay of 115In over the age of the solar system. This represents the first evidence of the 115In-115Sn decay system in natural samples. The radiogenic 115Sn signature of the BSE derives from a suprachondritic In/SnBSE, which reflects preferential partitioning of Sn into the Earth’s core.

Nuclear volume isotope fractionation of europium and other lanthanide elements

The nuclear volume component of equilibrium field shift isotope fractionations in europium and other lanthanide elements is estimated using Mössbauer spectroscopy and electronic structure calculations. This effect goes in the opposite direction from equilibrium mass-dependent fractionation, and in the case of europium is predicted to dominate over mass dependent fractionation for most materials. Including both effects, Eu2+-bearing species will have approximately 0.4-1‰ higher 153Eu/151Eu than Eu3+-bearing species at 25ºC (298 K), and about 0.3‰ higher 153Eu/151Eu at 700ºC (973 K). Field shift fractionation mainly depends on oxidation state; differences in coordination structure without changes in oxidation state appear to have much weaker associated fractionations. Nuclear volume isotope fractionation will become even more dominant over mass dependent fractionation at higher temperatures because nuclear volume effects scale with 1/T (K), vs. 1/T2 for mass-dependent fractionation. Fractionation favoring high 153Eu/151Eu in minerals that preferentially incorporate Eu2+, such as plagioclase, is consistent with recent measurements on igneous rocks showing low 153Eu/151Eu in samples with large negative europium anomalies (Lee and Tanaka, 2021). The present results agree with the recent conclusion that equilibrium fractionation cannot explain cosmochemical REE fractionations in primitive meteoritical materials (Hu et al., 2021), because the net fractionation is too small (~0.2‰ or less) at temperatures >1200 K where vapor-phase REE species are relevant.

Sources and Transformation Mechanisms of Atmospheric Particulate Bound Mercury Revealed by Mercury Stable Isotopes.

This study examined the isotopic composition of particulate bound mercury (PBM) in 10 Chinese megacities and explored the associated sources and transformation mechanisms. PBM in these cities was characterized by negative δ202Hg (mean: -2.00 to -0.78‰), slightly negative to highly positive Δ199Hg (mean: -0.04 to 0.47‰), and slightly positive Δ200Hg (mean: 0.02 to 0.06‰) values. The positive PBM Δ199Hg signatures were likely caused by physiochemical reactions in aerosols. The Δ199Hg/Δ201Hg ratio varied from 0.94 to 1.39 in the cities and increased with the increase in the corresponding mean Δ199HgPBM value. We speculate that, in addition to the photoreduction of oxidized Hg, other transformation mechanisms in aerosols (e.g., isotope exchange, complexation, and oxidation, which express nuclear volume effects) also shape the Δ199HgPBM signatures in the present study. These processes are likely enhanced in the presence of strong gas-particle partitioning of gaseous oxidized Hg (GOM) and elevated levels of redox active metals (e.g., Fe), halides, and elemental carbon. Based on Δ200HgPBM data presented in this and previous studies, we estimate that large proportions (∼47 ± 22%) of PBM were sourced from the oxidation of gaseous elemental Hg followed by the partitioning of GOM onto aerosols globally, indicating the transformation of Hg(0) to PBM as an important sink of atmospheric Hg(0).

Theory and Calculation of Nontraditional Stable Isotope Fractionation

This paper conducts processing on isotope anharmonic effect with molecular dynamics method and Monte Carlo method based on path integration. It introduces the theoretical calculation method of pressure effect, and finally the nuclear volume effect and its theoretical calculation method, stressing that the nuclear volume effect is an important part of isotopic studies of heavy metals in the future. This paper makes an analysis on the equilibrium fractionation theory based on simple harmonic approximation.

Equilibrium mercury and lead isotope fractionation caused by nuclear volume effects in crystals

To investigate equilibrium mercury (Hg) and lead (Pb) isotope fractionation caused by the nuclear volume effect (NVE) in crystals, the electron densities at nuclei (i.e., |Ψ(0)|2) for Hg- or Pb-bearing crystalline compounds were investigated by using the relativistic spin orbit zeroth-order regular approximation (ZORA) method with a three-dimensional periodic boundary condition based on the density functional theory (DFT). Many isotope fractionation factors of crystalline compounds are provided for the first time. Our results show, even at 1000 °C, NVE-driven Hg and Pb isotope fractionation are meaningfully large, i.e., range from 0.12‰ to 0.49‰ (202Hg/198Hg), from − 0.20‰ to 0.17‰ (208Pb/206Pb) and from − 0.08‰ to 0.06‰ (207Pb/206Pb) relative to Hg0 vapor and Pb0 vapor, respectively. Specifically, the fractionations range from − 0.06‰ to − 0.20‰ (208Pb/206Pb) and from − 0.02‰ to − 0.08‰ (207Pb/206Pb) for Pb2+-bearing species, from 0.10‰ to 0.17‰ (208Pb/206Pb) and from 0.04‰ to 0.06‰ (207Pb/206Pb) for Pb4+-bearing species in crystals. All calculated Hg-bearing species in crystals will enrich heavier isotope (202Hg) relative to Hg0 vapor. Meanwhile, Pb4+-bearing species enrich heavier Pb isotopes (208Pb and 207Pb) than Pb2+-bearing species in crystals, which the enrichment can be up to 0.37‰ (208Pb/206Pb) and 0.14‰ (207Pb/206Pb) at 1000 °C, due to their NVEs are in opposite directions. The NVE-driven MIFs of Hg isotopes, which are compared to the Hg202- Hg198 baseline, are up to − 0.158‰ ( $$\Delta {}_{{{\text{NV}}}}^{199} {\text{Hg}}$$ ), − 0.024‰ ( $$\Delta {}_{{{\text{NV}}}}^{200} {\text{Hg}}$$ ) and − 0.094‰ ( $$\Delta {}_{{{\text{NV}}}}^{201} {\text{Hg}}$$ ) relative to Hg0 vapor at 500 °C. For all studied Hg-bearing species in crystals, the MIFs of two odd-mass isotopes (i.e., $$\Delta {}_{{{\text{NV}}}}^{199} {\text{Hg}}$$ and $$\Delta {}_{{{\text{NV}}}}^{201} {\text{Hg}}$$ ) will be changed proportionally and their ratio (i.e., $$\Delta {}_{{{\text{NV}}}}^{199} {\text{Hg}}$$ / $$\Delta {}_{{{\text{NV}}}}^{201} {\text{Hg}}$$ ) will be a constant 1.67. The NVE can also cause mass-independent fractionations for 207Pb and 204Pb compared to the baseline of 208Pb and 206Pb. The largest NVE-driven MIFs are 0.043‰ ( $$\Delta {}_{{{\text{NV}}}}^{207} {\text{Pb}}$$ ) and − 0.040‰ ( $$\Delta {}_{{{\text{NV}}}}^{204} {\text{Pb}}$$ ) among all the studied species relative to Pb0 vapor at 500 °C. The magnitudes of odd-mass isotope MIF ( $$\Delta {}_{{{\text{NV}}}}^{207} {\text{Pb}}$$ ) and even-mass isotope MIF ( $$\Delta {}_{{{\text{NV}}}}^{204} {\text{Pb}}$$ ) are almost the same but with opposite signs, leading to the MIF ratio of them (i.e., $$\Delta {}_{{{\text{NV}}}}^{207} {\text{Pb}}$$ / $$\Delta {}_{{{\text{NV}}}}^{204} {\text{Pb}}$$ ) is − 1.08.

Isotope signatures of atmospheric mercury emitted from residential coal combustion

Residential coal combustion (RCC) is a major source of atmospheric mercury (Hg) in rural areas of China, but little is known about the isotope signatures of Hg from this source. In the present study, the isotope compositions of speciated Hg (Hg0, Hg2+, and Hgp) in flue gas emitted from RCC were investigated in two important coal-producing areas (Xingren (XR) and Jinsha (JS)) of Guizhou Province, Southwest China. The total Hg concentration in discharged flue gas is in the range of 1.80–9.65 μg/m3 at the two sites, and the emission ratio reaches 99.87%. Isotope signatures of total Hg in flue gas are similar to those of Hg in feed coal, with near-zero Δ199Hg and negative δ202Hg (−1.47‰ for XR and −3.00‰ for JS) in discharged flue gas. Such isotope signatures are very different from those of Hg emissions from modern coal-fired power plants with much higher δ202Hg signals. Negative shifts from Hg0 to Hg2+ in flue gas for δ202Hg (−0.94‰) and Δ199Hg (−0.51‰) were observed, suggesting that both mass-dependent fractionation and mass-independent fractionation occurred during RCC. The nuclear volume effect produced by chlorine oxidation of Hg0 to Hg2+ may play an important role in the observed mass-independent fractionation in Hg2+. Without any air pollution control devices, RCC potentially increases the atmospheric Hg levels and has a negative-shifting impact on the δ202Hg of atmospheric Hg.

New evidence for atmospheric mercury transformations in the marine boundary layer from stable mercury isotopes

Abstract. The marine boundary layer (MBL) is the largest transport place and reaction vessel of atmospheric mercury (Hg). The transformations of atmospheric Hg in the MBL are crucial for the global transport and deposition of Hg. Herein, Hg isotopic compositions of total gaseous mercury (TGM) and particle-bound Hg (PBM) collected during three cruises to Chinese seas in summer and winter were measured to reveal the transformation processes of atmospheric Hg in the MBL. Unlike the observation results at inland sites, isotopic compositions of TGM in the MBL were affected not only by mixing continental emissions but also largely by the oxidation of Hg0 primarily derived by Br atoms. Δ199Hg values of TGM were significantly positively correlated with air temperature in summer, indicating that processes inducing positive mass-independent fractionation of odd isotopes in TGM could be more active at low temperatures, while the relative processes might be weak in winter. In contrast, the positive Δ199Hg and high ratios of Δ199Hg∕Δ201Hg in PBM indicated that alternative oxidants other than Br or Cl atoms played a major role in the formation of Hg(II) in PBM, likely following the nuclear volume effect. Our results suggest the importance of local Hg environmental behaviors caused by an abundance of highly reactive species and provide new evidence for understanding the complicated transformations of atmospheric Hg in the MBL.

Stable Mercury Isotope Transition during Postdepositional Decomposition of Biomass in a Forest Ecosystem over Five Centuries.

Organic soil is an important transient reservoir of mercury (Hg) in terrestrial ecosystems, but the fate of deposited Hg in organic forest soil is poorly understood. To understand the dynamic changes of deposited Hg on forest floor, the composition of stable Hg and carbon (C) isotopes in decomposing litters and organic soil layer was measured to construct the 500 year history of postdepositional Hg transformation in a subtropical evergreen broad-leaf forest in Southwest China. Using the observational data and a multiprocess isotope model, the contributions of microbial reduction, photoreduction, and dark reduction mediated by organic matter to the isotopic transition were estimated. Microbial reduction and photoreduction play a dominant role in the initial litter decomposition during first 2 years. Dark redox reactions mediated by organic matter become the predominant process in the subsequent 420 years. After that, the values of Hg mass dependent fractionation (MDF), mass independent fractionation (MIF), and Δ199Hg/Δ201Hg ratio do not change significantly, indicating sequestration and immobilization of Hg in soil. The linear correlations between the isotopic signatures of Hg and C suggest that postdepositional transformation of Hg is closely linked to the fate of natural organic matter (NOM). Our findings are consistent with the abiotic dark reduction driven by nuclear volume effect reported in boreal and tropical forests. We recommend that the dark reduction process be incorporated in future model assessment of the global Hg biogeochemical cycle.

Mercury Isotope Fractionation during the Photochemical Reduction of Hg(II) Coordinated with Organic Ligands.

The photochemical reduction of Hg(II) is an important pathway in the environmental Hg cycle because it competes with Hg methylation and potentially limits the formation of bioaccumulative methylmercury. Hg stable isotope systematics have proven to be an effective tool for investigating the transport, transformation, and bioaccumulation of Hg. The dominant cause of mass independent isotope fractionation (MIF) of Hg in nature is the photochemical reduction of various species of Hg(II). However, it is difficult to fully interpret Hg stable isotope signatures due to the lack of mechanistic information about which Hg compounds are susceptible to MIF and why. This study investigates Hg isotope fractionation during the photochemical reduction of Hg(II) complexed to organic ligands, which are representative of the available binding sites in natural dissolved organic matter. The photochemical reduction of Hg(II) in the presence of cysteine resulted in both negative and positive MIF in residual Hg(II), where the sign depended on pH and dissolved oxygen level. In the presence of serine, either nuclear volume or magnetic isotope effects were observed depending on the wavelength of light and the extent of Hg(II) complexation by serine. In the presence of ethylenediamine, MIF was negative. Our Hg stable isotope results suggest that MDF and MIF are induced at different steps in the overall photochemical reduction reaction and that MIF does not depend on the rate-determining step but instead depends on photophysical aspects of the reaction such as intersystem crossing and hyperfine coupling. The behavior of Hg isotopes reported here will allow for a better understanding of the underlying reaction mechanisms controlling the Hg isotope signatures recorded in natural samples.

Uniform 182W isotope compositions in Eoarchean rocks from the Isua region, SW Greenland: The role of early silicate differentiation and missing late veneer

Abstract Eoarchean rocks from the Isua region in southern West Greenland are known to exhibit isotope anomalies of 182W and 142Nd. The excess 182W in many rocks from the Isua region have been explained by two endmember models: (1) missing late veneer or (2) silicate differentiation shortly after Earth’s formation. Furthermore, it has been proposed that pristine W isotope systematics in rocks from the Isua region (herein the Isua supracrustal belt and adjacent area) have been obscured by metamorphic disturbance. To address these issues, we present a comprehensive dataset, combining high precision 182W isotope data with trace element data, including high precision elemental W-Th-U-Ta abundance data. We present an improved analytical protocol that allows processing gram-sized samples with W abundances in the lower ng/g range. This protocol also results in markedly improved ion exchange column yields and cleaner W fractions, thereby minimizing nuclear volume effects on 183W. To compare with previous studies, our dataset includes some samples from previously investigated units in the Isua region (Isua Supracrustal Belt (ISB) mafic–ultramafic assemblages and Ameralik dikes). In addition, several Eoarchean key units in the Isukasia terrane (Isua region) and the Faeringehavn terrane (Nuuk region) have been examined for their W isotope composition in this study for the first time. These newly investigated units include recently recognized mantle-like peridotites from both terranes that display PGE abundances and patterns similar to modern depleted mantle peridotites, felsic lithologies from the ISB, as well as key amphibolite and TTG localities from low-strain domains south of the ISB. Virtually all rocks from the Isua region show significant W enrichment with W/Th of up to 160 in mafic to ultramafic samples. None of the samples from SW Greenland that were object of 182W isotope analysis in this study and virtually all previous studies appear to have preserved near canonical W/Th ratios (i.e., between 0.09 and 0.24). Independent of W enrichment, however, it can now be shown that there is a uniform 182W isotope excess in the different rock types from the Itsaq Gneiss Complex (IGC) (average 12.8 ppm ± 1 ppm, 95% confidence interval). Importantly, none of the rock suites investigated exhibit modern mantle-like 182W isotope signatures of µ182W = 0. By combining 182W signatures in the different lithologies with elemental W systematics, we therefore can infer that the 182W excess in Eoarchean rocks from the Isua region is widespread, and independent of W enrichment. Hence, we regard the 182W excess as an intrinsic feature of the Eoarchean assemblages in the Isua region. Notably, mantle-like peridotites from both the Isukasia and Faeringehavn terranes display the same 182W excess, as all other units, although they have been shown to display the full inventory of Highly Siderophile Elements (HSE) found in Phanerozoic mantle peridotites. Evidently, the W isotope budget in these rocks is clearly decoupled from HSE systematics, which hampers a straightforward explanation for 182W isotope excesses in terms of the missing late veneer model. As Platinum Group Element (PGE) patterns in mantle-like Eoarchean peridotites from the Isua region are similar to those in Phanerozoic rocks, we rather propose that to a large extent the 182W excesses are a vestige of early silicate differentiation processes, in line with positive 142Nd anomalies found in rocks from the Isua region, suggesting initial silicate differentiation prior to 4.50 Ga.

Equilibrium thallium isotope fractionation and its constraint on Earth’s late veneer

Equilibrium isotope fractionation of thallium (Tl) includes the traditional mass-dependent isotope fractionation effect and the nuclear volume effect (NVE). The NVE dominates the overall isotope fractionation, especially at high temperatures. Heavy Tl isotopes tend to be enriched in oxidized Tl3+-bearing species. Our NVE fractionation results of oxidizing Tl+ to Tl3+ can explain the positive enrichments observed in ferromanganese sediments. Experimental results indicate that there could be 0.2–0.3 e-unit fractionation between sulfides and silicates at 1650 °C. It is consistent with our calculation results, which are in the range of 0.17–0.38 e-unit. Importantly, Tl’s concentration in the bulk silicate Earth (BSE) can be used to constrain the amount of materials delivered to Earth during the late veneer accretion stage. Because the Tl concentration in BSE is very low and its Tl isotope composition is similar with that of chondrites, suggesting either no Tl isotope fractionation occurred during numerous evaporation events, or the Tl in current BSE was totally delivered by late veneer. If it is the latter, the Tl-content-based estimation could challenge the magnitude of late veneer which had been constrained by the amount of highly siderophile elements in BSE. Our results show that the late-accreted mass is at least five-times larger than the previously suggested magnitude, i.e., 0.5 wt% of current Earth’s mass. The slightly lighter 205Tl composition of BSE relative to chondrites is probable a sign of occurrence of Tl-bearing sulfides, which probably were removed from the mantle in the last accretion stage of the Earth.

Mercury Stable Isotope Fractionation during Abiotic Dark Oxidation in the Presence of Thiols and Natural Organic Matter.

Mercury (Hg) stable isotope fractionation has been widely used to trace Hg sources and transformations in the environment, although many important fractionation processes remain unknown. Here, we describe Hg isotope fractionation during the abiotic dark oxidation of dissolved elemental Hg(0) in the presence of thiol compounds and natural humic acid. We observe equilibrium mass-dependent fractionation (MDF) with enrichment of heavier isotopes in the oxidized Hg(II) and a small negative mass-independent fractionation (MIF) owing to nuclear volume effects. The measured enrichment factors for MDF and MIF (ε202Hg and E199Hg) ranged from 1.10‰ to 1.56‰ and from -0.16‰ to -0.18‰, respectively, and agreed well with theoretically predicted values for equilibrium fractionation between Hg(0) and thiol-bound Hg(II). We suggest that the observed equilibrium fractionation was likely controlled by isotope exchange between Hg(0) and Hg(II) following the production of the Hg(II)-thiol complex. However, significantly attenuated isotope fractionation was observed during the initial stage of Hg(0) oxidation by humic acid and attributed to the kinetic isotope effect (KIE). This research provides additional experimental constraints on interpreting Hg isotope signatures with important implications for the use of Hg isotope fractionation as a tracer of the Hg biogeochemical cycle.

Mercury Isotopes in Earth and Environmental Chemistry

In Earth and environmental chemistry magnetic isotopes are the universal means to identify reaction mechanisms. Mass-independent fractionation of isotopes as a signature of mechanism occurs by two ways: first, via magnetic isotope effect (MIE), which is controlled by magnetic, or hyperfine, coupling between unpaired electrons and magnetic nuclei in paramagnetic species (in radicals, particularly), and, second, via nuclear volume effect (NVE), which is induced by the difference in volumes of isotopic nuclei. MIE is the dependence of the reaction rates on the nuclear magnetic moment of reactants and fractionates magnetic and nonmagnetic isotopes; NVE fractionates isotopes with different nuclear volumes. Both effects, MIE and NVE, are supposed to coexist in condensed phases. Decisive test for their differentiation is illustrated by example of radical pairs with mercury nuclei: if isotope fractionation is controlled by MIE, the ratio Δ201Hg/Δ199Hg is expected to be in the limits 1.05–1.25 for isotopic enrichment and 0.80–0.92 for impoverishment. If isotope fractionation is controlled by NVE, this ratio is estimated to be in the range 0.50–0.62. In contrast to MIE-induced two-directional fractionation, which is controlled by direction of coherent spin conversion of radical pair (triplet–singlet or vice versa), the NVE induces one-directional, universal isotope fractionation, almost independent on the reaction mechanism.

Mercury isotope fractionation during transfer from post-desulfurized seawater to air

Samples of dissolved gaseous mercury (DGM) in the post-desulfurized seawater discharged from a coal-fired power plant together with samples of gaseous elemental mercury (GEM) over the post-desulfurized seawater surface were collected and analyzed to study the mercury isotope fractionation during transfer from post-desulfurized seawater to air. Experimental results showed that when DGM in the seawater was converted to GEM in the air, the δ202Hg and Δ199Hg values were changed, ranging from −2.98 to −0.04‰ and from −0.31 to 0.64‰, respectively. Aeration played a key role in accelerating the transformation of DGM to GEM, and resulted in light mercury isotopes being more likely to be enriched in the GEM. The ratio Δ199Hg/Δ201Hg was 1.626 in all samples, suggesting that mercury mass independent fractionation occurred owing to the nuclear volume effect during the transformation. In addition, mass independent fractionation of mercury even isotopes was found in the GEM above the post-desulfurized seawater surface in the aeration pool.

Mass-Dependent and -Independent Fractionation of Mercury Isotope during Gas-Phase Oxidation of Elemental Mercury Vapor by Atomic Cl and Br.

This study presents the first measurement of Hg stable isotope fractionation during gas-phase oxidation of Hg(0) vapor by halogen atoms (Cl(•), Br(•)) in the laboratory at 750 ± 1 Torr and 298 ± 3 K. Using a relative rate technique, the rate coefficients for Hg(0)+Cl(•) and Hg(0)+Br(•) reactions are determined to be (1.8 ± 0.5) × 10(-11) and (1.6 ± 0.8) × 10(-12) cm(3) molecule(-1) s(-1), respectively. Results show that heavier isotopes are preferentially enriched in the remaining Hg(0) during Cl(•) initiated oxidation, whereas being enriched in the product during oxidation by Br(•). The fractionation factors for (202)Hg/(198)Hg during the Cl(•) and Br(•) initiated oxidations are α(202/198) = 0.99941 ± 0.00006 (2σ) and 1.00074 ± 0.00014 (2σ), respectively. A Δ(199)Hg/Δ(201)Hg ratio of 1.64 ± 0.30 (2σ) during oxidation of Hg(0) by Br atoms suggests that Hg-MIF is introduced by the nuclear volume effect (NVE). In contrast, the Hg(0) + Cl(•) reaction produces a Δ(199)Hg/Δ(201)Hg-slope of 1.89 ± 0.18 (2σ), which in addition to a high degree of odd-mass-number isotope MIF suggests impacts from MIF effects other than NVE. This reaction also exhibits significant MIF of (200)Hg (Δ(200)Hg, up to -0.17‰ in the reactant) and is the first physicochemical process identified to trigger (200)Hg anomalies that are frequently detected in atmospheric samples.

Nuclear volume effects in equilibrium stable isotope fractionations of mercury, thallium and lead.

The nuclear volume effects (NVEs) of Hg, Tl and Pb isotope systems are investigated with careful evaluation on quantum relativistic effects via the Dirac’s formalism of full-electron wave function. Equilibrium 202Hg/198Hg, 205Tl/203Tl, 207Pb/206Pb and 208Pb/206Pb isotope fractionations are found can be up to 3.61‰, 2.54‰, 1.48‰ and 3.72‰ at room temperature, respectively, larger than fractionations predicted by classical mass-dependent isotope fractionations theory. Moreover, the NVE can cause mass-independent fractionations (MIF) for odd-mass isotopes and even-mass isotopes. The plot of vs. for Hg-bearing species falls into a straight line with the slope of 1.66, which is close to previous experimental results. For the first time, Pb4+-bearing species are found can enrich heavier Pb isotopes than Pb2+-bearing species to a surprising extent, e.g., the enrichment can be up to 4.34‰ in terms of 208Pb/206Pb at room temperature, due to their NVEs are in opposite directions. In contrast, fractionations among Pb2+-bearing species are trivial. Therefore, the large Pb fractionation changes provide a potential new tracer for redox conditions in young and closed geologic systems. The magnitudes of NVE-driven even-mass MIFs of Pb isotopes (i.e., ) and odd-mass MIFs (i.e., ) are almost the same but with opposite signs.

Theoretical Study of Isotope Enrichment Caused by Nuclear Volume Effect

Isotope separation is important in industry, such as uranium enrichment. It is also very important in geochemistry and cosmo-chemistry because heavy and light isotopes are gradually fractionated in global equilibrium processes. For isotopes of heavy elements such as uranium and gadolinium, this fractionation occurs mainly owing to the difference of nuclear charge radii between the isotopes. This is because electronic states of isotopologues are different because of the difference of nuclear charge radii. Nuclear volume terms (lnKnv) in the equilibrium constants of isotope fractionations can be calculated from the electronic energy difference of isotopologues, obtained by relativistic quantum chemical calculations with finite-size nuclear models. In this review, we summarize our theoretical results in uranium isotope separations, using U (III)-U (IV) and U (IV)-U (VI) redox reaction systems. Calculated nuclear volume term (lnKnv) is reasonably close to the ones estimated from experimental analysis of temperature dependence in equilibrium constants. We used the four-component Dirac-Coulomb Hartree-Fock method with the Fermi and Gaussian-type nuclear models in our calculations. We also briefly mention how the nuclear volume effect is important in geochemistry or cosmo-chemistry referring to recent relevant works.

Theoretical study on K, L, and M X-ray transition energies and rates of neptunium and its ions

The transition energies and electric dipole (E1) transition rates of the K, L, and M lines in neutral Np have been theoretically determined from the MultiConfiguration Dirac—Fock (MCDF) method. In the calculations, the contributions from Breit interaction and quantum electrodynamics (QED) effects (vacuum polarization and self-energy), as well as nuclear finite mass and volume effects, are taken into account. The calculated transition energies and rates are found to be in good agreement with other experimental and theoretical results. The accuracy of the results is estimated and discussed. Furthermore, we calculated the transition energies of the same lines radiating from the decaying transitions of the K-, L-, and M-shell hole states of Np ions with the charge states Np1+ to Np6+ for the first time. We found that for a specific line, the corresponding transition energies relating to all the Np ions are almost the same; it means the outermost electrons have a very small influence on the inner-shell transition processes.

Ris3: A program for relativistic isotope shift calculations

An atomic spectral line is characteristic of the element producing the spectrum. The line also depends on the isotope. The program ris3 (Relativistic Isotope Shift) calculates the electron density at the origin and the normal and specific mass shift parameters. Combining these electronic quantities with available nuclear data, isotope-dependent energy level shifts are determined. Program summaryProgram title:ris3Catalogue identifier: ADEK_v2_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADEK_v2_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 5147No. of bytes in distributed program, including test data, etc.: 32869Distribution format: tar.gzProgramming language: Fortran 77.Computer: HP ProLiant BL465c G7 CTO.Operating system: Centos 5.5, which is a Linux distribution compatible with Red Hat Enterprise Advanced Server.Classification: 2.1.Catalogue identifier of previous version: ADEK_v1_0Journal reference of previous version: Comput. Phys. Comm. 100 (1997) 81Subprograms used:Cat IdTitleReferenceADZL_v1_1grasp2K VERSION 1_1to be publishedDoes the new version supersede the previous version?: YesNature of problem:Prediction of level and transition isotope shifts in atoms using four-component relativistic wave functions.Solution method:The nuclear motion and volume effects are treated in first order perturbation theory. Taking the zero-order wave function in terms of a configuration state expansion |ΨPJMJ〉=∑μcμ|Φ(γμPJMj)〉, where P, J and MJ are, respectively, the parity and angular quantum numbers, the electron density at the nucleus and the normal and specific mass shift parameters may generally be expressed as ∑μ,νcμcν〈γμPJMj|V|γνPJMj〉 where V is the relevant operator. The matrix elements, in turn, can be expressed as sums over radial integrals multiplied by angular coefficients. All the angular coefficients are calculated using routines from the grasp2K version 1_1 package [1].Reasons for new version:This new version takes the nuclear recoil corrections into account within the (αZ)4m2/M approximation [2] and also allows storage of the angular coefficients for a series of calculations within a given isoelectronic sequence. Furthermore, the program JJ2LSJ, a module of the grasp2K version 1_1 toolkit that allows a transformation of ASFs from a jj-coupled CSF basis into an LSJ-coupled CSF basis, has been especially adapted to present ris3 results using LSJ labels of the states. This additional tool is called RIS3_LSJ.Summary of revisions:This version is compatible with the new angular approach of the grasp2K version 1_1 package [1] and can store necessary angular coefficients. According to the formalism of the relativistic nuclear recoil, the “uncorrected” expression of the normal mass shift has been fundamentally modified compared with its expression in [3].Restrictions:The complexity of the cases that can be handled is entirely determined by the grasp2K package [1] used for the generation of the electronic wave functions.Unusual features:Angular data is stored on disk and can be reused. LSJ labels are used for the states.Running time:As an example, we evaluated the isotope shift parameters and the electron density at the origin using the wave functions of Be-like system. We used the MCDHF wave function built on a complete active space (CAS) with n=8 (296 626 CSFs-62 orbitals) that contains 3 non-interacting blocks of given parity and J values involving 6 different eigenvalues in total. Calculations take around 10 h on one AMD Opteron 6100 @ 2.3 GHz CPU with 8 cores (64 GB DDR3 RAM 1.333 GHz). If angular files are available the time is reduced to 20 min. The storage of the angular data takes 139 MB and 7.2 GB for the one-body and the two-body elements, respectively.