Search

Oxidation of selenium (Se) largely drives the mobilization of soluble selenium oxyanions from rock and soil. Isotopic fractionation of selenium (82Se/76Se) has been used to track attenuating proces...

Adsorption plays an important role in the biogeochemical cycling of selenium (Se) in natural environments and Se isotope fractionation during adsorption is a significant but poorly studied part of Se isotope system. This paper examined Se(IV) and Se(VI) adsorption onto four naturally occurring metal oxides (hematite, manganese dioxide (β-MnO2), and α and γ-alumina oxides) and revealed Se isotope fractionation as a function of the absorbents used, Se species adsorbed, exposure time, and pH. The results show that Se(IV)/(VI) adsorption was initially rapid and was accompanied with kinetic isotope fractionations as large as 3‰, but slowed down as adsorption equilibrium was approached, eventually approaching isotopic equilibrium. The Se(IV) adsorption onto the studied metal oxides took at least 12 h to reach adsorption equilibrium, longer than Se(VI) adsorption (

Isotope dilution (ID) method has been widely applied to studies of elemental speciation and certification of the concentrations of geological reference materials. One of the key factors restricting the application of the ID method is the difficulty in identifying the optimal ratios of the isotope tracer (spike) to sample (S/N) and in estimating the error propagation. Here, using Se isotope as an example and employing a Monte Carlo method, we found that the optimal choice of spike and S/N are 77Sespike and 0.7, respectively. The S/N in the range from 0.1 to 4 can produce sufficiently low errors (

Selenium (Se) stable isotopes are a new geochemical tool with great potential as a tracer of redox processes and chemical cycling of chalcophiles and volatile elements. However, Se isotope measurements in low-Se samples present a formidable analytical challenge. In this study, we report a new method to measure Se stable isotopes (δ82/78Se; per mil deviation relative to Se NIST SRM 3149) with extremely high precision. Selenium has six stable isotopes and therefore is a good candidate for isotope analysis using a double spike approach, which has the advantage that it can correct for any stable isotope fractionation that may occur during sample processing. We have calibrated a novel 76Se–78Se double spike and have developed a rapid and precise analytical protocol on a multi-collector inductively coupled plasma mass spectrometer using an ESI hydride generation introduction system. Sensitivity is over 1000 V per ppm for the total Se signal; a measurement typically requires 25 ng of natural Se. Argon dimer interferences on masses 76, 78 and 80 were corrected in situ by measuring mass 80. Germanium interferences on masses 74 and 76 were corrected by measuring mass 73 and mass 75 was monitored to correct for arsenic hydride on mass 76. Wash-out times were in the order of 180 s, greatly reduced compared to previous studies that rely on on peak zero argon dimer corrections (wash-out times of up to one hour). The 2 s.e. error for a single analysis typically ranges from 0.01 to 0.025‰ (n = 80) for δ82/78Se. Long-term reproducibility and accuracy were estimated by multiple analyses of the Se Merck standard over numerous different analytical sessions, resulting in a mean δ82/78Se value of −0.989 ± 0.034‰ (n = 93; 2 s.d.), which is in excellent agreement with previous studies.

Purpose To investigate differences between prescribed and postimplant calculated dose in 192Ir high-dose-rate endorectal brachytherapy (HDR-EBT) by evaluating dose to clinical target volume (CTV) and organs at risk (OARs) calculated with a Monte Carlo–based dose calculation software, RapidBrachyMC. In addition, dose coverage, conformity, and homogeneity were compared among the radionuclides 192Ir, 75Se, and 169Yb for use in HDR-EBT. Methods and Materials Postimplant dosimetry was evaluated using 23 computed tomography (CT) images from patients treated with HDR-EBT using the 192Ir microSelectron v2 (Elekta AB, Stockholm, Sweden) source and the Intracavitary Mold Applicator Set (Elekta AB, Stockholm, Sweden), which is a flexible applicator capable of fitting a tungsten rod for OAR shielding. Four tissue segmentation schemes were evaluated: (1) TG-43 formalism, (2) materials and nominal densities assigned to contours of foreign objects, (3) materials and nominal densities assigned to contoured organs in addition to foreign objects, and (4) materials specified as in (3) but with voxel mass densities derived from CT Hounsfield units. Clinical plans optimized for 192Ir were used, with the results for 75Se and 169Yb normalized to the D90 of the 192Ir clinical plan. Results In comparison to segmentation scheme 4, TG-43–based dosimetry overestimates CTV D90 by 6% (P = .00003), rectum D50 by 24% (P = .00003), and pelvic bone D50 by 5% (P = .00003) for 192Ir. For 169Yb, CTV D90 is overestimated by 17% (P = .00003) and rectum D50 by 39% (P = .00003), and pelvic bone D50 is significantly underestimated by 27% (P = .007). Postimplant dosimetry calculations also showed that a 169Yb source would give 20% (P = .00003) lower rectum V60 and 17% (P = .00008) lower rectum D50. Conclusions Ignoring high-Z materials in dose calculation contributes to inaccuracies that may lead to suboptimal dose optimization and disagreement between prescribed and calculated dose. This is especially important for low-energy radionuclides. Our results also show that with future magnetic resonance imaging–based treatment planning, loss of CT density data will only affect calculated dose in nonbone OARs by 2% or less and bone OARs by 13% or less across all sources if material composition and nominal mass densities are correctly assigned.

The cross sections of the selenium isotopes 76Se, 77Se, 78Se and 80Se within 10.5–19.81 MeV neutron energy range have been measured through neutron activation method along with off-line γ-ray spectrometry. The quasi-monoenergetic neutrons were produced from the 7Li $$\left( {p, n} \right)$$ reaction at 14UD BARC-TIFR Pelletron Accelerator Facility, Mumbai, India. The statistical codes TALYS-1.9 and EMPIRE-3.2.2 were applied for the theoretical calculation of reaction cross sections with different level density models from 2 to 22 MeV neutron energies. Besides this, the Se $$\left( {n, p} \right)$$ As reaction cross sections were also calculated from different systematic formulae within 14–15 MeV neutron energies. The measured data were compared with existing literature data available in the EXFOR database, evaluated data of ENDF/B-VIII.0, JENDL-4.0 and TENDL-2019 libraries and with theoretical outcomes through TALYS-1.9 and EMPIRE-3.2.2 codes. The uncertainties in existing cross sections were calculated through the method of covariance analysis by including partial uncertainties and correlation among the different attributes. The $$\left( {n, p} \right)$$ reaction cross sections of selenium isotopes at higher neutron energies first time measured in the present work can be added as new data in the nuclear data library.

Isotope systematics of the redox sensitive and chalcophile element selenium (Se) were investigated on exhumed parts of subducted oceanic lithosphere to provide new constraints on slab dehydration conditions during subduction. The samples c,, show increasing delta(82/76)Se(NIST3149 )with higher abundances of fluid mobile elements, comprising a larger range (-1.89 to +0.48 parts per thousand) than that of mantle (-0.13 +/- 0.12 parts per thousand) and altered ocean crust (-0.35 to -0.07 parts per thousand). Our data point to pronounced, local scale redox variations within the subducting crust, wherein oxidative fluids dissolve sulfides and mobilise oxidised Se species. Subsequently recrystallising sulfides preferentially incorporate isotopically lighter, reduced Se, which shifts evolving fluids and late stage sulfides to higher delta Se-82/76(NIST3149). Redistribution of Se by repeated cydes of sulfide reworking within the subducted crust can be reconciled with episodes of oxidised fluid pulses from underlying slab mantle in modem subduction zones.

Significant efforts have been made to develop robust and reliable methods for simultaneous biothiols determination in different matrices, but there still exist the problems such as easy oxidation, tedious derivatization, and difficulty in discrimination, which brings unsatisfactory results in their accuracy and fast quantification in biological samples. To overcome these problems, a simultaneous biothiols detection method combining a "selenium signature" chemical probe and paper spray mass spectrometry (PS-MS) was proposed. In the strategy, the modified-paper substrate is used to enhance the analytical performance. Chemical probe Ebselen-NH2 that has a specific response to biothiols was designed and covalently fixed on the surface of an oxidized paper substrate. By the identification of derivatized product with distinctive selenium isotope distribution and employment of the optimized PS-MS method, qualitative and quantitative analysis of five biothiols including glutathione (GSH), cysteine (Cys), cysteinylglycine (CysGly), N-acetylcysteine (Nac), and homocysteine (Hcy) were realized. Biothiols in plasma and cell lysates were measured with satisfactory results. The established method not only provides a novel protocol for simultaneous determination of biothiols, but also is helpful for understanding the biological and clinical roles played by these bioactive small molecules.

The method of neutron diffraction with selenium isotope substitution is used to measure the structure of glassy As0.30Se0.70, As0.35Se0.65 and As0.40Se0.60. The method delivers three difference functions for each sample in which either the As-As, As-Se or Se-Se correlations are eliminated. The measured coordination numbers are consistent with the "8-N" rule and show that the As0.30Se0.70network is chemically ordered, a composition near to which there is a minimum in the fragility index and a boundary to the intermediate phase. Chemical ordering in glassy As0.35Se0.65 and As0.40Se0.60 is, however, broken by the appearance of As-As bonds, the fraction of which increases with the arsenic content of the glass. For the As0.40Se0.60 material, a substantial fraction of As-As and Se-Se defect pairs (~11%) is frozen into the network structure on glass formation.

Snake venoms are inherently complex. They are mixtures of multiple enzymes, peptides, lipids, carbohydrates, nucleosides, and metal ions. Metal ions make up a small portion of a snake's venom but play outsized roles in enzyme function and stability. Unlike enzyme primary structure, which is easily predicted from genomic sequences, a venom's metal ion content must be measured directly. We leveraged the high throughput and sensitivity of inductively coupled plasma mass spectrometry to analyze the metal ion content of seven North American snake venoms. All venoms were collected from snakes reared at one location, so we could discount variation from environmental or geographical factors. We profiled 71 metal isotopes. Selenium isotopes were consistently high across all venoms tested. When each venom's toxicity was graphed as a function of each different metal isotope, the only strong relationships between metal content and toxicity were for magnesium isotopes.

Oceanic lavas erupting today trace ocean-atmosphere oxygenation in Earth’s middle ages., Oxygenation of Earth’s oceans and atmosphere through time has consequences for subducted surface signatures that are now stored in the mantle. Here, we report significant mass-dependent selenium isotope variations in modern hot spot–influenced oceanic lavas. These variations are correlated with tracers of mantle source enrichment, which can only be explained by incorporation of abyssal pelagic sediments subducted from a redox-stratified mid-Proterozoic ocean. Selenium geochemical signatures of these sediments have mostly been preserved during long-term recycling and may therefore complement the global surface sediment record as ancient oxygen archives. Combined deep mantle and surface perspectives, together with emerging models for atmospheric oxygen based on selenium systematics, further imply a significantly oxygenated ocean-atmosphere system throughout the mid-Proterozoic.

It is emphasized the importance of using radioisotope products in industry, science and medicine. Information is given on the generation of isotope products in the IVV-2M research reactor of Research Institute of Nuclear Materials, and the plans for expanding the range of radioisotopes produced. The features of the selenium-75 isotope production are described. The necessity of thermohydraulic simulation of the target for producing selenium-75 in the conditions of the IVV-2M reactor is substantiated. The process of constructing a solid-state model of the target and simulating the thermal conditions for the production of isotopes is described. In this work, the analysis of thermohydraulic processes was performed with Solidworks Flow Simulation software. © 2020 American Institute of Physics Inc.. All rights reserved.

An analysis of \({}^{74-82}\mathrm{{Se}}\) within the framework of the interacting boson model (IBM) and the few-body aspects are presented. Selenium isotopes with mass number (A) ranging from 74 to 82 are typical vibrational nuclei that can be explained by the U(5) limit of the IBM. However, they are not fully symmetrical nuclei, and are represented by adding a perturbation term to account for the symmetry breaking. These nuclei tend to exhibit properties of a harmonic oscillator and an asymmetric deformed rotor. The low-energy level and B(E2) ratios are calculated using the IBM via direct diagonalization of the perturbed Hamiltonian and the E(5) symmetry breaking. Comparisons between the theoretical and experimental results of the even-even selenium isotopes with A ranging from 74 to 82 are presented.

This work was supported by an NSF Graduate Research Fellowship to MAK (DGE-1256082) and a NASA Exobiology grant to RB (NNX16AI37G). Mass-dependent variations in selenium stable isotope ratios have recently been developed as a paleo-redox proxy. Since the reduction of selenium oxyanions occurs at a relatively high redox potential, this system holds promise for probing conditions relevant to the evolution and diversification of eukaryotic and animal life, which required substantial dissolved oxygen levels. Although several studies have identified selenium isotopic variability during oxygenation events in Earth’s distant past, we still have only a broad understanding of the mechanisms controlling this isotopic variability. This currently limits the robust interpretation of selenium isotope variability to first-order mechanisms driving large-magnitude changes. Here, we explore selenium isotope variability within and among Paleozoic black shales deposited on the North American craton that have been well-studied using a variety of other paleo-environmental proxies. Using this combined dataset, we attempt to unravel the controls on selenium abundance and isotope ratios in organic-rich ancient marine sedimentary rocks. We find that in the Late Pennsylvanian units, an estuarine nutrient trap on the Midcontinent Shelf enabled vigorous selenium recycling, leading to very high concentrations in sediments and enrichment of heavy isotopes in the aqueous selenium reservoir. In contrast, we find that among the Late Devonian units, differences in local basinal hydrography led to a gradient in selenium abundance and isotopic fractionation, with the more restricted basins depleting their selenium reservoirs and causing enrichment of heavy isotopes in the residual aqueous reservoir. In both of these case studies, the additional context provided by complementary paleo-environmental proxies was critical for distinguishing between possible drivers of selenium isotopic variability. When extending such studies to other paleo-environmental settings, we suggest that the continued use of complementary datasets will enable the most robust use of the selenium paleo-redox proxy. Moreover, further development of techniques for high-precision and phase-specific selenium isotope measurements will greatly improve the ability to deduce subtle redox fluctuations with this proxy. Postprint

Because of the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, radioactive species were leaked out, including selenium isotopes (79Se). Developing a stable matrix that is suitable for longterm storage is necessary for the decommissioning process of the FDNPP. In the present work, the co-precipitation of SeO42− in cancrinite/sodalite as a potential stable matrix was investigated at various reaction times using a hydrothermal method. Over time, the SeO42− contents in the solid products gradually increased. The XRD patterns revealed that the reaction produced multi-phased precipitates, which were zeolite Na (P), sodalite, and cancrinite. As the SeO42− amount increased, the solid products were transformed to cancrinite. The calculated lattice parameter of sodalite and cancrinite showed an increase in lattice parameter a for sodalite and cancrinite, suggesting SeO42− incorporated into the sodalite/cancrinite structure. XRD, SEM, FTIR, 27Al-NMR, and 29Si-NMR results revealed the phase transformation of the solid products over time. Four stages of the co-precipitation mechanism are proposed, including the formation of zeolite P (Na), hydroxylation of zeolite P (Na), the formation of sodalite, and cancrinite reprecipitation.

Element transfer from the solar nebular gas to solids occurred either through direct condensation or via heterogeneous reactions between gaseous molecules and previously condensed solid matter. The precursors of altered sulfides observed in chondrites are for example attributed to reactions between gaseous hydrogen sulfide and metallic iron grains. The transfer of selenium to solids likely occurred through a similar pathway, allowing the formation of iron selenides concomitantly with sulfides. The formation rate of sulfide however remains difficult to assess. Here we investigate whether the Se isotopic composition of meteorites contributes to constrain sulfide formation during condensation stages of our solar system. We present high precision Se concentration and δ 82 / 78 Se data for 23 chondrites as well as the first δ 74 / 78 Se , δ 76 / 78 Se and δ 77 / 78 Se data for a sub-set of seven chondrites. We combine our dataset with previously published sulfur isotopic data and discuss aspects of sulfide formation for various types of chondrites. Our Se concentration data are within uncertainty to literature values and are consistent with sulfides being the dominant selenium host in chondrites. Our overall average δ 82 / 78 Se value for chondrites is − 0.21 ± 0.43 ‰ ( n = 23 , 2 s.d.), or − 0.14 ± 0.21 ‰ after exclusion of three weathered chondrites ( n = 20 , 2 s.d.). These average values are within uncertainty indistinguishable from a previously published estimate. For the first time however, we resolve distinct δ 82 / 78 Se between ordinary ( − 0.14 ± 0.07 ‰ , n = 9 , 2 s.d.), enstatite ( − 0.27 ± 0.05 ‰ , n = 3 , 2 s.d.) and CI carbonaceous chondrites ( − 0.01 ± 0.06 ‰ , n = 2 , 2 s.d.). We also resolve a Se isotopic variability among CM carbonaceous chondrites. In addition, we report on δ 74 / 78 Se , δ 76 / 78 Se and δ 77 / 78 Se values determined for 7 chondrites. Our data allow evaluating the mass dependency of the δ 82 / 78 Se variations. Mass-independent deficits ro excesses of 74Se, 76Se and 77Se are calculated relative to the observed 82Se/78Se ratios, and were observed negligible. This rules out poor mixing of nucleosynthetic components to account for the δ 82 / 78 Se variability and implies that the mass dependent Se isotopic variations were produced in a once-homogeneous disk. The mass-dependent isotopic difference between enstatite and ordinary chondrites may reflect the contribution of a kinetic sulfidation process at anomalously high H2S–H2Se contents in the region of enstatite chondrite formation. Experimental studies showed that high H2S contents favor the formation of compact sulfide layers around metallic grains. This decreases the reactive surface, which tends to inhibit the continuation of the sulfidation reaction. Under these conditions sulfide growth likely occurs under isotopic disequilibrium and favors the trapping of light S and Se isotopes in solids; This hypothesis provides an explanation for our Se isotope as well as for previously published S isotope data. On the other hand, high δ 82 / 78 Se values in carbonaceous chondrites may result from sample heterogeneities generated by parent body aqueous alteration, or could reflect the contribution of ices carrying photo-processed Se from the outer solar system.

Nuclear waste containing radionuclides including selenium isotopes, Se79, will be disposed of in future deep geological repositories. Due to the long lifetime of these radioisotopes, studies on the impact of microbial processes on their chemical speciation would contribute significantly to understanding the risks associated with these repositories. Here we report a green method for biogenic reduction of SeIJIV), production of amorphous Se(0) (a-Se) nanospheres and their subsequent transformation to one-dimensional (1D) trigonal selenium (t-Se) nanostructures using a combination of methods (XRD, STEM/HAADF, HRTEM/ EDX, ESEM, etc.). The bacterial strain used, Stenotrophomonas bentonitica, was isolated from Spanish bentonites considered as artificial barriers for future Spanish repositories. After 24 h of incubation, 30–200 nm sized biogenic individual a-Se nanospheres were synthesized and then started to coalesce, forming aggregates after 48 and 72 h of incubation. The 144 h sample presented a mixture of single crystal and polycrystalline 1D t-Se nanostructures with different shapes (e.g. nanowires, hexagonal, polygonal, etc.) and diameters of 30–400 nm, in addition to a-Se nanospheres. The HRTEM analysis showed that the 1D nanostructures presented different lattice spacings corresponding to the (100), (101) and (111) planes of t-Se. Thus, a-Se nanospheres were initially synthesized and then would transform into t-Se nanostructures. STEM/HAADF and ESEM revealed that the cells and their extracellular proteins play an important role in this transformation process. Due to the low solubility of t-Se nanostructures compared to that of a-Se nanospheres and SeIJIV), the mobility of selenium in future repositories may be significantly reduced., This work was supported by the Euratom research and training programme 2014-2018 under grant agreement no. 661880.

The isotopic compositions of Se in natural materials can be measured by multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) in combination with hydride generation and desolvation device. Although oceans are important targets for research, precise isotopic analysis of Se in seawater is generally difficult owing to its low concentrations and the much higher concentrations of other elements. We developed a robust, accurate method for the precise determination of Se isotopic composition in seawater. A hydride generator combined with a desolvation device with methane addition was coupled to MC-ICP-MS to measure Se isotopes precisely. Two new thiol resins were used to preconcentrate and separate Se from the seawater matrix efficiently, and Se was quickly eluted by small amounts of concentrated HNO3. No detectable Se isotope fractionation was observed during the preconcentration and separation procedure. The carbon-containing plasma increased Se sensitivity, suppressed the spectral interference signal, and improved precision by > 3 times. The precisions (2sd, n = 24) of Merck Se standard solutions for δ82/78Se, δ82/77Se, and δ82/76Se were 0.07‰, 0.10‰, and 0.16‰, respectively. The δ82/76Se values of standard solutions agreed well with results obtained by other research groups. The method was used to obtain a depth profile for dissolved inorganic Se (DISe) isotopes in seawater from the Northwestern Pacific Ocean. The range of δ82/76DISe was 0.41‰ to 1.59‰, indicating that Se isotopes fractionate sufficiently to clarify the biogeochemical cycling of this element in the ocean.

Funding during the compilation of this manuscript was provided by the NASA postdoctoral program. Postprint

The physical characteristics of the 75Se radionuclide make it a promising gamma radiator for use as a brachytherapy sealed source. This radionuclide combines relatively low-energy photon radiation emitted during decay with a sufficiently long half-life (approximately 120 days) and the possibility of obtaining high specific activity. All this makes this radionuclide attractive for automated injection brachytherapy. The aim of this work was to study the dosimetric characteristics of 75Se for its potential use in high and medium dose rate brachytherapy. According to the TG-43 formalism, the radial dose function g(r) and the anisotropy function F(r, θ) are calculated. 75Se as a radionuclide for sealed source brachytherapy has many advantages over widely used isotopes and can serve as an alternative to iridium sources.

The origin of Earth's volatiles has been attributed to a late addition of meteoritic material after core-mantle differentiation. The nature and consequences of this 'late veneer' are debated, but may be traced by isotopes of the highly siderophile, or iron-loving, and volatile element selenium. Here we present high-precision selenium isotope data for mantle peridotites, from double spike and hydride generation multi-collector inductively coupled plasma mass spectrometry. These data indicate that the selenium isotopic composition of peridotites is unaffected by petrological processes, such as melt depletion and melt-rock reaction, and thus a narrow range is preserved that is representative of the silicate Earth. We show that selenium isotopes record a signature of late accretion after core formation and that this signature overlaps only with that of the CI-type carbonaceous chondrites. We conclude that these isotopic constraints indicate the late veneer originated from the outer Solar System and was of lower mass than previously estimated. Thus, we suggest a late and highly concentrated delivery of volatiles enabled Earth to become habitable.

Selenium is a mineral that contributes to animal reproduction. The objective of this work was to evaluate conception rate and progesterone concentration in landrace ewes, during the reproductive season by organic selenium intake. 27 multiparous ewes were used with a body condition of 2.5; two groups were randomly designed: 11 ewes without selenium and 16 with selenium. Estrus was synchronized with intravaginal sponges containing fluorogestone acetate for 14 days, at the time of sponges removal, application of 400 UI of eCG was made. Artificial insemination (IA) was developed at a fixed time (55 hours after removal of sponges), consecutive application of 0.3 ppm day-1 of oral organic selenium was started seven days before IA. Progesterone concentration was evaluated in blood samples obtained along one estrus cycle (21 days), gestation diagnosis was developed at 35 days after the IA. Progesterone concentrations, between without selenium (5.28 ng mL-1) and treatment with organic selenium (6.58 ng mL-1), were not different between groups or between days (p ≥ 0.05), although in both groups the maximum progesterone concentration was observed on day 14 after the IA, in coincidence with a normal corpus luteum time. Also, conception rate was not different (p ≥ 0.05); in the group without selenium 81.8 % and with organic selenium 75 %. Based on the results, it is concluded that organic selenium application for seven days before IA did not influence progesterone concentration and conception rate in ewes.

Algebraic collective model (ACM) calculations for the even-even selenium isotopes $^{86,88}\mathrm{Se}$ have been performed to describe collective properties of these two transitional nuclei with only two and four valence neutrons, respectively. From the perspective of the ACM the nuclei turn out to be only weakly deformed, described by a very $\ensuremath{\gamma}$-soft potential. This is confirmed by Skyrme and Gogny energy density functional calculations. Additionally, the fully microscopic symmetry conserving configuration mixing method with the Gogny interaction has been applied to the study of these isotopes. The results show the transitional character of $^{86}\mathrm{Se}$ and the relevant role of the triaxial degree of freedom in the structure of these nuclei.

The isotope composition of selenium (Se) can provide important constraints on biological, geochemical, and cosmochemical processes taking place in different reservoirs on Earth and during planet formation. To provide precise qualitative and quantitative information on these processes, accurate and highly precise isotope data need to be obtained. The currently applied ICP-MS methods for Se isotope measurements are compromised by the necessity to perform a large number of interference corrections. Differences in these correction methods can lead to discrepancies in published Se isotope values of rock standards which are significantly higher than the acclaimed precision. An independent analytical approach applying a double spike (DS) and state-of-the-art TIMS may yield better precision due to its smaller number of interferences and could test the accuracy of data obtained by ICP-MS approaches. This study shows that the precision of Se isotope measurements performed with two different Thermo Scientific™ Triton™ Plus TIMS is distinctly deteriorated by about ±1‰ (2 s.d.) in δ 80/78 Se by a memory Se signal of up to several millivolts and additional minor residual mass bias which could not be corrected for with the common isotope fractionation laws. This memory Se has a variable isotope composition with a DS fraction of up to 20% and accumulates with increasing number of measurements. Thus it represents an accumulation of Se from previous Se measurements with a potential addition from a sample or machine blank. Several cleaning techniques of the MS parts were tried to decrease the memory signal, but were not sufficient to perform precise Se isotope analysis. If these serious memory problems can be overcome in the future, the precision and accuracy of Se isotope analysis with TIMS should be significantly better than those of the current ICP-MS approaches.

Batch experiments were performed to study adsorption and desorption of 75Se and 113Sn radiotracers at environmentally representative concentrations of ~0.3 ng L−1 and ~3 ng L−1, respectively. The radiotracers were incubated with wet bulk sediments from the Gironde Estuary and the Rhone River, combining freshwater and coastal seawater salinity (S = 0, S = 32) and three different Suspended Particulate Matter (SPM) concentrations (10 mg L−1, 100 mg L−1, 1000 mg L−1) to simulate six hydrologically contrasting situations for each particle type. Results showed no measurable adsorption for 75Se under the experimental conditions, whereas >90% of 113Sn rapidly adsorbed onto the particles during the first hours of exposure. Adsorption efficiency increased with increasing SPM concentration and seemed to be slightly greater for the Rhone River sediments, potentially related to the intrinsic mineral composition. Desorption of spiked sediments exposed to filtered, unspiked freshwater and seawater only occurred for 113Sn (

Neutron-deficient selenium isotopes are thought to undergo a rapid shape change from a prolate deformation near the line of beta stability towards oblate deformation around the line of N=Z. The point at which this shape change occurs is unknown, with inconsistent predictions from available theoretical models. A common feature in the models is the delicate nature of the point of transition, with the introduction of even a modest spin to the system sufficient to change the ordering of the prolate and oblate configurations. We present a measurement of the quadrupole moment of the first-excited state in radioactive ^{72}Se-a potential point of transition-by safe Coulomb excitation. This is the first low-energy Coulomb excitation to be performed with a rare-isotope beam at the reaccelerated beam facility at the National Superconducting Cyclotron Laboratory. By demonstrating a negative spectroscopic quadrupole moment for the first-excited 2^{+} state, it is found that any low-spin shape change in neutron-deficient selenium does not occur until ^{70}Se.

We have investigated the Se isotope effect in the layered bismuth chalcogenide ($\mathrm{BiC}{\mathrm{h}}_{2}$-based) superconductor $\mathrm{La}{\mathrm{O}}_{0.6}{\mathrm{F}}_{0.4}\mathrm{Bi}{(\mathrm{S},\mathrm{Se})}_{2}$ with $^{76}\mathrm{Se}$ and $^{80}\mathrm{Se}$. For all examined samples, the Se concentration, which is linked to the superconducting properties, is successfully controlled within $x=1.09--1.14$ in $\mathrm{La}{\mathrm{O}}_{0.6}{\mathrm{F}}_{0.4}\mathrm{Bi}{\mathrm{S}}_{2\ensuremath{-}x}\mathrm{S}{\mathrm{e}}_{x}$. From the magnetization and electrical resistivity measurements, changes in ${T}_{\mathrm{c}}$ are not observed for the $\mathrm{La}{\mathrm{O}}_{0.6}{\mathrm{F}}_{0.4}\mathrm{Bi}{(\mathrm{S},\mathrm{Se})}_{2}$ samples with $^{76}\mathrm{Se}$ and $^{80}\mathrm{Se}$ isotopes. Our result may indicate that the pairing in $\mathrm{La}{\mathrm{O}}_{0.6}{\mathrm{F}}_{0.4}\mathrm{Bi}{(\mathrm{S},\mathrm{Se})}_{2}$ is not mediated by phonons, which is consistent with recent theoretical and experimental studies suggesting unconventional superconductivity in the $\mathrm{BiC}{\mathrm{h}}_{2}$-based superconductors.

Selenium (Se) is an element that, in trace quantities, plays an important role in the normal function of a number of biological processes in humans. Many studies have demonstrated that selenium deficiency in the body may contribute to an increased risk for certain neoplastic, cardiovascular, osseous, and nervous system diseases including retardation of bone formation. However, at higher concentrations Se is cytotoxic. For these reasons it is desirable to have a means of monitoring selenium concentration in humans.This paper presents the outcome of a feasibility study carried out for measuring selenium in humans using in vivo neutron activation analysis (IVNAA). In this technique a small dose of neutrons is delivered to the organ of interest, the neutrons are readily captured by the target nuclei, and the γ-rays given off are detected outside of the body. For the present study, human hand (bone) tissue equivalent phantoms were prepared with varying amounts of Se. These were irradiated by a low energy fast neutron beam produced by the (7)Li(p,n)(7)Be reaction employing the high beam current Tandetron accelerator. The counting data saved using a 4π NaI(TI) detection system were analyzed. The selenium was detected via the neutron capture reaction, (76)Se(n,γ)(77 m)Se, whereas calcium was detected through the (48)Ca(n,γ)(49)Ca reaction for the purpose of normalization of the Se signals to the calcium signals. From the calibration lines drawn between Se/Ca concentrations and Se/Ca counts ratio, the minimum detection limits (MDLs) were computed for two sets of phantoms irradiated under different irradiation parameters.In this study the optimized MDL value was determined to be 81 ng g(-1) (Se/phantom mass) for an equivalent dose of 188 mSv to the phantom. This MDL was found at least 10 times lower than the reported data on Se concentration measured in bone tissues. It was concluded that the NAA technique would be a feasible means of performing in vivo measurements of selenium in humans. Currently the data on in vivo measurement of selenium in humans are limited; the results of the present study would greatly contribute to the present data.

The sorption mechanism of 75Se(IV) on Amberlite MB9L is investigated under a wide range of pH, initial concentration, and resin weight to give a proper solution for the decontamination as a result of radioactive selenium. The sorption ability of is found to be high except in highly acidic environment. A monolayer exchange mechanism is confirmed and the reaction rate is found to be controlled by diffusion. The overall equilibrium equation and sorption parameters are estimated. Thus, Amberlite MB9L can be used as barrier to avoid the release of radioactive selenium from the stored nuclear wastes when exposed to groundwater.

Selenium-73 is a positron emitting non-standard radionuclide, which is suitable for positron emission tomography. A copper-catalyzed reaction allowed no-carrier-added labeling of the anti-inflammatory seleno-organic compound Ebselen with (73) Se and (75) Se under addition of sulfur carrier in a one-step reaction. The new authentically labeled radioselenium molecule is thus available for preclinical evaluation and positron emission tomography studies.

Selenium (Se) undergoes redox transformations and isotopic fractionations at relatively high redox potentials and could therefore provide insight into changes in oceanic and atmospheric O2 levels over Earth’s history. We test this idea with Se data from the 2.5 Ga Mount McRae Shale (Hamersley Basin, Australia), which records temporary enrichments in abundances and isotopes of other redox-sensitive elements indicating a “whiff of oxygen” in Earth’s atmosphere before the Great Oxidation Event. Se isotopic ratios expressed as δ82/78Se and abundances relative to crustal background show significant positive excursions of up to 1.1‰ and an enrichment 13 times above background, respectively, overlapping with excursions in Mo and N isotopes and abundances. Because Se has a relatively high redox potential and photosynthetic oxidation pathways are unknown, our data thus suggest that Se was mobilized by free O2 during this interval. The isotopic fractionation likely occurred during transport of Se oxyanions from the site of weathering to the outer shelf. Although O2 could have been produced locally on land and may not necessarily have increased in the global atmosphere, our results strengthen the inference of an early origin of oxygenic photosynthesis long before the Paleoproterozoic Great Oxidation Event. This is the first report of a Se isotope excursion in the Precambrian rock record, and it confirms that Se isotopes can serve as a useful redox proxy in deep time.

It has been proposed that an “oxygen overshoot” occurred during the early Paleoproterozoic Great Oxidation Event (GOE) in association with the extreme positive carbon isotopic excursion known as the Lomagundi Event. Moreover, it has also been suggested that environmental oxygen levels then crashed to very low levels during the subsequent extremely negative Shunga–Francevillian carbon isotopic anomaly. These redox fluctuations could have profoundly influenced the course of eukaryotic evolution, as eukaryotes have several metabolic processes that are obligately aerobic. Here we investigate the magnitude of these proposed oxygen perturbations using selenium (Se) geochemistry, which is sensitive to redox transitions across suboxic conditions. We find that δ82/78Se values in offshore shales show a positive excursion from 2.32 Ga until 2.1 Ga (mean +1.03 ± 0.67‰). Selenium abundances and Se/TOC (total organic carbon) ratios similarly show a peak during this interval. Together these data suggest that during the GOE there was pervasive suboxia in near-shore environments, allowing nonquantitative Se reduction to drive the residual Se oxyanions isotopically heavy. This implies O2 levels of >0.4 μM in these settings. Unlike in the late Neoproterozoic and Phanerozoic, when negative δ82/78Se values are observed in offshore environments, only a single formation, evidently the shallowest, shows evidence of negative δ82/78Se. This suggests that there was no upwelling of Se oxyanions from an oxic deep-ocean reservoir, which is consistent with previous estimates that the deep ocean remained anoxic throughout the GOE. The abrupt decline in δ82/78Se and Se/TOC values during the subsequent Shunga–Francevillian anomaly indicates a widespread decrease in surface oxygenation.

Selenium isotopes are becoming an important paleoenvironmental proxy. However, few studies have focused on the behavior of Se isotopes during oxidative weathering. In this paper, a comprehensive set of Se isotopic composition and concentration data were collected from the weathering profiles of Se-rich shales of the Permian Maokou Formation in Yutangba and Shadi, China to investigate Se isotopic fractionation and Se enrichment during weathering processes. The δ82/76Se in fresh shales (148 ± 118 mg/kg Se, 1SD, n = 40) from Shadi and Yutangba drill cores varies from −1.69‰ to 1.74‰ with an average of 0.40 ± 0.71‰ (1SD, n = 40), consistent with the range in other Phanerozoic shales, suggesting that Se isotopes are not strongly fractionated during Se sequestration in the primary sedimentary environment. However, the strongly weathered Se-rich shales from Shadi and Yutangba profiles are isotopically lighter with average δ82/76Se values of −1.96 ± 1.08‰ (1SD, n = 5) and −1.08 ± 1.83‰ (1SD, n = 23), respectively. These data suggest that Se isotopes can be fractionated during oxidation and reduction processes associated with weathering, with heavier isotopes removed preferentially during oxidative weathering of shales. Such a shift, if found to be a global phenomenon, would have implications for models of the global Se cycle and interpretation of Se isotope data from past biogeochemical regimes. Locally altered shales exposed in a quarry at Yutangba are extremely enriched in Se with 1642 ± 1505 mg/kg (1SD, n = 45), approximately 10 times greater than that in unaltered drill core samples. These rocks display very strong variation in δ82/76Se over short distances, with a single 60 cm transect showing the most strongly negative and positive δ82/76Se values (−14.20‰ to +11.37‰) observed to date in natural samples. This suggests that Se has undergone multiple cycles of oxidation, mobilization, and re-reduction, resulting in a Se-rich redox front that has migrated downward through the organic-rich shales over time. δ82/76Se values vary sharply over distances as small as 10 cm, indicating that Se redox conditions change strongly with position and are controlled by fractures and rock layering. Our data and a simple conceptual model suggest that zones of increased permeability that are accessed first by infiltrating waters are isotopically light, whereas less accessible zones are heavy. Repeated redox cycling accentuates this pattern. Furthermore, the average δ82/76Se in Se-rich shales at the Yutangba weathering system is 0.45 ± 5.77‰ (1SD, n = 39), identical with that (0.40 ± 0.71‰) in fresh shales from same locality, implying that Se released by weathering accumulates in the redox front with little loss. The strong Se isotopic fractionation occurring in the redox front implies that Se isotopes can be extensively used in tracing geochemical processes of Se in groundwater system, especially related to fractures.

The measurement of selenium isotope ratios is of increasing interest for understanding redox conditions in present and past surface environments. Se has six stable isotopes, and is therefore well suited for isotope analysis by double spiking. However due to relatively large interferences on every isotope, and complex chemical purification methods that frequently do not generate 100% yields, rigorously determining the accuracy of measurements is critical. Here we present analyses of USGS shale standards (SCo-1 and SGR-1b), as representatives of material which might be of interest to Se isotope studies. We have made analyses using two separate double spikes (74Se–78Se and 78Se–82Se), and compare them to previously published results. In addition, we present models of the effects of uncorrected interferences on double spike inversions. This leads us to propose δ82/76Se (parts per thousand deviation of 82Se/76Se from NIST SRM-3149) values of −0.22 ± 0.15 for SCo-1, and +0.25 ± 0.17 for SGR-1b. Further, we present a new method of measuring Se isotopes by desolvation nebulisation. Se sensitivity is enhanced by a factor of 100–200 times by doping solutions with pure Mg, leading to almost a factor of two less material required compared to the more standard hydride generation. Interferences are different compared to our standard hydride generation protocol, but analyses of double spiked NIST-3149 shows that this method can generate accurate isotope ratios. Finally, mass independent fractionation (MIF) of sulphur isotopes has generated considerable interest for constraining the early oxygenation of the atmosphere. Given the chemical similarities between S and Se, Archean shales with S MIF might be expected to exhibit Se MIF. However, within our analytical uncertainty of ±0.4–0.5‱ (parts per 10 000), there is no resolvable Se MIF in these samples, indicating different atmospheric cycling of Se and S.

Nanobiotechnology represents an economic alternative for chemical and physical methods of nanoparticles formation. The objectives of this study were to synthesize selenium nanoparticles by microbial processes using anaerobic metal-reducing bacteria as well as to characterize mineralogical properties of the nanoparticles. The selenium nanoparticles were about 200 nm in size and ball shaped. Microbial processes for elemental selenium synthesis may be useful for recovery of natural selenate in the natural environments and immobilization of selenium isotope in the high level nuclear waste disposal sites.

RATIONALE Past stable isotopic studies of selenium and arsenic oxyanions within a biogeochemistry context have focused solely on selenium isotopes due to monoisotopic nature of arsenic and lack of attention to oxygen. A modern quantification method of δ18O values in selenate, selenite, arsenate, and arsenite is presented here, similar to methods for other inorganic oxyanions such as phosphate. METHODS Dissolved oxyanions were recovered after precipitation with silver or barium cations within controlled pH ranges and purified by drying and roasting under vacuum. Oxygen isotope ratio measurements were performed on 250–450 micrograms of solids using continuous flow high-temperature conversion elemental analyzer/isotope ratio mass spectrometry (CF-TCEA/IRMS). Each Se and As solid was evaluated for reproducibility and stability of δ18O values and the usefulness of this method for evaluating aqueous phase Se and As oxyanion reactions was addressed. RESULTS Only silver arsenate and barium selenate were shown to have stable, reproducible δ18O values over 5 months and were calibrated to the VSMOW scale. The method was applied to confirm complete exchange of oxygen isotopes between arsenate and solvent water at pH 7 which produced an O-isotope fractionation between arsenate and water of 6.0‰. Furthermore, the method revealed the ability of oxygen in selenate to kinetically fractionate during reduction to elemental selenium by a green rust compound which produced a fractionation (20.9‰) larger than reported δ80/76Se values for similar reactions. CONCLUSIONS The experimental and analytical conditions for δ18O analysis of Se and As oxyanions were detailed. δ18O analyses of As and Se oxyanions may be useful in biogeochemical studies for tracing chemical reaction pathways, determining environmental sources of Se, or diagnosing specific reaction mechanisms for As and Se oxyanions. Copyright © 2012 John Wiley & Sons, Ltd.

The analytical methodology for the in vivo study of selenium metabolism using two enriched selenium isotopes has been modified, allowing for the internal correction of spectral interferences and mass bias both for total selenium and speciation analysis. The method is based on the combination of an already described dual-isotope procedure with a new data treatment strategy based on multiple linear regression. A metabolic enriched isotope ((77)Se) is given orally to the test subject and a second isotope ((74)Se) is employed for quantification. In our approach, all possible polyatomic interferences occurring in the measurement of the isotope composition of selenium by collision cell quadrupole ICP-MS are taken into account and their relative contribution calculated by multiple linear regression after minimisation of the residuals. As a result, all spectral interferences and mass bias are corrected internally allowing the fast and independent quantification of natural abundance selenium ((nat)Se) and enriched (77)Se. In this sense, the calculation of the tracer/tracee ratio in each sample is straightforward. The method has been applied to study the time-related tissue incorporation of (77)Se in male Wistar rats while maintaining the (nat)Se steady-state conditions. Additionally, metabolically relevant information such as selenoprotein synthesis and selenium elimination in urine could be studied using the proposed methodology. In this case, serum proteins were separated by affinity chromatography while reverse phase was employed for urine metabolites. In both cases, (74)Se was used as a post-column isotope dilution spike. The application of multiple linear regression to the whole chromatogram allowed us to calculate the contribution of bromine hydride, selenium hydride, argon polyatomics and mass bias on the observed selenium isotope patterns. By minimising the square sum of residuals for the whole chromatogram, internal correction of spectral interferences and mass bias could be accomplished. As a result, the tracer/tracee ratio could be calculated for each selenium-containing species and a time relationship for synthesis and degradation established. Both selenite and selenized yeast labelled with (77)Se were employed for comparative purposes.

We have determined the isomeric ratios in 113In(γ, n)112m,gIn and 113In(γ, 2n)111m,gIn photonuclear reactions of natural indium induced by bremsstrahlungs with end-point energies in the giant dipole resonance (GDR) region. The investigated samples were irradiated at the electron accelerator Microtron MT-25 of the Flerov Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research, Dubna. The gamma spectra of the samples irradiated were measured with a spectroscopic system consisting of an 8192-channel analyzer and a high-energy resolution (180 keV at gamma ray 1332 keV of 60Co) HP(Ge) semiconductor detector Canberra. The GENIE2000 (Canberra) computer program was used for data processing. The results were discussed and compared with those of other authors. For both the mentioned reactions, the isomeric ratios in the bremsstrahlung energy range from 19 to 24 MeV in this work are new measurements.

Owing to recent studies which showed that Se supplementation in the diet can reduce the risk of several forms of cancer, efforts have been directed to identify anticarcinogenic activity in Se compounds from natural sources with the objective of using those as food supplements. As a part of a continuing research project directed at identifying Se-containing species in food stuffs, the distribution of selenium-containing proteins in water-soluble protein fraction of seeds of Bertholletia excelsa H.B.K., which typically have a high Se content, was studied under non-denaturing conditions and the effectiveness of protein fractional precipitation by ammonium sulfate was investigated with the objectives to preconcentrate the protein(s) of interest and to reduce the matrix complexity. By SEC–ICPMS, Se-containing proteins (selenoproteome with some additional proteins) were found demonstrating the usefulness of ICPMS as an “on-line assay” in sub-proteomics investigations. Fractions with Se-containing proteins, collected from SEC, were tryptically digested and tryptic digests were analyzed by MALDI-TOF-reflectron MS and capLC–ESI-QTOF-MS. Isotope patterns which are different from the typical isotope patterns of peptides containing C, H, O, N and S were used to identify selenium-containing peptides in the digests. Observed isotope patterns were slightly different from the predicted isotope patterns and partial deamidation of selenium-containing peptides is suggested to explain the modified isotope pattern. To our knowledge, this is the first report of the effect of partial deamidation of selenium-containing peptides on the observed selenium isotope pattern, although the evidence is indirect. According to the SEC–ICPMS study, Se-containing proteins in water-soluble protein fraction of Bertholletia excelsa H.B.K. seeds can be divided into two main sub-groups-high molecular weight Se-containing proteins and low molecular weight Se-containing proteins. LC–ESI-MS and MS/MS analysis of tryptic digest of low-molecular weight Se-containing proteins identified 2S albumins, which are rich in methionines; therefore, with a high probability of non-specific selenomethionine incorporation—as the proteins present in that fraction.

Selenium is an essential micronutrient for humans and animals, yet it is deficient in at least one billion people worldwide. Plants and plant-derived products transfer the soil-uptaken selenium to humans; therefore, the cultivation of plants enriched in selenium can be an effective way to improve the selenium status on human- kind. This paper focuses on determining the ability of bread wheat to accumulate selenium after supplementation. One of the methods for supplementing this element in plants is foliar application with selenium solutions. These supplemented crop of wheat samples—bread wheat; Triti- cum aestivum L.—were used to determine if there is an increase of selenium content in cereal grains by comparing them with cereals cultivated in 2009 and harvested in 2010 with no supplementation. The experiments were done using sodium selenate and sodium selenite at three different selenium concentrations: 4, 20 and 100 g per hectare. Total Se is assessed by cyclic neutron activation analysis (CNAA), through short irradiations on the fast pneumatic system (SIPRA) of the Portuguese Research Reactor (RPI-ITN). The short-lived nuclide 77m Se, that features a half-lifetime of 17.5 s, was used to determine the Se con- tent in SIPRA. The experiment was successful, since the selenium concentration increased in the cropped grains and reached values up to 35 times the non-supplemented ones.

We analyzed the Se isotopic composition of black shales and related kerogen and sulfide fractions from the Zunyi Ni–Mo–Se deposit, the La’erma Se–Au deposit and the Yutangba Se deposit in southern China to constrain metal sources and accumulation processes, both subjects of disagreement in the scientific community. Se at the Zunyi Ni–Mo–Se polymetallic deposit displayed a restricted range of δ82Se values (−1.6‰ to 2.4‰ with a mean of 0.6‰) suggesting a major hydrothermal origin where aqueous Se was probably transported as H2Se, along with H2S, and precipitated directly as selenides or in sulfides. Se at the La’erma Se–Au deposit covers a larger range in δ82Se values (−3.8‰ to 5.4‰ with a mean of 0.3‰), suggesting Se redistribution following redox transformations, leading to kinetic isotopic fractionation. The largest Se isotopic variation so far in natural terrestrial samples was found in the Yutangba Se deposit, with δ82Se values varying from −12.77‰ to 4.93‰. On the basis of variations in Se isotopes in the deposit, along with other geological and geochemical evidence, the “redox model” (supergene alteration) explains the occurrence of native Se in the deposit. Overall, hydrothermal systems may be a potentially important Se source to form economic deposits in comparison to seawater sources. Significantly, our study indicates that either secondary hydrothermal or supergene alteration is a key factor in Se enrichment in black shales. Redistribution of Se, and probably other redox-sensitive metals like Mo, Cr and V, leads to isotopic fractionation which may be used to fingerprint such alteration/precipitation processes.

The radioactive selenium isotope 79 Se can be a component of radioactive waste produced in nuclear power plants. The accidental release of 79 Se in the environment from power plants or nuclear waste repositories, and subsequent transfer of 79 Se into soils, plants and food chain, are relevant concerns in Europe. In environmental risk assessment models, the ability of plants to take up Se is often characterized by means of soil-to-plant transfer factors (TF). However, these recommendations take little or no account of the variability in plant Se accumulation among plant species and differences in Se distribution between plant parts. Also, such factors as soil type, form of Se, climatic conditions, as well as the chemical form in which Se is present in the soil, are not taken into consideration. This paper reviews the current knowledge on Se uptake by plants and compiles published data on the transfer of Se from soils and nutrient solutions into plants. The data were categorized according to the form of Se supply, i.e. when added as either selenate or selenite to nutrient solutions or soils, or whether plant Se accumulation was studied on soil containing only natural-occurring Se (native Se). Plant Se accumulation can vary more than two orders of magnitudes at a given soil Se concentration for a specific form of soil Se (i.e. “native” soil Se, Se added as selenate, or as selenite) among different plant taxa. Differences observed in the transfer of Se from soil into plants appear to result primarily from differences in the solubility of Se species in soil and only to a minor degree from differences in plant uptake efficiency among these species. Values of the TF for Se were found to lie between 0.01 and 100 with few exceptions. Transfer factor values derived from studies in which Se was added to soil as selenate or selenite were generally found to be one or more orders of magnitude higher for a given plant species and plant part than TF values derived for “native Se”. Situations where radioactive Se has been accidentally released into the environment may be better represented by TF values for experimentally added Se than by TF values computed for native soil Se. The uncertainty in selecting a TF value for modeling Se transfer from soil into plants can be substantially reduced by identifying the predominant Se form in the soil, the plant species, and the target plant parts. The large variability in TF values suggests that it is still important to understand the complexity of the soil-plant system when selecting TF values to assess risks arising from the transfer of accidentally released 79 Se from soil into plants.

Selenite (H(2)SeO(3)) reacts with thiol compounds (RSH) under acidic conditions to form selenotrisulfides (RSSeSR, i.e. monoselenodithiols). The stoichiometry of the reaction is proposed as 4RSH+H(2)SeO(3)-->RSSeSR+RSSR+3H(2)O. Surprisingly, we found novel polynuclear selenium-containing compounds, i.e. polyselenodipenicillamines (PenSSe(2-4)SPen), in the reaction of D-penicillamine (PenSH) with H(2)SeO(3). The selenium-centered features of PenSSe(2-4)SPen were determined by (1)H-NMR and LC-MS/MS analyses, showing that the selenium isotope abundance patterns of the compounds were in good agreement with the theoretically-calculated ones. In order to better understand the mechanisms for PenSSe(2-4)SPen production, various molar ratio of H(2)SeO(3) (1/8 to 4 times of PenSH) was reacted with PenSH, and the concentration of the products was calculated from integral values of dimethyl proton signals for PenSSe(1-2)SPen as compared with methyl proton signals for acetic acid (an internal standard). Total PenSSe(1-2)SPen concentration was increased with increasing of H(2)SeO(3), in which concomitant decrease of PenSSPen (disulfide form of PenSH) was observed. Based on these results, we proposed the PenSSe(2-4)SPen production mechanisms being involved in penicillamine selenopersulfides (PenSSe(1-2)H).

Neutron capture gamma rays were measured for all stable Se isotopes in an incident neutron energy region from 15 to 100 keV. A neutron time‐of‐flight method was adopted with a ns‐pulsed neutron source based on the 7Li(p,n)7Be reaction and with a large anti‐Compton NaI(Tl) spectrometer. A pulse‐height weighting technique was applied to the observed capture gamma‐ray pulse‐height spectra to obtain the capture yields. Using the standard capture cross sections of 197Au, the capture cross sections of stable Se isotopes were derived with an error of about 5%. The capture gamma‐ray spectra were obtained by unfolding the observed capture gamma‐ray pulse‐height spectra. The present results for the capture cross sections are compared with the previous measurements and the evaluations of JENDL‐3.3 and ENDF/B‐VI.8 and VII.0.

The quadrupole moments of 76,78,80,82,84,88Kr and 74,76,78,80,82Se isotopes are investigated in terms of the interacting boson model (IBM), and it was found that a good description of them can also be concluded in this model. Before the quadrupole moments were calculated, the positive-parity states and electromagnetic-transition rates (B(E2)) of even-mass Kr nuclei have also been obtained within the framework of IBM. It was seen that there is a good agreement between the presented results and the previous experimental data. The quadrupole moments of the neighboring Se isotopes were also obtained and it was seen that the results are satisfactorily agree well with the previous experimental data.

Neutron nuclear data on 28,29,30Si have been calculated for the evaluated nuclear data library JENDL-4. Simultaneously calculated are the total, elastic and inelastic scattering, and (n, p), (n, α), (n, γ), (n, 2n), (n, 3n), (n, np), and (n, nα) reaction cross sections, the angular distributions of emitted neutrons, and the energy distributions of emitted particles and γa-rays. The statistical model was applied to calculate these quantities. Coupled-channel optical model parameters were obtained so as to reproduce measured cross sections. Preequilibrium and direct-reaction processes were taken into account in addition to the compound process. It is confirmed that the present calculations are almost consistent with available experimental data. The calculated data are compiled into JENDL-4.

Elemental speciation is becoming a common analytical procedure for geochemical investigations. The various redox species of environmentally relevant metals can have vastly different biogeochemical properties, including sorption, solubility, bioavailability, and toxicity. The use of high performance liquid chromatography (HPLC) coupled to elemental specific detectors, such as inductively coupled plasma mass spectrometry (ICP–MS), has become one of the most important speciation methods employed. This is due to the separation versatility of HPLC and the sensitive and selective detection capabilities of ICP–MS. The current study compares standard mode ICP–MS to recently developed reaction cell (RC) ICP–MS, which has the ability to remove or reduce many common polyatomic interferences that can limit the ability of ICP–MS to quantitate certain analytes in complex matrices. Determination of chromium and selenium redox species is achieved using ion-exchange chromatography with elemental detection by standard and RC–ICP–MS, using various chromium and selenium isotopes. In this study, method performance and detection limits for the various permutations of the method (isotope monitored or ICP–MS detection mode) were found to be comparable and generally less than 1 μg L−1. The method was tested on synthetic laboratory samples, surface water, groundwater, and municipal tap water matrices.