WorldWideScience

Sample records for isotope effect study

  1. Isotope effects: definitions and consequences for pharmacologic studies

    International Nuclear Information System (INIS)

    Van Langenhove, A.

    1986-01-01

    The use of stable isotope-labeled compounds for pharmacologic studies requires careful consideration of the nature of the stable isotope label (2H, 13C, 15N, 18O) and its position of incorporation in the molecule. When deuterium is used, improper positioning can lead to significant primary isotope effects. Primary isotope effects occur when the breaking of the bond to the heavy isotope is the rate-limiting step in a reaction (or metabolic transformation). A reaction will proceed slower for the molecule with the heavy isotope label because of the mass difference between the light and the heavy isotope. In addition to these primary isotope effects, smaller but nevertheless important secondary isotope effects, physicochemical isotope effects, active hydrogen/deuterium exchange, or isotope effects associated with either the enzyme-catalyzed biotransformation or the mass spectrometric ionization and fragmentation can be operative. In mechanistic studies, isotope effects are used to their advantage; however, in pharmacokinetic studies, the occurrence of isotope effects can lead to grossly misleading biologic and analytic results: the metabolism of the drug will differ when in vivo isotope effects are operative, and isotope effects occurring during the analysis procedure will obscure the true metabolic profile of the drug

  2. Combining Solvent Isotope Effects with Substrate Isotope Effects in Mechanistic Studies of Alcohol and Amine Oxidation by Enzymes*

    Science.gov (United States)

    Fitzpatrick, Paul F.

    2014-01-01

    Oxidation of alcohols and amines is catalyzed by multiple families of flavin-and pyridine nucleotide-dependent enzymes. Measurement of solvent isotope effects provides a unique mechanistic probe of the timing of the cleavage of the OH and NH bonds, necessary information for a complete description of the catalytic mechanism. The inherent ambiguities in interpretation of solvent isotope effects can be significantly decreased if isotope effects arising from isotopically labeled substrates are measured in combination with solvent isotope effects. The application of combined solvent and substrate (mainly deuterium) isotope effects to multiple enzymes is described here to illustrate the range of mechanistic insights that such an approach can provide. PMID:25448013

  3. Uranium isotopic effect studies on cation and anion exchange resins

    International Nuclear Information System (INIS)

    Sarpal, S.K.; Gupta, A.R.

    1975-01-01

    Uranium isotope effects in exchange reactions involving hexavalent and tetravalent uranium, on ion exchange resins, have been re-examined. The earlier work on uranium isotope effects in electron exchange reactions involving hexavalent and tetravalent uranium, has been critically reviewed. New experimental data on these systems in hydrochloric acid medium, has been obtained, using break-through technique on anion-exchange columns. The isotope effects in these break-through experiments have been reinterpreted in a way which is consistent with the anion exchange behaviour of the various uranium species in these systems. (author)

  4. Isotope effects on nuclear shielding

    International Nuclear Information System (INIS)

    Hansen, P.E.

    1983-01-01

    This review concentrates upon empirical trends and practical uses of mostly secondary isotope effects, both of the intrinsic and equilibrium types. The text and the tables are arranged in the following fashion. The most 'popular' isotope effect is treated first, deuterium isotope effects on 13 C nuclear shielding, followed by deuterium on 1 H nuclear shieldings, etc. Focus is thus on the isotopes producing the effect rather than on the nuclei suffering the effect. After a brief treatment of each type of isotope effect, general trends are dealt with. Basic trends of intrinsic isotope effects such as additivity, solvent effects, temperature effects, steric effects, substituent effects and hyperconjugation are discussed. Uses of isotope effects for assignment purposes, in stereochemical studies, in hydrogen bonding and in isotopic tracer studies are dealt with. Kinetic studies, especially of phosphates, are frequently performed by utilizing isotope effects. In addition, equilibrium isotope effects are treated in great detail as these are felt to be new and very important and may lead to new uses of isotope effects. Techniques used to obtain isotope effects are briefly surveyed at the end of the chapter. (author)

  5. Stable isotope studies

    International Nuclear Information System (INIS)

    Ishida, T.

    1992-01-01

    The research has been in four general areas: (1) correlation of isotope effects with molecular forces and molecular structures, (2) correlation of zero-point energy and its isotope effects with molecular structure and molecular forces, (3) vapor pressure isotope effects, and (4) fractionation of stable isotopes. 73 refs, 38 figs, 29 tabs

  6. The isotope altitude effect reflected in groundwater: a case study from Slovenia.

    Science.gov (United States)

    Mezga, Kim; Urbanc, Janko; Cerar, Sonja

    2014-01-01

    This paper presents the stable isotope data of oxygen (δ(18)O) and hydrogen (δ(2)H) in groundwater from 83 sampling locations in Slovenia and their interpretation. The isotopic composition of water was monitored over 3 years (2009-2011), and each location was sampled twice. New findings on the isotopic composition of sampled groundwater are presented, and the data are also compared to past studies regarding the isotopic composition of precipitation, surface water, and groundwater in Slovenia. This study comprises: (1) the general characteristics of the isotopic composition of oxygen and hydrogen in groundwater in Slovenia, (2) the spatial distribution of oxygen isotope composition (δ(18)O) and d-excess in groundwater, (3) the groundwater isotope altitude effect, (4) the correlation between groundwater d-excess and the recharge area altitude of the sampling location, (5) the relation between hydrogen and oxygen isotopes in groundwater in comparison to the global precipitation isotope data, (6) the groundwater isotope effect of distance from the sea, and (7) the estimated relation between the mean temperature of recharge area and δ(18)O in groundwater.

  7. Studies of isotopic effects in the excited electronic states of molecular systems

    International Nuclear Information System (INIS)

    1982-01-01

    Rare gas halogen (RGH) lasers serve as convenient tools for a range of photophysical processes which exhibit isotope effects. This document summarizes progress in the production of molecular systems in their electronic excited states with the aid of RGH lasers, and the various isotopic effects one can study under these conditions. We conclude that the basic physical mechanisms involved in the isotopically sensitive characteristics of excited molecular electronic states are sufficiently selective to be useful in both the detection and separation of many atomic materials

  8. Mechanistic studies on the bovine liver mitochondrial dihydroorotate dehydrogenase using kinetic deuterium isotope effects

    International Nuclear Information System (INIS)

    Hines, V.; Johnston, M.

    1989-01-01

    Dihydroorotates deuteriated at both C 5 and C 6 have been prepared and used to probe the mechanism of the bovine liver mitochondrial dihydroorotate dehydrogenase. Primary deuterium isotope effects on k cat are observed with both (6RS)-[5(S)- 2 H]- and (6RS)-[6- 2 H]dihydroorotates (3 and 6, respectively); these effects are maximal at low pH. At pH 6.6, D V = 3.4 for the C 5 -deuteriated dihydroorotate (3), and D V = 2.3 for the C 6 -deuteriated compound (6). The isotope effects approach unity at pH 8.8. Analysis of the pH dependence of the isotope effects on k cat reveals a shift in the rate-determining step of the enzyme mechanism as a function of pH. Dihydroorotate oxidation appears to require general base catalysis; this step is completely rate-determining at low pH and isotopically sensitive. Reduction of the cosubstrate, coenzyme Q 6 , is rate-limiting at high pH and is isotopically insensitive; this step appears to require general acid catalysis. The results of double isotope substitution studies and analysis for substrate isotope exchange with solvent point toward a concerted mechanism for oxidation of dihydroorotate. This finding serves to distinguish further the mammalian dehydrogenase from its parasitic cognate, which catalyzes a stepwise oxidation reaction

  9. Isotope effect study of κ-(BEDT-TTF)2Cu(NCS)2: Labeling in the anion

    International Nuclear Information System (INIS)

    Kini, A.M.; Wang, H.H.; Schlueter, J.A.

    1995-01-01

    Since the initial discovery of organic superconductivity in 1979, a large number of organic superconductors have now been synthesized. However, the mechanism of electron-pairing in these novel superconductors has remained largely unresolved. Isotope effect studies constitute an important experimental tool for the investigation of whether or not the electron-pairing mechanism in organic superconductors is phonon-mediated, as in conventional superconductors. Recent isotope effect studies in the authors' laboratory, involving seven different isotopically labeled BEDT-TTF (or ET) derivatives, have demonstrated the following: (1) intramolecular phonon modes involving C double-bond C and Csingle bondS stretching vibrations in the ET donor molecule are not the dominant mediators of electron-pairing, and (2) in κ-(ET) 2 Cu(NCS) 2 , there exist two competing isotope effects--a normal mass effect, i.e., lowering of T c upon isotopic labeling, when the ET molecular mass is increased by concurrent 13 C and 34 S labeling, in addition to an inverse isotope effect upon deuterium labeling in ET. It is of great interest to investigate if there is an isotope effect when the charge-compensating anions, which are also located within the non-conducting layer in the superconducting cation-radical salts, are isotopically labeled. The existence of an isotope effect when the anions are labeled would be indicative of electron-pairing with the mediation of vibrational frequencies associated with the anions. In this paper, the authors present the results of the first isotope effect study in which isotopic labeling in the anion portion of κ-(ET) 2 Cu(NCS) 2 is carried out. The authors find no isotope effect when the carbon and nitrogen atoms of the thiocyanate groups in the anion are replaced with 13 C and 15 N isotopes

  10. Memory Effects Study of Measuring Radioactive Xenon Isotopes With β-γ Coincidence Method

    International Nuclear Information System (INIS)

    Jia Huaimao; Wang Shilian; Wang Jun; Li Qi; Zhao Yungang; Fan Yuanqing; Zhang Xinjun

    2010-01-01

    The β-γ coincidence technique is a kind of the key important method to detect radioactive xenon isotopes for the Comprehensive Nuclear-Test-Ban Treaty (CTBT). This paper describes noble gases memory effects of β-γ coincidence detector. Xenon memory effects were measured and its influence on detector's minimum detectable activity (MDA) was evaluated. The methods of reducing xenon memory effects were studied. In conclusion, aluminium coated plastic scintillator and YAP scintillator can remarkably decrease xenon memory effects. (authors)

  11. Studies on the magnetic after-effect of hydrogen isotopes in hexagonal crystals

    International Nuclear Information System (INIS)

    Herbst, G.

    1979-01-01

    The behaviour of hydrogen isotopes in hexagonal gadolinium, in intermetallic compounds of the RECo 5 type (RE = rare earth metal), and in cobalt alloys with small concentrations of alloyed impurity atoms was studied using the magnetic after-effect method in the temperature range between 4.2 K and 300 K. (orig./WBU) [de

  12. A new cascade method for studying isotope effect in chemical exchange system without valance change

    International Nuclear Information System (INIS)

    Wen Xiaoning; Luo Wenzong

    1987-01-01

    A new cascade method for studying isotope effect in chemical exchange system without valance change is developed and described. This method is simple to use and consumes less extractant as compared with the commonly used Woodward method. It is also convenient for unstable systems

  13. Noncovalent Hydrogen Isotope Effects

    Science.gov (United States)

    Buchachenko, A. L.; Breslavskaya, N. N.

    2018-02-01

    Zero-point energies (ZPE) and isotope effects, induced by intermolecular, noncovalent vibrations, are computed and tested by experimental data. The ZPE differences of H- and D-complexes of water with hydrogen, methane, and water molecules are about 100-300 cal/mol; they result to isotope effects IE of 1.20-1.70. Semi-ionic bonds between metal ions and water ligands in M(H2O) 6 2+ complexes are much stronger; their ZPEs are about 12-14 kcal/mol per molecule and result to IE of 1.9-2.1 at 300 K. Protonated (deuterated) water and biwater exhibit the largest ZPE differences and isotope effects; the latter are 25-28 and 12-13 for water and biwater, respectively. Noncovalent IEs contribute markedly into the experimentally measured effects and explain many anomalous and even magic properties of the effects, such as the dependence of IE on the solvents and on the presence of the third substances, enormously large isotope effects at the mild conditions, the difference between IEs measured in the reactions of individual protiated and deuterated compounds and those measured in their mixture. Noncovalent IEs are not negligible and should be taken into account to make correct and substantiated conclusions on the reaction mechanisms. The kinetic equations are derived for the total isotope effects, which include noncovalent IEs as additive factors.

  14. ICP-MS as the method of the determination of gallium, indium and thallium isotope ratios in the studies of isotope effects in the chromatography systems

    International Nuclear Information System (INIS)

    Herdzik, I.

    2006-01-01

    The procedure of the determination of gallium, indium and thallium isotope ratios and its application to the studies of the isotope effects in chromatography systems by the ICP-MS method (inductively coupled plasma-mass spectrometry) are presented. It was shown that it is possible to determine the isotope ratios of gallium ( 69/71 Ga), indium ( 113/115 In) and thallium ( 203/205 Tl) with the relative standard deviation 0.03-0.07%. Such precision appeared to be sufficient to calculate the unit separation factors in the column chromatographic processes. (author) [pl

  15. A multielement isotopic study of refractory FUN and F CAIs: Mass-dependent and mass-independent isotope effects

    Science.gov (United States)

    Kööp, Levke; Nakashima, Daisuke; Heck, Philipp R.; Kita, Noriko T.; Tenner, Travis J.; Krot, Alexander N.; Nagashima, Kazuhide; Park, Changkun; Davis, Andrew M.

    2018-01-01

    Calcium-aluminum-rich inclusions (CAIs) are the oldest dated objects that formed inside the Solar System. Among these are rare, enigmatic objects with large mass-dependent fractionation effects (F CAIs), which sometimes also have large nucleosynthetic anomalies and a low initial abundance of the short-lived radionuclide 26Al (FUN CAIs). We have studied seven refractory hibonite-rich CAIs and one grossite-rich CAI from the Murchison (CM2) meteorite for their oxygen, calcium, and titanium isotopic compositions. The 26Al-26Mg system was also studied in seven of these CAIs. We found mass-dependent heavy isotope enrichment in all measured elements, but never simultaneously in the same CAI. The data are hard to reconcile with a single-stage melt evaporation origin and may require reintroduction or reequilibration for magnesium, oxygen and titanium after evaporation for some of the studied CAIs. The initial 26Al/27Al ratios inferred from model isochrons span a range from <1 × 10-6 to canonical (∼5 × 10-5). The CAIs show a mutual exclusivity relationship between inferred incorporation of live 26Al and the presence of resolvable anomalies in 48Ca and 50Ti. Furthermore, a relationship exists between 26Al incorporation and Δ17O in the hibonite-rich CAIs (i.e., 26Al-free CAIs have resolved variations in Δ17O, while CAIs with resolved 26Mg excesses have Δ17O values close to -23‰). Only the grossite-rich CAI has a relatively enhanced Δ17O value (∼-17‰) in spite of a near-canonical 26Al/27Al. We interpret these data as indicating that fractionated hibonite-rich CAIs formed over an extended time period and sampled multiple stages in the isotopic evolution of the solar nebula, including: (1) an 26Al-poor nebula with large positive and negative anomalies in 48Ca and 50Ti and variable Δ17O; (2) a stage of 26Al-admixture, during which anomalies in 48Ca and 50Ti had been largely diluted and a Δ17O value of ∼-23‰ had been achieved in the CAI formation region; and (3

  16. Laboratory study of nitrate photolysis in Antarctic snow. II. Isotopic effects and wavelength dependence

    Energy Technology Data Exchange (ETDEWEB)

    Berhanu, Tesfaye A.; Erbland, Joseph; Savarino, Joël [Laboratoire de Glaciologie et Géophysique de l’Environnement, CNRS, F-38041 Grenoble (France); Univ. Grenoble Alpes, LGGE, F-38041 Grenoble (France); Meusinger, Carl; Johnson, Matthew S. [Copenhagen Center for Atmospheric Research (CCAR), Department of Chemistry, University of Copenhagen, Copenhagen (Denmark); Jost, Rémy [Laboratoire de Interdisciplinaire de Physique (LIPHY) Univ. de Grenoble, Grenoble (France); Bhattacharya, S. K. [Research Center for Environmental Changes, Academia Sinica, Nangang, Taipei 115, Taiwan (China)

    2014-06-28

    Atmospheric nitrate is preserved in Antarctic snow firn and ice. However, at low snow accumulation sites, post-depositional processes induced by sunlight obscure its interpretation. The goal of these studies (see also Paper I by Meusinger et al. [“Laboratory study of nitrate photolysis in Antarctic snow. I. Observed quantum yield, domain of photolysis, and secondary chemistry,” J. Chem. Phys. 140, 244305 (2014)]) is to characterize nitrate photochemistry and improve the interpretation of the nitrate ice core record. Naturally occurring stable isotopes in nitrate ({sup 15}N, {sup 17}O, and {sup 18}O) provide additional information concerning post-depositional processes. Here, we present results from studies of the wavelength-dependent isotope effects from photolysis of nitrate in a matrix of natural snow. Snow from Dome C, Antarctica was irradiated in selected wavelength regions using a Xe UV lamp and filters. The irradiated snow was sampled and analyzed for nitrate concentration and isotopic composition (δ{sup 15}N, δ{sup 18}O, and Δ{sup 17}O). From these measurements an average photolytic isotopic fractionation of {sup 15}ε = (−15 ± 1.2)‰ was found for broadband Xe lamp photolysis. These results are due in part to excitation of the intense absorption band of nitrate around 200 nm in addition to the weaker band centered at 305 nm followed by photodissociation. An experiment with a filter blocking wavelengths shorter than 320 nm, approximating the actinic flux spectrum at Dome C, yielded a photolytic isotopic fractionation of {sup 15}ε = (−47.9 ± 6.8)‰, in good agreement with fractionations determined by previous studies for the East Antarctic Plateau which range from −40 to −74.3‰. We describe a new semi-empirical zero point energy shift model used to derive the absorption cross sections of {sup 14}NO{sub 3}{sup −} and {sup 15}NO{sub 3}{sup −} in snow at a chosen temperature. The nitrogen isotopic fractionations obtained by applying

  17. Isotopic effect giant resonances

    International Nuclear Information System (INIS)

    Buenerd, M.; Lebrun, D.; Martin, P.; Perrin, G.; Saintignon, P. de; Chauvin, J.; Duhamel, G.

    1981-10-01

    The systematics of the excitation energy of the giant dipole, monopole, and quadrupole resonances are shown to exhibit an isotopic effect. For a given element, the excitation energy of the transition decreases faster with the increasing neutron number than the empirical laws fitting the overall data. This effect is discussed in terms of the available models

  18. Using Beads and Divided Containers to Study Kinetic and Equilibrium Isotope Effects in the Laboratory and in the Classroom

    Science.gov (United States)

    Campbell, Dean J.; Brewer, Emily R.; Martinez, Keri A.; Fitzjarrald, Tamara J.

    2017-01-01

    The purpose of this laboratory experiment is to study fundamental concepts of kinetics and equilibria and the isotope effects associated with both of these concepts. The concepts of isotopes in introductory and general chemistry courses are typically used within the contexts of atomic weights and radioactivity. Kinetic and equilibrium isotope…

  19. Computational study of substrate isotope effect probes of transition state structure for acetylcholinesterase catalysis

    International Nuclear Information System (INIS)

    Sikorski, R.S.; Malany, S.; Seravalli, J.; Quinn, D.M.

    2002-01-01

    Secondary isotope effects for carbonyl addition reactions of methyl thioacetate, acetone and acetaldehyde have been calculated by ab initio quantum mechanical methods in an effect to interpret measured β-deuterium isotope effects on acetylcholinesterase-catalysed hydrolysis of acetylthiocholine. The calculated β-deuterium isotope effect for equilibrium addition of methanol to methyl thioacetate is D3 K eq = 0.965, and the corresponding effect for addition of methoxide ion to methyl thioacetate wherein three waters are hydrogen bonded to the carbonyl oxyanion is D3 K eq = 1.086. Neither of these calculated isotope effects is an inverse as the experimental β-deuterium isotope effect for acetylcholinesterase-catalysed hydrolysis of acetylthiocholine, D3 K eq = 0.90±0.03. Structural comparisons show that the water-solvated methoxide adduct of methyl thioacetate is more expanded than is the natural methanol addition adduct, and suggest that the degree of which the isotope effect is inverse (i.e. less than) is inversely correlated to the degree of expansion of the adduct. A similar correlation of α-deuterium and β-deuterium secondary isotope effects with the degree of expansion of the adducts is found for equilibrium additions of methanol and methoxide ion to acetylaldehyde. These computational results suggest that the markedly inverse β-deuterium isotope effect for the acetylcholinesterase reaction arises from enzymatic compression of the transition state. (author)

  20. Quantum Dynamics Study of the Isotopic Effect on Capture Reactions: HD, D2 + CH3

    Science.gov (United States)

    Wang, Dunyou; Kwak, Dochan (Technical Monitor)

    2002-01-01

    Time-dependent wave-packet-propagation calculations are reported for the isotopic reactions, HD + CH3 and D2 + CH3, in six degrees of freedom and for zero total angular momentum. Initial state selected reaction probabilities for different initial rotational-vibrational states are presented in this study. This study shows that excitations of the HD(D2) enhances the reactivities; whereas the excitations of the CH3 umbrella mode have the opposite effects. This is consistent with the reaction of H2 + CH3. The comparison of these three isotopic reactions also shows the isotopic effects in the initial-state-selected reaction probabilities. The cumulative reaction probabilities (CRP) are obtained by summing over initial-state-selected reaction probabilities. The energy-shift approximation to account for the contribution of degrees of freedom missing in the six dimensionality calculation is employed to obtain approximate full-dimensional CRPs. The rate constant comparison shows H2 + CH3 reaction has the biggest reactivity, then HD + CH3, and D2 + CH3 has the smallest.

  1. Equilibrium deuterium isotope effect of surprising magnitude

    International Nuclear Information System (INIS)

    Goldstein, M.J.; Pressman, E.J.

    1981-01-01

    Seemingly large deuterium isotope effects are reported for the preference of deuterium for the α-chloro site to the bridgehead or to the vinyl site in samples of anti-7-chlorobicyclo[4.3.2]undecatetraene-d 1 . Studies of molecular models did not provide a basis for these large equilibrium deuterium isotope effects. The possibility is proposed that these isotope effects only appear to be large for want of comparison with isotope effects measured for molecules that might provide even greater contrasts in local force fields

  2. Isotopic study of the effect of Tarbela reservoir on the groundwater system in the downstream areas

    International Nuclear Information System (INIS)

    Sajjad, M.I.; Tasneem, M.A.; Hussain, S.D.; Khan, I.H.; Ali, M.; Latif, Z.

    1994-04-01

    Isotopic studies were carried out on the right side of river Indus, downstream of Tarbela dam to study the effect of Tarbela Reservoir on the groundwater system. The main objectives of the study were to determine the hydraulic connection, if any, between the Tarbela Lake and the groundwater appearing in the ponds near Gadon Amazai, see the effect of Tarbela dam on the groundwater system in the downstream areas, compute the relative contribution of different recharge sources towards groundwater system and to estimate residence time of groundwater in the area. Isotopic data reveals that the ponds near Gadoon Amazai area are being recharged by local rains and there is no contribution of Tarbela lake. The area around Gadoon Amazai, Topi and Kalabat is solely recharged by local rains while the area around Swabi, Zaida and Lahor has mixed recharge with major contribution from local canal system. Tritium data suggests that the residence time of groundwater in the study area varies from a few years to 30 years. Te groundwater in the area has low dissolved salt contents and is, generally, of good quality. (author) 19 figs

  3. Isotope effects on chemical equilibria

    International Nuclear Information System (INIS)

    Golding, P.D.

    1974-01-01

    The thermodynamic equilibrium constants of three deuterated substituted acetic acids are reported. The calculation of secondary isotope effects of the second kind for the three isotopic acid pairs has been accomplished by the appropriate comparison of thermodynamic equilibrium constants, and by the comparison of isotopic slopes. The effect of substituent variation on the isotope effects reported here disqualifies the simple inductive model as a legitimate description of secondary isotope effects of the second kind. The correlation of diminishing isotope effect per deuterium atom with increasing acidity is also invalidated by the present results. The syntheses of 9-thia-9,10-dihydrophenanthrene-9-oxide and thioxanthene-10-oxide are described. These compounds have been partially deuterated at their respective methylene positions. Spectral evidence indicates stereoselectivity of the methylene protons in the exchange reactions of both compounds. (author)

  4. Study of the matrix specific mass discrimination effects during inductively coupled plasma mass spectrometry isotope ratio measurements

    International Nuclear Information System (INIS)

    Vassileva, E.; Quetel, Ch.R.

    2004-01-01

    Sample matrix related effects on mass discrimination during inductively coupled plasma mass spectrometry (ICP-MS) isotope ratio measurements have only been rarely reported. However, they can lead to errors larger than the uncertainty claimed on the ratio results when not properly taken into account or corrected for. These matrix specific affects were experienced during an Isotope Dilution Mass Spectrometry (IDMS) campaign we carried out for the certification of the Cd amount content in some food digest samples (7% acidity and salts content around 450μg g -1 ). Dilution was not possible for Cd only present at the low ng g -1 level. Up to 1% difference was observed on Cd isotope ratio results between measurements performed directly or after matrix separation. This was a significant difference considering that less than 1.5% relative combined uncertainty was eventually estimated for these IDMS measurements. Similar results could be obtained either way after the implementation of necessary corrections. The direct measurement approach associated to a correction for mass discrimination effects using the food digest sample itself (and the IUPAC table values as reference for the natural Cd isotopic composition) was preferred as it was the easiest. Consequently, the impact of matrix effects on mass discrimination during isotope ratio measurements with two types of ICP- MS (quadrupole and magnetic sector instruments) was studied for 4 elements (Li, Cu, Cd and Tl). Samples of varying salinity (up to 0.25%) and acidity (up to 7%) characteristics were prepared using isotopic certified reference materials of these elements. The long term and short-term stability, respectively reproducibility and repeatability, of the results, as well as the evolution of the difference to certified ratio values were monitored. As expected the 13 investigated isotopic ratios were all sensitive to variations in salt and acid concentrations. Our experiments also showed that simultaneous variation

  5. A study of hydrogen isotopes fuel control by wall effect in magnetic fusion devices

    Energy Technology Data Exchange (ETDEWEB)

    Motevalli, S.M., E-mail: motavali@umz.ac.ir; Safari, M.

    2016-11-15

    Highlights: • A particle balance model for the main plasma and wall inventory in magnetic fusion device has been represented. • The dependence of incident particles energy on the wall has been considered in 10–300 eV for the sputtering yield and recycling coefficient. • The effect of fueling methods on plasma density behavior has been studied. - Abstract: Determination of plasma density behavior in magnetic confinement system needs to study the plasma materials interaction in the facing components such as first wall, limiter and divertor. Recycling of hydrogen isotope is an effective parameter in plasma density rate and plasma fueling. Recycling coefficient over the long pulse operation, gets to the unity, so it has a significant effect on steady state in magnetic fusion devices. Typically, sputtered carbon atoms from the plasma facing components form hydrocarbons and they redeposit on the wall. In this case little rate of hydrogen loss occurs. In present work a zero dimensional particle equilibrium model has been represented to determine particles density rate in main plasma and wall inventory under recycling effect and codeposition of hydrogen in case of continues and discontinues fueling methods and effective parameters on the main plasma decay has been studied.

  6. Study on the Effect of the Separating Unit Optimization on the Economy of Stable Isotope Separation

    Directory of Open Access Journals (Sweden)

    YANG Kun

    2015-01-01

    Full Text Available An economic criterion called as yearly net profit of single separating unit (YNPSSU was presented to evaluate the influence of structure optimization on the economy. Using YNPSSU as a criterion, economic analysis was carried out for the structure optimization of separating unit in the case of separating SiF4 to obtain the 28Si and 29Si isotope. YNPSSU was calculated and compared with that before optimization. The results showed that YNPSSU was increased by 12.3% by the structure optimization. Therefore, the structure optimization could increase the economy of the stable isotope separation effectively.

  7. Kinetic isotope effect studies of the S-adenosylmethionine synthetase reaction

    International Nuclear Information System (INIS)

    Markham, G.D.; Parkin, D.W.; Schramm, V.L.

    1986-01-01

    S-adenosylmethionine (AdoMet) synthetase catalyzes a unique substitution reaction at the 5' carbon of MgATP. Kinetic isotope effect (V/K) measurements have been used to investigate the mechanism of AdoMet synthetase from E. coli. Changes in 3 H/ 14 C ratios when AdoMet is formed from a mixture of either ([5'- 14 C]ATP and [5'- 12 C,1'- 3 H]ATP) or ([5'- 3 H]ATP and [5'- 1 H,1'- 14 C]ATP) were examined. The effects of varying the concentrations of the co-substrate methionine and the monovalent cation activator K + were investigated. Substitution of 14 C for 12 C at the 5' position of ATP yields a primary V/K kinetic isotope effect ( 12 C/ 14 C) of 1.128 +/- 0.004 at low K + and methionine concentrations. The observed isotope effect diminishes slightly to 1.107 +/- 0.003 when both K + and methionine are present at saturating concentrations, suggesting that MgATP has only a low commitment to catalysis from at conditions near Vmax. No secondary V/K 3 H isotope effect from [5'- 3 H]ATP was detected ( 1 H/ 3 H) = 0.997 +/- 0.003. The magnitude of the primary 14 C isotope effect and the small secondary 3 H effect demonstrate that AdoMet synthesis occurs with a S/sub N/ 2 transition state which is symmetric with respect to the sulfur nucleophile and the departing tripolyphosphate group

  8. Isotope effects in photochemical rearrangements

    International Nuclear Information System (INIS)

    Sommer, F.

    1983-01-01

    Taking anthracene resp. 9-deuteroanthracene as the initial substance, different substitution products have been prepared. The products originating by direct photolysis have been characterized and their structure has been determined. By comparing the measured kinetic isotope effect and the quantum yield of the nondeuterated and the monodeuterated fluorenes formed it could been demonstrated that the isotope effect mainly is due to the reaction rates and the influence of the deuterium substitution upon the radiationless desactivation against that is small. (HBR) [de

  9. Study of isotope effects in the hydrogen transport of an 8% CrWVTa martensitic steel

    International Nuclear Information System (INIS)

    Esteban, G.A.; Sedano, L.A.; Perujo, A.; Douglas, K.

    2001-01-01

    A time-dependent gas-phase isovolumetric desorption technique has been used to assess the isotope effects in the diffusive transport parameters of hydrogen in an 8% CrWVTa reduced activation martensitic steel in the temperature range of 423-892 K and driving pressures from 4 x 10 4 - 1 x 10 5 Pa. The experiments have been run with both protium and deuterium obtaining their respective transport parameters, diffusivity (D), Sieverts' constant (K S ), permeability (Φ), trap site density (η t ) and the trapping activation energy (E t ). Isotope effects on steel are analysed and compared with α-iron. A new way to derive more accurate tritium transport parameters is proposed. (orig.)

  10. A study on the isotope effects in the reduction of carbon dioxide by zinc

    International Nuclear Information System (INIS)

    Senegacnik, M.

    1957-06-01

    We have determined the isotope effects which occur in the reduction of carbon dioxide by zinc. It has been shown that in the case of irreversible surface reactions, Bernstein's equation which permits the calculation of the fractionation factor is still valid. These experimental factors are in good agreement with those obtained by calculating the partition functions of the adsorbed activated complexes. In the reaction mechanism used, the model of the activated complex corresponds to the dissociation of one of the carbon oxygen bonds CO 2 → CO + O. Perturbations arising from the slight reversibility of the reaction Zn + CO 2 ↔ ZnO + CO on the isotope effects on the carbon and oxygen atoms have also been calculated. (author) [fr

  11. Relative rate study of the kinetic isotope effect in the 13CH3D + Cl reaction

    DEFF Research Database (Denmark)

    Joelsson, Lars Magnus Torvald; Forecast, Roslyn; Schmidt, Johan Albrecht

    2014-01-01

    The 13CH3D/12CH4kinetic isotope effect, α13CH3D, of CH4 + Cl is determined for the first time, using the relative rate technique and Fourier transform infrared (FTIR) spectroscopy. α13CH3D is found to be 1.60 ± 0.04. In addition, a quantum chemistry/transition state theory model with tunneling...

  12. Sensitized charge carrier injection into organic crystals studied by isotope effects in weak magnetic fields

    International Nuclear Information System (INIS)

    Bube, W.; Michel-Beyerle, M.E.; Haberkorn, R.; Steffens, E.

    1977-01-01

    The magnetic field (H approximately 50 Oe) dependence of the rhodamine sensitized triplet exciton density in anthracene crystals is influenced by isotopic substitution. This confirms the hyperfine interaction as mechanism explaining the change of the spin multiplicity in the initially formed singlet state of the radical pair. The isotope effect occurs in the sensitizing dye ( 14 N/ 15 N) rather than at the molecular site of the injected charge within the crystal. This can be understood in terms of the high hopping frequency of the charge carriers as compared to the time constant of the hyperfine induced singlet-triplet transition. Since the dye molecules adsorb in an oriented fashion, the angular dependence of the magnetic field modulation of the triplet exciton density can be interpreted without assuming any additional interactions. (Auth.)

  13. Isotope effect on hydrated electron relaxation dynamics studied with time-resolved liquid jet photoelectron spectroscopy

    Science.gov (United States)

    Elkins, Madeline H.; Williams, Holly L.; Neumark, Daniel M.

    2016-05-01

    The excited state relaxation dynamics of the solvated electron in H2O and D2O are investigated using time-resolved photoelectron spectroscopy in a liquid microjet. The data show that the initial excited state decays on a time scale of 75 ± 12 fs in H2O and 102 ± 8 fs in D2O, followed by slower relaxation on time scales of 400 ± 70 fs and 390 ± 70 fs that are isotopically invariant within the precision of our measurements. Based on the time evolution of the transient signals, the faster and slower time constants are assigned to p → s internal conversion (IC) of the hydrated electron and relaxation on the ground electronic state, respectively. This assignment is consistent with the non-adiabatic mechanism for relaxation of the hydrated electron and yields an isotope effect of 1.4 ± 0.2 for IC of the hydrated electron.

  14. Hydrogen and carbon vapour pressure isotope effects in liquid fluoroform studied by density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Oi, Takao; Mitome, Ryota; Yanase, Satoshi [Sophia Univ., Tokyo (Japan). Faculty of Science and Technology

    2017-06-01

    H/D and {sup 12}C/{sup 13}C vapour pressure isotope effects (VPIEs) in liquid fluoroform (CHF{sub 3}) were studied at the MPW1PW91/6-31 ++ G(d) level of theory. The CHF{sub 3} monomer and CHF{sub 3} molecules surrounded by other CHF{sub 3} molecules in every direction in CHF{sub 3} clusters were used as model molecules of vapour and liquid CHF{sub 3}. Although experimental results in which the vapour pressure of liquid {sup 12}CHF{sub 3} is higher than that of liquid {sup 12}CDF{sub 3} and the vapour pressure of liquid {sup 13}CHF{sub 3} is higher than that of liquid {sup 12}CHF{sub 3} between 125 and 212 K were qualitatively reproduced, the present calculations overestimated the H/D VPIE and underestimated the {sup 12}C/{sup 13}C VPIE. Temperature-dependent intermolecular interactions between hydrogen and fluorine atoms of neighbouring molecules were required to explain the temperature dependences of both H/D and {sup 12}C/{sup 13}C VPIEs.

  15. Stable-isotope studies

    International Nuclear Information System (INIS)

    Anon.

    1975-01-01

    Structures of bacteriochlorophyll b and the Krasnovskii photoreduction products of chlorophyll a are given. All 55 13 C and 4 15 N NMR transitions in chlorophyl a and its magnesium-free derivative pheophytin a were assigned. ESR of triplet states of chlorophylls a, b, c/sub z/, and c 2 and bacteriochlorophyll a are reported. Experiments in the cultivation of 13 C-enriched morning glory plants indicated that the isotope enrichment can produce observable morphological changes. (U.S.)

  16. Isotope studies in brain diseases

    Energy Technology Data Exchange (ETDEWEB)

    Silfverskioeld, B [Department of Neurology, Soedersjukhuset, S-100 64 Stockholm (Sweden)

    1978-09-01

    Serial pictures of cerebral isotope flow and accumulation after intravenous injection provide several kinds of valuable diagnostic information. The reliability can be increased by using computer-processed pictures on a TV screen and by numerical analysis in accordance with paritcular programs constructed for our routine work. An isotope study should be done when computerized transmission tomography scans have failed to provide a conclusive diagnosis. It should then be performed with optimal technique in order to reduce the need of angiograms.

  17. Kinetic isotope effect studies on milk xanthine oxidase and on chicken liver xanthine dehydrogenase

    International Nuclear Information System (INIS)

    D'Ardenne, S.C.; Edmondson, D.E.

    1990-01-01

    The effect of isotopic substitution of the 8-H of xanthine (with 2 H and 3 H) on the rate of oxidation by bovine xanthine oxidase and by chicken xanthine dehydrogenase has been measured. V/K isotope effects were determined from competition experiments. No difference in H/T (V/K) values was observed between xanthine oxidase and xanthine dehydrogenase. Xanthine dehydrogenase exhibited a larger T/D (V/K) value than that observed for xanthine oxidase. Observed H/T (V/K) values for either enzyme are less than those H/T (V/K) values calculated with D/T (V/K) data. These discrepancies are suggested to arise from the presence of a rate-limiting step(s) prior to the irreversible C-H bond cleavage step in the mechanistic pathways of both enzymes. These kinetic complexities preclude examination of whether tunneling contributes to the reaction coordinate for the H-transfer step in each enzyme. No observable exchange of tritium with solvent is observed during the anaerobic incubation of [8- 3 H]xanthine with either enzyme, which suggests the reverse commitment to catalysis (C r ) is essentially zero. With the assumption of adherence to reduced mass relationships, the intrinsic deuterium isotope effect ( D k) for xanthine oxidation is calculated. By the use of these values and steady-state kinetic data, the minimal rate for the hydrogen-transfer step is calculated to be ∼75-fold faster than k cat for xanthine oxidase and ∼10-fold faster than k cat for xanthine dehydrogenase. Values calculated for each enzyme were found to be identical within experimental uncertainty

  18. Isotopic study of Karst water

    International Nuclear Information System (INIS)

    Leskovsek-Sefman, H.

    1985-01-01

    Measurement of the isotopic composition of water formed part of an extended investigation of the water drainage system in the Slovenian Karst. These studies were planned to complement geological and speleological investigations which are already being performed in this area, with the knowledge of the mechanism of changes in the isotopic composition of water in the natural environment on some smaller locations, Planina cave near Postojna where the vertical percolation of meteoric water through the karstified carbonate ceiling was studied and the water catchment areas of some small rivers, Ljubljanica, Rizana and Idrijca. Mass spectrometric investigations of the isotopic composition of some elements ( 18 O, D, 13 C and T) in water and in dissolved carbonates, as well as the isotopic composition of 18 O and 13 C in cave carbonates were performed. The results allow to conclude that the waters in karst aquifers in spite of producing the homogenisation to a great extent, qualitative determination of the retention time and of the prevailing sources for some springs and surface and underground water flows is nevertheless possible. The isotopic composition of 18 O in water and of 18 O and 13 C in dissolved carbonates depends on climatic conditions and on denudation processes. The investigation of cave carbonates revealed that they have different isotopic compositions of 18 O and 13 C because of different locations and also different ages

  19. Theoretical Study of H/D Isotope Effects on Nuclear Magnetic Shieldings Using an ab initio Multi-Component Molecular Orbital Method

    Directory of Open Access Journals (Sweden)

    Masanori Tachikawa

    2013-05-01

    Full Text Available We have theoretically analyzed the nuclear quantum effect on the nuclear magnetic shieldings for the intramolecular hydrogen-bonded systems of σ-hydroxy acyl aromatic species using the gauge-including atomic orbital technique combined with our multi-component density functional theory. The effect of H/D quantum nature for geometry and nuclear magnetic shielding changes are analyzed. Our study clearly demonstrated that the geometrical changes of hydrogen-bonds induced by H/D isotope effect (called geometrical isotope effect: GIE is the dominant factor of deuterium isotope effect on 13C chemical shift.

  20. Study of the effect of Chinese medicine on calcium absorption with isotopic tracer technique

    International Nuclear Information System (INIS)

    Hu, S.M.; Mao, X.Y.; Feng, W.Y.; OY, H.; Wang, M.; Xu, D.D.; Zhang, F.; Chai, Z.F.

    2005-01-01

    The present work was undertaken to study the effect of Chinese medicine on calcium absorption. Female Wistar rats, 3 months old, weighing 250-275 g, were randomly divided into ten groups of 5 rats each. The rats were individually housed in stainless steel metabolic cages in an environmentally controlled room (temperature, 20 degree C; relative humidity, 30%-60%; reversed light : dark cycle, 12:12 hr). Isotopic tracer technique was conducted to study the absorption of calcium acetate and calcium acetate + Chinese medicine in rats. The two calcium supplements were irradiated in a nuclear reactor for 4.95 d at neutron flux of φ=6.1 x 10 13 n/cm 2 ·s. Then they were prepared from concentrated 47 Ca solution (10 mg/ml) with cyclodextrin. The animals received oral doses of 25 mg calcium as calcium acetate or calcium acetate + Chinese medicine via an intragastric gavage. The animals were fasted overnight preceding and food was resumed 3 hrs after the gavage. Blood, heart, lung, liver, spleen, stomach, kidney, small intestine, large intestine and femur samples of the rats were taken upon sacrifice at 0.5, 1, 2, 4, 12, 24, 48, 72, 120, 168 hrs after dosing and assayed for 47 Ca. Urine and feces samples were collected separately after dosing and assayed for 47 Ca. The radioactivity of the samples was counted with a high pure Ge detector and a PC-based Ortec MCA. Its energy resolution was l.85 keV at 1332.5 keV and the relative detection efficiency was 30 %. The dead time was controlled within 10 % to reduce the count loss. Weighed 47 CaCO 3 was used as reference materials. A big distance between the samples and detector was kept to overcome the geometric effect caused by different shape and size of the samples. The gamma energy spectra were analyzed with a multipurpose gamma ray spectrum analysis software package. The parameters were evaluated by means of general linear model, using analysis of covariance with SAS 6.12 for Windows. The results showed that peroral 47 Ca was

  1. Isotope effect and isotope separation. A chemist's view

    International Nuclear Information System (INIS)

    Ishida, Takanobu

    2002-01-01

    What causes the isotope effects (IE)? This presentation will be centered around the equilibrium isotope effects due to the differences in the nuclear masses. The occurrence of the equilibrium constant, K, of isotope exchange reactions which differ from the values predicted by the classical theory of statistical mechanics, K cl , is explored. The non-classical K corresponds to the unit-stage separation factor, α, that is different from unity and forms a basis of an isotope separation process involving the chemical exchange reaction. Here, the word 'chemical exchange' includes not only the isotope exchange chemical reactions between two or more chemical species but also the isotope exchanges involving the equilibria between liquid and vapor phases and liquid-gas, liquid solution-gas, liquid-liquid, and solid-liquid phases. In Section I, origins of the isotope effect phenomena will be explored and, in the process, various quantities used in discussions of isotope effect that have often caused confusions will be unambiguously defined. This Section will also correlate equilibrium constant with separation factor. In Section II, various forms of temperature-dependence of IE and separation factor will be discussed. (author)

  2. Isotope effect on hydrated electron relaxation dynamics studied with time-resolved liquid jet photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Elkins, Madeline H.; Williams, Holly L. [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Neumark, Daniel M., E-mail: dneumark@berkeley.edu [Department of Chemistry, University of California, Berkeley, California 94720 (United States); Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720 (United States)

    2016-05-14

    The excited state relaxation dynamics of the solvated electron in H{sub 2}O and D{sub 2}O are investigated using time-resolved photoelectron spectroscopy in a liquid microjet. The data show that the initial excited state decays on a time scale of 75 ± 12 fs in H{sub 2}O and 102 ± 8 fs in D{sub 2}O, followed by slower relaxation on time scales of 400 ± 70 fs and 390 ± 70 fs that are isotopically invariant within the precision of our measurements. Based on the time evolution of the transient signals, the faster and slower time constants are assigned to p → s internal conversion (IC) of the hydrated electron and relaxation on the ground electronic state, respectively. This assignment is consistent with the non-adiabatic mechanism for relaxation of the hydrated electron and yields an isotope effect of 1.4 ± 0.2 for IC of the hydrated electron.

  3. Non-linear Isotope Effects

    DEFF Research Database (Denmark)

    Schmidt, Johan Albrecht

    ’s stratosphere is nearly mass dependent, and only a small fraction of the observed anomalous oxygen-17 excess can be attributed to N2O photolysis. In contrast, stratospheric photolysis produces a significant inverse clumped isotope effect.(ii) Stratospheric OCS photolysis significantly enrich the remaining OCS...

  4. Isotopic effects in mechanistic studies of biotransformations of fluorine derivatives of L-alanine catalysed by L-alanine dehydrogenase

    International Nuclear Information System (INIS)

    Szymańska-Majchrzak, Jolanta; Pałka, Katarzyna; Kańska, Marianna

    2017-01-01

    Synthesis of 3-fluoro-[2- 2 H]-L-alanine (3-F-[ 2 H]-L-Ala) in reductive amination of 3-fluoropyruvic acid catalysed by L-alanine dehydrogenase (AlaDH) was described. Fluorine derivative was used to study oxidative deamination catalysed by AlaDH applied kinetic (for 3-F-L-Ala in H 2 O - KIE’s on V max : 1.1; on V max /K M : 1.2; for 3-F-L-Ala in 2 H 2 O – on V max : 1.4; on V max /K M : 2.1) and solvent isotope effect methods (for 3-F-L-Ala - SIE’s on V max : 1.0; on V max /K M : 0.87; for 3-F-[2- 2 H]-L-Ala – on V max : 1.4; on V max /K M : 1.5). Studies explain some details of reaction mechanism. - Highlights: • Synthesis of 3-fluoro-[2- 2 H]-L-alanine was performed. • The reactions were catalysed using the enzyme L-alanine dehydrogenase. • Performed reactions involved fluorinated analogues of L-alanine. • Solvent isotope effects of deuterium were determined. • Kinetic isotope effects were determined for obtained 3-fluoro-L-alanine. • The mechanism of reaction catalysed by L-alanine dehydrogenase was proposed.

  5. Lithium isotopic separation: preliminary studies

    International Nuclear Information System (INIS)

    Macedo, Sandra Helena Goulart de

    1998-01-01

    In order to get the separation of natural isotopes of lithium by electrolytic amalgamation, an electrolytic cell with a confined mercury cathode was used to obtain data for the design of a separation stage. The initial work was followed by the design of a moving mercury cathode electrolytic cell and three experiments with six batches stages were performed for the determination of the elementary separation factor. The value obtained, 1.053, was ill agreement: with the specialized literature. It was verified in all experiments that the lithium - 6 isotope concentrated in the amalgam phase and that the lithium - 7 isotope concentrated in the aqueous phase. A stainless-steel cathode for the decomposition of the lithium amalgam and the selective desamalgamation were also studied. In view of the results obtained, a five stages continuous scheme was proposed. (author)

  6. The effect of dipolar interaction on the magnetic isotope effect

    DEFF Research Database (Denmark)

    Mojaza, Matin; Pedersen, Jørgen Boiden; Lukzen, Nikita

    2010-01-01

    A multi-channel kinetic description is used to study the magnetic isotope effect (MIE) in zero magnetic field. The maximal isotope effect is equal to the number of channels, two for the hyperfine interaction but four for the electron spin dipole–dipole interaction of the intermediate radical pair....... Quantum mechanical calculations agree with these conclusion and show that large MIE may be obtained even in the presence of a strong exchange interaction. The observed magnesium isotope effect on the rate of enzymatic synthesis of adenosine triphosphate (ATP) is approximately 3 implying that the dipolar...... interaction is responsible for the effect. Our calculations provide support for the proposed mechanism....

  7. On the isotope effects of ZrCoX3 (X = H, D and T): a first-principles study

    International Nuclear Information System (INIS)

    Chattaraj, D.; Parida, S.C.; Dash, Smruti; Majumder, C.

    2013-01-01

    In the ITER project, the ZrCo-X (X= H, D and T) systems have gained considerable attention because of its use in the hydrogen isotope storage. The isotopic effects on the ZrCoX 3 (X= H, D and T) compounds have been studied in terms of the variation of the thermodynamic parameters using the DFT and frozen phonon approach. A significant difference between the ZrCoH 3 and its isotopic analogues has been noticed in terms of zero point energy (ZPE) and phonon frequencies. The zero point energies are 65.47 kJ/mol, 48.07 kJ/mol and 39.32 kJ/mol for ZrCoH 3 , ZrCoD 3 and ZrCoT 3 , respectively. The enthalpy of formation of ZrCoX 3 compounds, including the ZPE contributions, are -124.84, -142.24 and -150.99 kJ/(mole of compound) for X = H, D and T, respectively. (author)

  8. The study on effect of zeolite on nitrogen use efficiency of corn by 15N-isotope dilution method

    International Nuclear Information System (INIS)

    Li Changhong; Li Huaxing; Zhang Xinming; Liu Yuanjin

    2002-01-01

    A pot experiment was carried out to study the effect of natural zeolite on nitrogen use efficiency of corn by using 15 N-isotope dilution method. The results showed that application of zeolite could improve the corn growth and enhance the biomass of the corn seedling. By using zeolite, nitrogen use efficiency (NUE) of corn was increased by 23.2%-33.1% as compared with no-zeolite treatment; and the residual nitrogen has no significant difference between zeolite treatment and no-zeolite treatment

  9. Isotope effect of glycinium phosphite NH3CH2COOH·H2PO3 studied by neutron diffraction

    International Nuclear Information System (INIS)

    Magome, Eisuke; Komukae, Masaru; Machida, Mitsuo; Tamura, Yuuki

    2007-01-01

    To study the isotope effect of glycinium phosphite (GPI), temperature dependences of the 5 0 6-bar and 3 0 1 0-bar structure factors of GPI and the 1 1 0 3-bar and 9 0 8-bar structure factors of deuterated GPI (DGPI) were analyzed in the ferroelectric phase by using the quasi-one-dimensional Ising model. The Ising model reproduces well the behavior of all the structure factors in the wide temperature region. The parameters for the intrachain and interchain interactions are determined to be 312 and 7.1 K for GPI, and 477 and 8.4 K for DGPI on average, respectively. (author)

  10. Laser isotope separation studies in JAERI

    International Nuclear Information System (INIS)

    Arisawa, Takashi; Shiba, Koreyuki

    1986-01-01

    For uranium enrichment, Japan Atomic Energy Research Institute (JAERI) has been studying atomic vapor laser isotope separation since 1976, in addition to such separation methods as gas diffusion, chemical exchange and gas-dynamic techniques. Studies carried out to date in JAERI is briefly summarized in the first part of the report. Then, some major separation techniques which have been studied in JAERI are outlined, and typical results obtained are presented. A large part is devoted to the multiple-photon photoionization technique, which is commonly known as the atomic laser isotope separation method for uranium enrichment. It has such advantages as 1) very high spectral selectivity for the relevant isotope and 2) highly improved photoionizing effect by means of two- and three-step resonance photoionization processes. Here, the atomic laser isotope separation method is discussed in detail with respect to the evaporation process, energy levels, photoionization, selectivity, photoionization schemes, ion recovery, separation in macroscopic amounts, and separation of trace amounts of isotopes. Typical observed and claculated results related to these subjects are shown. In addition, the report briefly describes some other separation processes including laser induced chemical reaction, multiple photo-dissociation, multiple-photo excitation and UV dissociation, laser induced thermal diffusion, and laser centrifugation. (Nogami, K.)

  11. Using species-specific enriched stable isotopes to study the effect of fresh mercury inputs in soil-earthworm systems.

    Science.gov (United States)

    Álvarez, C Rodríguez; Jiménez-Moreno, M; Bernardo, F J Guzmán; Martín-Doimeadios, R C Rodríguez; Nevado, J J Berzas

    2018-01-01

    The fate of mercury (Hg) in the soil-earthworm system is still far from being fully understood, especially regarding recurrent and challenging questions about the importance of the reactivity of exogenous Hg species. Thus, to predict the potential effect of Hg inputs in terrestrial ecosystems, it is necessary to evaluate separately the reactivity of the endogenous and exogenous Hg species and, for this purpose, the use of enriched stable isotope tracers is a promising tool. In the present work, earthworms (Lumbricus terrestris) were exposed to historically Hg contaminated soils from the Almadén mining district, Spain. The soils were either non-spiked, which contain only endogenous or native Hg naturally occurring in the soil, or spiked with isotopically enriched inorganic Hg ( 199 IHg), representing exogenous or spiked Hg apart from the native one. The differential reactivity of endogenous and exogenous Hg in the soil conditioned the processes of methylation, mobilization, and assimilation of inorganic Hg by earthworms. Both endogenous and exogenous Hg species also behave distinctly regarding their bioaccumulation in earthworms, as suggested by the bioaccumulation factors, being the endogenous methylmercury (MeHg) the species more readily bioaccumulated by earthworms and in a higher extent. To the best of our knowledge, this work demonstrates for the first time the potential of enriched stable isotopes to study the effects of fresh Hg inputs in soil-earthworm systems. The findings of this work can be taken as a case study on the dynamics of Hg species in complex terrestrial systems and open a new door for future experiments. Copyright © 2017 Elsevier Inc. All rights reserved.

  12. Use of Isotopes for Studying Reaction Mechanisms

    Indian Academy of Sciences (India)

    In the first part of this series, we discussed how isotopes can be used as markers to determine the nature of intermediates in chemical reactions. The second part covered the effect of isotopes on equilibria and reactions, in processes where the bond to the isotopic a tom is broken. We showed with specific examples how.

  13. Structural and kinetic isotope effect studies of nicotinamidase (Pnc1) from Saccharomyces cerevisiae.

    Science.gov (United States)

    Smith, Brian C; Anderson, Mark A; Hoadley, Kelly A; Keck, James L; Cleland, W Wallace; Denu, John M

    2012-01-10

    Nicotinamidases catalyze the hydrolysis of nicotinamide to nicotinic acid and ammonia. Nicotinamidases are absent in mammals but function in NAD(+) salvage in many bacteria, yeast, plants, protozoa, and metazoans. We have performed structural and kinetic investigations of the nicotinamidase from Saccharomyces cerevisiae (Pnc1). Steady-state product inhibitor analysis revealed an irreversible reaction in which ammonia is the first product released, followed by nicotinic acid. A series of nicotinamide analogues acting as inhibitors or substrates were examined, revealing that the nicotinamide carbonyl oxygen and ring nitrogen are critical for binding and reactivity. X-ray structural analysis revealed a covalent adduct between nicotinaldehyde and Cys167 of Pnc1 and coordination of the nicotinamide ring nitrogen to the active-site zinc ion. Using this structure as a guide, the function of several residues was probed via mutagenesis and primary (15)N and (13)C kinetic isotope effects (KIEs) on V/K for amide bond hydrolysis. The KIE values of almost all variants were increased, indicating that C-N bond cleavage is at least partially rate limiting; however, a decreased KIE for D51N was indicative of a stronger commitment to catalysis. In addition, KIE values using slower alternate substrates indicated that C-N bond cleavage is at least partially rate limiting with nicotinamide to highly rate limiting with thionicotinamide. A detailed mechanism involving nucleophilic attack of Cys167, followed by elimination of ammonia and then hydrolysis to liberate nicotinic acid, is discussed. These results will aid in the design of mechanism-based inhibitors to target pathogens that rely on nicotinamidase activity.

  14. Structural and Kinetic Isotope Effect Studies of Nicotinamidase (Pnc1) from S. cerevisiae†

    Science.gov (United States)

    Smith, Brian C.; Anderson, Mark A.; Hoadley, Kelly A.; Keck, James L.; Cleland, W. Wallace; Denu, John M.

    2011-01-01

    Nicotinamidases catalyze the hydrolysis of nicotinamide to nicotinic acid and ammonia. Nicotinamidases are absent in mammals but function in NAD+ salvage in many bacteria, yeast, plants, protozoa, and metazoans. We have performed structural and kinetic investigations of the nicotinamidase from S. cerevisiae (Pnc1). Steady-state product inhibitor analysis revealed an irreversible reaction where ammonia is the first product released, followed by nicotinic acid. A series of nicotinamide analogs acting as inhibitors or substrates were examined revealing that the nicotinamide carbonyl oxygen and ring nitrogen are critical for binding and reactivity. X-ray structural analysis revealed a covalent adduct between nicotinaldehyde and Cys167 of Pnc1 and coordination of the nicotinamide ring nitrogen to the active-site zinc ion. Using this structure as a guide, the function of several residues was probed via mutagenesis and primary 15N and 13C kinetic isotope effects (KIE) on V/K for amide bond hydrolysis. The KIE values of almost all variants were increased indicating that C-N bond cleavage is at least partially rate limiting; however, a decreased KIE for D51N was observed indicative of a higher commitment to catalysis. In addition, KIE values using slower alternate substrates indicated that C-N bond cleavage is at least partially rate limiting with nicotinamide to highly rate limiting with thionicotinamide. A detailed mechanism is discussed involving nucleophilic attack of Cys167, followed by elimination of ammonia and then hydrolysis to liberate nicotinic acid. These results will aid design of mechanism-based inhibitors to target pathogens that rely on nicotinamidase activity. PMID:22229411

  15. Structural and Kinetic Isotope Effect Studies of Nicotinamidase (Pnc1) from Saccharomyces cerevisiae

    International Nuclear Information System (INIS)

    Smith, Brian C.; Anderson, Mark A.; Hoadley, Kelly A.; Keck, James L.; Cleland, W. Wallace; Denu, John M.

    2012-01-01

    Nicotinamidases catalyze the hydrolysis of nicotinamide to nicotinic acid and ammonia. Nicotinamidases are absent in mammals but function in NAD + salvage in many bacteria, yeast, plants, protozoa, and metazoans. We have performed structural and kinetic investigations of the nicotinamidase from Saccharomyces cerevisiae (Pnc1). Steady-state product inhibitor analysis revealed an irreversible reaction in which ammonia is the first product released, followed by nicotinic acid. A series of nicotinamide analogues acting as inhibitors or substrates were examined, revealing that the nicotinamide carbonyl oxygen and ring nitrogen are critical for binding and reactivity. X-ray structural analysis revealed a covalent adduct between nicotinaldehyde and Cys167 of Pnc1 and coordination of the nicotinamide ring nitrogen to the active-site zinc ion. Using this structure as a guide, the function of several residues was probed via mutagenesis and primary 15 N and 13 C kinetic isotope effects (KIEs) on V/K for amide bond hydrolysis. The KIE values of almost all variants were increased, indicating that C-N bond cleavage is at least partially rate limiting; however, a decreased KIE for D51N was indicative of a stronger commitment to catalysis. In addition, KIE values using slower alternate substrates indicated that C-N bond cleavage is at least partially rate limiting with nicotinamide to highly rate limiting with thionicotinamide. A detailed mechanism involving nucleophilic attack of Cys167, followed by elimination of ammonia and then hydrolysis to liberate nicotinic acid, is discussed. These results will aid in the design of mechanism-based inhibitors to target pathogens that rely on nicotinamidase activity.

  16. Structural and Kinetic Isotope Effect Studies of Nicotinamidase (Pnc1) from Saccharomyces cerevisiae

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Brian C.; Anderson, Mark A.; Hoadley, Kelly A.; Keck, James L.; Cleland, W. Wallace; Denu, John M. (UW)

    2012-05-08

    Nicotinamidases catalyze the hydrolysis of nicotinamide to nicotinic acid and ammonia. Nicotinamidases are absent in mammals but function in NAD{sup +} salvage in many bacteria, yeast, plants, protozoa, and metazoans. We have performed structural and kinetic investigations of the nicotinamidase from Saccharomyces cerevisiae (Pnc1). Steady-state product inhibitor analysis revealed an irreversible reaction in which ammonia is the first product released, followed by nicotinic acid. A series of nicotinamide analogues acting as inhibitors or substrates were examined, revealing that the nicotinamide carbonyl oxygen and ring nitrogen are critical for binding and reactivity. X-ray structural analysis revealed a covalent adduct between nicotinaldehyde and Cys167 of Pnc1 and coordination of the nicotinamide ring nitrogen to the active-site zinc ion. Using this structure as a guide, the function of several residues was probed via mutagenesis and primary {sup 15}N and {sup 13}C kinetic isotope effects (KIEs) on V/K for amide bond hydrolysis. The KIE values of almost all variants were increased, indicating that C-N bond cleavage is at least partially rate limiting; however, a decreased KIE for D51N was indicative of a stronger commitment to catalysis. In addition, KIE values using slower alternate substrates indicated that C-N bond cleavage is at least partially rate limiting with nicotinamide to highly rate limiting with thionicotinamide. A detailed mechanism involving nucleophilic attack of Cys167, followed by elimination of ammonia and then hydrolysis to liberate nicotinic acid, is discussed. These results will aid in the design of mechanism-based inhibitors to target pathogens that rely on nicotinamidase activity.

  17. Radiogenic age and isotopic studies

    International Nuclear Information System (INIS)

    1991-01-01

    This is one of an annual collection of reports presenting data from the Geochronology Section of the Continental Geoscience Division of the Geological Survey of Canada (GSC). The main purpose of this collection is to make geochronological and other radiogenic isotope data produced by the section available promptly to the geological community. Reports make full presentation of the data, relate these to field settings and make comparatively short interpretations. Other geochronological and isotope data produced in the laboratory but published in outside journals or separate GSC publications are summarized at the end of this report. Reports in this issue give U-Pb zircon ages for rocks in Newfoundland, Yukon Territory, Manitoba, Ontario, and the Northwest Territories; present a compilation of K-Ar ages; and discuss Precambrian activity in New Brunswick, the geochronology of rock from the Northwest Territories, and reconnaissance Nd studies of rocks from the Northwest Territories. (figs., tabs., refs.)

  18. Radiogenic age and isotopic studies

    International Nuclear Information System (INIS)

    1992-01-01

    This is one of an annual collection of reports presenting data from the Geochronology Section of the Continental Geoscience Division of the Geological Survey of Canada (GSC). The main purpose of this collection is to make geochronological and other radiogenic isotope data produced by the section available promptly to the geological community. Reports make full presentation of the data, relate these to field settings and make comparatively short interpretations. Other geochronological and isotope data produced in the laboratory but published in outside journals or separate GSC publications are summarized at the end of this report. Report 5 contains 24 papers from most regions of Canada, but particularly from British Columbia. The Geochronology Laboratory has, over the years, provided substantial U-Pb dating for the Cordilleran Division of the Geological Survey of Canada in Vancouver, and the results of a number of these studies are presented this year. A compilation of K-Ar ages is given. (figs., tabs., refs.)

  19. Studies on the optogalvanic effect and isotope-selective excitation of ytterbium in a hollow cathode discharge lamp using a pulsed dye laser.

    Science.gov (United States)

    Kumar, Pankaj; Kumar, Jitendra; Prakash, Om; Saini, Vinod K; Dixit, Sudhir K; Nakhe, Shankar V

    2013-09-01

    This paper presents studies on the pulsed optogalvanic effect and isotope-selective excitation of Yb 555.648 nm (0 cm(-1) → 17 992.007 cm(-1)) and 581.067 nm (17 992.007 cm(-1) → 35 196.98 cm(-1)) transitions, in a Yb/Ne hollow cathode lamp. The Yb atoms were excited by narrow linewidth (500-1000 MHz) Rh110 and Rh6G dye based pulsed lasers. Optogalvanic signal inversion for ground state transition at 555.648 nm was observed beyond a hollow cathode discharge current of 8.5 mA, in contrast to normal optogalvanic signal at 581.067 nm up to maximum current of 14 mA. The isotope-selective excitation studies of Yb were carried out by recording Doppler limited optogalvanic signals as a function of dye laser wavelength. For the 581.067 nm transition, three even isotopes, (172)Yb, (174)Yb, and (176)Yb, and one odd isotope, (171)Yb, were clearly resolved. These data were compared with selective isotope excitation by 10 MHz linewidth continuous-wave dye laser. For 555.648 nm transition, isotopes were not clearly resolved, although isotope peaks of low modulation were observed.

  20. Study on the effect of different fertilizer on the stable nitrogen isotope of soil, leaf and cucumber

    International Nuclear Information System (INIS)

    Yuan Yuwei; Zhang Zhiheng; Xu Mingfei; Yang Guiling; Zheng Jici; Wang Qiang; Zhao Ming

    2010-01-01

    The effect of combined application of organic and chemical fertilizers on stable nitrogen isotope abundance (δ 15 N-%), nitrate and nitrate reductase active was studied for the soil, cucumber and leaf,respectively. The results showed that the δ 15 N of cucumber was with the trend of low, high and low as the application rate of organic manure decreased, and it was significantly different (P 0.05) for the other treatments. The δ 15 N of cucumber was not significantly different during different harvest time (P>0.05) for the same treatment. The correlation of δ 15 N between the cucumber and the leaf was 0.9836 for the different treatment, whose δ 15 N was more affected more by the fertilizer and less by the soil. The content of nitrate in cucumber was reducing with the rate of organic manure decreasing, which had a bad correlation (r=0.6568) with the δ 15 N of cucumber; however the active of nitrate reductase was increasing which had a positive correlation with the treatments of control treatment, 100%, 80% and 60% of organic manure applied (r=0.9187), and a negative correlation with the treatments of 60%, 40%, 20% of organic manure and 100% chemical fertilizer applied (r=-0.9773). To sum up, the δ 15 N can be used as marks to discriminate the cucumbers grown with organic manure and chemical fertilizer, but the pattern of fractionation and distribution of the stable nitrogen isotope should be further studied. (authors)

  1. Experimental study on isotope fractionation of evaporating water of different initial isotopic composition

    International Nuclear Information System (INIS)

    Pooja Devi; Jain, A.K.; Rao, M.S.; Kumar, B.

    2014-01-01

    The studies of evaporative isotopic fractionation in controlled conditions are of particular importance for understanding the mechanism of evaporation fractionation in natural conditions. We present the measurements of the average isotopic fractionation factors during the evaporation of water having different initial isotopic compositions at constant temperature. The results show that the isotopic composition of residual water become more enriched over the time and the initial isotopic composition of evaporating water has considerable effect on the average isotopic fractionation factors. The average isotopic fractionation factors in evaporation of Water A and Water B under the present experimental conditions were found to be 0.9817 ± 0.0044 and 0.9887 ± 0.0031 for oxygen and 0.9178 ± 0.0182 and 0.9437 ± 0.0169 for hydrogen, respectively. The findings of this work should lead to a better understanding and use of stable isotope techniques in isotope hydrology by using a simple technique of evaporation pan. (author)

  2. Isotope effect studies of chicken liver NADP malic enzyme: role of the metal ion and viscosity dependence

    International Nuclear Information System (INIS)

    Grissom, C.B.; Cleland, W.W.

    1988-01-01

    The role of the metal ion in the oxidative decarboxylation of malate by chicken liver NADP malic enzyme and details of the reaction mechanism have been investigated by 13 C isotope effects. With saturating NADP and the indicated metal ion at a total concentration 10-fold higher than its K/sub m/, the following primary 13 C kinetic isotope effects at C 4 of malate [ 13 (VK/sub mal/)] were observed at pH 8.0: Mg 2+ , 1.0336; Mn 2+ , 1.0365; Cd 2+ , 1.0366; Zn 2+ , 1.0337; Co 2+ , 1.0283; Ni 2+ , 1.025. Knowing the partitioning of the intermediate oxalacetate between decarboxylation to pyuvate and reduction to malate allows calculation of the intrinsic carbon isotope effect for decarboxylation to pyuvate and reduction to malate allows calculation of the intrinsic carbon isotope effect for decarboxylation. For Mg 2+ as activator, this was 1.049 with NADP and 1.046 with 3-acetylpyridine adenine dinucleotide phosphate, although the intrinsic primary deuterium isotope effects on dehydrogenation were 5.6 and 4.2, and the partition ratios of the oxalacetate intermediate for decarboxylation as opposed to hydride transfer were 0.11 and 3.96. It was not possible to calculate reasonable intrinsic carbon isotope effects with the other metal ions by use of the partitioning ratio of oxalacetate because of decarboxylation by another mechanism. The variation of 13 (VK/sub mal/) with pH was used to dissect the total forward and external components. When the authors attempted to use the variation of 13 (VK/sub mal/) with solution viscosity to determine the internal and external commitments, incorrect values were obtained because of a specific effect of the viscosogen in decreasing the K/sub m/ for malate, so that VK/sub mal/ actually increased with viscosity instead of decreasing, as theory predicts

  3. Isotope studies on soil and fertilizer nitrogen

    International Nuclear Information System (INIS)

    Olson, R.A.

    1979-01-01

    Reductions in isotope cost in the 1960s and equipment innovations, have extended compared to 1940, the research of soil and plant scientists so that 15 N is now an indispensable tool when working with N. Leadership of FAO/IAEA coordinated research programmes and the Nitrogen Laboratory of the Tennessee Valley Authority helped greatly in bringing about this expanded usage. Recognized isotope effects are of insufficient magnitude to invalidate tracer measurements of field crop uptake in the treatment year if enrichment of 0.3 at.% excess 15 N or greater is employed. Thus, use of 15 N depleted tracer with potential of 0.366% 15 N differential from the standard isotope ratio of N in air is feasible. Its manufacture has allowed further economy in the isotope tag and ultimate treatment of field-scale plots. Interest in Δ 15 N measurements for predicting the NO - 3 contaminant source in surface and ground waters has depreciated. Variations in natural isotope ratio of soil N commonly exceed the differences in Δ 15 N values of the presumed source materials. 15 N provides the only correct measure of fertilizer N utilization efficiency. The field study examples of irrigated maize demonstrate that little or no fertilizer N is likely to escape the root zone where the rate applied does not exceed that required for maximum yield; also, that light and frequent irrigations afford higher yields than heavier, less frequent irrigations. Delaying fertilizer N applications until the crop is well established affords not only higher yields, but greater residual fertilizer N for future crops. Measured effective root activity for absorbing NO - 3 has been invaluable in estimating fertilizer requirements of a crop in relation to residual mineral N in soil at planting and projecting the depth at which the NO - 3 becomes an environmental hazard. The tag likewise is indispensable in determining symbiotic N fixation

  4. Secondary deuterium isotope effects in the hydrolysis of some acetals

    International Nuclear Information System (INIS)

    Paterson, R.V.

    Secondary α-deuterium kinetic isotope effects have been determined in the hydrolyses of some acetals. Benzaldehyde dimethyl acetal and 2-phenyl-1,3-dioxolan show isotope effects in agreement with an A1 mechanism. 2-Phenyl-4,4,5,5-tetramethyl-1,3-dioxolan, which has been shown to undergo hydrolysis by an A2 type mechanism, has an isotope effect in agreement with participation by water in the transition state. Hydrolysis of benzylidene norbornanediols, although complicated by isomerisation, has an isotope effect in agreement with an A2 mechanism. Kinetic isotope effects in acetals which have a neighbouring carboxyl group have also been determined. Hydrolysis of 2-carboxybenzaldehyde dimethyl acetal in aqueous and 82% w/w dioxan-water buffers has isotope effects in agreement with a large degree of carbonium ion character in the transition state. Anderson and Capon proposed nucleophilic participation in the hydrolysis of this acetal in 82% dioxan-water. The isotope effect determined in this study is not in agreement with this finding. Hydrolysis of 2-(2'-carboxyphenyl)-4,4,5,5-tetramethyl-1,3-dioxolan shows an isotope effect larger than the corresponding dioxolan without the carboxyl group in agreement with some carbonium ion character in the transition state. A new synthesis of a deuterated aldehyde is described which might be general for aldehydes which will not form benzoins readily. (author)

  5. Macrocyclic ligand decorated ordered mesoporous silica with large-pore and short-channel characteristics for effective separation of lithium isotopes: synthesis, adsorptive behavior study and DFT modeling.

    Science.gov (United States)

    Liu, Yuekun; Liu, Fei; Ye, Gang; Pu, Ning; Wu, Fengcheng; Wang, Zhe; Huo, Xiaomei; Xu, Jian; Chen, Jing

    2016-10-18

    Effective separation of lithium isotopes is of strategic value which attracts growing attention worldwide. This study reports a new class of macrocyclic ligand decorated ordered mesoporous silica (OMS) with large-pore and short-channel characteristics, which holds the potential to effectively separate lithium isotopes in aqueous solutions. Initially, a series of benzo-15-crown-5 (B15C5) derivatives containing different electron-donating or -withdrawing substituents were synthesized. Extractive separation of lithium isotopes in a liquid-liquid system was comparatively studied, highlighting the effect of the substituent, solvent, counter anion and temperature. The optimal NH 2 -B15C5 ligands were then covalently anchored to a short-channel SBA-15 OMS precursor bearing alkyl halides via a post-modification protocol. Adsorptive separation of the lithium isotopes was fully investigated, combined with kinetics and thermodynamics analysis, and simulation by using classic adsorption isotherm models. The NH 2 -B15C5 ligand functionalized OMSs exhibited selectivity to lithium ions against other alkali metal ions including K(i). Additionally, a more efficient separation of lithium isotopes could be obtained at a lower temperature in systems with softer counter anions and solvents with a lower dielectric constant. The highest value separation factor (α = 1.049 ± 0.002) was obtained in CF 3 COOLi aqueous solution at 288.15 K. Moreover, theoretical computation based on the density functional theory (DFT) was performed to elucidate the complexation interactions between the macrocyclic ligands and lithium ions. A suggested mechanism involving an isotopic exchange equilibrium was proposed to describe the lithium isotope separation by the functionalized OMSs.

  6. Low-dose in vivo pharmacokinetic and deuterium isotope effect studies of N-nitrosodimethylamine in rats

    International Nuclear Information System (INIS)

    Mico, B.A.; Swagzdis, J.E.; Hu, H.S.; Keefer, L.K.; Oldfield, N.F.; Garland, W.A.

    1985-01-01

    The rates of elimination of N-nitrosodimethylamine (NDMA) and its fully deuterated analogue (N-nitrosodi[ 2 H6]methylamine, [ 2 H6]NDMA) were studied in vivo to explore the origins of the difference in their carcinogenicity. Male Fischer 344 rats, 7.5 weeks of age, were given nitrosamine bolus doses of 1.35 mumol/kg by tail vein injection and 2.02 or 4.05 mumol/kg by p.o. gavage. Animals were sacrificed at various time points from 2.5 to 180 min after i.v. administration or 5 to 120 min after p.o. dosage, and their blood was analyzed for NDMA by gas chromatography-high resolution mass spectrometry. After i.v. injection, blood nitrosamine concentrations declined in an apparently biexponential manner with a terminal half-life of 10 min for NDMA and 12 min for [ 2 H6]NDMA. The apparent total systemic blood clearances for NDMA and [ 2 H6]NDMA were 39 and 26 ml/min/kg, respectively. The apparent steady-state volumes of distribution were nearly identical (297 and 309 ml/kg, respectively). The areas under the curve after 2.02- and 4.05-mumol/kg p.o. doses were proportional to dose. The apparent bioavailability of NDMA was 8%, while that of [ 2 H6]NDMA was 21%. Isotope effects calculated as the ratios of first-pass metabolism, total systemic clearances, bioavailabilities, and intrinsic hepatic clearances were 1.2, 1.5, 2.6, and 3.2, respectively. The isotope effect determined from blood concentrations measured after simultaneous administration of NDMA and [ 2 H6]NDMA by steady-state infusion (each at 1.5 mumol/kg/h) was 2.6 +/- 0.9 (SD)

  7. Hydrogeological and isotopic studies for selected springs in Sinai Peninsula

    Energy Technology Data Exchange (ETDEWEB)

    Hamza, M S; Awad, M A; El-gamal, S A [Atomic Energy Authority, Cairo Egypt and Middle Eastern Regional Radioisotope Center for The Arab Countries, Dokki, 12311, Cairo (Egypt); Hammad, F A [Desert Research Centre, Materia, Cairo, (Egypt)

    1995-10-01

    This paper deals with the hydrogeology and isotopic composition of water samples collected from selected spring in sinai (e.g. Algudierate, Alqusiema, qidis and Isram) in order to identify their genesis, their interaction with the host rocks and mixing trend. Results of isotopic composition have indicated the similarity in the hydrogeologic situation of Ain qidis and Ain-al-gudierate, while Ain Isram has shown a marked difference in its stable isotope and this could be due to evaporation effect. The isotopic and hydrochemical constituents of the studied springs reflect eater of a meteoric origin with a possible contamination from surficial materials (evaporates) and deeper aquifers. 6 figs., 2 tabs.

  8. Effects of must concentration techniques on wine isotopic parameters.

    Science.gov (United States)

    Guyon, Francois; Douet, Christine; Colas, Sebastien; Salagoïty, Marie-Hélène; Medina, Bernard

    2006-12-27

    Despite the robustness of isotopic methods applied in the field of wine control, isotopic values can be slightly influenced by enological practices. For this reason, must concentration technique effects on wine isotopic parameters were studied. The two studied concentration techniques were reverse osmosis (RO) and high-vacuum evaporation (HVE). Samples (must and extracted water) have been collected in various French vineyards. Musts were microfermented at the laboratory, and isotope parameters were determined on the obtained wine. Deuterium and carbon-13 isotope ratios were studied on distilled ethanol by nuclear magnetic resonance (NMR) and isotope ratio mass spectrometry (IRMS), respectively. The oxygen-18 ratio was determined on extracted and wine water using IRMS apparatus. The study showed that the RO technique has a very low effect on isotopic parameters, indicating that this concentration technique does not create any isotopic fractionation, neither at sugar level nor at water level. The effect is notable for must submitted to HVE concentration: water evaporation leads to a modification of the oxygen-18 ratio of the must and, as a consequence, ethanol deuterium concentration is also modified.

  9. Medium Effects in Reactions with Rare Isotopes

    International Nuclear Information System (INIS)

    Bertulani, C A; Karakoç, M

    2012-01-01

    We discuss medium effects in knockout reactions with rare isotopes of weakly-bound nuclei at intermediate energies. We show that the poorly known corrections may lead to sizable modifications of knockout cross sections and momentum dsitributions.

  10. Spectroscopic and Quantum Mechanical Calculation Study of the Effect of Isotopic Substitution on NIR Spectra of Methanol.

    Science.gov (United States)

    Grabska, Justyna; Czarnecki, Mirosław A; Beć, Krzysztof B; Ozaki, Yukihiro

    2017-10-19

    In this work, we studied methanol and its deuterated derivatives (CH 3 OH, CH 3 OD, CD 3 OH, CD 3 OD) by NIR spectroscopy and anharmonic quantum chemical calculations. Vibrational bands corresponding to up to three quanta transitions (first and second overtones, binary and ternary combination modes) were predicted by the use of the VPT2 route. The accuracy of prediction of NIR modes was evaluated through density functional theory (DFT) with selected density functionals and basis sets. On the basis of the theoretical NIR spectra, detailed band assignments for all studied molecules were proposed. It was found that the pattern of bands in NIR spectra of deuterated methanols can be used for identification of isotopically equalized forms. Calculations of NIR spectra of all possible forms of CXXXOX (X = H, D) molecules demonstrated that the isotopic contamination can be identified due to a coexistence of bands specific to OH and OD groups. Also, bands from partially deuterated methyl groups can be distinguished in NIR spectra. Since the VPT2 framework is known to be sensitive to inaccuracy in the case of highly anharmonic modes, we obtained an independent insight by numerical solving of the time-independent Schrödinger equation corresponding to the O-X stretching mode scanned within -0.4 to 2.0 Å over a dense grid of 0.005 Å. This way the energies of vibrational levels of the CX1X2X3OX4 (X = H, D) isotopomers and the corresponding transition frequencies were obtained with high accuracy (<0.1 cm -1 ). The change in normal coordinate influences the reduced mass of the oscillator and thus its frequency. Our results lead to a conclusion that the effect of deuterization of the methyl group introduces a very specific and consistent frequency shift of the first overtone of the O-X stretching mode depending on the substitution of X1, X2, or X3 positions (<2 cm -1 ). However, the pattern of this shift is not reproduced accurately and is also largely overestimated by VPT2

  11. Isotope effect in gamma-radiolysis of absorbed ammonia

    Energy Technology Data Exchange (ETDEWEB)

    Lyapina, T G; Kotov, A G [Nauchno-Issledovatel' skij Fiziko-Khimicheskij Inst., Moscow (USSR)

    1975-07-01

    The radiolysis of NH/sub 3/ of various isotopic compounds adsorbed on silica gel or zeolite at 77degK was studied. Experimental data were treated using the kinetic equation dR/dt=GI-kIR where R=radical concentration, G=radical yield, k=radical termination constant and I=radiation dose rate. Both the values of G and R for NH/sub 3/ adsorbed on silica gel are affected by the isotopic effect of /sup 15/N, but not on zeolite. The isotopic effect is explained by the influence of protonated acidity of the silica gel surface.

  12. Isotope shift studies in gadolinium spectra

    International Nuclear Information System (INIS)

    Ahmad, S.A.; Saksena, G.D.; Venugopalan, A.

    1976-01-01

    Isotope shift studies have been carried out in the gadolinium spectrum using a recording Fabry-Perot spectrometer and gadolinium samples enriched in 156 Gd and 160 Gd isotopes. Isotope shifts Δsigma(156-160) have been recorded in 134 lines in the region 3930-4140 A. Some of these lines involve the recently identified even configuration 4f 8 5d6s of Gd I and the newly classified transition 4f 8 6s-4f 8 6p of Gd II. From the isotope shift measurements of lines involving the 4f 8 6s-4f 8 6p transition in Gd II, the isotope shift, ΔT(156-160)=87 mK, has been obtained for the 4f 8 6s configuration. Electronic configurations have been suggested for a number of energy levels and configuration mixing has been pointed out in certain cases. (Auth.)

  13. Bibliography on vapour pressure isotope effects

    International Nuclear Information System (INIS)

    Illy, H.; Jancso, G.

    1976-03-01

    The bibliography of research on vapour pressure isotope effects from 1919 to December 1975 is presented in chronological order. Within each year the references are listed alphabetically according to the name of the first author of each work. The bibliography is followed by a Compound Index containing the names o compounds, but the type of isotopic substituation is not shown. The Author Index includes all authors of the papers. (Sz.N.Z.)

  14. Mass-independent isotope effects in chemical exchange reaction

    International Nuclear Information System (INIS)

    Nishizawa, Kazushige

    2000-01-01

    Isotope effects of some elements in chemical exchange reaction were investigated by use of liquid-liquid extraction, liquid membrane or chromatographic separation. Cyclic polyether was used for every method. All polyethers used in a series of the studies were made clear that they distinguished the isotopes not only by their nuclear masses but also by their nuclear sizes and shapes. Chromium isotopes, for example, were recognized to have enrichment factors being proportional to δ 2 > which is a parameter to show field shift or the nuclear size and shape of the isotope. It follows that the chromium isotopes are separated not by their masses but by their field shift effects. Nuclear spin also played a great role to separate odd mass number isotopes from even mass number isotopes in even atomic number elements. Contribution of the nuclear spin (I=3/2) of 53 Cr to total enrichment factor, ε 53/52 = -0.00028, for 53 Cr to 52 Cr was observed to be, ε spin = -0.0025. (author)

  15. Isotope effects of sulfur in chemical reactions

    International Nuclear Information System (INIS)

    Mikolajczuk, A.

    1999-01-01

    Sulfur is an important component of organic matter because it forms compounds with many elements. Due to high chemical activity of sulfur, it takes part in biological and geological processes in which isotope effects are occurring. It has been shown during last years research of isotope effects that we have take into account not only mass difference but also many other physical properties of nuclides e.g. even or odd number of neutrons in nuclei, shape and distribution of charge, turn of nuclear spin etc. The factor remains that new theoretical ideas have been formed on the base of data, being obtained in fractionation processes of heavy element isotope, particularly uranium. Now it is being well known that effects unconnected with vibration energy have also caused an effect on fractionation of considerably lighter elements like iron and magnesium. The important question is, if these effects would come to light during the separation of sulfur isotopes. Sulfur have three even isotopes M = (32, 34, 36) and one odd M 33). This problem is still open. (author)

  16. Radiogenic age and isotopic studies

    International Nuclear Information System (INIS)

    Parrish, R.R.

    1990-01-01

    This is one of an annual collection of reports presenting data from the Geochronology Section of the Continental Geoscience Division of the Geological Survey of Canada (GSC). The main purpose of this collection is to make geochronological and other radiogenic isotope data produced by the section available promptly to the geological community. Reports make full presentation of the data, relate these to field settings and make comparatively short interpretations. Other geochronological and isotope data produced in the laboratory but published in outside journals or separate GSC publications are summarized at the end of this report. Reports in this issue cover methods for Rb-Sr and Sm-Nd isotopic analyses; 40 Ar- 39 Ar ages for the New Quebec Crater and for basaltic rocks; U-Pb ages for a differentiated mafic sill in the Ogilvie Mountains, plutonic rocks in the Contwoyto-Nose Lakes are, zircons from the Anton Complex, the Clinton-Colden gabbro-anorthosite intrusion, the Himag plutonic suite, the Campbell granite, the Central Gneiss Belt, Silurian granites, a metarhyolite, plagiogranite and gabbro, and the Wage shear zone; Rb-Sr ages for granitic rocks; K-Ar and Rb-Sr geochronology of granites; a compilation of K-Ar ages; ages of archean and proterozoic mylonites and pre-Misi granitoid domes; and reconnaissance geochronology of Baffin Island

  17. Shifts in rotifer life history in response to stable isotope enrichment: testing theories of isotope effects on organismal growth

    Science.gov (United States)

    2017-01-01

    In ecology, stable isotope labelling is commonly used for tracing material transfer in trophic interactions, nutrient budgets and biogeochemical processes. The main assumption in this approach is that the enrichment with a heavy isotope has no effect on the organism growth and metabolism. This assumption is, however, challenged by theoretical considerations and experimental studies on kinetic isotope effects in vivo. Here, I demonstrate profound changes in life histories of the rotifer Brachionus plicatilis fed 15N-enriched algae (0.4–5.0 at%); i.e. at the enrichment levels commonly used in ecological studies. These findings support theoretically predicted effects of heavy isotope enrichment on growth, metabolism and ageing in biological systems and underline the importance of accounting for such effects when using stable isotope labelling in experimental studies. PMID:28405367

  18. Glutathione reductase: solvent equilibrium and kinetic isotope effects

    International Nuclear Information System (INIS)

    Wong, K.K.; Vanoni, M.A.; Blanchard, J.S.

    1988-01-01

    Glutathione reductase catalyzes the NADPH-dependent reduction of oxidized glutathione (GSSG). The kinetic mechanism is ping-pong, and we have investigated the rate-limiting nature of proton-transfer steps in the reactions catalyzed by the spinach, yeast, and human erythrocyte glutathione reductases using a combination of alternate substrate and solvent kinetic isotope effects. With NADPH or GSSG as the variable substrate, at a fixed, saturating concentration of the other substrate, solvent kinetic isotope effects were observed on V but not V/K. Plots of Vm vs mole fraction of D 2 O (proton inventories) were linear in both cases for the yeast, spinach, and human erythrocyte enzymes. When solvent kinetic isotope effect studies were performed with DTNB instead of GSSG as an alternate substrate, a solvent kinetic isotope effect of 1.0 was observed. Solvent kinetic isotope effect measurements were also performed on the asymmetric disulfides GSSNB and GSSNP by using human erythrocyte glutathione reductase. The Km values for GSSNB and GSSNP were 70 microM and 13 microM, respectively, and V values were 62 and 57% of the one calculated for GSSG, respectively. Both of these substrates yield solvent kinetic isotope effects greater than 1.0 on both V and V/K and linear proton inventories, indicating that a single proton-transfer step is still rate limiting. These data are discussed in relationship to the chemical mechanism of GSSG reduction and the identity of the proton-transfer step whose rate is sensitive to solvent isotopic composition. Finally, the solvent equilibrium isotope effect measured with yeast glutathione reductase is 4.98, which allows us to calculate a fractionation factor for the thiol moiety of GSH of 0.456

  19. Isotope effects in pericyclic reactions, ch. 2

    International Nuclear Information System (INIS)

    Dolbier, W.R. Jr.

    1975-01-01

    A distinction is made between primary and secondary isotope effects, the primary ones being based on the relative large vibrational frequencies and ensuing large zeroprint energies for C-H vibrations whereas the secondary effects are observed in systems where the vibrational modes of the isotopically labelled site are perturbed during transformation from reactant to product. Both effects are utilised in the elucidation of mechanism in pericyclic processes. The main processes dealt with in this chapter are cycloadditions of all types and sigmatropic rearrangements

  20. Metabolic studies in man using stable isotopes

    International Nuclear Information System (INIS)

    Faust, H.; Jung, K.; Krumbiegel, P.

    1993-01-01

    In this project, stable isotope compounds and stable isotope pharmaceuticals were used (with emphasis on the application of 15 N) to study several aspects of nitrogen metabolism in man. Of the many methods available, the 15 N stable isotope tracer technique holds a special position because the methodology for application and nitrogen isotope analysis is proven and reliable. Valid routine methods using 15 N analysis by emission spectrometry have been demonstrated. Several methods for the preparation of biological material were developed during our participation in the Coordinated Research Programme. In these studies, direct procedures (i.e. use of diluted urine as a samples without chemical preparation) or rapid isolation methods were favoured. Within the scope of the Analytical Quality Control Service (AQCS) enriched stable isotope reference materials for medical and biological studies were prepared and are now available through the International Atomic Energy Agency. The materials are of special importance as the increasing application of stable isotopes as tracers in medical, biological and agricultural studies has focused interest on reliable measurements of biological material of different origin. 24 refs

  1. Study of neutron-deficient Sn isotopes

    International Nuclear Information System (INIS)

    Auger, G.

    1982-05-01

    The formation of neutron deficient nuclei by heavy ion reactions is investigated. The experimental technique is presented, and the results obtained concerning Sn et In isotopes reported: first excited states of 106 Sn, high spin states in 107 Sn and 107 In; Yrast levels of 106 Sn, 107 Sn, 108 Sn; study of neutron deficient Sn and In isotopes formed by the desintegration of the compound nucleus 112 Xe. All these results are discussed [fr

  2. Inverse isotope effect in iron-based superconductor

    International Nuclear Information System (INIS)

    Shirage, Parasharam M.; Kihou, Kunihiro; Miyazawa, Kiichi; Lee, Chul-Ho; Kito, Hijiri; Yoshida, Yoshiyuki; Eisaki, Hiroshi; Tanaka, Yasumoto; Iyo, Akira

    2010-01-01

    We have found that (Ba, K)Fe 2 As 2 superconductor (a transition temperature, T c ∼ 38 K) shows an inverse Iron isotope effect (α Fe = -0.18 ± 0.03, where T c ∼ M -αFe and M is the iron isotope mass), i.e. the sample containing the larger iron mass depicts higher T c . Systematic studies using three types of Fe-isotopes ( 54 Fe, natural Fe and 57 Fe) reveal a clear inverse shift on T c by measurements of temperature dependent magnetization and resistivity. The inverse isotope effect that is the first case in high-T c superconductors strongly suggests that superconducting mechanism of the iron-based system is not explained by conventional BCS theory mediated by phonons.

  3. N-loss isotope effects in the Peru oxygen minimum zone studied using a mesoscale eddy as a natural tracer experiment

    Science.gov (United States)

    Bourbonnais, Annie; Altabet, Mark A.; Charoenpong, Chawalit N.; Larkum, Jennifer; Hu, Haibei; Bange, Hermann W.; Stramma, Lothar

    2015-06-01

    Mesoscale eddies in Oxygen Minimum Zones (OMZs) have been identified as important fixed nitrogen (N) loss hotspots that may significantly impact both the global rate of N-loss as well as the ocean's N isotope budget. They also represent "natural tracer experiments" with intensified biogeochemical signals that can be exploited to understand the large-scale processes that control N-loss and associated isotope effects (ɛ; the ‰ deviation from 1 in the ratio of reaction rate constants for the light versus heavy isotopologues). We observed large ranges in the concentrations and N and O isotopic compositions of nitrate (NO3-), nitrite (NO2-), and biogenic N2 associated with an anticyclonic mode-water eddy in the Peru OMZ during two cruises in November and December 2012. In the eddy's center where NO3- was nearly exhausted, we measured the highest δ15N values for both NO3- and NO2- (up to ~70‰ and 50‰) ever reported for an OMZ. Correspondingly, N deficit and biogenic N2-N concentrations were also the highest near the eddy's center (up to ~40 µmol L-1). δ15N-N2 also varied with biogenic N2 production, following kinetic isotopic fractionation during NO2- reduction to N2 and, for the first time, provided an independent assessment of N isotope fractionation during OMZ N-loss. We found apparent variable ɛ for NO3- reduction (up to ~30‰ in the presence of NO2-). However, the overall ɛ for N-loss was calculated to be only ~13-14‰ (as compared to canonical values of ~20-30‰) assuming a closed system and only slightly higher assuming an open system (16-19‰). Our results were similar whether calculated from the disappearance of DIN (NO3- + NO2-) or from the appearance of N2 and changes in isotopic composition. Further, we calculated the separate ɛ values for NO3- reduction to NO2- and NO2- reduction to N2 of ~16-21‰ and ~12‰, respectively, when the effect of NO2- oxidation could be removed. These results, together with the relationship between N and O of NO

  4. Field experimentation in isotope-aided studies

    International Nuclear Information System (INIS)

    Zapata, F.

    1990-01-01

    Isotopic-aided studies involve the application of isotopically labelled fertilizer as tracers for the quantitative and precise determination of the fate of specific nutrient elements in the soil/plant system. The planning of isotopic-aided studies requires a different approach from that followed in the design of normal fertilizer trials because of the cost and supply of isotopically labelled materials, the use of highly specialized equipment and the need for skillful trained staff in the use of isotope techniques both in the field/greenhouse and the laboratory. This report is intended to highlight the main points to be considered while applying those techniques in the field or greenhouse. It has been well established that nuclear techniques are a powerful tool in agricultural research. One should take advantage of the use of such techniques if the following criteria are met: The isotope method is the only way to solve a particular question or to obtain a specific piece of information. There are other methods available for such a purpose but the nuclear method provides a direct and quick means to obtain the needed information resulting in higher economic return

  5. Study of the isotopic contamination with the Grenoble isotope separator

    International Nuclear Information System (INIS)

    Boge, Marc

    1970-01-01

    To know the limits of enrichment of the Grenoble electromagnetic isotope separator, we have studied the scattering of ions on the residual gas, and the chromatism. With Neodymium (Nd + ≅ 500 μA, NdO + ≅ 120 μA, Nd 2+ ≅ 70 μA) the second magnet has been used to analyse the ions which passed through the first stage slit. Therefore, we have measured the scattering with and without charge exchange of Nd + and the dissociation of NdO + . The chromatism has been studied by means of an electrostatic analyser, as a third stage. The limits of enrichment are obtained for Argon, Uranium and Neodymium. (author) [fr

  6. Clumped isotope effects during OH and Cl oxidation of methane

    DEFF Research Database (Denmark)

    Whitehill, Andrew R.; Joelsson, Lars Magnus T.; Schmidt, Johan Albrecht

    2017-01-01

    A series of experiments were carried out to determine the clumped (13CH3D) methane kinetic isotope effects during oxidation of methane by OH and Cl radicals, the major sink reactions for atmospheric methane. Experiments were performed in a 100 L quartz photochemical reactor, in which OH was produ......A series of experiments were carried out to determine the clumped (13CH3D) methane kinetic isotope effects during oxidation of methane by OH and Cl radicals, the major sink reactions for atmospheric methane. Experiments were performed in a 100 L quartz photochemical reactor, in which OH...... effects for singly substituted species were consistent with previous experimental studies. For doubly substituted methane, 13CH3D, the observed kinetic isotope effects closely follow the product of the kinetic isotope effects for the 13C and deuterium substituted species (i.e., 13,2KIE = 13KIE × 2KIE...... reactions. In a closed system, however, this effect is overtaken by the large D/H isotope effect, which causes the residual methane to become anti-clumped relative to the initial methane. Based on these results, we demonstrate that oxidation of methane by OH, the predominant oxidant for tropospheric methane...

  7. Carbon-13 and oxygen-18 isotope effects in the decarboxylation of nicotinic acid of natural isotopic composition

    International Nuclear Information System (INIS)

    Zielinski, M.; Zielinska, A.; Papiernik-Zielinska, H.; McKenzie, J.A.; Bernasconi, S.; Paul, H.

    1998-01-01

    Carbon-13 and oxygen-18 isotope effects in the decarboxylation of nicotinic acid of natural isotopic composition above and below its melting temperature have been studied and compared with the primary (PKIE) and secondary kinetic isotope effects (SKIE) of 13 C and 18 O, respectively, in the decarboxylation of other heterocyclic acids. The temperature dependence of the secondary oxygen-18 isotope effects is negative in the total 221-255 deg C temperature interval investigated initially. The 13 C KIE measured above melting point of N.A. (temperature interval 235-270 deg C) are located in the range 1.007-1.009. Below melting point of nicotinic acid the 13 C KIE are larger and reveal the negative temperature dependence ( 13 C KIE decreases with decreasing the reaction temperature from 1.013/at 230 deg C to 1.0114/at 221 deg C). A discussion of the above isotopic results is presented. (author)

  8. Isotopic effects on phonon anharmonicity in layered van der Waals crystals: Isotopically pure hexagonal boron nitride

    Science.gov (United States)

    Cuscó, Ramon; Artús, Luis; Edgar, James H.; Liu, Song; Cassabois, Guillaume; Gil, Bernard

    2018-04-01

    Hexagonal boron nitride (h -BN) is a layered crystal that is attracting a great deal of attention as a promising material for nanophotonic applications. The strong optical anisotropy of this crystal is key to exploit polaritonic modes for manipulating light-matter interactions in 2D materials. h -BN has also great potential for solid-state neutron detection and neutron imaging devices, given the exceptionally high thermal neutron capture cross section of the boron-10 isotope. A good knowledge of phonons in layered crystals is essential for harnessing long-lived phonon-polariton modes for nanophotonic applications and may prove valuable for developing solid-state 10BN neutron detectors with improved device architectures and higher detection efficiencies. Although phonons in graphene and isoelectronic materials with a similar hexagonal layer structure have been studied, the effect of isotopic substitution on the phonons of such lamellar compounds has not been addressed yet. Here we present a Raman scattering study of the in-plane high-energy Raman active mode on isotopically enriched single-crystal h -BN. Phonon frequency and lifetime are measured in the 80-600-K temperature range for 10B-enriched, 11B-enriched, and natural composition high quality crystals. Their temperature dependence is explained in the light of perturbation theory calculations of the phonon self-energy. The effects of crystal anisotropy, isotopic disorder, and anharmonic phonon-decay channels are investigated in detail. The isotopic-induced changes in the phonon density of states are shown to enhance three-phonon anharmonic decay channels in 10B-enriched crystals, opening the possibility of isotope tuning of the anharmonic phonon decay processes.

  9. INTRAMOLECULAR ISOTOPE EFFECTS IN HYDROCARBON MASS SPECTRA

    Energy Technology Data Exchange (ETDEWEB)

    Stevenson, D. P.; Schachtschneider, J. H.

    1963-07-15

    Approximate calculations based on the quasi-equilibrium rate theory of the origin of mass spectra are shown to lead to an approximately correct magnitude for the intramolecular ( pi /sup -/) isotope effect on C--H bond dissociation probabilities of various deuterohydrocarbons. (auth)

  10. Stable isotope studies: Progress report, March 1985--August 1987

    International Nuclear Information System (INIS)

    Ishida, Takanobu.

    1987-01-01

    Studies have been carried out in the following areas: Stable Isotope Fractionation (1) Effects of chemical poisons and surface modifiers on polycrystalline platinum electrode surfaces have been investigated with a goal to develop a new form of heterogeneous catalyst for the hydrogen isotope exchange between dihydrogen and water. (2) A new nitrogen-15 fractionation process has been developed, based on the isotope exchange between liquid N 2 O 3 -N 2 O 4 mixture and their vapor phase at a subambient temperature and a raised pressure. (3) A closed chemical recycle process has been developed for use in connection with the refluxer in the Nitrox-type nitrogen-15 plant. Isotope Effects (1) The vapor pressure isotope effect (VPIE) study of liquid fluoromethanes have been completed. (2) The VPIE study of solid and liquid ammonia has been completed. (3) A theoretical foundation of the additivity for the vibrational zero-point energy (ZPE) has been developed. Studies of Liquid Ammonia. With an aim to study intermolecular interaction (and the inversion phenomenon, in particular) in liquid ammonia, and to further investigate various ammonia solutions, a molecular dynamics (MD) study has been initiated. An MD program has been completed, and force field functions have been developed for an ensemble of non-rigid ammonia molecules. 107 refs., 41 figs., 10 tabs

  11. Fundamental studies in isotope chemistry. Progress report, 1 July 1976--30 Jun 1977

    International Nuclear Information System (INIS)

    Bigeleisen, J.; Harris, T.H.

    1977-01-01

    The current thrust of the program is the use of isotope effects to study the fundamental properties of matter, measurement and calculation of isotope fractionation factors of systems of potential technological importance and the correlation of isotope effects with molecular structure. The first measurements of the isotopic fractionation factors for two components in a solution were completed by the study of argon-krypton mixtures. The measurements cover the range from pure argon to pure krypton and extrapolate very well to previous measurements on the pure components. The vapor pressure isotope effects between solid-vapor and liquid-vapor for the rare gases neon, argon, and krypton is given

  12. Transport hysteresis and hydrogen isotope effect on confinement

    Science.gov (United States)

    Itoh, S.-I.; Itoh, K.

    2018-03-01

    A Gedankenexperiment on hydrogen isotope effect is developed, using the transport model with transport hysteresis. The transport model with hysteresis is applied to case where the modulational electron cyclotron heating is imposed near the mid-radius of the toroidal plasmas. The perturbation propagates either outward or inward, being associated with the clockwise (CW) hysteresis or counter-clockwise (CCW) hysteresis, respectively. The hydrogen isotope effects on the CW and CCW hysteresis are investigated. The local component of turbulence-driven transport is assumed to be the gyro-Bohm diffusion. While the effect of hydrogen mass number is screened in the response of CW hysteresis, it is amplified in CCW hysteresis. This result motivates the experimental studies to compare CW and CCW cases in order to obtain further insight into the physics of hydrogen isotope effects.

  13. Isotopic studies in soil and plant nutrition

    International Nuclear Information System (INIS)

    Pasricha, N.S.

    2001-01-01

    One of the most important peaceful applications of isotopes is in research for the enhancement of our understanding for increased crop production and better management of resources with higher economic efficiency and environmental safety. Nuclear techniques helped in generating useful information on such aspects as use-efficiency of fertilizer nutrients, quantifying their losses from soil and their biological transformations. Such information was, hitherto, obtained indirectly by conventional methods. Radio and stable isotopes have also been successfully employed for getting information in such diverse fields as soil erosion, turnover of soil organic matter, pesticide retention in soil ground water recharge etc. The property of 137 Cs adhering tightly to certain exchange surface in soil and its chemically inert nature has made it a useful tool for soil erosion studies. In this paper, applications of isotopes in the research and other such studies as degradation, movement and retention of pesticides, movement of nitrate in soil, biological and ammoniacal nitrogen fixation in soil is discussed

  14. The effects of α-cellulose extraction and blue-stain fungus on retrospective studies of carbon and oxygen isotope variation in live and dead trees.

    Science.gov (United States)

    English, Nathan B; McDowell, Nate G; Allen, Craig D; Mora, Claudia

    2011-10-30

    Tree-ring carbon and oxygen isotope ratios from live and recently dead trees may reveal important mechanisms of tree mortality. However, wood decay in dead trees may alter the δ(13)C and δ(18)O values of whole wood obscuring the isotopic signal associated with factors leading up to and including physiological death. We examined whole sapwood and α-cellulose from live and dead specimens of ponderosa pine (Pinus ponderosa), one-seed juniper (Juniperous monosperma), piñon pine (Pinus edulis) and white fir (Abies concolor), including those with fungal growth and beetle frass in the wood, to determine if α-cellulose extraction is necessary for the accurate interpretation of isotopic compositions in the dead trees. We found that the offset between the δ(13)C or δ(18)O values of α-cellulose and whole wood was the same for both live and dead trees across a large range of inter-annual and regional climate differences. The method of α-cellulose extraction, whether Leavitt-Danzer or Standard Brendel modified for small samples, imparts significant differences in the δ(13)C (up to 0.4‰) and δ(18) O (up to 1.2‰) of α-cellulose, as reported by other studies. There was no effect of beetle frass or blue-stain fungus (Ophiostoma) on the δ(13)C and δ(18)O of whole wood or α-cellulose. The relationships between whole wood and α-cellulose δ(13)C for ponderosa, piñon and juniper yielded slopes of ~1, while the relationship between δ(18)O of whole wood and α-cellulose was less clear. We conclude that there are few analytical or sampling obstacles to retrospective studies of isotopic patterns of tree mortality in forests of the western United States. Published in 2011 by John Wiley & Sons, Ltd.

  15. The effects of α-cellulose extraction and blue-stain fungus on retrospective studies of carbon and oxygen isotope variation in live and dead trees†

    Science.gov (United States)

    English, N.B.; McDowell, N.G.; Allen, Craig D.; Mora, C.

    2011-01-01

    Tree-ring carbon and oxygen isotope ratios from live and recently dead trees may reveal important mechanisms of tree mortality. However, wood decay in dead trees may alter the δ13C and δ18O values of whole wood obscuring the isotopic signal associated with factors leading up to and including physiological death. We examined whole sapwood and α-cellulose from live and dead specimens of ponderosa pine (Pinus ponderosa), one-seed juniper (Juniperous monosperma), piñon pine (Pinus edulis) and white fir (Abies concolor), including those with fungal growth and beetle frass in the wood, to determine if α-cellulose extraction is necessary for the accurate interpretation of isotopic compositions in the dead trees. We found that the offset between the δ13C or δ18O values of α-cellulose and whole wood was the same for both live and dead trees across a large range of inter-annual and regional climate differences. The method of α-cellulose extraction, whether Leavitt-Danzer or Standard Brendel modified for small samples, imparts significant differences in the δ13C (up to 0.4‰) and δ18O (up to 1.2‰) of α-cellulose, as reported by other studies. There was no effect of beetle frass or blue-stain fungus (Ophiostoma) on the δ13C and δ18O of whole wood or α-cellulose. The relationships between whole wood and α-cellulose δ13C for ponderosa, piñon and juniper yielded slopes of ~1, while the relationship between δ18O of whole wood and α-cellulose was less clear. We conclude that there are few analytical or sampling obstacles to retrospective studies of isotopic patterns of tree mortality in forests of the western United States.

  16. Salt effects on isotope partitioning and their geochemical implications: An overview

    International Nuclear Information System (INIS)

    Horita, J.; Cole, D.R.; Fortier, S.M.

    1996-01-01

    Essential to the use of stable isotopes as natural tracers and geothermometers is the knowledge of equilibrium isotope partitioning between different phases and species, which is usually a function of temperature only. The one exception known to date is oxygen and hydrogen isotope fractionation between liquid water and other phases (steam, gases, minerals), which changes upon the addition of salts to water, i.e., the isotope salt salt effect. Our knowledge of this effect, the difference between activity and composition (a-X) of isotopic water molecules in salt solutions, is very limited and controversial, especially at elevated temperatures. For the last several years, we have been conducting a detailed, systematic experimental study at Oak Ridge National Laboratory to determine the isotope salt effects from room temperature to elevated temperatures (currently to 500 degree C). From this effort, a simple, coherent picture of the isotope salt effect is emerging, that differs markedly from the complex results reported in the literature. In this communication, we present an overview on the isotope salt effect, obtained chiefly from our study. Observed isotope salt effects in salt solutions are significant even at elevated temperatures. The importance and implications of the isotope salt effect for isotopic studies of brine-dominated systems are also discussed in general terms

  17. The strengths and limitations of effective centroid force models explored by studying isotopic effects in liquid water

    Science.gov (United States)

    Yuan, Ying; Li, Jicun; Li, Xin-Zheng; Wang, Feng

    2018-05-01

    The development of effective centroid potentials (ECPs) is explored with both the constrained-centroid and quasi-adiabatic force matching using liquid water as a test system. A trajectory integrated with the ECP is free of statistical noises that would be introduced when the centroid potential is approximated on the fly with a finite number of beads. With the reduced cost of ECP, challenging experimental properties can be studied in the spirit of centroid molecular dynamics. The experimental number density of H2O is 0.38% higher than that of D2O. With the ECP, the H2O number density is predicted to be 0.42% higher, when the dispersion term is not refit. After correction of finite size effects, the diffusion constant of H2O is found to be 21% higher than that of D2O, which is in good agreement with the 29.9% higher diffusivity for H2O observed experimentally. Although the ECP is also able to capture the redshifts of both the OH and OD stretching modes in liquid water, there are a number of properties that a classical simulation with the ECP will not be able to recover. For example, the heat capacities of H2O and D2O are predicted to be almost identical and higher than the experimental values. Such a failure is simply a result of not properly treating quantized vibrational energy levels when the trajectory is propagated with classical mechanics. Several limitations of the ECP based approach without bead population reconstruction are discussed.

  18. Isotopic modeling of the sub-cloud evaporation effect in precipitation

    Energy Technology Data Exchange (ETDEWEB)

    Salamalikis, V., E-mail: vsalamalik@upatras.gr [Laboratory of Atmospheric Physics, Department of Physics, University of Patras, GR 26500 Patras (Greece); Argiriou, A.A. [Laboratory of Atmospheric Physics, Department of Physics, University of Patras, GR 26500 Patras (Greece); Dotsika, E. [Stable Isotope Unit, Institute of Nanoscience and Nanotechnology, National Center of Scientific Research ‘Demokritos’, Ag. Paraskevi Attikis, 15310 Athens (Greece)

    2016-02-15

    In dry and warm environments sub-cloud evaporation influences the falling raindrops modifying their final stable isotopic content. During their descent from the cloud base towards the ground surface, through the unsaturated atmosphere, hydrometeors are subjected to evaporation whereas the kinetic fractionation results to less depleted or enriched isotopic signatures compared to the initial isotopic composition of the raindrops at cloud base. Nowadays the development of Generalized Climate Models (GCMs) that include isotopic content calculation modules are of great interest for the isotopic tracing of the global hydrological cycle. Therefore the accurate description of the underlying processes affecting stable isotopic content can improve the performance of iso-GCMs. The aim of this study is to model the sub-cloud evaporation effect using a) mixing and b) numerical isotope evaporation models. The isotope-mixing evaporation model simulates the isotopic enrichment (difference between the ground and the cloud base isotopic composition of raindrops) in terms of raindrop size, ambient temperature and relative humidity (RH) at ground level. The isotopic enrichment (Δδ) varies linearly with the evaporated raindrops mass fraction of the raindrop resulting to higher values at drier atmospheres and for smaller raindrops. The relationship between Δδ and RH is described by a ‘heat capacity’ model providing high correlation coefficients for both isotopes (R{sup 2} > 80%) indicating that RH is an ideal indicator of the sub-cloud evaporation effect. Vertical distribution of stable isotopes in falling raindrops is also investigated using a numerical isotope-evaporation model. Temperature and humidity dependence of the vertical isotopic variation is clearly described by the numerical isotopic model showing an increase in the isotopic values with increasing temperature and decreasing RH. At an almost saturated atmosphere (RH = 95%) sub-cloud evaporation is negligible and the

  19. Isotopic modeling of the sub-cloud evaporation effect in precipitation

    International Nuclear Information System (INIS)

    Salamalikis, V.; Argiriou, A.A.; Dotsika, E.

    2016-01-01

    In dry and warm environments sub-cloud evaporation influences the falling raindrops modifying their final stable isotopic content. During their descent from the cloud base towards the ground surface, through the unsaturated atmosphere, hydrometeors are subjected to evaporation whereas the kinetic fractionation results to less depleted or enriched isotopic signatures compared to the initial isotopic composition of the raindrops at cloud base. Nowadays the development of Generalized Climate Models (GCMs) that include isotopic content calculation modules are of great interest for the isotopic tracing of the global hydrological cycle. Therefore the accurate description of the underlying processes affecting stable isotopic content can improve the performance of iso-GCMs. The aim of this study is to model the sub-cloud evaporation effect using a) mixing and b) numerical isotope evaporation models. The isotope-mixing evaporation model simulates the isotopic enrichment (difference between the ground and the cloud base isotopic composition of raindrops) in terms of raindrop size, ambient temperature and relative humidity (RH) at ground level. The isotopic enrichment (Δδ) varies linearly with the evaporated raindrops mass fraction of the raindrop resulting to higher values at drier atmospheres and for smaller raindrops. The relationship between Δδ and RH is described by a ‘heat capacity’ model providing high correlation coefficients for both isotopes (R"2 > 80%) indicating that RH is an ideal indicator of the sub-cloud evaporation effect. Vertical distribution of stable isotopes in falling raindrops is also investigated using a numerical isotope-evaporation model. Temperature and humidity dependence of the vertical isotopic variation is clearly described by the numerical isotopic model showing an increase in the isotopic values with increasing temperature and decreasing RH. At an almost saturated atmosphere (RH = 95%) sub-cloud evaporation is negligible and the

  20. Applications of Radium Isotopes to Ocean Studies

    Energy Technology Data Exchange (ETDEWEB)

    Moore, W. S. [Department of Earth and Ocean Sciences, University of South Carolina, Columbia, SC (United States)

    2013-07-15

    With half-lives ranging from 3.7 days to 1600 a, naturally occurring radium isotopes have been used to study a variety of processes in the ocean. New techniques, which allow rapid analyses of the short lived isotopes, {sup 224}Ra (half-life = 3.7 days) and {sup 223}Ra (half-life = 11 days), have lead to many novel ways to apply radium to oceanography. This paper will focus on how the use of these isotopes has led to breakthroughs in quantifying: (1) the residence time of water in estuaries, (2) coastal ocean mixing rates and (3) submarine groundwater discharge (SGD). With this new understanding of rates and fluxes in the near shore environment, scientists and coastal managers are now able to evaluate sources of nutrients, carbon, and metals and their impact on the coastal ocean. For example, it is now known that SGD rivals rivers as a nutrient source to many coastal environments. (author)

  1. Isotope and mixture effects on neoclassical transport in the pedestal

    Science.gov (United States)

    Pusztai, Istvan; Buller, Stefan; Omotani, John T.; Newton, Sarah L.

    2017-10-01

    The isotope mass scaling of the energy confinement time in tokamak plasmas differs from gyro-Bohm estimates, with implications for the extrapolation from current experiments to D-T reactors. Differences in mass scaling in L-mode and various H-mode regimes suggest that the isotope effect may originate from the pedestal. In the pedestal, sharp gradients render local diffusive estimates invalid, and global effects due to orbit-width scale profile variations have to be taken into account. We calculate neoclassical cross-field fluxes from a radially global drift-kinetic equation using the PERFECT code, to study isotope composition effects in density pedestals. The relative reduction to the peak heat flux due to global effects as a function of the density scale length is found to saturate at an isotope-dependent value that is larger for heavier ions. We also consider D-T and H-D mixtures with a focus on isotope separation. The ability to reproduce the mixture results via single-species simulations with artificial ``DT'' and ``HD'' species has been considered. These computationally convenient single ion simulations give a good estimate of the total ion heat flux in corresponding mixtures. Funding received from the International Career Grant of Vetenskapsradet (VR) (330-2014-6313) with Marie Sklodowska Curie Actions, Cofund, Project INCA 600398, and Framework Grant for Strategic Energy Research of VR (2014-5392).

  2. Anharmonic phonons and the isotope effect in superconductivity

    International Nuclear Information System (INIS)

    Crespi, V.H.; Cohen, M.L.; Penn, D.R.

    1991-01-01

    Anharmonic interionic potentials are examined in an Einstein model to study the unusual isotope-effect exponents for the high-T c oxides. The mass dependences of the electron-phonon coupling constant λ and the average phonon frequency √ left-angle ω 2 right-angle are computed from weighted sums over the oscillator levels. The isotope-effect exponent is depressed below 1/2 by either a double-well potential or a potential with positive quadratic and quartic parts. Numerical solutions of Schroedinger's equation for double-well potentials produce λ's in the range 1.5--4 for a material with a vanishing isotope-effect parameter α. However, low phonon frequencies limit T c to roughly 15 K. A negative quartic perturbation to a harmonic well can increase α above 1/2. In the extreme-strong-coupling limit, α is 1/2, regardless of anharmonicity

  3. H/D isotope effects in high temperature proton conductors

    DEFF Research Database (Denmark)

    Bonanos, Nikolaos; Huijser, A.; Poulsen, Finn Willy

    2015-01-01

    The atomic mass ratio of ca. 2 between deuterium and hydrogen is the highest for any pair of stable isotopes and results in significant and measurable H/D isotope effects in high temperature proton conductors containing these species. This paper discusses H/D isotope effects manifested in O-H/O-D...

  4. Isotope effect on confinement in DT plasmas

    International Nuclear Information System (INIS)

    Fukuyama, A.; Itoh, K.; Itoh, S.; Yagi, M.; Azumi, M.

    1994-03-01

    Isotope effect on the energy confinement time is discussed for the DT plasma. The transport theory which is based on the ballooning mode turbulence is applied. When the DT plasma is produced under the condition of β p >1, the energy confinement time of DT plasma (50% mixture) is expected to be about 1.2 times better than the D plasma with the same operation condition. (author)

  5. Charge state distribution studies of pure and oxygen mixed krypton ECR plasma - signature of isotope anomaly and gas mixing effect.

    Science.gov (United States)

    Kumar, Pravin; Mal, Kedar; Rodrigues, G

    2016-11-01

    We report the charge state distributions of the pure, 25% and 50% oxygen mixed krypton plasma to shed more light on the understanding of the gas mixing and the isotope anomaly [A. G. Drentje, Rev. Sci. Instrum. 63 (1992) 2875 and Y Kawai, D Meyer, A Nadzeyka, U Wolters and K Wiesemann, Plasma Sources Sci. Technol. 10 (2001) 451] in the electron cyclotron resonance (ECR) plasmas. The krypton plasma was produced using a 10 GHz all-permanent-magnet ECR ion source. The intensities of the highly abundant four isotopes, viz. 82 Kr (~11.58%), 83 Kr (~11.49%), 84 Kr (~57%) and 86 Kr (17.3%) up to ~ +14 charge state have been measured by extracting the ions from the plasma and analysing them in the mass and the energy using a large acceptance analyzer-cum-switching dipole magnet. The influence of the oxygen gas mixing on the isotopic krypton ion intensities is clearly evidenced beyond +9 charge state. With and without oxygen mixing, the charge state distribution of the krypton ECR plasma shows the isotope anomaly with unusual trends. The anomaly in the intensities of the isotopes having quite closer natural abundance, viz. 82 Kr, 86 Kr and 83 Kr, 86 Kr is prominent, whereas the intensity ratio of 86 Kr to 84 Kr shows a weak signature of it. The isotope anomaly tends to disappear with increasing oxygen mixing in the plasma. The observed trends in the intensities of the krypton isotopes do not follow the prediction of linear Landau wave damping in the plasma. Copyright © 2016 John Wiley & Sons, Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

  6. Radiochemical studies of neutron deficient actinide isotopes

    International Nuclear Information System (INIS)

    Williams, K.E.

    1978-04-01

    The production of neutron deficient actinide isotopes in heavy ion reactions was studied using alpha, gamma, x-ray, and spontaneous fission detection systems. A new isotope of berkelium, 242 Bk, was produced with a cross-section of approximately 10 μb in reactions of boron on uranium and nitrogen on thorium. It decays by electron capture with a half-life of 7.0 +- 1.3 minutes. The alpha-branching ratio for this isotope is less than 1% and the spontaneous fission ratio is less than 0.03%. Studies of (Heavy Ion, pxn) and (Heavy Ion, αxn) transfer reactions in comparison with (Heavy ion, xn) compound nucleus reactions revealed transfer reaction cross-sections equal to or greater than the compound nucleus yields. The data show that in some cases the yield of an isotope produced via a (H.I.,pxn) or (H.I.,αxn) reaction may be higher than its production via an xn compound nucleus reaction. These results have dire consequences for proponents of the ''Z 1 + Z 2 = Z/sub 1+2/'' philosophy. It is no longer acceptable to assume that (H.I.,pxn) and (H.I.,αxn) product yields are of no consequence when studying compound nucleus reactions. No evidence for spontaneous fission decay of 228 Pu, 230 Pu, 232 Cm, or 238 Cf was observed indicating that strictly empirical extrapolations of spontaneous fission half-life data is inadequate for predictions of half-lives for unknown neutron deficient actinide isotopes

  7. Radiochemical studies of neutron deficient actinide isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Williams, K.E.

    1978-04-01

    The production of neutron deficient actinide isotopes in heavy ion reactions was studied using alpha, gamma, x-ray, and spontaneous fission detection systems. A new isotope of berkelium, /sup 242/Bk, was produced with a cross-section of approximately 10 ..mu..b in reactions of boron on uranium and nitrogen on thorium. It decays by electron capture with a half-life of 7.0 +- 1.3 minutes. The alpha-branching ratio for this isotope is less than 1% and the spontaneous fission ratio is less than 0.03%. Studies of (Heavy Ion, pxn) and (Heavy Ion, ..cap alpha..xn) transfer reactions in comparison with (Heavy ion, xn) compound nucleus reactions revealed transfer reaction cross-sections equal to or greater than the compound nucleus yields. The data show that in some cases the yield of an isotope produced via a (H.I.,pxn) or (H.I.,..cap alpha..xn) reaction may be higher than its production via an xn compound nucleus reaction. These results have dire consequences for proponents of the ''Z/sub 1/ + Z/sub 2/ = Z/sub 1+2/'' philosophy. It is no longer acceptable to assume that (H.I.,pxn) and (H.I.,..cap alpha..xn) product yields are of no consequence when studying compound nucleus reactions. No evidence for spontaneous fission decay of /sup 228/Pu, /sup 230/Pu, /sup 232/Cm, or /sup 238/Cf was observed indicating that strictly empirical extrapolations of spontaneous fission half-life data is inadequate for predictions of half-lives for unknown neutron deficient actinide isotopes.

  8. Deuterium secondary isotope kinetic effects in imine formation reactions

    International Nuclear Information System (INIS)

    Amaral, L. do; Rossi, M.H.

    1986-01-01

    The kinetic α-deuterium isotope effects, K D /K H , for reaction mechanisms is studied. The reaction of pH function to m-bromobenzaldehyde, semicarbazide nucleophile, methoxy-amine and hydroxylamine are analysed. (M.J.C.) [pt

  9. Solid state NMR of isotope labelled murine fur: a powerful tool to study atomic level keratin structure and treatment effects

    Energy Technology Data Exchange (ETDEWEB)

    Wong, Wai Ching Veronica; Narkevicius, Aurimas; Chow, Wing Ying; Reid, David G.; Rajan, Rakesh [University of Cambridge, Department of Chemistry (United Kingdom); Brooks, Roger A. [University of Cambridge, Department of Trauma and Orthopaedic Surgery, Addenbrooke’s Hospital (United Kingdom); Green, Maggie [University of Cambridge, Central Biomedical Resources, School of Clinical Medicine (United Kingdom); Duer, Melinda J., E-mail: mjd13@cam.ac.uk [University of Cambridge, Department of Chemistry (United Kingdom)

    2016-10-15

    We have prepared mouse fur extensively {sup 13}C,{sup 15}N-labelled in all amino acid types enabling application of 2D solid state NMR techniques which establish covalent and spatial proximities within, and in favorable cases between, residues. {sup 13}C double quantum–single quantum correlation and proton driven spin diffusion techniques are particularly useful for resolving certain amino acid types. Unlike 1D experiments on isotopically normal material, the 2D methods allow the chemical shifts of entire spin systems of numerous residue types to be determined, particularly those with one or more distinctively shifted atoms such as Gly, Ser, Thr, Tyr, Phe, Val, Leu, Ile and Pro. Also the partial resolution of the amide signals into two signal envelopes comprising of α-helical, and β-sheet/random coil components, enables resolution of otherwise overlapped α-carbon signals into two distinct cross peak families corresponding to these respective secondary structural regions. The increase in resolution conferred by extensive labelling offers new opportunities to study the chemical fate and structural environments of specific atom and amino acid types under the influence of commercial processes, and therapeutic or cosmetic treatments.

  10. Secondary isotope effects on alpha-cleavage reactions

    International Nuclear Information System (INIS)

    Ingemann, S.; Hammerum, S.

    1980-01-01

    Kinetic deuterium isotope effects on mass spectral reactions have in several instances been utilized to provide structural information and to answer mechanistic questions. Typically, the influence of the deuterium label on the rate of one of a number of competing reactions has been studied. Secondary isotope effects have usually been assumed to be relatively insignificant in comparison with the observed kinetic effects, even though various workers have shown that secondary isotope effects may indeed exert a considerable influence on the rates of competing simple cleavages. Recent studies have provided quantitative data to show that the mere presence of deuterium atoms up to six bonds away may influence the rate of a simple cleavage reaction. In relation to an investigation of rearrangements accompanying simple cleavage reactions, a semi-quantitative measure was needed of the variation of the secondary isotope effect with the number of bonds between the deuterium label and the point of rupture. The influence has therefore been examined of the presence of remote deuterium atoms on a typical simple cleavage reaction, the α-cleavage of aliphatic amines. As a model compound, N-methyldipentylamine was chosen, systematically labelled with deuterium. (author)

  11. Mechanism of inactivation of human leukocyte elastase by a chloromethyl ketone: kinetic and solvent isotope effect studies

    International Nuclear Information System (INIS)

    Stein, R.L.; Trainor, D.A.

    1986-01-01

    The mechanism of inactivation of human leukocyte elastase (HLE) by the chloromethyl ketone MeOSuc-Ala-Ala-Pro-Val-CH 2 Cl was investigated. The dependence of the first-order rate constant for inactivation on concentration of chloromethyl ketone is hyperbolic and suggests formation of a reversible Michaelis complex prior to covalent interaction between the enzyme and inhibitor. However, the observed Ki value is 10 microM, at least 10-fold lower than dissociation constants for complexes formed from interaction of HLE with structurally related substrates or reversible inhibitors, and suggests that Ki is a complex kinetic constant, reflecting the formation and accumulation of both the Michaelis complex and a second complex. It is proposed that this second complex is a hemiketal formed from attack of the active site serine on the carbonyl carbon of the inhibitor. The accumulation of this intermediate may be a general feature of reactions of serine proteases and chloromethyl ketones derived from specific peptides and accounts for the very low Ki values observed for these reactions. The solvent deuterium isotope effect (SIE) on the inactivation step (ki) is 1.58 +/- 0.07 and is consistent with rate-limiting, general-catalyzed attack of the active site His on the methylene carbon of the inhibitor with displacement of chloride anion. The general catalyst is thought to be the active site Asp. In contrast, the SIE on the second-order rate constant for HLE inactivation, ki/Ki, is inverse and equals 0.64 +/- 0.05

  12. Non - Adiabaticity and Novel Isotope Effect in the Doped Cuprates

    International Nuclear Information System (INIS)

    Kresin, V.; WOLF, S. A.

    1995-01-01

    This paper reports a novel isotope effect which is due to a strong non-adiabaticity that manifests itself in the dependence of the carrier concentration on the isotopic mass. The critical temperature in turn depends on the carrier concentration giving rise to a unique and non-phononic isotope shift. (author)

  13. Isotope studies on rice fertilization

    International Nuclear Information System (INIS)

    1978-01-01

    The aim of the report is to provide practical information on the efficient utilization of nitrogen fertilizers in rice production. Results obtained from field investigations during the years 1970 to 1974 in ten countries (Bangladesh, Burma, Indonesia, Republic of Korea, Sri Lanka, Taiwan, Thailand, Vietnam, India, Philippines), using 15 N-labelled nitrogen fertilizers (ammonium sulfate, urea) are given. The experiments, which were conducted both during the dry and wet seasons, included comparison of varieties, effect of placement, source and time of nitrogen fertilizer application on the yield and quality of rice. The data from the project is presented in table form. In most of the experiments, the addition of nitrogen increased the rice grain yield. The role of soil nitrogen vs. fertilizer nitrogen is compared, and it is concluded that the physiological growth stage at which fertilizer-derived nitrogen is absorbed is of great importance

  14. Use of Isotopes for Studying Reaction Mechanisms -RE ...

    Indian Academy of Sciences (India)

    can give even greater details of chemical processes. Isotopic substitution ... isotope effect (KIE) would depend on the location of the isotope with respect to ... magnitude of KIE is given by kH/ko. ... How can one explain these variations? Theory.

  15. Stable isotope methods: The effect of gut contents on isotopic ratios of zooplankton

    Science.gov (United States)

    Hill, J. M.; McQuaid, C. D.

    2011-05-01

    In the past decade there has been an increased awareness of the potential for methodological bias resulting from multiple pre-analytical procedures in foodweb interpretations based on stable isotope techniques. In the case of small organisms, this includes the effect of gut contents on whole body signatures. Although gut contents may not reflect actual assimilation, their carbon and nitrogen values will be isotopically lighter than after the same material has been assimilated. The potential skewing of isotopic ratios in whole organism samples is especially important for aquatic environments as many studies involve trophic relationships among small zooplankton. This is particularly important in pelagic waters, where herbivorous zooplankton comprise small taxa. Hence this study investigated the effect of gut contents on the δ13C and δ15N ratios of three size classes of zooplankton (1.0-2.0, 2.0-4.0 and >4.0 mm) collected using bongo net tows in the tropical waters of the south-west Indian Ocean. Animals were collected at night, when they were likely to be feeding, sieved into size classes and separated into genera. We focused on Euphausia spp which dominated zooplankton biomass. Three treatment types were processed: bulk animals, bulk animals without guts and tail muscle from each size class at 10 bongo stations. The δ15N ratios were influenced by zooplankton size class, presumably reflecting ontogenetic changes in diet. ANOVA post hoc results and correlations in δ15N signatures among treatments suggest that gut contents may not affect overall nitrogen signatures of Euphausia spp., but that δ13C signatures may be significantly altered by their presence. Carbon interpretations however, were complicated by potential effects of variation in chitin, lipids and metabolism among tissues and the possibility of opportunistic omnivory. Consequently we advocate gut evacuation before sacrifice in euphausiids if specific tissue dissection is impractical and recommend

  16. Deciphering biodegradation effects on light hydrocarbons in crude oils using their stable carbon isotopic composition: a case study from the Gullfaks oil field, offshore Norway

    OpenAIRE

    Andrea Vieth-Hillebrand [Vieth; Heinz Wilkes

    2006-01-01

    Compound-specific isotope analysis has become an important tool in environmental studies and is an especially powerful way to evaluate biodegradation of hydrocarbons. Here, carbon isotope ratios of light hydrocarbons were used to characterise in-reservoir biodegradation in the Gullfaks oil field, offshore Norway. Increasing biodegradation, as characterised, for example, by increasing concentration ratios of Pr/n-C17 and Ph/n-C18, and decreasing concentrations of individual light hydrocarbons ...

  17. Isotope and multiband effects in layered superconductors.

    Science.gov (United States)

    Bussmann-Holder, Annette; Keller, Hugo

    2012-06-13

    In this review we consider three classes of superconductors, namely cuprate superconductors, MgB(2) and the new Fe based superconductors. All of these three systems are layered materials and multiband compounds. Their pairing mechanisms are under discussion with the exception of MgB(2), which is widely accepted to be a 'conventional' electron-phonon interaction mediated superconductor, but extending the Bardeen-Cooper-Schrieffer (BCS) theory to account for multiband effects. Cuprates and Fe based superconductors have higher superconducting transition temperatures and more complex structures. Superconductivity is doping dependent in these material classes unlike in MgB(2) which, as a pure compound, has the highest values of T(c) and a rapid suppression of superconductivity with doping takes place. In all three material classes isotope effects have been observed, including exotic ones in the cuprates, and controversial ones in the Fe based materials. Before the area of high-temperature superconductivity, isotope effects on T(c) were the signature for phonon mediated superconductivity-even when deviations from the BCS value to smaller values were observed. Since the discovery of high T(c) materials this is no longer evident since competing mechanisms might exist and other mediating pairing interactions are discussed which are of purely electronic origin. In this work we will compare the three different material classes and especially discuss the experimentally observed isotope effects of all three systems and present a rather general analysis of them. Furthermore, we will concentrate on multiband signatures which are not generally accepted in cuprates even though they are manifest in various experiments, the evidence for those in MgB(2), and indications for them in the Fe based compounds. Mostly we will consider experimental data, but when possible also discuss theoretical models which are suited to explain the data.

  18. Carbon-13 kinetic isotope effects in the decarbonylation of lactic acid of natural isotopic composition in phosphoric acid medium

    International Nuclear Information System (INIS)

    Zielinski, M.; Czarnota, G.; Papiernik-Zielinska, H.; Kasprzyk, G.; Gumolka, L.; Staedter, W.

    1993-01-01

    The 13 C kinetic isotope effect fractionation in the decarbonylation of lactic acid (LA) of natural isotopic composition by concentrated phosphoric acids (PA) and by 85% H 3 PO 4 has been studied in the temperature interval of 60-150 deg C. The values of the 13 C (1) isotope effects in the decarbonylation of lactic acid in 100% H 3 PO 4 , in pyrophosphoric acid and in more concentrated phosphoric acids are intermediate between the values calculated assuming that the C (1)- OH bond is broken in the rate-controlling step of dehydration and those calculated for rupture of the carbon-carbon bond in the transition state. In the temperature interval of 90-130 deg C the experimental 13 C fractionation factors determined in concentrated PA approach quite closely the 13 C fractionation corresponding to C (2)- C (1) bond scission. The 13 C (1) kinetic isotope effects in the decarbonylation of LA in 85% orthophosphoric acid in the temperature range of 110-150 deg C coincide with the 13 C isotope effects calculated assuming that the frequency corresponding to the C (1) -OH vibration is lost in the transition state of decarbonylation. A change of the mechanism of decarbonylation of LA in going from concentrated PA medium to 85% H 3 PO 4 has been suggested. A possible secondary 18 O and a primary 18 O kinetic isotope effect in decarbonylation of lactic acid in phosphoric acids media have been discussed, too. (author) 21 refs.; 3 tabs

  19. The effect of exposure to employees from mining and milling operations in a uranium mine on lead isotopes--a pilot study.

    Science.gov (United States)

    Gulson, Brian L; Mizon, Karen J; Dickson, Bruce L; Korsch, Michael J

    2005-03-01

    Potential exposure during mining and milling of uranium ore has resulted in the industry being highly regulated. Exposure can arise from inhalation of the daughter product radioactive gas radon (222Rn), inhalation of radioactive dust particles from mining and milling, direct irradiation from outside the body, and ingestion of radionuclides (e.g. uranium or radium) in food or water. Making use of the highly unusual lead isotopic signature for uranium ores (high 206Pb/204Pb from the high uranium content, low 208Pb/204Pb from the low Th/U ratio), we undertook a pilot study of nine male mine employees and three controls from the Ranger uranium mine in the Northern Territory Australia to determine if it was feasible to use lead isotopes in blood to identify exposure to uranium-derived materials. The lead isotopic data for the mine employees and controls plot in two distinct fields which are consistent with predicted isotopic patterns. Assuming retention of 10% of the ingested lead, then the increases seen in 206Pb represent intakes of between 0.9 and 15 mg, integrated over the years of exposure. The small amount of lead does not affect blood lead concentrations, but appears to be sufficient to be detectable with sensitive isotopic methods. Further studies, including those on urine, should be undertaken to confirm the veracity of the lead isotope method in monitoring exposure of uranium industry employees.

  20. The effect of exposure to employees from mining and milling operations in a uranium mine on lead isotopes. A pilot study

    International Nuclear Information System (INIS)

    Gulson, Brian L.; Mizon, Karen J.; Dickson, Bruce L.; Korsch, Michael J.

    2005-01-01

    Potential exposure during mining and milling of uranium ore has resulted in the industry being highly regulated. Exposure can arise from inhalation of the daughter product radioactive gas radon ( 222 Rn), inhalation of radioactive dust particles from mining and milling, direct irradiation from outside the body, and ingestion of radionuclides (e.g. uranium or radium) in food or water. Making use of the highly unusual lead isotopic signature for uranium ores (high 206 Pb/ 204 Pb from the high uranium content, low 208 Pb/ 204 Pb from the low Th/U ratio), we undertook a pilot study of nine male mine employees and three controls from the Ranger uranium mine in the Northern Territory Australia to determine if it was feasible to use lead isotopes in blood to identify exposure to uranium-derived materials. The lead isotopic data for the mine employees and controls plot in two distinct fields which are consistent with predicted isotopic patterns. Assuming retention of 10% of the ingested lead, then the increases seen in 206 Pb represent intakes of between 0.9 and 15 mg, integrated over the years of exposure. The small amount of lead does not affect blood lead concentrations, but appears to be sufficient to be detectable with sensitive isotopic methods. Further studies, including those on urine, should be undertaken to confirm the veracity of the lead isotope method in monitoring exposure of uranium industry employees

  1. Hofmann elimination of p-nitrophenylethyl-1-C-14-trimethylammonium bromide: a carbon-14 isotope effect study (Preprint no. AR-24)

    International Nuclear Information System (INIS)

    Ramamurthy, T.V.; Fry, Arthur

    1991-01-01

    The alpha carbon isotope effects in the Hofmann elimination of p-nitrophenylethyl-1-C-14-trimethylammonium bromide compound have been measured under changing buffer concentrations with a view to correlate mechanistic change. Since there are alpha-carbon isotope effects and the effects are small it is quite likely that the reaction is of the ElcB type, predominately irreversible, with the incursion of slightly increasing fractions of reaction by the reversible mechanism as the buffer concentration is increased. (author). 4 refs., 2 tab

  2. Expanding the isotopic toolbox: Applications of hydrogen and oxygen stable isotope ratios to food web studies

    OpenAIRE

    Hannah B Vander Zanden; David X Soto; Gabriel J Bowen; Keith A Hobson; Keith A Hobson

    2016-01-01

    The measurement of stable carbon (δ13C) and nitrogen (δ15N) isotopes in tissues of organisms has formed the foundation of isotopic food web reconstructions, as these values directly reflect assimilated diet. In contrast, stable hydrogen (δ2H) and oxygen (δ18O) isotope measurements have typically been reserved for studies of migratory origin and paleoclimate reconstruction based on systematic relationships between organismal tissue and local environmental water. Recently, innovative applicat...

  3. Expanding the Isotopic Toolbox: Applications of Hydrogen and Oxygen Stable Isotope Ratios to Food Web Studies

    OpenAIRE

    Vander Zanden, Hannah B.; Soto, David X.; Bowen, Gabriel J.; Hobson, Keith A.

    2016-01-01

    The measurement of stable carbon (δ13C) and nitrogen (δ15N) isotopes in tissues of organisms has formed the foundation of isotopic food web reconstructions, as these values directly reflect assimilated diet. In contrast, stable hydrogen (δ2H) and oxygen (δ18O) isotope measurements have typically been reserved for studies of migratory origin and paleoclimate reconstruction based on systematic relationships between organismal tissue and local environmental water. Recently, innovative applicatio...

  4. Broadband non-selective excitation of plutonium isotopes for isotope ratio measurements in resonance ionization mass spectrometry: a theoretical study.

    Science.gov (United States)

    Sankari, M

    2012-10-15

    Making isotope ratio measurements with minimum isotope bias has always been a challenging task to mass spectrometrists, especially for the specific case of plutonium, owing to the strategic importance of the element. In order to use resonance ionization mass spectrometry (RIMS) as a tool for isotope ratio measurements, optimization of the various laser parameters and other atomic and system parameters is critical to minimize isotopic biases. Broadband simultaneous non-selective excitation of the isotopes of plutonium in the triple resonance excitation scheme with λ(1) = 420.77 nm, λ(2) = 847.28 nm, and λ(3) = 767.53 nm based on density matrix formalism has been theoretically computed for the determination of isotope ratios. The effects of the various laser parameters and other factors such as the atomization temperature and the dimensions of the atomic beam on the estimation of isotope ratios were studied. The effects of Doppler broadening, and time-dependent excitation parameters such as Rabi frequencies, ionization rate and the effect of non-Lorenztian lineshape have all been incorporated. The average laser powers and bandwidths for the three-excitation steps were evaluated for non-selective excitation. The laser intensity required to saturate the three-excitation steps were studied. The two-dimensional lineshape contour and its features were investigated, while the reversal of peak asymmetry of two-step and two-photon excitation peaks under these conditions is discussed. Optimized powers for the non-selective ionization of the three transitions were calculated as 545 mW, 150 mW and 545 mW and the laser bandwidth for all the three steps was ~20 GHz. The isotopic bias between the resonant and off-resonant isotope under the optimized conditions was no more than 9%, which is better than an earlier reported value. These optimized laser power and bandwidth conditions are better than in the earlier experimental work since these comprehensive calculations yield

  5. Use of isotope effects to elucidate enzyme mechanisms

    International Nuclear Information System (INIS)

    Cleland, W.W.

    1982-01-01

    The chemical bond breaking steps are normally not rate limiting for enzymatic reactions. However, comparison of deuterium and tritium isotope effects on the same reaction, especially when coupled with 13 C isotope effects for the same step measured with deuterated as well as unlabeled substrates, allows calculation of the intrinsic isotope effects on the bond breaking steps and thus a determination of the commitments to catalysis for the reactants. The variation in observed isotope effects as a function of reactant concentration can be used to determine kinetic mechanisms, while the pH variation of isotope effects can determine the stickiness of the reactants and which portions of the reactant mechanism are pH dependent. Finally the size of primary and secondary intrinsic isotope effects can be used to determine transition state structure

  6. Isotope shift studies in gadolinium spectra

    International Nuclear Information System (INIS)

    Ahmad, S.A.; Saksena, G.D.; Venugopalan, A.

    1975-01-01

    Isotope shift studies have been carried out in the gadolinium spectrum using a recording Fabry-Perot spectrometer and gadolinium samples enriched in 156 Gd and 160 Gd isotopes. The source used is a liquid-nitrogen-cooled hollow cathode with Ne as the carrier gas and operating at about 30 mA. Isotope shifts Δsigma (156-160) have been recorded in 350 transitions of Gd I and Gd II. In the case of the Gd I spectrum, the transitions studied presently involve almost all the reported configurations assigned to the energy levels of Gd I. The odd configurations are 4f 7 5d6s 2 , 4f 7 5d 2 6s, 4f 7 5d 3 , 4f 8 6s6p, 4f 7 5d6s7s and 4f 7 6s 2 6p, and the even ones are 4f 8 6s 2 , 4f 7 5d6s6p, 4f 7 6s 2 6p, 4f 8 5d6s and 4f 7 5d 2 6p. In the case of the Gd II spectrum isotope shifts in the lines of the newly classified transition 4f 8 6s - 4f 8 6p have been studied and isotope shift ΔT (156-160) 87 mK has been obtained for the 4f 8 6s configuration. The other transitions of Gd II involve the odd configurations 4f 7 5d6s, 4f 7 6s 2 , 4f 7 5d 2 and 4f 8 6p and the even ones 4f 7 6s6p, 4f 8 5d, 4f 7 5d6p and 4f 8 6p. The ΔT (156-160) of a large number of odd and even levels of Gd I and Gd II have been evaluated. Electronic configurations have been suggested for a number of energy levels and configuration mixing has been pointed out in certain cases. A number of hitherto unreported transitions have been found and using a monoisotopic sample of Gd, that is 160 Gd, their separations from the closest listed transitions have been measured. (author)

  7. Dynamic isotope studies in liver disease

    Energy Technology Data Exchange (ETDEWEB)

    Weits, J

    1978-01-01

    Much information in the field of liver research has been gained by dynamic isotope studies. Clinically, these studies can help to settle selection criteria for different types of surgical shunt, which relieve the complications of portal hypertension. By performing splenoportoscintigraphy, splenic and portal vein thrombosis can be easily and safely excluded. So-called hypoxaemia of cirrhosis can most easily be diagnosed. Suprahepatic caval vein obstruction in a patient with cryptogenic liver disease is easily excluded by a radionuclide cavogram after injection of pertechnetate into a foot vein.

  8. Isotope effect on superconductivity and Raman phonons of Pyrochlore Cd2Re2O7

    Science.gov (United States)

    Razavi, F. S.; Hajialamdari, M.; Reedyk, M.; Kremer, R. K.

    2018-06-01

    Cd2Re2O7 is the only α-Pyrochlore exhibiting superconductivity with a transition temperature (Tc) of ∼ 1 K. In this study, we present the effect of oxygen isotope (18O) as well as combined 18O and cadmium isotope (116Cd) substitution on the superconductivity and Raman scattering spectrum of Cd2Re2O7. The change of Tc and the energy gap Δ(T) are reported using various techniques including point contact spectroscopy. The shift in Raman phonon frequencies upon isotope substitution will be compared with measurement of the isotope effect on the superconducting transition temperature.

  9. NMR studies of isotopically labeled RNA

    Energy Technology Data Exchange (ETDEWEB)

    Pardi, A. [Univ. of Colorado, Boulder, CO (United States)

    1994-12-01

    In summary, the ability to generate NMR quantities of {sup 15}N and {sup 13}C-labeled RNAs has led to the development of heteronuclear multi-dimensional NMR techniques for simplifying the resonance assignment and structure determination of RNAs. These methods for synthesizing isotopically labeled RNAs are only several years old, and thus there are still relatively few applications of heteronuclear multi-dimensional NMR techniques to RNA. However, given the critical role that RNAs play in cellular function, one can expect to see an increasing number of NMR structural studies of biologically active RNAs.

  10. 2015 Accomplishments-Tritium aging studies on stainless steel. Effects of hydrogen isotopes, crack orientation, and specimen geometry on fracture toughness

    Energy Technology Data Exchange (ETDEWEB)

    Morgan, Michael J. [Savannah River Site (SRS), Aiken, SC (United States). Savannah River National Lab. (SRNL)

    2016-01-01

    This study reports on the effects of hydrogen isotopes, crack orientation, and specimen geometry on the fracture toughness of stainless steels. Fracture toughness variability was investigated for Type 21-6-9 stainless steel using the 7K0004 forging. Fracture toughness specimens were cut from the forging in two different geometric configurations: arc shape and disc shape. The fracture toughness properties were measured at ambient temperature before and after exposure to hydrogen gas and compared to prior studies. There are three main conclusions that can be drawn from the results. First, the fracture toughness properties of actual reservoir forgings and contemporary heats of steel are much higher than those measured in earlier studies that used heats of steel from the 1980s and 1990s and forward extruded forgings which were designed to simulate reservoir microstructures. This is true for as-forged heats as well as forged heats exposed to hydrogen gas. Secondly, the study confirms the well-known observation that cracks oriented parallel to the forging grain flow will propagate easier than those oriented perpendicular to the grain flow. However, what was not known, but is shown here, is that this effect is more pronounced, particularly after hydrogen exposures, when the forging is given a larger upset. In brick forgings, which have a relatively low amount of upset, the fracture toughness variation with specimen orientation is less than 5%; whereas, in cup forgings, the fracture toughness is about 20% lower than that forging to show how specimen geometry affects fracture toughness values. The American Society for Testing Materials (ASTM) specifies minimum specimen section sizes for valid fracture toughness values. However, sub-size specimens have long been used to study tritium effects because of the physical limitation of diffusing hydrogen isotopes into stainless steel at mild temperatures so as to not disturb the underlying forged microstructure. This study shows

  11. Electron screening effects in (p,α) reactions induced on boron isotopes studied via the Trojan Horse Method

    International Nuclear Information System (INIS)

    Lamia, L; Spitaleri, C; Cherubini, S; Gulino, M; Puglia, S M R; Rapisarda, G G; Romano, S; Sergi, M L; Carlin, N; Gameiro Munhoz, M; Gimenez Del Santo, M; Kiss, G G; Somorjai, E; Kroha, V; Kubono, S; La Cognata, M; Pizzone, R G; Li, C; Wen, Qungang; Mukhamedzhanov, A

    2013-01-01

    The Trojan Horse Method is a powerful indirect technique allowing one to measure the bare nucleus S(E)-factor and the electron screening potential for astrophysically relevant reactions without the needs of extrapolations. The case of the (p,α) reactions induced on the two boron isotopes 10,11 B is here discussed in view of the recent Trojan Horse (TH) applications to the quasi-free 10,11 B+ 2 H reactions. The comparison between the TH and the low-energy direct data allowed us to determine the electron screening potential for the 11 B(p,α) reaction, while preliminary results on the 10 B(p,α) reaction have been extracted.

  12. Study on atmospheric hydrogen enrichment by cryopump method and isotope separation by gas chromatography

    International Nuclear Information System (INIS)

    Taniyama, Yuki; Momoshima, Noriyuki

    2001-01-01

    To obtain the information of source of atmospheric hydrogen tritium an analysis of tritium isotopes is thought to be effective. So an atmospheric hydrogen enrichment apparatus and a cryogenic gas chromatographic column were made. Experiments were carried out to study the performance of cryopump to enrich atmospheric hydrogen and the column to separate hydrogen isotopes that obtained by cryopump method. The cryopump was able to process about 1000 1 atmosphere and the column was able to separate hydrogen isotopes with good resolution. (author)

  13. Isotope effects in photo dissociation of ozone with visible light

    Science.gov (United States)

    Früchtl, Marion; Janssen, Christof; Röckmann, Thomas

    2014-05-01

    Ozone (O3) plays a key role for many chemical oxidation processes in the Earth's atmosphere. In these chemical reactions, ozone can transfer oxygen to other trace gases. This is particularly interesting, since O3 has a very peculiar isotope composition. Following the mass dependent fractionation equation δ17O = 0.52 * δ18O, most fractionation processes depend directly on mass. However, O3 shows an offset to the mass dependent fractionation line. Processes, which show such anomalies, are termed mass independent fractionations (MIF). A very well studied example for a chemical reaction that leads to mass independent fractionation is the O3 formation reaction. To what degree O3 destruction reactions need to be considered in order to understand the isotope composition of atmospheric O3 is still not fully understood and an open question within scientific community. We set up new experiments to investigate the isotope effect resulting from photo dissociation of O3 in the Chappuis band (R1). Initial O3 is produced by an electric discharge. After photolysis O3 is collected in a cold trap at the triple point temperature of nitrogen (63K). O3 is then converted to O2 in order to measure the oxygen isotopes of O3 using isotope ratio mass spectrometry. To isolate O3 photo dissociation (R1) from O3 decomposition (R2) and secondary O3 formation (R3), we use varying amounts of carbon monoxide (CO) as O atom quencher (R4). In this way we suppress the O + O3 reaction (R3) and determine the isotope fractionation in R1 and R2 separately. We present first results on the isotope effects in O3 photo dissociation with visible light in the presence of different bath gases. Results are interpreted based on chemical kinetics modeling. (R1) O3 + hυ → O (3P) + O2 (R2) O3 + O (3P) → 2 O2 (R3) O + O2 + M → O3 + M (R4) O (3P) + CO + M → CO2 + M

  14. Study of groundwater recharge in Rechna Doab using isotope techniques

    International Nuclear Information System (INIS)

    Sajjad, M.I.; Tasneem, M.A.; Ahmed, M.; Hussain, S.D.; Khan, I.H.; Akram, W.

    1992-04-01

    Isotopic studies were performed in the Rechna Doab area to understand the recharge mechanism, investigate the relative contributions from various sources such as rainfall, rivers and canal system and to estimate the turn over times and replenishment rate of groundwater. The isotopic data suggest that the groundwater in the project area can be divided into different zones each having its own characteristic isotopic composition. The enriched isotopic values show rain recharge and depleted isotopic values are associated with river/canal system while the intermediate isotopic values show a mixing of two or more sources of water. The major contribution, however, comes from canal system. The isotopic data suggest that there is no quick movement of groundwater in the area. 18 figs. (author)

  15. Isotopic Analysis of Fingernails as a USGS Open House Demonstration of the Use of Stable Isotopes in Foodweb Studies

    Science.gov (United States)

    Silva, S. R.; Kendall, C.; Young, M. B.; Choy, D.

    2011-12-01

    The USGS Isotope Tracers Project uses stable isotopes and tritium to add a unique dimension of chemical information to a wide range of environmental investigations. The use and application of isotopes is usually an unfamiliar and even esoteric topic to the general public. Therefore during three USGS open house events, as a public outreach effort, we demonstrated the use of stable isotopes by analyzing nitrogen and carbon isotopes from very small fragments of fingernail from willing participants. We titled the exhibit "You Are What You Eat". The results from all participants were plotted on a graph indicating the general influence of different food groups on the composition of body tissues as represented by fingernails. All participants were assigned a number and no personal-identification information was collected. A subset of participants provided us with an estimate of the number of days a week various foods were eaten and if they were vegetarians, vegans or non-vegetarians. Volunteers from our research group were on hand to explain and discuss fundamental concepts such as how foods attain their isotopic composition, the difference between C3 and C4 plants, the effects of assimilation, trophic enrichment, and the various uses of stable isotopes in environmental studies. The results of the fingernail analyses showed the variation of the range of isotopic compositions among about 400 people at each event, the distinct influence of C4 plants (mainly corn and cane sugar) on our carbon isotopic composition, and the isotopic differences between vegetarians and non vegetarians among other details (http://wwwrcamnl.wr.usgs.gov/isoig/projects/fingernails/). A poll of visitors attending the open house event in 2006 indicated that "You Are What You Eat" was among the most popular exhibits. Following the first two open house events we were contacted by a group of researchers from Brazil who had completed a very similar study. Our collaboration resulted in a publication in

  16. A model of the isotope effect of the oxide superconductor

    International Nuclear Information System (INIS)

    Zhang Liyuan.

    1989-03-01

    In this paper, a possible mechanism of producing negative correlation energy centers is proposed. Combining this electronic attractive potential with phonon mediated attractive potential between carriers the isotope effect exponent of La-Sr-Cu-O system is quantitatively explained. Generally, the isotope effect exponent is smaller than 1/2 in this mechanism. (author). 20 refs, 1 fig

  17. Stable isotope composition of atmospheric carbon monoxide. A modelling study

    International Nuclear Information System (INIS)

    Gromov, Sergey S.

    2014-01-01

    This study aims at an improved understanding of the stable carbon and oxygen isotope composition of the carbon monoxide (CO) in the global atmosphere by means of numerical simulations. At first, a new kinetic chemistry tagging technique for the most complete parameterisation of isotope effects has been introduced into the Modular Earth Submodel System (MESSy) framework. Incorporated into the ECHAM/MESSy Atmospheric Chemistry (EMAC) general circulation model, an explicit treatment of the isotope effects on the global scale is now possible. The expanded model system has been applied to simulate the chemical system containing up to five isotopologues of all carbon- and oxygen-bearing species, which ultimately determine the δ 13 C, δ 18 O and Δ 17 O isotopic signatures of atmospheric CO. As model input, a new stable isotope-inclusive emission inventory for the relevant trace gases has been compiled. The uncertainties of the emission estimates and of the resulting simulated mixing and isotope ratios have been analysed. The simulated CO mixing and stable isotope ratios have been compared to in-situ measurements from ground-based observatories and from the civil-aircraft-mounted CARIBIC-1 measurement platform. The systematically underestimated 13 CO/ 12 CO ratios of earlier, simplified modelling studies can now be partly explained. The EMAC simulations do not support the inferences of those studies, which suggest for CO a reduced input of the highly depleted in 13 C methane oxidation source. In particular, a high average yield of 0.94 CO per reacted methane (CH 4 ) molecule is simulated in the troposphere, to a large extent due to the competition between the deposition and convective transport processes affecting the CH 4 to CO reaction chain intermediates. None of the other factors, assumed or disregarded in previous studies, however hypothesised to have the potential in enriching tropospheric CO in 13 C, were found significant when explicitly simulated. The

  18. Isotopes in soil-plant nutrition studies

    International Nuclear Information System (INIS)

    1962-01-01

    Radioisotopes have greatly facilitated investigating the characteristics of plant nutrients in the soil, in measuring soil moisture, in studying the uptake of nutrients by plants and in devising efficient methods of fertilizer application, and are now being widely used in soil-plant nutrition research. A recent international symposium on the use of radioisotopes in soil-plant nutrition studies showed the varied ways in which isotopes can contribute to agricultural production by helping to investigate soil characteristics and soil-plant relationships. The symposium, jointly sponsored by the International Atomic Energy Agency and the Food and Agriculture Organization of the United Nations, was held in Bombay from 26 February to 2 March 1962, at the invitation of the Government of India

  19. Some isotope hydrological studies in Southern Africa

    International Nuclear Information System (INIS)

    Verhagen, B.Th.

    2001-01-01

    Four case studies involving the use of the environmental isotopes 14 C and 3 H, in the and to semi-arid Kalahari region of Southern Africa are described and general conclusions regarding the qualitative aspects of recharge and discharge characteristics of the systems are based on these measurements. In each of the studies, diffuse, local recharge was found to be the dominant recharge mechanism. Recharge via river beds was found to be limited at the regional scale. The balancing discharge mechanism for groundwater was found to be via evapotranspiration. Groundwater salinity and mineralisation as well as the regional hydrogeology are controlled by geological structure rather than lithologies or residence times and the absence of hypersaline groundwaters indicates that the aquifers are periodically flushed during pluvial periods, thus pointing to long-term hydroclimatic controls over the observed present-day hydrology. (author)

  20. Isotope effects on the optical spectra of semiconductors

    Science.gov (United States)

    Cardona, Manuel; Thewalt, M. L. W.

    2005-10-01

    Since the end of the cold war, macroscopic amounts of separated stable isotopes of most elements have been available “off the shelf” at affordable prices. Using these materials, single crystals of many semiconductors have been grown and the dependence of their physical properties on isotopic composition has been investigated. The most conspicuous effects observed have to do with the dependence of phonon frequencies and linewidths on isotopic composition. These affect the electronic properties of solids through the mechanism of electron-phonon interaction, in particular, in the corresponding optical excitation spectra and energy gaps. This review contains a brief introduction to the history, availability, and characterization of stable isotopes, including their many applications in science and technology. It is followed by a concise discussion of the effects of isotopic composition on the vibrational spectra, including the influence of average isotopic masses and isotopic disorder on the phonons. The final sections deal with the effects of electron-phonon interaction on energy gaps, the concomitant effects on the luminescence spectra of free and bound excitons, with particular emphasis on silicon, and the effects of isotopic composition of the host material on the optical transitions between the bound states of hydrogenic impurities.

  1. An experimental study on the effect of carbonic anhydrase on the oxygen isotope exchange kinetics and equilibrium in the carbonic acid system

    Science.gov (United States)

    Uchikawa, J.; Zeebe, R. E.

    2011-12-01

    Stable oxygen isotopes of marine biogenic carbonates are often depleted in 18O relative to the values expected for thermodynamic equilibrium with ambient seawater. One possibility is that 18O-depletion in carbonates is kinetically controlled. The kinetic isotope effect associated with the hydration of CO2 results in 18O-depleted HCO3-. If the HCO3- is utilized before re-establishing equilibrium with ambient water under rapid calcification, the 18O-depletion will be recorded in carbonates. But one caveat in this kinetic model is the fact that many marine calcifiers posses carbonic anhydrase, a zinc-bearing enzyme that catalyzes the CO2 hydration reaction. It is expected that this enzyme accelerates 18O-equilibration in the carbonic acid system by facilitating direct oxygen isotope exchange between HCO3- and H2O via CO2 hydration. Clearly this argues against the conceptual framework of the kinetic model. Yet the critical variable here is the effectiveness of the carbonic anhydrase, which is likely to depend on its concentration and the carbonate chemistry of the aqueous medium. It is also hitherto unknown whether the presence of carbonic anhydrase alters the equilibrium oxygen isotope fractionations between dissolved carbonate species and water. We performed a series of quantitative inorganic carbonate precipitation experiments to examine the changes in the oxygen isotope equilibration time as a function of carbonic anhydrase concentrations. We conducted experiments at pH 8.3 and 8.9. These pH values are similar to the average surface ocean pH and the elevated pH levels observed within calcification microenvironments of certain corals and planktonic foraminifera. A summary of our new experimental results will be presented.

  2. Great isotope effects in compounding of sodium isotopes by macrocyclic polyether

    International Nuclear Information System (INIS)

    Knoechel, A.; Wilken, R.D.

    1978-01-01

    Isotope effects appear in the compounding of the two sodium isotopes 24 Na + and 22 Na + with macrocyclic polyethers, whose value was determined for the 13 best known polyethers. A radiometric process was used for determining the different half life periods of the nuclides used. To separate the compound and non-compound types, these were distributed between water and chloroform. The isotope ratio in the chloroform phase was compared with the output isotope ratio and the separation facfor determined from this. When using crown ethers, there was enrichment of 24 Na + by a significant amount (large crown ether) up to 3.1 +- 0.4% for 18 crown 6. The remarkably high results can be correlated by Biegeleisen's theory with other chemical conditions. There is a report on the first results of transferring these conditions to the H + /T + system. (orig.) [de

  3. Calcium hydroxide isotope effect in calcium isotope enrichment by ion exchange

    International Nuclear Information System (INIS)

    Jepson, B.E.; Shockey, G.C.

    1984-01-01

    The enrichment of calcium isotopes has been observed in ion-exchange chromatography with an aqueous phase of calcium hydroxide and a solid phase of sulfonic acid resin. The band front was exceedingly sharp as a result of the acid-base reaction occuring at the front of the band. Single-stage separation coefficients were found to be epsilon( 44 Ca/ 40 Ca) = 11 x 10 -4 and epsilon( 48 Ca/ 40 Ca) = 18 x 10 -4 . The maximum column separation factors achieved were 1.05 for calcium-44 and 1.09 for calcium-48 with the heavy isotopes enriching in the fluid phase. The calcium isotope effect between fully hydrated aqueous calcium ions and undissociated aqueous calcium hydroxide was estimated. For the calcium-44/40 isotope pair the separation coefficient was 13 x 10 -4 . 20 references, 2 figures

  4. Isotope effect in the Knight shift of potassium

    International Nuclear Information System (INIS)

    Sahm, W.; Schwenk, A.

    1975-01-01

    The Knight shifts of the potassium isotopes 39 K and 41 K were determined with high accuracy: Ksup((39)) = 0.274 35(10)% and Ksup((41)) = 0.274 93(12)%. The relative isotope effect ΔK/K = -0.210 (20)% is in agreement with the hyperfine structure anomaly 39 Δ 41 . (orig.) [de

  5. Selected bibliography on deuterium isotope effects and heavy water

    International Nuclear Information System (INIS)

    Dave, S.M.; Donde, M.M.

    1983-01-01

    In recent years, there has been a great deal of interest in using deuterium and heavy water not only in nuclear industry but also in various fields of basic as well as applied research in physics, chemistry and biology. As a result, the literature is being enriched with a large number of research papers and technical reports published each year. Thus, to enable the scientists to have an easy reference to these works, an endeavour has been made in this selected bibliography, to enlist the publications related to these fields. Since the interest is concerned mainly with heavy water production processes, deuterium isotope effects etc., several aspects (e.g. nuclear) of deuterium have not been covered here. The material in this bibliography which cites 2388 references has been classified under six broad headings, viz. (1) Production of heavy water, (2) Study of deuterium isotope effects, (3) Analysis and Properties of heavy water, (4) Laser Separation of deuterium, (5) Isotopic exchange reactions, and (6) Miscellaneous. The sources of information used for this compilation are chemical abstracts, nuclear science abstracts, INIS Atomindex and also some scattered search through journals and reports available in the B.A.R.C. library. However, in spite of sincere attempts for a wide coverage, no claim is being made towards the exhaustiveness of this bibliography. (author)

  6. Carbon and hydrogen isotopic effects of stomatal density in Arabidopsis thaliana

    Science.gov (United States)

    Lee, Hyejung; Feakins, Sarah J.; Sternberg, Leonel da S. L.

    2016-04-01

    Stomata are key gateways mediating carbon uptake and water loss from plants. Varied stomatal densities in fossil leaves raise the possibility that isotope effects associated with the openness of exchange may have mediated plant wax biomarker isotopic proxies for paleovegetation and paleoclimate in the geological record. Here we use Arabidopsis thaliana, a widely used model organism, to provide the first controlled tests of stomatal density on carbon and hydrogen isotopic compositions of cuticular waxes. Laboratory grown wildtype and mutants with suppressed and overexpressed stomatal densities allow us to directly test the isotope effects of stomatal densities independent of most other environmental or biological variables. Hydrogen isotope (D/H) measurements of both plant waters and plant wax n-alkanes allow us to directly constrain the isotopic effects of leaf water isotopic enrichment via transpiration and biosynthetic fractionations, which together determine the net fractionation between irrigation water and n-alkane hydrogen isotopic composition. We also measure carbon isotopic fractionations of n-alkanes and bulk leaf tissue associated with different stomatal densities. We find offsets of +15‰ for δD and -3‰ for δ13C for the overexpressed mutant compared to the suppressed mutant. Since the range of stomatal densities expressed is comparable to that found in extant plants and the Cenozoic fossil record, the results allow us to consider the magnitude of isotope effects that may be incurred by these plant adaptive responses. This study highlights the potential of genetic mutants to isolate individual isotope effects and add to our fundamental understanding of how genetics and physiology influence plant biochemicals including plant wax biomarkers.

  7. Computational Replication of the Primary Isotope Dependence of Secondary Kinetic Isotope Effects in Solution Hydride-Transfer Reactions: Supporting the Isotopically Different Tunneling Ready State Conformations.

    Science.gov (United States)

    Derakhshani-Molayousefi, Mortaza; Kashefolgheta, Sadra; Eilers, James E; Lu, Yun

    2016-06-30

    We recently reported a study of the steric effect on the 1° isotope dependence of 2° KIEs for several hydride-transfer reactions in solution (J. Am. Chem. Soc. 2015, 137, 6653). The unusual 2° KIEs decrease as the 1° isotope changes from H to D, and more in the sterically hindered systems. These were explained in terms of a more crowded tunneling ready state (TRS) conformation in D-tunneling, which has a shorter donor-acceptor distance (DAD) than in H-tunneling. To examine the isotopic DAD difference explanation, in this paper, following an activated motion-assisted H-tunneling model that requires a shorter DAD in a heavier isotope transfer process, we computed the 2° KIEs at various H/D positions at different DADs (2.9 Å to 3.5 Å) for the hydride-transfer reactions from 2-propanol to the xanthylium and thioxanthylium ions (Xn(+) and TXn(+)) and their 9-phenyl substituted derivatives (Ph(T)Xn(+)). The calculated 2° KIEs match the experiments and the calculated DAD effect on the 2° KIEs fits the observed 1° isotope effect on the 2° KIEs. These support the motion-assisted H-tunneling model and the isotopically different TRS conformations. Furthermore, it was found that the TRS of the sterically hindered Ph(T)Xn(+) system does not possess a longer DAD than that of the (T)Xn(+) system. This predicts a no larger 1° KIE in the former system than in the latter. The observed 1° KIE order is, however, contrary to the prediction. This implicates the stronger DAD-compression vibrations coupled to the bulky Ph(T)Xn(+) reaction coordinate.

  8. Mechanistic deductions from kinetic isotope effects and pH studies of pyridoxal phosphate dependent carbon-carbon lyases: Erwinia herbicola and Citrobacter freundii tyrosine phenol-lyase

    International Nuclear Information System (INIS)

    Kiick, D.M.; Phillips, R.S.

    1988-01-01

    The pH dependence of the kinetic parameters and primary deuterium isotope effects have been determined for tyrosine phenol-lyase from both Erwinia herbicola and Citrobacter freundii. The primary deuterium isotope effects indicate that proton abstraction from the 2-position of the substrate is partially rate-limiting for both enzymes. The C. freundii enzyme primary deuterium isotope effects [DV = 3.5 and D(V/Ktyr) = 2.5] are pH independent, indicating that tyrosine is not sticky (i.e., does not dissociate slower than it reacts to give products). Since Vmax for both tyrosine and the alternate substrate S-methyl-L-cysteine is also pH independent, substrate binds only to the correctly protonated form of the enzyme. For the E. herbicola enzyme, both Vmax and V/K for tyrosine or S-methyl-L-cysteine are pH dependent, as well as both DV and D(V/Ktyr). Thus, while both the protonated and unprotonated enzyme can bind substrate, and may be interconverted directly, only the unprotonated Michaelis complex is catalytically competent. At pH 9.5, DV = 2.5 and D(V/Ktyr) = 1.5. However, at pH 6.4 the isotope effect on both parameters is equal to 4.1. From these data, the forward commitment factor (cf = 5.2) and catalytic ratio (cvf = 1.1) for tyrosine and S-methyl-L-cysteine (cf = 2.2, cvf = 24) are calculated. Also, the Michaelis complex partition ratio (cf/cvf) for substrate and products is calculated to be 4.7 for tyrosine and 0.1 for S-methyl-L-cysteine

  9. Symmetry effects in neutron scattering from isotopically enriched Se isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Lachkar, J.; Haouat, G.; McEllistrem, M. T.; Patin, Y.; Sigaud, J.; Cocu, F.

    1975-06-01

    Differential cross sections for neutron elastic and inelastic scattering from {sup 76}Se, {sup 78}Se, {sup 80}Se and {sup 82}Se, have been measured at 8-MeV incident neutron energy and from {sup 76}Se and {sup 82}Se at 6- and 10-MeV incident energies. The differences observed in the elastic scattering cross sections are interpretable as the effects of isospin term in the scattering potentials. A full analysis of the elastic scattering data are presented.

  10. Isotope effect on the zero point energy shift upon condensation

    International Nuclear Information System (INIS)

    Kornblum, Z.C.

    1977-01-01

    The various isotope-dependent and independent atomic and molecular properties that pertain to the isotopic difference between the zero point energy (ZPE) shifts upon condensation have been derived. The theoretical development of the change of the ZPE associated with the internal molecular vibrations, due to the condensation of the gaseous molecules, has been presented on the basis of Wolfsberg's second-order perturbation treatment of the isotope-dependent London dispersion forces between liquid molecules. The isotope effect on the ZPE shift is related to the difference between the sums of the integrated intensities of the infrared absorption bands of the two gaseous isotopic molecules. Each intensity sum is expressed, in part, in terms of partial derivatives of the molecular dipole moment with respect to atomic cartesian coordinates. These derivatives are related to the isotope-independent effective charges of the atoms, which are theoretically calculated by means of a modified CNDO/2 computer program. The effective atomic charges are also calculated from available experimental infrared intensity data. The effects of isotopic substitutions of carbon-13 for carbon-12 and/or deuterium for protium, in ethylene, methane, and the fluorinated methanes, CH 3 F, CH 2 F 2 , CHF 3 , and CF 4 , on the ZPE shift upon condensation are calculated. These results compare well with the Bigeleisen B-factors, which are experimentally obtained from vapor pressure measurements of the isotopic species. Each of the following molecular properties will tend to increase the isotopic difference between the ZPE shifts upon condensation: (1) large number of highly polar bonds, (2) high molecular weight, (3) non-polar (preferably) or massive molecule, (4) non-hydrogenous molecule, and (5) closely packed liquid molecules. These properties will result in stronger dispersion forces in the liquid phase between the lighter molecules than between the isotopically heavier molecules

  11. Isotope angiocardiography. Method and preliminary own studies

    Energy Technology Data Exchange (ETDEWEB)

    Stepinska, J; Ruzyllo, W; Konieczny, W [Centrum Medyczne Ksztalcenia Podyplomowego, Warsaw (Poland)

    1979-01-01

    Method of technetium isotope 99 m pass through the heart recording with the aid of radioisotope scanner connected with seriograph and computer is being presented. Preliminary tests were carried out in 26 patients with coronary disease without or with previous myocardial infarction, cardiomyopathy, ventricular septal defect and in patients with artificial mitral and aortic valves. The obtained scans were evaluated qualitatively and compared with performed later contrast X-rays of the heart. Size of the right ventricle, volume and rate of left atrial evacuation, size and contractability of left ventricle were evaluated. Similarity of direct and isotope angiocardiographs, non-invasional character and repeatability of isotope angiocardiography advocate its usefulness.

  12. Theory of the isotope effect in superconducting compounds

    International Nuclear Information System (INIS)

    Culetto, F.J.; Rainer, D.

    1978-05-01

    We present a theoretical analysis of the isotope effect on the superconducting transition temperature. Our method is to calculate via formal perturbation theory the response of the transition temperature to small changes of the masses of the various constituents of the compound. We discuss the relation between the isotope effect and various more fundamental parameters in strong coupling superconductors. As illustrative examples, we consider the systems Pd-H(D) alloys and the binary Chevrel phase superconductor Mo 6 Se 8 , and show that analysis of the isotope effect can yield useful information concerning interaction mechanisms in these compounds. (orig.)

  13. Biosynthetic effects on the stable carbon isotopic compositions of agal lipids: Implications for deciphering the carbon isotopic biomarker record

    NARCIS (Netherlands)

    Sinninghe Damsté, J.S.; Schouten, S.; Klein Breteler, W.C.M.; Blokker, P.; Schogt, N.; Rijpstra, W.I.C.; Grice, K.; Baas, M.

    1998-01-01

    Thirteen species of algae covering an extensive range of classes were cultured and stable carbon isotopic compositions of their lipids were analysed in order to assess carbon isotopic fractionation effects during their biosynthesis. The fatty acids were found to have similar stable carbon isotopic

  14. The effect of zero-point energy differences on the isotope dependence of the formation of ozone: a classical trajectory study.

    Science.gov (United States)

    Schinke, Reinhard; Fleurat-Lessard, Paul

    2005-03-01

    The effect of zero-point energy differences (DeltaZPE) between the possible fragmentation channels of highly excited O(3) complexes on the isotope dependence of the formation of ozone is investigated by means of classical trajectory calculations and a strong-collision model. DeltaZPE is incorporated in the calculations in a phenomenological way by adjusting the potential energy surface in the product channels so that the correct exothermicities and endothermicities are matched. The model contains two parameters, the frequency of stabilizing collisions omega and an energy dependent parameter Delta(damp), which favors the lower energies in the Maxwell-Boltzmann distribution. The stabilization frequency is used to adjust the pressure dependence of the absolute formation rate while Delta(damp) is utilized to control its isotope dependence. The calculations for several isotope combinations of oxygen atoms show a clear dependence of relative formation rates on DeltaZPE. The results are similar to those of Gao and Marcus [J. Chem. Phys. 116, 137 (2002)] obtained within a statistical model. In particular, like in the statistical approach an ad hoc parameter eta approximately 1.14, which effectively reduces the formation rates of the symmetric ABA ozone molecules, has to be introduced in order to obtain good agreement with the measured relative rates of Janssen et al. [Phys. Chem. Chem. Phys. 3, 4718 (2001)]. The temperature dependence of the recombination rate is also addressed.

  15. Isotope effects in lithium hydride and lithium deuteride crystals by molecular dynamics simulations.

    Science.gov (United States)

    Dammak, Hichem; Antoshchenkova, Ekaterina; Hayoun, Marc; Finocchi, Fabio

    2012-10-31

    Molecular dynamics (MD) simulations have been carried out to study isotope effects in lithium hydride and lithium deuteride crystals. Quantum effects on nuclear motion have been included through a quantum thermal bath (QTB). The interatomic forces were described either within the density functional theory (DFT) in the generalized gradient approximation (GGA) or by the phenomenological approach using the shell model. For both models, the isotopic shift in the lattice parameter can be successfully predicted by QTB-MD simulations. The slope of the experimental isotopic shift in pressure is satisfactorily reproduced by QTB-MD within DFT-GGA, in contrast to both density functional perturbation theory and QTB-MD with the shell model. We have analyzed the reasons for these discrepancies through the vibrational densities of states and the isotopic shifts in bulk modulus. The results illustrate the importance of anharmonic contributions to vibrations and to the isotopic pressure shift between LiH and LiD.

  16. Biological isotopy. Introduction to the isotopic effects and to their applications in biology

    International Nuclear Information System (INIS)

    Tcherkez, G.

    2010-01-01

    Since their discovery in the beginning of the 20. century, the study of stable isotopes has considerably developed. This domain, which remained limited in its applications until the 1990's, has become particularly important thereafter thanks to its practical applications and in particular to its economical impacts. Many techniques used in fraud control, in drugs use control, in selection of high-yield plants etc are based on isotopic abundance measurements. This reference book gives a synthesis of our actual knowledge on the use of stable isotopes and of isotope fractionation in biology. It presents the basic notions of isotopic biochemistry and explains the origin of the isotopic effects. The application principles of these effects to metabolism, to organisms physiology, to environmental biology etc are explained and detailed using examples and exercises. The first chapters present the basic knowledge which defines, from a mathematical point-of-view, the isotopic effects of chemical reactions or of physical processes taking place in biology. The measurements principle of natural isotopes abundance is then synthesised. Finally, all these notions are applied at different scales: enzymes, physiology, metabolism, environment, ecosystems and fraud crackdown. (J.S.)

  17. Detection of a deuterium isotope effect in di- and trisubstituted alkylphenylnitrosoureas. An SCE study in Chinese hamster V79-E cells.

    Science.gov (United States)

    Thust, R; Mendel, J; Bach, B; Schwarz, H

    1985-06-01

    The genotoxicity of 1-methyl-3-phenyl-1-nitrosourea (MPNU), 1-methyl-3-(p-chlorophenyl)-1-nitrosourea (C1-MPNU), 1-ethyl-3-phenyl-1-nitrosourea (EPNU), 1,3-dimethyl-3-phenyl-1-nitrosourea (DMPNU) and their derivatives substituted by deuterium in different positions was studied using sister chromatid exchange (SCE) induction in Chinese hamster V79-E cells. Deuterium substitution in the 1-methyl group of MPNU (MPNU-d3) and C1-MPNU (C1-MPNU-d3) diminished the SCE-inducing capacity by 20-30% and by 30-40% in DMPNU (DMPNU-d3B). There was no altered SCE activity detected when the phenyl group of MPNU (MPNU-d5) or the 3-methyl group of DMPNU (DMPNU-d3A) was deuterium labeled. No isotope effect was detected in deuterated EPNU derivatives, presumably due to the instability of these compounds. It is surmised that the easier delocalization of the positive charge in the deuterated alkyl diazonium ion causes a diminished reactivity and therefore influences the type and amount of DNA alkylation. Furthermore, the experiments with DMPNU and its derivatives revealed that, in contrast to mono- and disubstituted nitrosoureas, the biological activities of these very stable trisubstituted nitrosoureas are strongly influenced by a serum factor in the culture fluid.

  18. Detection of a deuterium isotope effect in di- and trisubstituted alkylphenylnitrosoureas. An SCE study in Chinese hamster V79-E cells

    International Nuclear Information System (INIS)

    Thust, R.; Mendel, J.; Bach, B.; Schwarz, H.

    1985-01-01

    The genotoxicity of 1-methyl-3-phenyl-1-nitrosourea (MPNU), 1-methyl-3-(p-chlorophenyl)-1-nitrosourea (C1-MPNU), 1-ethyl-3-phenyl-1-nitrosourea (EPNU), 1,3-dimethyl-3-phenyl-1-nitrosourea (DMPNU) and their derivatives substituted by deuterium in different positions was studied using sister chromatid exchange (SCE) induction in Chinese hamster V79-E cells. Deuterium substitution in the 1-methyl group of MPNU (MPNU-d3) and C1-MPNU (C1-MPNU-d3) diminished the SCE-inducing capacity by 20-30% and by 30-40% in DMPNU (DMPNU-d3B). There was no altered SCE activity detected when the phenyl group of MPNU (MPNU-d5) or the 3-methyl group of DMPNU (DMPNU-d3A) was deuterium labeled. No isotope effect was detected in deuterated EPNU derivatives, presumably due to the instability of these compounds. It is surmised that the easier delocalization of the positive charge in the deuterated alkyl diazonium ion causes a diminished reactivity and therefore influences the type and amount of DNA alkylation. Furthermore, the experiments with DMPNU and its derivatives revealed that, in contrast to mono- and disubstituted nitrosoureas, the biological activities of these very stable trisubstituted nitrosoureas are strongly influenced by a serum factor in the culture fluid

  19. Study ω and φ photoproduction in the nucleon isotopic channels

    International Nuclear Information System (INIS)

    Zhao, Q.

    2002-01-01

    We present results for the photoproduction of ω and φ meson in the nucleon isotopic channels. A recently developed quark model with an effective Lagrangian is employed to account for the non-diffractive s- and u-channel processes; the diffractive feature arising from the natural parity exchange is accounted for by the t-channel pomeron exchange, while the unnatural parity exchange is accounted for by the t-channel pion exchange. In the ω production, the isotopic effects could provide more information concerning the search of 'missing resonances', while in the φ production, the isotopic effects could highlight non-diffractive resonance excitation mechanisms at large angles. (author)

  20. Role of effective distance in the fission mechanism study by the double-energy measurement for uranium isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Baba, Hiroshi; Saito, Tadashi; Takahashi, Naruto [Osaka Univ., Suita (Japan)] [and others

    1997-09-01

    Fission product kinetic energies were measured by the double-energy method for thermal-neutron fission of {sup 235,233}U and proton-induced fission of {sup 238}U at the 15.8-MeV excitation. From the obtained energy-mass correlation data, the kinetic-energy distribution was constructed from each mass bin to evaluate the first moment of the kinetic energy for a given fragment mass. The resulting kinetic energy was then converted to the effective distance between the charge centers at the moment of scission. The effective distances deduced for the proton-induced fission was concluded to be classified into two constant values, one for asymmetric and the other for symmetric mode, irrespective of the mass though an additional component was further extracted in the asymmetric mass region. This indicates that the fission takes place via two well-defined saddles, followed by the random neck rupture. On the contrary, the effective distances obtained for thermal-neutron induced fission turned out to lie along the contour line at the same level as the equilibrium deformation in the two-dimensional potential map. This strongly suggests that it is essentially a barrier-penetrating type of fission rather than the over-barrier fission. (author). 73 refs.

  1. Role of effective distance in the fission mechanism study by the double-energy measurement for uranium isotopes

    International Nuclear Information System (INIS)

    Baba, Hiroshi; Saito, Tadashi; Takahashi, Naruto

    1997-01-01

    Fission product kinetic energies were measured by the double-energy method for thermal-neutron fission of 235,233 U and proton-induced fission of 238 U at the 15.8-MeV excitation. From the obtained energy-mass correlation data, the kinetic-energy distribution was constructed from each mass bin to evaluate the first moment of the kinetic energy for a given fragment mass. The resulting kinetic energy was then converted to the effective distance between the charge centers at the moment of scission. The effective distances deduced for the proton-induced fission was concluded to be classified into two constant values, one for asymmetric and the other for symmetric mode, irrespective of the mass though an additional component was further extracted in the asymmetric mass region. This indicates that the fission takes place via two well-defined saddles, followed by the random neck rupture. On the contrary, the effective distances obtained for thermal-neutron induced fission turned out to lie along the contour line at the same level as the equilibrium deformation in the two-dimensional potential map. This strongly suggests that it is essentially a barrier-penetrating type of fission rather than the over-barrier fission. (author). 73 refs

  2. Kinetic isotope effect in the thermolysis of methylenecyclobutane

    International Nuclear Information System (INIS)

    Chickos, J.S.

    1979-01-01

    The intramolecular kinetic isotope effect for the thermolysis of equilibrated methylenecyclobutane-d 2 was investigated at 515 0 C as a function of pressure. A high-pressure value of k/sub H/k/sub D/ (ethylene/ethylene-d 2 ) = 0.9 was obtained at 13 cm of N 2 pressure. This value decreased to 0.86 at 70 μm total pressure. No intermolecular kinetic isotope effect was measured for the formation of ethylene from labeled and unlabeled methylenecyclobutane. The pressure and temperature dependence of the intramolecular kinetic isotope effect was used as evidence in establishing the inverse nature of the effect. The isotope effect observed was explained in terms of competing equilibrium and kinetic isotope effects in which the equilibrium isotope effects dominate. It was concluded on the bases of these results that an acyclic intermediate is involved in the fragmentation of methylenecyclobutane to ethylene and allene. The results also support the notion that deuterium prefers to accumulate at the methylene group with the greatest p character in the carbon--hydrogen bond. 1 figure, 4 tables

  3. Absence of isotope effect of diffusion in a metallic glass

    International Nuclear Information System (INIS)

    Heesemann, A.; Raetzke, K.; Faupel, F.; Hoffmann, J.; Heinemann, K.

    1995-01-01

    The isotope effect E = d ln(D)/d ln (1/√m) of Co diffusion in structurally relaxed Co 86 Zr 14 and Co 81 Zr 19 glasses has been measured by means of a radiotracer technique. Within experimental accuracy no isotope effect was detected (E < 0.04). This suggests a highly cooperative diffusion mechanism. The connection between diffusion and collective low-frequency relaxations in glasses is discussed. (orig.)

  4. Li Isotope Studies of Olivine in Mantle Xenoliths by SIMS

    Science.gov (United States)

    Bell, D. R.; Hervig, R. L.; Buseck, P. R.

    2005-01-01

    Variations in the ratio of the stable isotopes of Li are a potentially powerful tracer of processes in planetary and nebular environments [1]. Large differences in the 7Li/6Li ratio between the terrestrial upper mantle and various crustal materials make Li isotope composition a potentially powerful tracer of crustal recycling processes on Earth [2]. Recent SIMS studies of terrestrial mantle and Martian meteorite samples report intra-mineral Li isotope zoning [3-5]. Substantial Li isotope heterogeneity also exists within and between the components of chondritic meteorites [6,7]. Experimental studies of Li diffusion suggest the potential for rapid isotope exchange at elevated temperatures [8]. Large variations in 7Li, exceeding the range of unaltered basalts, occur in terrestrial mantle-derived xenoliths from individual localities [9]. The origins of these variations are not fully understood.

  5. Preliminary economic feasibility study of MIP (Medical Isotopes Producer)

    International Nuclear Information System (INIS)

    Mon, G. H.; O, S. Y.

    2004-01-01

    Preliminary economic feasibility study of MIP (Medical Isotopes Producer), which is used liquid nuclear fuel to produce medical isotopes of Mo-99 and Sr-89, was performed. To do this, this study was estimated the IRR(Internal Rate of Return) and PBP(Pay-back Period) about optimistic and pessimistic cases for market penetration of Asia and U.S.A. isotope markets. And sensitivity analysis is also performed about capital cost and price of Mo-99 and Sr-89. According to the results, IRR was between 14.9% and 24.3%, and PBP was between 4.8 years and 7.8 years. These suggest that MIP has economic merits. MIP can produce other medical isotopes such as Sr-90, I-131, Xe-133, Cs-137. So, it is necessary to do cost-benefit analysis considering production of these other isotopes

  6. Stable-isotope studies. Progress report, March 1, 1980-August 25, 1982

    International Nuclear Information System (INIS)

    Ishida, T.

    1982-01-01

    Investigations during the past two-and-a half year priod have been directed toward the following three areas: (1) studies of vapor pressure isotope effects (fluoroform, methyl fluoride, methylene difluorides, ammonia); (2) studies on the fractionation of nitrogen isotope systems; and (3) theory of isotope effect. Studies on the fractionation of nitrogen isotope fractionaton systems involved two fronts. One is a study of 15 N-production by means of a countercurrent isotope exchange in a packed column between a gas phase, which is a mixture of various NO/sub x/, and a liquid phase, which is mainly N 2 O 3 and N 2 O 4 . The second deals with a concept of closed reflux cycle for the Nitrox and/or the NO/N 2 O 3 -process. In the theoretical field, studies of isotopic reduced partition function ratio has led to revelations of interesting correlations between molecular structures, molecular forces, and the isotope effects. The investigations for this period are summarized and a more thorough discussion is presented for each ongoing research

  7. Hydrochemical and isotope study of Lake Titicaca

    International Nuclear Information System (INIS)

    Gonfiantini, R.; Cioni, R.; Paredes, M.

    2002-01-01

    The chemical and isotopic compositions of Lake Titicaca and its inflow waters (precipitation, tributaries, groundwater) were determined with the aim of establishing the lake chemical and isotope balance. The three main regions of the lake, i.e. the Lago Mayor, the eastern and the western basins of Lago Menor, connected in cascade, show significant chemical and isotopic differences. Chloride and sodium balance indicates that an average of about 92% of the inflow water evaporates, and the remaining 8 % is lost through Rio Desaguadero and infiltration. The balance of each basin is also obtained, including the inter-basin fluxes. The stable isotope balance in not possible because no data are available on the mean atmospheric vapour isotopic composition. However, this was tentatively computed using the fluxes obtained from chemistry. The vapour δ-values are slightly more negative than those of rainfall. Tritium, noble gases and chloro-fluoro-carbons in vertical profiles show that the lake is vertically well mixed and there is no water segregation at depth. (author)

  8. H/D Isotope Effects in Hydrogen Bonded Systems

    Directory of Open Access Journals (Sweden)

    Aleksander Filarowski

    2013-04-01

    Full Text Available An extremely strong H/D isotope effect observed in hydrogen bonded A-H…B systems is connected with a reach diversity of the potential shape for the proton/deuteron motion. It is connected with the anharmonicity of the proton/deuteron vibrations and of the tunneling effect, particularly in cases of short bridges with low barrier for protonic and deuteronic jumping. Six extreme shapes of the proton motion are presented starting from the state without possibility of the proton transfer up to the state with a full ionization. The manifestations of the H/D isotope effect are best reflected in the infra-red absorption spectra. A most characteristic is the run of the relationship between the isotopic ratio nH/nD and position of the absorption band shown by using the example of NHN hydrogen bonds. One can distinguish a critical range of correlation when the isotopic ratio reaches the value of ca. 1 and then increases up to unusual values higher than . The critical range of the isotope effect is also visible in NQR and NMR spectra. In the critical region one observes a stepwise change of the NQR frequency reaching 1.1 MHz. In the case of NMR, the maximal isotope effect is reflected on the curve presenting the dependence of Δd (1H,2H on d (1H. This effect corresponds to the range of maximum on the correlation curve between dH and ΔpKa that is observed in various systems. There is a lack in the literature of quantitative information about the influence of isotopic substitution on the dielectric properties of hydrogen bond except the isotope effect on the ferroelectric phase transition in some hydrogen bonded crystals.

  9. Isotope effect on the zero point energy shift upon condensation

    International Nuclear Information System (INIS)

    Kornblum, Z.C.; Ishida, T.

    1977-07-01

    The various isotope-dependent and independent atomic and molecular properties that pertain to the isotopic difference between the zero point energy (ZPE) shifts upon condensation were derived. The theoretical development of the change of the ZPE associated with the internal molecular vibrations, due to the condensation of the gaseous molecules, is presented on the basis of Wolfsberg's second-order perturbation treatment of the isotope-dependent London dispersion forces between liquid molecules. The isotope effect on the ZPE shift is related to the difference between the sums of the integrated intensities of the infrared absorption bands of the two gaseous isotopic molecules. The effective atomic charges are also calculated from available experimental infrared intensity data. The effects of isotopic substitutions of carbon-13 for carbon-12 and/or deuterium for protium, in ethylene, methane, and the fluorinated methanes, CH 3 F, CH 2 F 2 , CHF 3 , and CF 4 , on the ZPE shift upon condensation are calculated. These results compare well with the Bigeleisen B-factors, which are experimentally obtained from vapor pressure measurements of the isotopic species. Each of the following molecular properties will tend to increase the isotopic difference between the ZPE shifts upon condensation: (1) large number of highly polar bonds, (2) high molecular weight, (3) non-polar (preferably) or massive molecule, (4) non-hydrogenous molecule, and (5) closely packed liquid molecules. These properties will result in stronger dispersion forces in the liquid phase between the lighter molecules than between the isotopically heavier molecules. 36 tables, 9 figures

  10. Experimental protocols for and studies of the effects of surface passivation and water isotopes on the gliding speed of microtubules propelled by kinesin-1

    Science.gov (United States)

    Maloney, Roger Andrew

    This dissertation explores how the kinesin-1 and microtubule system is affected by surface passivation and water isotopes. Surface passivation was found to affect the gliding speed that microtubules exhibit in the gliding motility assay and the lengths of microtubules supported by the passivation. It was also found that gliding speeds of microtubules are very sensitive to temperature changes. Studies changing the water isotope were a first attempt to investigate if changing the solvent changed the osmotic pressure of the solution kinesin and microtubules were in. No osmotic pressure changes were observed, however, the experiments using different isotopes of water did illuminate the possibility that kinesin may be sensitive to viscosity changes in the solvent. This experiment also suggests further experiments that can be specifically designed to probe osmotic pressure changes. This thesis was also the first thesis ever, to the best of the author's knowledge, to be done in a completely open format. All information and notebook entries that are related to it, as well as the thesis itself, can be found on the website OpenWetWare. The thesis can also be found there including all the different versions that went into its editing. The philosophy and process of making data open and accessible to every one is also discussed.

  11. Full-dimensional analytical potential energy surface describing the gas-phase Cl + C2H6 reaction and kinetics study of rate constants and kinetic isotope effects.

    Science.gov (United States)

    Rangel, Cipriano; Espinosa-Garcia, Joaquin

    2018-02-07

    Within the Born-Oppenheimer approximation a full-dimensional analytical potential energy surface, PES-2017, was developed for the gas-phase hydrogen abstraction reaction between the chlorine atom and ethane, which is a nine body system. This surface presents a valence-bond/molecular mechanics functional form dependent on 60 parameters and is fitted to high-level ab initio calculations. This reaction presents little exothermicity, -2.30 kcal mol -1 , with a low height barrier, 2.44 kcal mol -1 , and intermediate complexes in the entrance and exit channels. We found that the energetic description was strongly dependent on the ab initio level used and it presented a very flat topology in the entrance channel, which represents a theoretical challenge in the fitting process. In general, PES-2017 reproduces the ab initio information used as input, which is merely a test of self-consistency. As a first test of the quality of the PES-2017, a theoretical kinetics study was performed in the temperature range 200-1400 K using two approaches, i.e. the variational transition-state theory and quasi-classical trajectory calculations, with spin-orbit effects. The rate constants show reasonable agreement with experiments in the whole temperature range, with the largest differences at the lowest temperatures, and this behaviour agrees with previous theoretical studies, thus indicating the inherent difficulties in the theoretical simulation of the kinetics of the title reaction. Different sources of error were analysed, such as the limitations of the PES and theoretical methods, recrossing effects, and the tunnelling effect, which is negligible in this reaction, and the manner in which the spin-orbit effects were included in this non-relativistic study. We found that the variation of spin-orbit coupling along the reaction path, and the influence of the reactivity of the excited Cl( 2 P 1/2 ) state, have relative importance, but do not explain the whole discrepancy. Finally, the

  12. Steric effects on the primary isotope dependence of secondary kinetic isotope effects in hydride transfer reactions in solution: caused by the isotopically different tunneling ready state conformations?

    Science.gov (United States)

    Maharjan, Binita; Raghibi Boroujeni, Mahdi; Lefton, Jonathan; White, Ormacinda R; Razzaghi, Mortezaali; Hammann, Blake A; Derakhshani-Molayousefi, Mortaza; Eilers, James E; Lu, Yun

    2015-05-27

    The observed 1° isotope effect on 2° KIEs in H-transfer reactions has recently been explained on the basis of a H-tunneling mechanism that uses the concept that the tunneling of a heavier isotope requires a shorter donor-acceptor distance (DAD) than that of a lighter isotope. The shorter DAD in D-tunneling, as compared to H-tunneling, could bring about significant spatial crowding effect that stiffens the 2° H/D vibrations, thus decreasing the 2° KIE. This leads to a new physical organic research direction that examines how structure affects the 1° isotope dependence of 2° KIEs and how this dependence provides information about the structure of the tunneling ready states (TRSs). The hypothesis is that H- and D-tunneling have TRS structures which have different DADs, and pronounced 1° isotope effect on 2° KIEs should be observed in tunneling systems that are sterically hindered. This paper investigates the hypothesis by determining the 1° isotope effect on α- and β-2° KIEs for hydride transfer reactions from various hydride donors to different carbocationic hydride acceptors in solution. The systems were designed to include the interactions of the steric groups and the targeted 2° H/D's in the TRSs. The results substantiate our hypothesis, and they are not consistent with the traditional model of H-tunneling and 1°/2° H coupled motions that has been widely used to explain the 1° isotope dependence of 2° KIEs in the enzyme-catalyzed H-transfer reactions. The behaviors of the 1° isotope dependence of 2° KIEs in solution are compared to those with alcohol dehydrogenases, and sources of the observed "puzzling" 2° KIE behaviors in these enzymes are discussed using the concept of the isotopically different TRS conformations.

  13. Bibliography on vapor pressure isotope effects

    International Nuclear Information System (INIS)

    Jancso, G.

    1980-04-01

    The first Bibliography on Vapour Pressure Isotope and covered the literature of the period from 1919 through December 1975. The present Supplement reviews the literature from January 1976 through December 1979. The bibliography is arranged in chronological order; within each year the references are listed alphabetically according to the name of the first author of each work. (author)

  14. D/H isotope effects in π-complexes of deuterated hexamethylbenzenes with the nitrosonium cation

    International Nuclear Information System (INIS)

    Borodkin, G.I.; Elanov, I.R.; Shakirov, M.M.; Shubin, V.G.

    1993-01-01

    The isotope effects of deuterium, manifested in the 13 C NMR spectra of complexes of deuterated hexamethylbenzenes C 6 (CD 3 ) n ·(CH 3 ) 6-n with the nitrosonium cation, have been studied. The small values observed for the isotopic perturbation are evidence of π-bonding of the NO + group to the hexamethylbenzene molecule. The applicability of an additive scheme of calculation of isotope effects for the ring carbon atoms of the complexes, based on the increment of replacement of the CH 3 group by CD 3 in hexamethylbenzene, has been demonstrated

  15. Effect Of Substrates On The Fractionation Of Hydrogen Isotopes During Lipid-Biosynthesis By Haloarcula marismortui

    Science.gov (United States)

    Dirghangi, S. S.; Pagani, M.

    2010-12-01

    Lipids form an important class of proxies for paleoclimatological research, and hydrogen isotope ratios of lipids are being increasingly used for understanding changes in the hydrological system. Proper understanding of hydrogen isotope fractionation during lipid biosynthesis is therefore important and attention has been directed toward understanding the magnitude of hydrogen isotope fractionation that occurs during lipid biosynthesis in various organisms. Hydrogen isotope ratios of lipids depend on the hydrogen isotopic composition of the ambient water, hydrogen isotopic composition of NADPH used during biosynthesis, growth conditions, pathways of lipid biosynthesis, and substrates in the case of heterotrophic organisms. Recently it has been observed that NADPH contributes a significant part of the hydrogen in fatty acids synthesized by bacteria during heterotrophic growth (Zhang et al, 2009). As NADPH is formed by reduction of NADP+ during metabolism of substrates, different metabolic pathways form NADPH with different D/H ratios, which in turn results in variation in D/H ratios of lipids (Zhang et al, 2009). Therefore, substrates play a significant role in hydrogen isotopic compositions of lipids. For this study, we are investigating the effects of substrates on hydrogen isotope fractionation during biosynthesis of isoprenoidal lipids by heterotrophically growing halophilic archaea. Haloarcula marismortui is a halophilic archaea which synthesizes Archaeol (a diether lipid) and other isoprenoidal lipids. We have grown Haloarcula marismortui in pure cultures on three different substrates and are in the process of evaluating isotopic variability of Archaeol and other lipids associated with substrate and the D/H composition of ambient water. Our results will be helpful for a better understanding of hydrogen isotope fractionations during lipid synthesis by archaea. Also, halophilic archaea are the only source of archaeol in hypersaline environments. Therefore, our

  16. Isotopic approach to the provenance study of artifacts

    International Nuclear Information System (INIS)

    Mabuchi, Hisao

    1994-01-01

    Isotopic abundance ratios, which are proved to be generally constant, are known to vary, for certain elements, from one place to another. Light elements, such as hydrogen, lithium, boron, carbon, nitrogen, oxygen and sulfur, show measurable variations of their isotope ratios due to isotopic fractionation which takes place during geochemical or biochemical processes. Isotope ratios of strontium and lead vary due to the decay of long-lived radioactive nuclides 87 Rb and 238 U- 235 U- 232 Th, respectively. Such isotopic anomalies can be applicable to provenance studies of archaeological objects. Thus, 13 C/ 12 C, 18 O/ 16 O, or 87 Sr/ 86 Sr were used to examine the authenticity of Greek marble statues. Also, lead isotope ratios have been used since mid-1960s extensively for provenance studies of glasses and bronzes of different civilizations. As an example, the author presents a series of his own works on lead isotope ratios applied to ancient Japanese bronzes, which are summarized as follows. 1) It was generally observed that lead isotope ratios reflect difference in culture to which bronzes belong. 2) Mirrors in the Western Han period (206 B.C. - A.D.8) are clearly distinguished by lead isotope ratios from those made after the mid-Eastern Han period (ca.A.D.150 - 300). 3) Korean mirrors and weapons excavated from the Yayoi sites contain lead of easily recognizable Mississippi Valley type. 4) Bronze objects made in Japan (imitative Han style mirrors, Dotaku, imitative weapons, arrowheads etc.) in the Yayoi and Kofun periods are classified by lead isotope ratios in the following order: the Korean mirror type to the Western Han mirror type in the Yayoi period and the mid- to post- Han mirror type in the Kofun period. 5) Indigenous Japanese lead seems to have been used after the mid-7th century. (J.P.N.)

  17. Design study of fuel circulating system using Pd-alloy membrane isotope separation method

    International Nuclear Information System (INIS)

    Naito, T.; Yamada, T.; Yamanaka, T.; Aizawa, T.; Kasahara, T.; Nishikawa, M.; Asami, N.

    1980-01-01

    Design study on the fuel circulating system (FCS) for a tokamak experimental fusion reactor (JXFR) has been carried out to establish the system concept, to plan the development program, and to evaluate the feasibility of diffusion system. The FCS consists of main vacuum system, fuel gas refiners, isotope separators, fuel feeders, and auxiliary systems. In the system design, Pd-alloy membrane permeation method is adopted for fuel refining and isotope separating. All impurities are effectively removed and hydrogen isotopes are sufficiently separated by Pd-alloy membrane. The isotope separation system consists of 1st (47 separators) and 2nd (46 separators) cascades for removing protium and separating deuterium, respectively. In the FCS, while cryogenic distillation method appears to be practicable, Pd-alloy membrane diffusion method is attractive for isotope separation and refining of fuel gas. The choice will have to be based on reliability, economic, and safety analyses

  18. Raman spectroscopic studies of isotopic diatomic molecules and a technique for measuring stable isotope ratios using Raman scattering

    International Nuclear Information System (INIS)

    Harney, R.C.

    1976-01-01

    A method for measuring stable isotope ratios using Raman scattering has been developed. This method consists of simultaneously counting photons scattered out of a high-intensity laser beam by different isotopically-substituted molecules. A number of studies of isotopic diatomic molecules have been made. The Q-branches of the Raman spectra of the isotopic molecules 14 N 15 N and 16 O 18 O were observed at natural abundance in nitrogen and oxygen samples. Comparison of the ratios of the intensities of the Q-branches of the major nitrogen and oxygen isotopic molecules with mass spectrometric determinations of the isotopic compositions yielded scattering cross sections of 14 N 15 N relative to 14 N 14 N and 16 O 18 O relative to 16 O 16 O. These cross section ratios differ from unity, a difference which can be explained by considering nuclear mass effects on the Franck-Condon factors of the molecular transitions. The measured intensities of the 14 N 15 N and 16 O 18 O Q-branches provided the baseline data needed to make the previously-mentioned extrapolation. High-resolution (approximately 0.15 cm -1 ) spectra of the Q-branches of 14 N 14 N and 16 O 16 O yielded a direct determination of α/sub e/ (the difference between the rotational constant in the ground and first excited vibrational states) for these molecules. The measured values are in excellent agreement with those obtained by other means. Complete Raman spectra (pure rotation, rotation-vibration, and high-resolution Q-branch) were obtained on a sample of pure 18 O 18 O. Analysis of this data yielded the molecular parameters: the equilibrium internuclear separation r/sub e/, the moment of inertia I/sub e/, and the energy parameters α/sub e/, B/sub e/, and ΔG/sub 1 / 2 /. These are in good agreement with data obtained by microwave spectroscopy

  19. Isotope effects in the equilibrium and non-equilibrium vaporization of tritiated water and ice

    International Nuclear Information System (INIS)

    Baumgaertner, F.; Kim, M.-A.

    1990-01-01

    The vaporization isotope effect of the HTO/H 2 O system has been measured at various temperatures and pressures under equilibrium as well as non-equilibrium conditions. The isotope effect values measured in equilibrium sublimation or distillation are in good agreement with the theoretical values based on the harmonic oscillator model. In non-equilibrium vaporization at low temperatures ( 0 C), the isotope effect decreases rapidly with decreasing system pressure and becomes negligible when the system pressure is lowered more than one tenth of the equilibrium vapor pressure. At higher temperatures, the isotope effect decreases very slowly with decreasing system pressure. Discussion is extended for the application of the present results to the study of biological enrichment of tritium. (author)

  20. Thermal Conductivity of Nanotubes: Effects of Chirality and Isotope Impurity

    OpenAIRE

    Gang, Zhang; Li, Baowen

    2005-01-01

    We study the dependence of thermal conductivity of single walled nanotubes (SWNT) on chirality and isotope impurity by nonequilibrium molecular dynamics method with accurate potentials. It is found that, contrary to electronic conductivity, the thermal conductivity is insensitive to the chirality. The isotope impurity, however, can reduce the thermal conductivity up to 60% and change the temperature dependence behavior. We also study the dependence of thermal conductivity on tube length for t...

  1. Effects of organic amendments on water use efficiency evaluated by a stable isotope technique. A case study in experimental mine restoration.

    Science.gov (United States)

    Luna Ramos, Lourdes; Delgado Huertas, Antonio; Miralles Mellado, Isabel; Solé Benet, Albert

    2017-04-01

    Water deficit and low infiltration reduce restoration success in semiarid post-mine soils, where high mortality of plants has been observed in early years of the restoration. Species that originate from arid and semi-arid regions are often considered appropriate for xeriscaping, but there have been relatively few direct measurements of main water related parameters as water use efficiency (WUE) in restoration strategies. In this respect, the goal of this study was to analyse the efficiency with which native plants use water when organic amendments and mulches are applied in mine soil restorations. The experimental design was established in a calcareous quarry in Almería (SE Spain), under arid climate. We tested two organic amendments (sewage sludge from water treatment plant and compost from vegetable residues) and gravel mulch. Three plant species were planted in 50 m2 experimental plots: Macrochloa tenacissima, Genista umbellata and Anthyllis cytisoides. Soil moisture was monitored at a depth of 0.1 m during 4 years and at the end of this period stable isotope of Carbon (δ13C), considered as an effective method to evaluate the plant intrinsic WUE, was measured. We did not observe significant differences in soil moisture among the different soil restoration treatments. With regard to WUE, species is the factor most important to establish differences. Anthyllis cytisoides showed the lowest mean δ13C values, indicating low WUE. On the contrary, Macrochloa tenacissima presented high δ13C values. Moreover, species showed higher δ13C values when gravel mulch was applied. To increase WUE in restored soils under arid conditions it is necessary to apply water conservation methods and to use the most appropriate species.

  2. Temperature and Pressure Depences on the Isotopic Fractionation Effect in the Thermal Decomposition of Ozone

    Directory of Open Access Journals (Sweden)

    Su-Ju Kim

    1997-12-01

    Full Text Available To understand the mass-independent isotopic fractionation effects, thermal decomposition of ozone was performed. Initial oxygen gas was converted to ozone completely. Then, the ozone was decomposed to oxygen at various temperatures(30~150C. Isotopic compositions of product oxygen and residual ozone were measured using a stable isotope mass spectrometer. The experimental results were compared with the studies which were peformed at the similar conditions. From the raw experimental data, the functions of the instantaneous fractionation factors were calculated by the least square fit. The results clearly showed the temperature dependence. They also showed the pressure dependence and the surface effect. This study may play an important role in the study of ozone decomposition mechanism. It can be applied to explain the mass-independent isotopic pattern found in stratospheric ozone and in meteorites.

  3. Lithium isotope effect accompanying electrochemical intercalation of lithium into graphite

    CERN Document Server

    Yanase, S; Oi, T

    2003-01-01

    Lithium has been electrochemically intercalated from a 1:2 (v/v) mixed solution of ethylene carbonate (EC) and methylethyl carbonate (MEC) containing 1 M LiClO sub 4 into graphite, and the lithium isotope fractionation accompanying the intercalation was observed. The lighter isotope was preferentially fractionated into graphite. The single-stage lithium isotope separation factor ranged from 1.007 to 1.025 at 25 C and depended little on the mole ratio of lithium to carbon of the lithium-graphite intercalation compounds (Li-GIC) formed. The separation factor increased with the relative content of lithium. This dependence seems consistent with the existence of an equilibrium isotope effect between the solvated lithium ion in the EC/MEC electrolyte solution and the lithium in graphite, and with the formation of a solid electrolyte interfaces on graphite at the early stage of intercalation. (orig.)

  4. Ionic conductivity in aqueous solutions: deuterium isotope effect

    International Nuclear Information System (INIS)

    Samanta, Alok; Ghosh, Swapan K.

    1997-01-01

    A simple theoretical investigation of the calculation of ionic conductivity in aqueous solution is presented. The dipolar hard sphere model for the solvent which has been successful elsewhere has been employed here and it has been possible to reproduce the experimental results quite accurately for both water and heavy water using only two parameters. In a more detailed theoretical approach one should employ better models for water with proper account of its vibrations, liberations and also hydrogen bonding. It is also of interest to study the temperature effect and the concentration dependence of the conductivity. The time-dependent friction can also be calculated from the present formalism and be used for the study of isotope effect in proton transfer reactions or other aspects of chemical dynamics

  5. Concentration effect on inter-mineral equilibrium isotope fractionation: insights from Mg and Ca isotopic systems

    Science.gov (United States)

    Huang, F.; Wang, W.; Zhou, C.; Kang, J.; Wu, Z.

    2017-12-01

    Many naturally occurring minerals, such as carbonate, garnet, pyroxene, and feldspar, are solid solutions with large variations in chemical compositions. Such variations may affect mineral structures and modify the chemical bonding environment around atoms, which further impacts the equilibrium isotope fractionation factors among minerals. Here we investigated the effects of Mg content on equilibrium Mg and Ca isotope fractionation among carbonates and Ca content on equilibrium Ca isotope fractionation between orthopyroxene (opx) and clinopyroxene (cpx) using first-principles calculations. Our results show that the average Mg-O bond length increases with decreasing Mg/(Mg+Ca) in calcite when it is greater than 1/48[1] and the average Ca-O bond length significantly decreases with decreasing Ca/(Ca+Mg+Fe) in opx when it ranges from 2/16 to 1/48[2]. Equilibrium isotope fractionation is mainly controlled by bond strengths, which could be measured by bond lengths. Thus, 103lnα26Mg/24Mg between dolomite and calcite dramatically increases with decreasing Mg/(Mg+Ca) in calcite [1] and it reaches a constant value when it is lower than 1/48. 103lnα44Ca/40Ca between opx and cpx significantly increases with decreasing Ca content in opx when Ca/(Ca+Mg+Fe) ranges from 2/16 to 1/48 [2]. If Ca/(Ca+Mg+Fe) is below 1/48, 103lnα44Ca/40Ca is not sensitive to Ca content. Based on our results, we conclude that the concentration effect on equilibrium isotope fractionation could be significant within a certain range of chemical composition of minerals, which should be a ubiquitous phenomenon in solid solution systems. [1] Wang, W., Qin, T., Zhou, C., Huang, S., Wu, Z., Huang, F., 2017. GCA 208, 185-197. [2] Feng, C., Qin, T., Huang, S., Wu, Z., Huang, F., 2014. GCA 143, 132-142.

  6. A latitudinal study of oxygen isotopes within horsehair

    Science.gov (United States)

    Thompson, E.; Bronk Ramsey, C.; McConnell, J. R.

    2016-12-01

    This study aims to explore the hypothesis that 'if oxygen isotope ratios deplete with decreasing temperature then a study of oxygen isotope ratios within horsehair from Oxfordshire to Iceland will show a latitudinal depletion gradient'. By looking at oxygen isotope values at different geographical positions, we can track the relationship with latitude and with different regional climate features. This will provide a firmer understanding of how to compare climate records from different locations. Additionally, a comparison of the horse breeds from this study to those analysed within previous studies will create an even better understanding of the intra-species variation within the δ18O values of horsehair. A total of 24 horses were sampled on the 7th March from Thordale Stud in Shetland, the Icelandic Food And Veterinary Authority in Iceland, the Exmoor Pony Centre in Exmoor and the Pigeon House Equestrian Centre in Oxfordshire. By starting the sampling process from the most recent growth at the follicle, the sampling date becomes a chronological marker, temporally fixing the first sample within a sequential set of data points extending for one year or longer, depending on the length of each individual hair. The samples were analysed for oxygen isotope values using an IRMS coupled within a Sercon HTEA. Preliminary results show a latitudinal gradient is evident on comparison between the locations, consistent with the findings of Darling and Talbot's study of fresh water isotopes in the British Isles (2003). These results support the hypothesis, showing that a study of oxygen isotope ratios within horse hair from Oxfordshire to Iceland showing a latitudinal depletion gradient, consistent with a depletion of oxygen isotope ratios due to decreasing temperatures. Darling, W. and Talbot, J. (2003). The O and H stable isotope composition of freshwaters in the British Isles. 1. Rainfall. Hydrol. Earth System Science, 7(2), pp.163-181.

  7. Pollution and Climate Effects on Tree-Ring Nitrogen Isotopes

    Science.gov (United States)

    Savard, M. M.; Bégin, C.; Marion, J.; Smirnoff, A.

    2009-04-01

    Georgian Bay reflect deposition of NOx emissions from cars and coal-power plants, with higher proportions from coal burning in Georgian Bay (Savard et al., 2009b). This interpretation is conceivable because recent monitoring indicates that coal-power plant NOx emissions play an important role in the annual N budget in Ontario, but they are negligible on the Quebec side. CONCLUSION Interpretations of long tree-ring N isotopic series in terms of effects generated by airborne N-species have been previously advocated. Here we further propose that the contrasted isotopic trends obtained for wood samples from two regions reflect different regional anthropogenic N deposition combined with variations of climatic conditions. This research suggests that nitrogen tree-ring series may record both regional climatic conditions and anthropogenic perturbations of the N cycle. REFERENCES Savard, M.M., Bégin,C., Marion, J., Aznar, J.-C., Smirnoff, A., 2009a. Changes of Air Quality in an urban region as inferred from tree-ring width and stable isotopes. Chapter 9 in "Relating Atmospheric Source Apportionment to Vegetation Effects: Establishing Cause Effect Relationships" (A. Legge ed.). Elsevier, Amsterdam; doi: 10.1016/S1474-8177(08)00209x. Savard, M.M., Bégin, C., Smirnoff, A., Marion, J., Rioux-Paquette, E., 2009b. Tree-ring nitrogen isotopes reflect climatic effects and anthropogenic NOx emissions. Env. Sci. Tech (doi: 10.1021/es802437k).

  8. Isotopic-tracer-aided studies on undesirable effects of heavy metals in the soil-plant system. Part of a coordinated programme on isotopic-tracer-aided studies of agrochemical residue - soil biota interactions

    International Nuclear Information System (INIS)

    Oberlaender, H.E.

    1982-07-01

    Uptake of isotopically labelled mercury (Hg-203), cadmium (Cd-115m) and zinc (Zn-65) from a calcareous chernozem and a podzolized brown earth by spring and winter varieties of wheat, rye and barley was investigated in pot experiments carried out until maturity of the plants. The labelled heavy metals, applied at concentrations innocuous to plant growth (0.5 ppm Hg or Cd, 50 ppm Zn) were determined radiometrically in the straw and in the grains of the harvested plants, as well as in the milling products (bran, semolina and flour) obtained by standard procedures of grain processing. Uptake of mercury was several hundred times smaller than the uptake of cadmium, if both metals were applied to the soil in equal amounts. Whereas the uptake of mercury from the acid soil was insignificant or not detectable, cadmium was taken up from this soil at a much higher rate than from the alkaline soil. Thus, not mercury, but cadmium imposes the greatest hazard on the food chain. Winter varieties of cereals took up more mercury and cadmium than did spring varieties. The content of heavy metals in the plants decreased considerably when plants approached maturity. During translocation through the plants the metals were gradually retained when passing from the stalks (''straw'') into the grains, and from the seed-cover (''bran'') into the endosperm (''flour''). The heavy metal contents of the grain fractions decreased in the order: bran > semolina > flour. Concentrations of heavy metals in flour were 3-8 times smaller than in straw, showing that flour is least affected by heavy metal pollution of cereals via the soil. The metal content of the various flour types was correlated with their percentage of bran and with their ash content. By adding an ion-exchanger to the soil the pattern of relative distribution of heavy metals in mature plants was not changed, but the cadmium content of all cereal products was considerably lowered

  9. Mass independent isotope effects and their observations in nature

    International Nuclear Information System (INIS)

    Thiemens, M.H.

    2002-01-01

    In 1983, Thiemens and Heidenreich reported the first chemically produced mass independent isotope effect. A significant feature of the fractionation was that it identically produced the isotopic relation observed in the calcium-aluminum inclusions in the Allende meteorite. This δ 17 O=δ 18 O composition had previously been thought to represent a nucleosynthetic component as no chemical process was capable of producing a mass independent isotopic composition. It now appears nearly certain that the meteoritic oxygen isotopic anomalies were produced by chemical, rather than nuclear, processes. Since oxygen is the major element in stony planets this represents a major event in the formation of the solar system. In a recent review (Thiemens, 1999), it has been shown that mass independent isotopic compositions are pervasive in the Earth's atmosphere. Molecules which have been demonstrated to possess mass independent isotopic compositions include: O 2 , O 3 , CO 2 , CO, and N 2 O. In each case, the specific nature of the mass independent isotopic composition has provided details of their atmospheric chemistry that could not have been obtained by any other measurement technique. Most recently, solid materials have been observed to possess mass independent isotopic composition. In this paper, these observations are briefly discussed. These solid reservoirs include: 1) carbonates and sulphates from Mars, 2) terrestrial aerosol sulphate, 3) sulphides and sulphates from the Earth, ranging in time from 3.8 to 2.2 billion years before present, 4) sulphates from the Namibian desert and 5) the Antartic Dry Valleys. The information obtained from these measurements is extraordinarily wide ranging, extending from understanding the history of Martian atmosphereregolith interaction to the evolution of the oxygen in the Earth's earliest atmosphere. As was the case for gas phase species, this information and insight could not have been obtained by any other measurement technique

  10. Multicomponent DFT study of geometrical H/D isotope effect on hydrogen-bonded organic conductor, κ-H3(Cat EDT-ST)2

    Science.gov (United States)

    Yamamoto, Kaichi; Kanematsu, Yusuke; Nagashima, Umpei; Ueda, Akira; Mori, Hatsumi; Tachikawa, Masanori

    2017-04-01

    We theoretically investigated a significant contraction of the hydrogen-bonding O⋯O distance upon H/D substitution in our recently developed purely organic crystals, κ-H3(Cat-EDT-ST)2 (H-ST) and its isotopologue κ-D3(Cat-EDT-ST)2 (D-ST), having π-electron systems coupled with hydrogen-bonding fluctuation. The origin of this geometrical H/D isotope effect was elucidated by using the multicomponent DFT method, which takes the H/D nuclear quantum effect into account. The optimized O⋯O distance in H-ST was found to be longer than that in D-ST due to the anharmonicity of the potential energy curve along the Osbnd H bond direction, which was in reasonable agreement with the experimental trend.

  11. Product study of 1-adamantyl and 1-bicyclo[2.2.2]octyl radicals in hydrocarbon solvents. An unusually large hydrogen isotope effect

    International Nuclear Information System (INIS)

    Engel, P.S.; Chae, W.K.; Baughman, S.A.; Marschke, G.E.; Lewis, E.S.; Timberlake, J.W.; Luedtke, A.E.

    1983-01-01

    1-Adamantyl (ada.) and 1-bicyclo[2.2.2]octyl (bo.) radicals have been generated by photolysis of the corresponding azoalkanes in various hydrocarbon solvents. Both radicals abstract hydrogen readily from saturated hydrocarbons and they add to aromatic rings much faster than tert-butyl. does. Despite its reactivity, ada. is remarkably selective in hydrogen atom abstraction, preferring a benzylic hydrogen 25:1 over a cyclohexane hydrogen. The effect of solvent viscosity indicates that formation of the radical dimers biada and bibo occurs in the solvent cage. The most striking result of this work is a deuterium isotope effect of 25 for hydrogen transfer from cyclohexane to ada. at 65 0 C. Steric compression in the transition state is postulated to cause an unusually large tunnel correction and hence a large k/sub H//k/sub D/. 6 tables

  12. Expanding the isotopic toolbox: Applications of hydrogen and oxygen stable isotope ratios to food web studies

    Directory of Open Access Journals (Sweden)

    Hannah B Vander Zanden

    2016-03-01

    Full Text Available The measurement of stable carbon (δ13C and nitrogen (δ15N isotopes in tissues of organisms has formed the foundation of isotopic food web reconstructions, as these values directly reflect assimilated diet. In contrast, stable hydrogen (δ2H and oxygen (δ18O isotope measurements have typically been reserved for studies of migratory origin and paleoclimate reconstruction based on systematic relationships between organismal tissue and local environmental water. Recently, innovative applications using δ2H and, to a lesser extent, δ18O values have demonstrated potential for these elements to provide novel insights in modern food web studies. We explore the advantages and challenges associated with three applications of δ2H and δ18O values in food web studies. First, large δ2H differences between aquatic and terrestrial ecosystem end members can permit the quantification of energy inputs and nutrient fluxes between these two sources, with potential applications for determining allochthonous vs. autochthonous nutrient sources in freshwater systems and relative aquatic habitat utilization by terrestrial organisms. Next, some studies have identified a relationship between δ2H values and trophic position, which suggests that this marker may serve as a trophic indicator, in addition to the more commonly used δ15N values. Finally, coupled measurements of δ2H and δ18O values are increasing as a result of reduced analytical challenges to measure both simultaneously and may provide additional ecological information over single element measurements. In some organisms, the isotopic ratios of these two elements are tightly coupled, whereas the isotopic disequilibrium in other organisms may offer insight into the diet and physiology of individuals. Although a coherent framework for interpreting δ2H and δ18O data in the context of food web studies is emerging, many fundamental uncertainties remain. We highlight directions for targeted research that

  13. Isotope study in geothermal fields in Java Island

    International Nuclear Information System (INIS)

    Wandowo, Z.A.

    1995-01-01

    Study in two geothermal fields, Dieng and Kamojang, in Java island by utilizing isotope technique has been carried out. Isotopic data of wells, springs and other geothermal manifestations providing informations on the recharge area of precipitation contributed to geothermal resources, flow paths and origin of geothermal fluids. The data of oxygen shift has also provided information on the characteristic the fields. (author). 8 refs, 5 figs, 3 tabs

  14. Measurement of environmental tritium for isotope hydrology studies

    International Nuclear Information System (INIS)

    1973-01-01

    The Section of Isotope Hydrology of the IAEA Division of Research and Laboratories gains valuable hydrological information from studies of the concentration of environmental tritium in precipitation, surface and groundwater samples from various sites around the world. This photo story shows the steps in the measurement of these very low levels of tritium in water as performed in the Isotope Hydrology Laboratory of the Agency. (author)

  15. Isotopes based assessment of groundwater renewal and related anthropogenic effects in water scarce areas: Sand dunes study in Qasim area, Saudi Arabia

    International Nuclear Information System (INIS)

    Al-Sagaby, A.; Moallim, A.

    2001-01-01

    The investigation of recharge in the sand dune, Qasim, Saudi Arabia, with the help of chloride concentration and isotope content has revealed inconsistent pattern and less homogeneity. Monotonic chloride concentration and isotope content was the result of seasonal recharge occurrence in the study area. In addition, applying chloride mass-balance method, recharge rate calculation in the sand dune site, Qasim, Saudi Arabia, was made. The results (1.80 and 1.84mmy -1 - dune site) estimated during this project using this method was a long way below the recharge rates (30mmy -1 , 13.4mmy -1 in the dune site and 5mmy -1 in the swale site) obtained with the application of tritium method in the previous years (1994 and 1996). 1.80 and 1.84mmy -1 was for CRP-Saud-9405 project and was calculated 1997 and 1998 respectively. The reason for the lower recharge rate with the application of chloride mass-balance method could be the source of chloride input and high evaporation, which causes accumulation of chloride salts in the area. (author)

  16. Studies of geothermal background and isotopic geochemistry of thermal waters in Jiangxi Province

    International Nuclear Information System (INIS)

    Zhou Wenbin; Sun Zhanxue; Li Xueli; Shi Weijun

    1996-10-01

    The terrestrial heat flow measurement, isotope and geochemical techniques have been systematically applied to the geothermal systems in Jiangxi Province. Results show that the thermal waters in the study area all belong to the low-medium temperature convective geothermal system, which essentially differs from high temperature geothermal systems with deep magmatic heat sources. It has been proven that the isotope and geochemical techniques are very useful and effective in geothermal exploration. (13 refs., 14 tabs., 8 figs.)

  17. The status of applying stable isotope in the studies of environmental science

    International Nuclear Information System (INIS)

    Bai Zhipeng; Zhang Liwen; Zhu Tan; Feng Yinchang

    2007-01-01

    The stable isotope composition is characteristic in the pollution source, and it is relatively fixed in the process of transferring and reaction. At present the precise analysis result of stable isotope ratio can be obtained easily. So the stable isotopes can be applied to the pollution affair arbitration and source study. The concept and analytical method of stable isotopes are introduced. The research status of the stable isotopes in the field of environmental science and the isotope fractionation is reviewed. (authors)

  18. Nuclear transformations studies in selenium isotopes

    International Nuclear Information System (INIS)

    Lopez M, B.E.

    1976-01-01

    A compilation is made with regard to the chemical effects produced by nuclear transformations, such as the chemical effects of the beta decay and the chemical effects of the reaction (n,γ) in selenium radioisotopes. As a particular case the chemical effect of the isomeric transition of sup(81m)Se(VI) in potassium selenate crystals marked with radioactive selenium is studied experimentally and the method of adsorption in activated carbon is applied for the analytical separation of the traces of the nuclear isomer tetravalent sup(81b)Se(IV) of one fraction which contains the mixture of the selenium radioisotopes. (author)

  19. An Experimental and Theoretical Study on the Kinetic Isotope Effect of C2H6 and C2D6 Reaction with OH

    KAUST Repository

    Khaled, Fathi; Giri, Binod; Szőri, Milá n; Viskolcz, Bé la; Farooq, Aamir

    2015-01-01

    We report experimental and theoretical results for the deuterated kinetic isotope effect (DKIE) of the reaction of OH with ethane (C2H6) and deuterated ethane (C2D6). The reactions were investigated behind reflected shock waves over 800–1350 K by monitoring OH radicals near 306.69 nm using laser absorption. In addition, high level CCSD(T)/cc-pV(T,Q)Z//MP2/cc-pVTZ quantum chemical and statistical rate theory calculations were performed which agreed very well with the experimental findings. The results reported herein provide the first experimental evidence that DKIE for alkanes asymptotes to a value of 1.4 at high temperatures.

  20. Isotopic labeling study of oxygen diffusion in amorphous LaScO3 high-κ films on Si(100) and its effects on the electrical characteristics

    International Nuclear Information System (INIS)

    Lopes, J.M.J.; Littmark, U.; Roeckerath, M.; Durgun Oezben, E.; Lenk, S.; Schubert, J.; Mantl, S.; Breuer, U.; Besmehn, A.; Staerk, A.; Grande, P.L.; Sortica, M.A.; Radtke, C.

    2009-01-01

    The influence of post-deposition oxygen anneals on the properties of amorphous LaScO 3 films on Si(100) is reported. The use of an isotopically ( 18 O 2 ) enriched atmosphere allowed to investigate the 16 O- 18 O exchange and the oxygen diffusion across the dielectric layer. Such effects are connected to the formation of an interfacial layer. Oxygen annealing leads to nearly ideal capacitance-voltage curves, lower leakage currents and interface trap densities, as well as to κ-values up to 33 for the LaScO 3 films. These results are attributed to the suppression of oxygen-related trap centers and the achievement of a stoichiometric oxygen content. (orig.)

  1. An Experimental and Theoretical Study on the Kinetic Isotope Effect of C2H6 and C2D6 Reaction with OH

    KAUST Repository

    Khaled, Fathi

    2015-10-30

    We report experimental and theoretical results for the deuterated kinetic isotope effect (DKIE) of the reaction of OH with ethane (C2H6) and deuterated ethane (C2D6). The reactions were investigated behind reflected shock waves over 800–1350 K by monitoring OH radicals near 306.69 nm using laser absorption. In addition, high level CCSD(T)/cc-pV(T,Q)Z//MP2/cc-pVTZ quantum chemical and statistical rate theory calculations were performed which agreed very well with the experimental findings. The results reported herein provide the first experimental evidence that DKIE for alkanes asymptotes to a value of 1.4 at high temperatures.

  2. A study on the isotope effects in the reduction of carbon dioxide by zinc; Etude des effets isotopiques dans la reduction du gaz carbonique par le zinc

    Energy Technology Data Exchange (ETDEWEB)

    Senegacnik, M [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1957-06-15

    We have determined the isotope effects which occur in the reduction of carbon dioxide by zinc. It has been shown that in the case of irreversible surface reactions, Bernstein's equation which permits the calculation of the fractionation factor is still valid. These experimental factors are in good agreement with those obtained by calculating the partition functions of the adsorbed activated complexes. In the reaction mechanism used, the model of the activated complex corresponds to the dissociation of one of the carbon oxygen bonds CO{sub 2} {yields} CO + O. Perturbations arising from the slight reversibility of the reaction Zn + CO{sub 2} {r_reversible} ZnO + CO on the isotope effects on the carbon and oxygen atoms have also been calculated. (author) [French] Nous avons etudie les effets isotopiques qui ont lieu dans la reduction du gaz carbonique par le zinc. La validite de l'equation de Bernstein qui permet de calculer le facteur de fractionnement a ete demontree pour le cas d'une reaction irreversible de surface. Ces facteurs de fractionnement experimentaux sont en bon accord avec ceux obtenus par le calcul des fonctions de partition isotopiques des complexes actives adsorbes. Dans le mecanisme de reaction utilise, le modele du complexe active correspond a la dissociation d'une des liaisons carbone oxygene CO{sub 2} {yields} CO + O. Les effets perturbateurs de la reversibilite de la reduction Zn + CO{sub 2} {r_reversible} ZnO + CO sur les effets isotopiques du carbone et ceux de l'oxygene ont ete egalement evalues. (auteur)

  3. A study on the isotope effects in the reduction of carbon dioxide by zinc; Etude des effets isotopiques dans la reduction du gaz carbonique par le zinc

    Energy Technology Data Exchange (ETDEWEB)

    Senegacnik, M. [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1957-06-15

    We have determined the isotope effects which occur in the reduction of carbon dioxide by zinc. It has been shown that in the case of irreversible surface reactions, Bernstein's equation which permits the calculation of the fractionation factor is still valid. These experimental factors are in good agreement with those obtained by calculating the partition functions of the adsorbed activated complexes. In the reaction mechanism used, the model of the activated complex corresponds to the dissociation of one of the carbon oxygen bonds CO{sub 2} {yields} CO + O. Perturbations arising from the slight reversibility of the reaction Zn + CO{sub 2} {r_reversible} ZnO + CO on the isotope effects on the carbon and oxygen atoms have also been calculated. (author) [French] Nous avons etudie les effets isotopiques qui ont lieu dans la reduction du gaz carbonique par le zinc. La validite de l'equation de Bernstein qui permet de calculer le facteur de fractionnement a ete demontree pour le cas d'une reaction irreversible de surface. Ces facteurs de fractionnement experimentaux sont en bon accord avec ceux obtenus par le calcul des fonctions de partition isotopiques des complexes actives adsorbes. Dans le mecanisme de reaction utilise, le modele du complexe active correspond a la dissociation d'une des liaisons carbone oxygene CO{sub 2} {yields} CO + O. Les effets perturbateurs de la reversibilite de la reduction Zn + CO{sub 2} {r_reversible} ZnO + CO sur les effets isotopiques du carbone et ceux de l'oxygene ont ete egalement evalues. (auteur)

  4. Kinetic isotope effects and aliphatic diazo-compounds

    International Nuclear Information System (INIS)

    Albery, W.J.; Conway, C.W.; Hall, J.A.

    1976-01-01

    Results are reported for the variation of the rate of decomposition of ethyl diazomalonate (EDM) and diazomalonate anions with pH and for the deuterium solvent isotope effect for EDM. The shape of the pH profile is explained by successive protonations of the anions. Ethyl diazoacetate is observed as an intermediate in the decomposition of EDM. The degree of proton transfer in the EDM transition state is deduced from the solvent isotope effect and the results together with those for other aliphatic diazo-compounds are discussed in terms of the Marcus theory. (author)

  5. Low temperature isotope effects of hydrogen diffusion in metallic glasses

    International Nuclear Information System (INIS)

    Hofmann, A.; Kronmueller, H.

    1989-01-01

    Snoek-like relaxation peaks of Hydrogen and Deuterium in amorphous Fe 80 B 20 , Fe 40 Ni 40 P 14 B 6 and Fe 91 Zr 9 are detected. At low H, D concentrations the peaks are near 200 K and show small isotope effects of the average activation energies (anti Q H ≅ 0.6 eV, anti Q D - anti Q H ≤ 10 meV). For higher H, D-contents the peaks shift to lower temperatures around to 120 K and show distinct isotope effects in the activation energies (anti Q H ≅ 0.3 eV, anti Q D - anti Q H ≅ 30 meV) and in the amplitude of the low temperature tails of the relaxation peaks. This points to isotope mass dependent deviations from the Arrhenius law due to nonthermal tunneling processes. (orig.)

  6. Proceedings of the study of environmental change using isotope techniques

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2002-10-01

    Global warming is acknowledged as a major crisis facing society today, principally due to anticipated impacts on the environment, and availability and distribution of water resources. Scientific understanding of recent human-induced climate change, as well as evaluation of potential mitigation strategies, is progressively being developed through studies of atmospheric greenhouse gases and modern water energy carbon cycling processes. These efforts have been advanced through study of past global climate changes to understand mechanisms that play a role in determining natural climate fluctuations observed in ice cores, lake and sea sediments, corals, paleo-groundwater, cave deposits, tree rings, and other archives. Predictive models incorporating natural and human-induced climate change processes contribute to a better appreciation for the sensitivity of climate to specific anthropogenic perturbations. Increasingly, isotopes are being integrated in climate change studies. For example, isotope methodologies offer substantial improvements in the ability to label the origin and fate of greenhouse gases, and for studying the water and carbon cycle response to past climate changes, a high priority area for action identified by the Intergovernmental Panel on Climate Change (IPCC). Isotopes are also widely used as diagnostic variables for validation of models aimed at providing a prognosis of future environmental conditions. The International Atomic Energy Agency (IAEA) has long supported research and development of isotope applications for climate studies. The joint IAEA/WMO Global Network for Isotopes in Precipitation managed by the IAEA has for the last four decades provided the basic isotope data necessary for integrating stable oxygen and hydrogen isotopes in climate models. The IAEA has also sponsored co-ordinated research projects on Isotope Variations of Carbon Dioxide and other Trace Gases in the Atmosphere and Isotope-Aided Studies of Atmospheric Carbon Dioxide

  7. Proceedings of the study of environmental change using isotope techniques

    International Nuclear Information System (INIS)

    2002-01-01

    Global warming is acknowledged as a major crisis facing society today, principally due to anticipated impacts on the environment, and availability and distribution of water resources. Scientific understanding of recent human-induced climate change, as well as evaluation of potential mitigation strategies, is progressively being developed through studies of atmospheric greenhouse gases and modern water energy carbon cycling processes. These efforts have been advanced through study of past global climate changes to understand mechanisms that play a role in determining natural climate fluctuations observed in ice cores, lake and sea sediments, corals, paleo-groundwater, cave deposits, tree rings, and other archives. Predictive models incorporating natural and human-induced climate change processes contribute to a better appreciation for the sensitivity of climate to specific anthropogenic perturbations. Increasingly, isotopes are being integrated in climate change studies. For example, isotope methodologies offer substantial improvements in the ability to label the origin and fate of greenhouse gases, and for studying the water and carbon cycle response to past climate changes, a high priority area for action identified by the Intergovernmental Panel on Climate Change (IPCC). Isotopes are also widely used as diagnostic variables for validation of models aimed at providing a prognosis of future environmental conditions. The International Atomic Energy Agency (IAEA) has long supported research and development of isotope applications for climate studies. The joint IAEA/WMO Global Network for Isotopes in Precipitation managed by the IAEA has for the last four decades provided the basic isotope data necessary for integrating stable oxygen and hydrogen isotopes in climate models. The IAEA has also sponsored co-ordinated research projects on Isotope Variations of Carbon Dioxide and other Trace Gases in the Atmosphere and Isotope-Aided Studies of Atmospheric Carbon Dioxide

  8. Contribution to optimisation of Environmental Isotopes tracing in Hydrogeology. Case study of Madagascar

    International Nuclear Information System (INIS)

    RAJAOBELISON, J.

    2003-01-01

    The aim of this work is to suggest some improvements on the theory of interpretation and on the methodological approach for the optimum use of environmental isotopes tracing applied to hydrogeological investigation. A review of the theory of environmental isotopes used in hydrogeology has been made. The main constraints have been highlighted and led to some comments and proposals of improvement, in particular with regard to the continental effect on stable isotopes, to the seasonal variation of groundwater 1 4C content, and to the appropriate model for fractured crystalline aquifers. A literature survey on ten specific scientific papers, dealing with isotopic hydrology in miscellaneous types of aquifers and catchments, allowed to draw a synthesis of the hydrogeological, geochemical and isotopic constraints. A proposal of optimum methodological approach, taking into account the above mentioned constraints, have been inferred. The results of an on-going hydrogeological investigation carried out in the Southern crystalline basement and coastal sedimentary aquifers of Madagascar highlights an unusual methodological approach based on the lack of initial basic hydrogeological data. Besides, it shows to what extent the experience of the above mentioned research works can apply in the specific case of the complex aquifers of Madagascar. The lessons gained from this study contribute to enrich the synthesis of environmental isotopes constraints in hydrogeology and lead to a more realistic methodological approach proposal wich is likely to better make profitable the isotope hydrology technology

  9. Neutron-rich polonium isotopes studied with in-source laser spectroscopy

    CERN Document Server

    Dexters, Wim; Cocolios, T E

    This work studies the unknown region of neutron rich polonium isotopes. The polonium isotopes, with Z=84, lie above the magic lead nuclei (Z=82). The motivation for this research can mainly be found in these lead nuclei. When looking at the changes in the mean square charge radii beyond the N=126 shell gap, a kink is observed. This kink is also found in the radon (Z=86) and radium (Z=88) isotopes. The observed effect cannot be reproduced with our current models. The polonium isotopes yield more information on the kink and they are also able to link the known charge radii in lead isotopes to those in radon and radium. Additionally, the nuclear moments of the odd-neutron isotope $^{211}$Po are investigated. This nucleus has two protons and one neutron more than the doubly magic nucleus $^{208}$Pb. Nuclear moments of isotopes close to this doubly magic nucleus are good tests for the theoretic models. Besides pushing the models to their limits, the nuclear moments of $^{211}$Po also yield new information on the f...

  10. Cl and C isotope analysis to assess the effectiveness of chlorinated ethene degradation by zero-valent iron: Evidence from dual element and product isotope values

    International Nuclear Information System (INIS)

    Audí-Miró, Carme; Cretnik, Stefan; Otero, Neus; Palau, Jordi; Shouakar-Stash, Orfan; Soler, Albert

    2013-01-01

    Highlights: ► TCE and cis-DCE Cl isotope fractionation was investigated for the first time with ZVI. ► A C–Cl bond is broken in the rate-limiting step during ethylene ZVI dechlorination. ► Dual C/Cl isotope plot is a promising tool to discriminate abiotic degradation. ► Product-related carbon isotopic fractionation gives evidence of abiotic degradation. ► Hydrogenolysis and β-dichloroelimination pathways occur simultaneously. - Abstract: This study investigated C and, for the first time, Cl isotope fractionation of trichloroethene (TCE) and cis-dichloroethene (cis-DCE) during reductive dechlorination by cast zero-valent iron (ZVI). Hydrogenolysis and β-dichloroelimination pathways occurred as parallel reactions, with ethene and ethane deriving from the β-dichloroelimination pathway. Carbon isotope fractionation of TCE and cis-DCE was consistent for different batches of Fe studied. Transformation of TCE and cis-DCE showed Cl isotopic enrichment factors (ε Cl ) of −2.6‰ ± 0.1‰ (TCE) and −6.2‰ ± 0.8‰ (cis-DCE), with Apparent Kinetic Isotope Effects (AKIE Cl ) for Cl of 1.008 ± 0.001 (TCE) and 1.013 ± 0.002 (cis-DCE). This indicates that a C–Cl bond breakage is rate-determining in TCE and cis-DCE transformation by ZVI. Two approaches were investigated to evaluate if isotope fractionation analysis can distinguish the effectiveness of transformation by ZVI as opposed to natural biodegradation. (i) Dual isotope plots. This study reports the first dual (C, Cl) element isotope plots for TCE and cis-DCE degradation by ZVI. The pattern for cis-DCE differs markedly from that reported for biodegradation of the same compound by KB-1, a commercially available Dehalococcoides-containing culture. The different trends suggest an expedient approach to distinguish abiotic and biotic transformation, but this needs to be confirmed in future studies. (ii) Product-related isotope fractionation. Carbon isotope ratios of the hydrogenolysis product cis

  11. Molecular modeling study of lithium isotopic separation by crown-ethers in ethanol

    International Nuclear Information System (INIS)

    Dehez, F.

    2002-01-01

    The isotopic separation of lithium ion isotopes is studied at the CEA in Pierrelatte using a liquid chromatography technique. Exchange systems are composed by crown-ethers grafted on silica (12C4, 15C5, B15C5, DB15C5, 18C6, B18C6). Lithium is introduced as a salt melted in ethanol. This work concerns the theoretical study of lithium isotopic exchange reactions with those systems. After a brief presentation of isotope separation techniques and isotopic effects (Chap.I), we describe the methods of theoretical chemistry used in this work (Chap. II). In chapter III, we test AM1 and PM3 semi-empirical methods for the treatment of Li + /crown-ether species. Then, we calculate isotopic separation factors via ab initio and semi-empirical calculations for the exchange reactions in vacuum. The different crown-ethers are considered with and without graftings arms. Studies of exchange reactions in ethanol are presented in chapter IV. First, each species of the reaction are solvated by a few ethanol molecules. Isotopic separation factors calculated show a large effect of the solvent on the exchange reaction. The effect of the grafting arm has been investigated using hybrid quantum mechanics/molecular mechanics (QM/MM) molecular dynamics for species with the 12C4. Trajectories have been generated successively with 7 Li and 6 Li. Atomic velocity autocorrelation functions have allowed the access to vibrational frequencies necessary to calculate isotopic separation factors. The last chapter is devoted to methodological developments made during this Ph.D. We propose an approach to treat long range electrostatic interactions in hybrid QM/MM method, relying on a lattice summation technique. (author) [fr

  12. Effectiveness of different pre-treatments in recovering pre-burial isotopic ratios of charred plants.

    Science.gov (United States)

    Brinkkemper, O; Braadbaart, F; van Os, B; van Hoesel, A; van Brussel, A A N; Fernandes, R

    2018-02-15

    Isotopic analysis of archaeological charred plant remains offers useful archaeological information. However, adequate sample pre-treatment protocols may be necessary to provide a contamination-free isotopic signal while limiting sample loss and achieving a high throughput. Under these constraints, research was undertaken to compare the performance of different pre-treatment protocols. Charred archaeological plant material was selected for isotopic analysis (δ 13 C and δ 15 N values) by isotope ratio mass spectrometry from a variety of plant species, time periods and soil conditions. Preservation conditions and the effectiveness of cleaning protocols were assessed through Fourier transform infrared spectroscopy and X-ray fluorescence (XRF) spectrometry. An acid-base-acid protocol, successfully employed in radiocarbon dating, was used to define a contamination-free isotopic reference. Acid-base-acid isotopic measurements were compared with those obtained from untreated material and an acid-only protocol. The isotopic signals of untreated material and the acid-only protocol typically did not differ more than 1‰ from those of the acid-base-acid reference. There were no significant isotopic offsets between acid-base-acid and acid-only or untreated samples. Sample losses in the acid-base-acid protocol were on average 50 ± 17% (maximum = 98.4%). Elemental XRF measurements showed promising results in the detection of more contaminated samples albeit with a high rate of false positives. For the large range of preservation conditions described in the study, untreated charred plant samples, water cleaned of sediments, provide reliable stable isotope ratios of carbon and nitrogen. The use of pre-treatments may be necessary under different preservation conditions or more conservative measurement uncertainties should be reported. Copyright © 2017 John Wiley & Sons, Ltd.

  13. Isotope Effect on the Thermal Conductivity of Graphene

    Directory of Open Access Journals (Sweden)

    Hengji Zhang

    2010-01-01

    Full Text Available The thermal conductivity (TC of isolated graphene with different concentrations of isotope (C13 is studied with equilibrium molecular dynamics method at 300 K. In the limit of pure C12 or C13 graphene, TC of graphene in zigzag and armchair directions are ~630 W/mK and ~1000W/mK, respectively. We find that the TC of graphene can be maximally reduced by ~80%, in both armchair and zigzag directions, when a random distribution of C12 and C13 is assumed at different doping concentrations. Therefore, our simulation results suggest an effective way to tune the TC of graphene without changing its atomic and electronic structure, thus yielding a promising application for nanoelectronics and thermoelectricity of graphene-based nano device.

  14. Isotope effects in the evaporation of water: a status report of the Craig-Gordon model.

    Science.gov (United States)

    Horita, Juske; Rozanski, Kazimierz; Cohen, Shabtai

    2008-03-01

    The Craig-Gordon model (C-G model) [H. Craig, L.I. Gordon. Deuterium and oxygen 18 variations in the ocean and the marine atmosphere. In Stable Isotopes in Oceanographic Studies and Paleotemperatures, E. Tongiorgi (Ed.), pp. 9-130, Laboratorio di Geologia Nucleare, Pisa (1965).] has been synonymous with the isotope effects associated with the evaporation of water from surface waters, soils, and vegetations, which in turn constitutes a critical component of the global water cycle. On the occasion of the four decades of its successful applications to isotope geochemistry and hydrology, an attempt is made to: (a) examine its physical background within the framework of modern evaporation models, (b) evaluate our current knowledge of the environmental parameters of the C-G model, and (c) comment on a general strategy for the use of these parameters in field applications. Despite its simplistic representation of evaporation processes at the water-air interface, the C-G model appears to be adequate to provide the isotopic composition of the evaporation flux. This is largely due to its nature for representing isotopic compositions (a ratio of two fluxes of different isotopic water molecules) under the same environmental conditions. Among many environmental parameters that are included in the C-G model, accurate description and calculations are still problematic of the kinetic isotope effects that occur in a diffusion-dominated thin layer of air next to the water-air interface. In field applications, it is of importance to accurately evaluate several environmental parameters, particularly the relative humidity and isotopic compositions of the 'free-atmosphere', for a system under investigation over a given time-scale of interest (e.g., hourly to daily to seasonally). With a growing interest in the studies of water cycles of different spatial and temporal scales, including paleoclimate and water resource studies, the importance and utility of the C-G model is also likely to

  15. Chemical Ligation and Isotope Labeling to Locate Dynamic Effects during Catalysis by Dihydrofolate Reductase.

    Science.gov (United States)

    Luk, Louis Y P; Ruiz-Pernía, J Javier; Adesina, Aduragbemi S; Loveridge, E Joel; Tuñón, Iñaki; Moliner, Vincent; Allemann, Rudolf K

    2015-07-27

    Chemical ligation has been used to alter motions in specific regions of dihydrofolate reductase from E. coli and to investigate the effects of localized motional changes on enzyme catalysis. Two isotopic hybrids were prepared; one with the mobile N-terminal segment containing heavy isotopes ((2) H, (13) C, (15) N) and the remainder of the protein with natural isotopic abundance, and the other one with only the C-terminal segment isotopically labeled. Kinetic investigations indicated that isotopic substitution of the N-terminal segment affected only a physical step of catalysis, whereas the enzyme chemistry was affected by protein motions from the C-terminal segment. QM/MM studies support the idea that dynamic effects on catalysis mostly originate from the C-terminal segment. The use of isotope hybrids provides insights into the microscopic mechanism of dynamic coupling, which is difficult to obtain with other studies, and helps define the dynamic networks of intramolecular interactions central to enzyme catalysis. © 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

  16. Chlorine isotope effects from isotope ratio mass spectrometry suggest intramolecular C-Cl bond competition in trichloroethene (TCE) reductive dehalogenation.

    Science.gov (United States)

    Cretnik, Stefan; Bernstein, Anat; Shouakar-Stash, Orfan; Löffler, Frank; Elsner, Martin

    2014-05-20

    Chlorinated ethenes are prevalent groundwater contaminants. To better constrain (bio)chemical reaction mechanisms of reductive dechlorination, the position-specificity of reductive trichloroethene (TCE) dehalogenation was investigated. Selective biotransformation reactions (i) of tetrachloroethene (PCE) to TCE in cultures of Desulfitobacterium sp. strain Viet1; and (ii) of TCE to cis-1,2-dichloroethene (cis-DCE) in cultures of Geobacter lovleyi strain SZ were investigated. Compound-average carbon isotope effects were -19.0‰ ± 0.9‰ (PCE) and -12.2‰ ± 1.0‰ (TCE) (95% confidence intervals). Using instrumental advances in chlorine isotope analysis by continuous flow isotope ratio mass spectrometry, compound-average chorine isotope effects were measured for PCE (-5.0‰ ± 0.1‰) and TCE (-3.6‰ ± 0.2‰). In addition, position-specific kinetic chlorine isotope effects were determined from fits of reactant and product isotope ratios. In PCE biodegradation, primary chlorine isotope effects were substantially larger (by -16.3‰ ± 1.4‰ (standard error)) than secondary. In TCE biodegradation, in contrast, the product cis-DCE reflected an average isotope effect of -2.4‰ ± 0.3‰ and the product chloride an isotope effect of -6.5‰ ± 2.5‰, in the original positions of TCE from which the products were formed (95% confidence intervals). A greater difference would be expected for a position-specific reaction (chloride would exclusively reflect a primary isotope effect). These results therefore suggest that both vicinal chlorine substituents of TCE were reactive (intramolecular competition). This finding puts new constraints on mechanistic scenarios and favours either nucleophilic addition by Co(I) or single electron transfer as reductive dehalogenation mechanisms.

  17. Chlorine Isotope Effects from Isotope Ratio Mass Spectrometry Suggest Intramolecular C-Cl Bond Competition in Trichloroethene (TCE Reductive Dehalogenation

    Directory of Open Access Journals (Sweden)

    Stefan Cretnik

    2014-05-01

    Full Text Available Chlorinated ethenes are prevalent groundwater contaminants. To better constrain (biochemical reaction mechanisms of reductive dechlorination, the position-specificity of reductive trichloroethene (TCE dehalogenation was investigated. Selective biotransformation reactions (i of tetrachloroethene (PCE to TCE in cultures of Desulfitobacterium sp. strain Viet1; and (ii of TCE to cis-1,2-dichloroethene (cis-DCE in cultures of Geobacter lovleyi strain SZ were investigated. Compound-average carbon isotope effects were −19.0‰ ± 0.9‰ (PCE and −12.2‰ ± 1.0‰ (TCE (95% confidence intervals. Using instrumental advances in chlorine isotope analysis by continuous flow isotope ratio mass spectrometry, compound-average chorine isotope effects were measured for PCE (−5.0‰ ± 0.1‰ and TCE (−3.6‰ ± 0.2‰. In addition, position-specific kinetic chlorine isotope effects were determined from fits of reactant and product isotope ratios. In PCE biodegradation, primary chlorine isotope effects were substantially larger (by −16.3‰ ± 1.4‰ (standard error than secondary. In TCE biodegradation, in contrast, the product cis-DCE reflected an average isotope effect of −2.4‰ ± 0.3‰ and the product chloride an isotope effect of −6.5‰ ± 2.5‰, in the original positions of TCE from which the products were formed (95% confidence intervals. A greater difference would be expected for a position-specific reaction (chloride would exclusively reflect a primary isotope effect. These results therefore suggest that both vicinal chlorine substituents of TCE were reactive (intramolecular competition. This finding puts new constraints on mechanistic scenarios and favours either nucleophilic addition by Co(I or single electron transfer as reductive dehalogenation mechanisms.

  18. Studies of carbon--isotope fractionation. Annual progress report, December 1, 1974--November 30, 1975

    International Nuclear Information System (INIS)

    Ishida, T.

    1975-01-01

    The vapor pressure isotope effect of 13 C/ 12 C-substitution in CClF 3 was measured at temperatures between 169 0 and 206 0 K by means of cryogenic distillation. The 13 C/ 12 C-vapor pressure isotope effect in CHF 3 was also studied at temperatures between 161 0 and 205 0 K by a similar method. The construction of a cryostat has progressed as scheduled. The investigation of carbon isotope exchange equilibria between carbon dioxide and various carbamates dissolved in various organic solvents has continued. The five-stage system of Taylor-Ghate design was improved to shorten the transient time. A single stage apparatus was designed, built, and tested. These systems are used to measure the equilibrium constants and various phase equilibria involved in the carbon dioxide--carbamate system. The investigation of the explicit method of total isotope effect has made progress. A satisfactory approximation was found for the classical partition function of a Morse oscillator. The method gives a reasonable result at rho identical with 1 / 2 √(u/sub e//x/sub e/) greater than 1.5. The medium cluster approach was applied to isotopic methanes to investigate the effects of intermolecular distance and mutual orientations of molecules in the liquid upon vapor pressure isotope effect. It was found that all geometrical effects studied tend to vanish as the size of clusters is increased. Isotope effect in the zero-point energy shifts on condensation was calculated on the basis of London dispersion forces in liquid and a semi-empirical molecular orbital theory, and was favorably compared with experimental results

  19. The essential role of isotopes in studies of water resources

    International Nuclear Information System (INIS)

    1977-01-01

    In studies of surface water, isotope techniques are used to measure water runoff from rain and snow, flow rates of streams and rivers, leakage from lakes, reservoirs and canals and the dynamics of various bodies of water. Studies of groundwater resources (springs, wells) today are virtually unthinkable without isotope techniques. Basically, these techniques are simple and relatively quick. Among the many questions which may be asked of hydrologists about a given groundwater supply, often the most critical one concerns the safe yield so that the source will not run dry, or for a source to be 'mined', the total yield. Isotope techniques can be used to solve such problems as: identification of the origin of groundwater, determination of its age, flow velocity and direction, interrelations between surface waters and ground waters, possible connections between different aquifers, local porosity, transmissivity and dispersivity of an aquifer. The cost of such investigations is often small in comparison to the cost of classical hydrological techniques, and in addition they are able to provide information which sometimes cannot be obtained by other techniques. The IAEA provides assistance to countries in the application of isotope techniques in water resources studies and other hydrology field projects. The examples given of field studies are intended to give some idea of how these techniques are being applied to specific problems in various regions of the world. Most are discussed briefly, but in some cases a more detailed description has been given in order to demonstrate the application of environmental isotope techniques

  20. Coastal niches for terrestrial predators: a stable isotope study

    Energy Technology Data Exchange (ETDEWEB)

    Mellbrand, K.; Hamback, P.A., E-mail: peter.hamback@botan.su.se [Stockholm Univ., Dept. of Botany, Stockholm (Sweden)

    2010-12-15

    The purpose of this study was to identify the use of marine versus terrestrial food items by terrestrial arthropod predators on Baltic Sea shores. The inflow of marine nutrients in the area consists mainly of marine algal detritus and emerging aquatic insects (e.g., chironomids). Diets of coastal arthropods were examined using carbon and nitrogen stable isotope analysis in a two source mixing model. The results suggest that spiders are the terrestrial predators mainly utilizing nutrients and energy of marine origin on Baltic Sea shores, whereas insect predators such as beetles and heteropterans mainly utilize nutrients and energy derived from terrestrial sources, possibly owing to differences in hunting behaviour. That spiders are the predators which benefit the most from the marine inflow suggest that eventual effects of marine subsidies for the coastal ecosystem as a whole are likely mediated by spiders. (author)

  1. Coastal niches for terrestrial predators: a stable isotope study

    International Nuclear Information System (INIS)

    Mellbrand, K.; Hamback, P.A.

    2010-01-01

    The purpose of this study was to identify the use of marine versus terrestrial food items by terrestrial arthropod predators on Baltic Sea shores. The inflow of marine nutrients in the area consists mainly of marine algal detritus and emerging aquatic insects (e.g., chironomids). Diets of coastal arthropods were examined using carbon and nitrogen stable isotope analysis in a two source mixing model. The results suggest that spiders are the terrestrial predators mainly utilizing nutrients and energy of marine origin on Baltic Sea shores, whereas insect predators such as beetles and heteropterans mainly utilize nutrients and energy derived from terrestrial sources, possibly owing to differences in hunting behaviour. That spiders are the predators which benefit the most from the marine inflow suggest that eventual effects of marine subsidies for the coastal ecosystem as a whole are likely mediated by spiders. (author)

  2. Investigating the effects of abyssal peridotite alteration on Si, Mg and Zn isotopes

    Science.gov (United States)

    Savage, P. S.; Wimpenny, J.; Harvey, J.; Yin, Q.; Moynier, F.

    2013-12-01

    Around 1/3 of Earth's divergent ridge system is now classified as "slow" spreading [1], exposing ultramafic rocks (abyssal peridotites) at the seafloor. Such material is often highly altered by serpentinisation and steatisation (talc formation). It is crucial to understand such processes in order to access the original composition of the mantle, and to quantify any impact on ocean composition. Here we examine the effect of both serpentinisation and steatisation on Si, Mg and Zn isotopes. Hydrothermal alteration and seafloor weathering are both sources of oceanic Si [2] and weathering of abyssal peridotites is a source of oceanic Mg [3]; hence isotopic fractionation as a result of seafloor alteration could affect oceanic Si and Mg isotope composition. Zinc isotopes can provide complimentary information; the magnitude and direction of fractionation is highly dependent on complexing ligand [4] and can provide compositional information on the fluids driving metasomatism. For this study, two cores from the well-characterised abyssal peridotites recovered on ODP Leg 209 were examined [5]. Hole 1274a peridotites exhibit variable serpentinisation at ~200°C, whereas samples from Hole 1268a have been comprehensively serpentinised and then subsequently steatised to talc facies at ~350°C, by a low Mg/Si, low pH fluid. The Si, Mg and Zn isotope compositions of 1274a samples are extremely homogeneous, identical to that of pristine mantle rocks (BSE) i.e., serpentinisation at this locality was predominantly isochemical [5]. In contrast, samples from 1268a show greater isotopic variability. In all samples, Mg is enriched in the heavier isotopes relative to BSE, consistent with formation of isotopically heavy secondary phases [6]. For Si, serpentinised samples are slightly enriched in the lighter isotopes compared to BSE, again consistent with the behaviour of Si during formation of secondary phases [7]. Within the steatised samples, some exhibit enrichments in the lighter Si

  3. Fine print in isotope effects: the glucose anomeric equilibrium and binding of glucose to human brain hexokinase

    International Nuclear Information System (INIS)

    Lewis, B.E; Schramm, V.L.

    2002-01-01

    Binding isotope effects are a sensitive measure of changes in molecular vibrational character that occur during ligand-receptor binding. In this study, we have measured isotope effects on the binding of glucose to human brain hexokinase using the ultrafiltration method, with the following results: 0.991±0.001, 0.908±0.003, 1.010±0.001, 0.974±0.002, 1.022±0.002 for [ 14 C]-glucose mixed with [1- 3 H]-, [2- 3 H]-, [3- 3 H]-, [5- 3 H]-, [6,6- 3 H]-glucose, respectively. Comparing the observed data with isotope effects on the anomeric equilibrium in glucose reported previously proves the existence of binding isotope effects in this system. Preliminary computational results are presented to explain the observed binding isotope effects in terms of hydrogen bond patterns and molecular crowding found in the binary complex of sugar and enzyme. (author)

  4. Magic numbers and isotopic effect of ion clusters

    International Nuclear Information System (INIS)

    Wang Guanghou

    1989-04-01

    The magic numbers and isotopic effect as well as stable configurations in relation to the charge state of the clusters are discussed. Ionic (atomic) clusters are small atomic aggregates, a physical state between gas and solid states, and have many interesting properties, some of them are more or less similar to those in nuclei

  5. Nitrogen and Oxygen Isotopic Studies of the Marine Nitrogen Cycle.

    Science.gov (United States)

    Casciotti, Karen L

    2016-01-01

    The marine nitrogen cycle is a complex web of microbially mediated reactions that control the inventory, distribution, and speciation of nitrogen in the marine environment. Because nitrogen is a major nutrient that is required by all life, its availability can control biological productivity and ecosystem structure in both surface and deep-ocean communities. Stable isotopes of nitrogen and oxygen in nitrate and nitrite have provided new insights into the rates and distributions of marine nitrogen cycle processes, especially when analyzed in combination with numerical simulations of ocean circulation and biogeochemistry. This review highlights the insights gained from dual-isotope studies applied at regional to global scales and their incorporation into oceanic biogeochemical models. These studies represent significant new advances in the use of isotopic measurements to understand the modern nitrogen cycle, with implications for the study of past ocean productivity, oxygenation, and nutrient status.

  6. Progress in isotope hydrological study at Olak Lempit, Selangor

    International Nuclear Information System (INIS)

    Md Shahid Ayub

    2002-01-01

    This case study ia an on going project. Initial results from environmental isotopes and CFCs suggested short circuit to the groundwater flow. Removal of confining layer (if any) by mining activities could be the cause. It is also suggested the existence of saltwater / fresh water interface at the south-western fringe of the study area. This study is not yet conclusive. (Author)

  7. Carbon-13 kinetic isotope effects in the decarbonylations of lactic acid containing 13C at the natural abundance level

    International Nuclear Information System (INIS)

    Zielinski, M.; Czarnota, G.; Papiernik-Zielinska, H.

    1992-01-01

    The 13 C kinetic isotope fractionation in the decarbonylation of lactic acid of natural isotopic composition by sulfuric acid has been studied in the temperature range of 20-80 deg C. The 13 C (1) isotope separation in the decarbonylation of lactic acid by concentrated sulfuric acid depends strongly on the temperature above 40 deg C. Below this temperature the 13 C isotope effect in the decarbonylation of lactic acid by concentrated sulfuric acid is normal similarly as has been found in the decarbonylation of lactic [1- 14 C] acid. The experimental values of k (12C) /k (13C) ratios of isotopic rate constants for 12 C and 13 C are close to, but slightly higher than theoretical 13 C-kinetic isotope effects calculated (neglecting tunneling) under the asumption that the C (1) -OH bond is broken in the rate-controlling step of the dehydration reaction. Dilution of concentrated sulfuric acid with water up to 1.4 molar (H 2 O)/(H 2 SO 4 ) ratio caused the increase of the 13 C isotope fractionation from 1.0273 found in concentrated sulfuric acid at 80.5 deg C to 1.0536±0.0008 (at 80.6 deg C). A discussion of the abnormally high temperature dependence of 14 C and 13 C isotope fractionation in this reaction and the discussion of the problem of relative 14 C/ 13 C kinetic isotope effects is given. (author) 18 refs.; 2 tabs

  8. Transient competitive complexation in biological kinetic isotope fractionation explains nonsteady isotopic effects: Theory and application to denitrification in soils

    Science.gov (United States)

    Maggi, Federico; Riley, William J.

    2009-12-01

    The theoretical formulation of biological kinetic isotope fractionation often assumes first-order or Michaelis-Menten kinetics, the latter solved under the quasi-steady state assumption. Both formulations lead to a constant isotope fractionation factor, therefore they may return incorrect estimations of isotopic effects and misleading interpretations of isotopic signatures when fractionation is not a steady process. We have analyzed the isotopic signature of denitrification in biogeochemical soil systems by Menyailo and Hungate (2006) in which high and variable 15N-N2O enrichment during N2O production and inverse isotope fractionation during N2O consumption could not be explained with first-order kinetics and the Rayleigh equation, or with Michaelis-Menten kinetics. When Michaelis-Menten kinetics were coupled to Monod kinetics to describe biomass and enzyme dynamics, and the quasi-steady state assumption was relaxed, transient Michaelis-Menten-Monod kinetics accurately reproduced the observed concentrations, and variable and inverse isotope fractionations. These results imply a substantial revision in modeling isotopic effects, suggesting that steady state kinetics such as first-order, Rayleigh, and classic Michaelis-Menten kinetics should be superseded by transient kinetics in conjunction with biomass and enzyme dynamics.

  9. Isotope techniques in the study of environmental change

    International Nuclear Information System (INIS)

    1998-01-01

    The International Atomic Energy Agency, among its efforts to promote the wider use of isotope techniques in hydrology and related environmental disciplines, organized an International Symposium on Applications of Isotope Techniques in Studying Past and Current Environmental Changes in the Hydrosphere and the Atmosphere, held in 1993 in Vienna. The broad scientific interest and abundant participation in the symposium, as well as the rapid progress seen in this field since then, encouraged the IAEA to organize a second symposium of this kind. It was held from 14 to 18 April 1997 in Vienna and brought together 177 scientists representing 46 Member States, UNESCO, FAO, WMO, the World Climate Research Programme (WCRP) and the International Geosphere-Biosphere Programme (IGBP). The symposium was structured in five sessions of oral presentations, a poster session and a round table discussion that focused on trends and future requirements in isotope hydrology and on applications in climate and environmental research. The major themes covered by the presentations included the use of isotopic tracers in studies of atmospheric and hydrospheric changes and of the human impact on water and the environment. Special emphasis was placed on isotopic archives of climatic and environmental change. Some contributions addressed new technical approaches

  10. Isotope and hydrogeochemical studies of southern Jiangxi geothermal systems, China

    International Nuclear Information System (INIS)

    Zhou Wenbin; Li Xueli; Shi Weijun; Sun Zhanxue

    1999-01-01

    Southern Jiangxi is a geothermally active region, especially in Hengjing area. According to the work plan of IAEA Regional Collaboration in the Development of Geothermal Energy Resources and Environment Management through Isotope Techniques in East Asia and the Pacific (RAS-8-075), field investigation was carried out in Hengjing, southern Jiangxi Province, to demonstrate the use of isotope and geochemical techniques in low to medium temperature geothermal system. During the field investigation, 19 samples were taken from cold springs, hot springs and surface water in the area to determine their hydrochemical and gas compositions, hydrogen, oxygen, carbon and helium isotopes. The results of the study have shown that the geothermal waters in the studying region are of the same characteristics with the local meteoric water in oxygen and hydrogen isotope composition, indicating the geothermal waters are mainly derived from the local precipitation, while the gas composition and carbon and helium isotopes reveal that some gases in the geothermal waters have mantle origin. (author)

  11. A theoretical study of cluster radioactivity in platinum isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Joseph, Deepthy Maria; Ashok, Nithu; Joseph, Antony [University of Calicut, Department of Physics, Malappuram, Kerala (India)

    2018-01-15

    The probable cluster decay modes in platinum isotopes are predicted with the help of effective liquid drop model. The calculated half-lives are compared with those of universal decay law model and with the experimental data. The investigation affirms the decisive role of neutron magicity in the phenomenon of cluster radioactivity. It is found that the probability of cluster emission decreases with the increase in the neutron number of parent nucleus. Geiger-Nuttall plots of the probable decay modes show linear behaviour, which in turn leads to the equation for logarithmic half-life for the clusters emitted from Pt isotopes. (orig.)

  12. Ageing and structural effects on the sorption characteristics of Cd2+ by clinoptilolite and Y-type zeolite studied using isotope exchange technique

    International Nuclear Information System (INIS)

    Ahmed, I.A.M.; Young, S.D.; Crout, N.M.J.

    2010-01-01

    This research investigates the long-term kinetics of Cd 2+ sorption and desorption by calcium-exchanged clinoptilolite (CaCpt) and Y-type (CaY) zeolite using isotopic exchange with 109 Cd while maintaining pH at circumneutral values. The effects of Si/Al ratio and crystal structure of these zeolitic materials on intracrystalline transport of Cd are discussed. A first-order kinetic model was developed to describe the progressive transfer of Cd 2+ to a less reactive form within the zeolite structure, following initial sorption and subsequent desorption of Cd subject to different initial contact times. The kinetic model differentiates between two forms of sorbed Cd 2+ designated 'labile' and 'non-labile' in which the labile form is in immediate equilibrium with the free Cd 2+ ion activity in solution. A model combining diffusion and first-order kinetics for cation exchange was also employed to determine Cd 2+ diffusivity and intracrystalline exchange rates in CaY and CaCpt. The efficiency of Permeable Reactive Barriers (PRBs) containing zeolitic materials in protecting water systems against lateral flow of metal-contaminated leachate was simulated for three contrasting zeolites. The slow transfer of Cd between labile and non-labile forms was particularly important in moderating high concentration pulses of Cd traversing the PRB. In addition, the reversibility of Cd fixation effectively restored the sorption capability of the zeolite through slow leakage to drainage water.

  13. Protonation mechanism and location of rate-determining steps for the Ascaris suum nicotinamide adenine dinucleotide-malic enzyme reaction from isotope effects and pH studies

    International Nuclear Information System (INIS)

    Kiick, D.M.; Harris, B.G.; Cook, P.F.

    1986-01-01

    The pH dependence of the kinetic parameters and the primary deuterium isotope effects with nicotinamide adenine dinucleotide (NAD) and also thionicotinamide adenine dinucleotide (thio-NAD) as the nucleotide substrates were determined in order to obtain information about the chemical mechanism and location of rate-determining steps for the Ascaris suum NAD-malic enzyme reaction. The maximum velocity with thio-NAD as the nucleotide is pH-independent from pH 4.2 to 9.6, while with NAD, V decreases below a pK of 4.8. V/K for both nucleotides decreases below a pK of 5.6 and above a pK of 8.9. Both the tartronate pKi and V/Kmalate decrease below a pK of 4.8 and above a pK of 8.9. Oxalate is competitive vs. malate above pH 7 and noncompetitive below pH 7 with NAD as the nucleotide. The oxalate Kis increases from a constant value above a pK of 4.9 to another constant value above a pK of 6.7. The oxalate Kii also increases above a pK of 4.9, and this inhibition is enhanced by NADH. In the presence of thio-NAD the inhibition by oxalate is competitive vs. malate below pH 7. For thio-NAD, both DV and D(V/K) are pH-independent and equal to 1.7. With NAD as the nucleotide, DV decreases to 1.0 below a pK of 4.9, while D(V/KNAD) and D(V/Kmalate) are pH-independent. Above pH 7 the isotope effects on V and the V/K values for NAD and malate are equal to 1.45, the pH-independent value of DV above pH 7. Results indicate that substrates bind to only the correctly protonated form of the enzyme. Two enzyme groups are necessary for binding of substrates and catalysis. Both NAD and malate are released from the Michaelis complex at equal rates which are equal to the rate of NADH release from E-NADH above pH 7. Below pH 7 NADH release becomes more rate-determining as the pH decreases until at pH 4.0 it completely limits the overall rate of the reaction

  14. Isotope effects accompanying evaporation of water from leaky containers.

    Science.gov (United States)

    Rozanski, Kazimierz; Chmura, Lukasz

    2008-03-01

    Laboratory experiments aimed at quantifying isotope effects associated with partial evaporation of water from leaky containers have been performed under three different settings: (i) evaporation into dry atmosphere, performed in a dynamic mode, (ii) evaporation into dry atmosphere, performed in a static mode, and (iii) evaporation into free laboratory atmosphere. The results demonstrate that evaporative enrichment of water stored in leaky containers can be properly described in the framework of the Craig-Gordon evaporation model. The key parameter controlling the degree of isotope enrichment is the remaining fraction of water in the leaking containers. Other factors such as temperature, relative humidity, or extent of kinetic fractionation play only minor roles. Satisfactory agreement between observed and predicted isotope enrichments for both (18)O and (2)H in experiments for the case of evaporation into dry atmosphere could be obtained only when molecular diffusivity ratios of isotope water molecules as suggested recently by Cappa et al. [J. Geophys. Res., 108, 4525-4535, (2003).] were adopted. However, the observed and modelled isotope enrichments for (2)H and (18)O could be reconciled also for the ratios of molecular diffusivities obtained by Merlivat [J. Chem. Phys., 69, 2864-2871 (1978).], if non-negligible transport resistance in the viscous liquid sub-layer adjacent to the evaporating surface is considered. The evaporation experiments revealed that the loss of mass of water stored in leaky containers in the order of 1%, will lead to an increase of the heavy isotope content in this water by ca. 0.35 and 1.1 per thousand, for delta (18)O and delta (2)H, respectively.

  15. Dew water effects on leaf water using a stable isotope approach

    Science.gov (United States)

    Kim, K.; Lee, X.

    2009-12-01

    The presence of dew is a common meteorological phenomenon in field conditions and takes into account for significant portion of hydrologic processes in terrestrial ecosystems. The isotope composition of leaf water plays an important role in the isotopic water and carbon fluxes between terrestrial plants and the atmosphere. However, the consequence of dew formation in the plant-atmosphere relations has been ignored in many studies. The objective of this study is to improve our understanding of environmental and biological controls on the leaf water in equilibrium with dew water through laboratory experiments. Five species of plants (soybean, corn, sorghum, wheat, cotton) were grown hydroponically with water of a known isotopic content in a greenhouse. On the day of the experiment, they were first moved to ambient environment in full sunlight for at least 6 hr and then into a dark container inside the lab for up to 48 hr in which water vapor isotope ratios, temperature, and humidity were controlled. This arrangement created a step change in the forcing on the plant isotopic exchange. Leaves were sampled prior to the transfer to the dark container and 6 more times every 4 - 12 hr over the experiment. Humidity inside the container was saturated to mimic dew events in field conditions. Water from the leaf samples was extracted by a vacuum line and was analyzed for both δD and δ18O. The dataset will allow us to evaluate leaf water isotopic theories by exploring the transitions of the isotopic ratio of leaf water in response to the step change. Specifically, we are interested in whether the stomatal opening is an effective pathway for gaseous exchange in total darkness and how the transitional behaviors of the isotopic ratio of leaf water differ between the C3 and C4 photosynthesis pathways.

  16. The effect of pressure, isotopic (H/D) substitution, and other variables on miscibility in polymer-solvent systems. The nature of the demixing process; dynamic light scattering and small angle neutron scattering studies. Final report

    International Nuclear Information System (INIS)

    Van Hook, W.A.

    2000-01-01

    A research program examining the effects of pressure, isotope substitution and other variables on miscibility in polymer solvent systems is described. The techniques employed included phase equilibrium measurements and dynamic light scattering and small angle neutron scattering

  17. The Isotopologue Record of Repeat Vital Effect Offenders: Tracking (Dis)equilibrium Effects in Sea Urchins and Nannofossil Using Clumped Isotopes

    Science.gov (United States)

    John, C. M.; Davies, A.; Drury, A. J.

    2016-12-01

    Vital effects vary between species and affect various isotopic systems in unequal proportion. The magnitude of the response of different isotopic systems might thus be key in understanding biologically-mediated disequilibrium, especially in groups that show a tendency to be "repeat offenders" with regards to vital effects. Here we present carbon, oxygen, and clumped isotope data from echinoderm calcite and nannofossil ooze, both of which exhibit strong vital effects in bulk isotopes. Our study is the first to investigate the clumped isotope (dis)equilibrium of echinoids. Results from two echinoids, three marine gastropods and a bivalve mollusk from modern beach deposits of Bali, Indonesia, highlight a significant offset in clumped isotopes of a regular echinoid test from expected values, interpreted as evidence of a similar "vital effect" as observed in surface corals. This is in contrast to the test of an irregular "sand dollar" echinoid, with clumped isotope values within error of expected sea surface temperature. Furthermore, data on the inter-skeletal variability in the clumped isotopic composition of two regular echinoid species shows that the spines of the echinoids are in equilibrium with seawater with respect to clumped isotopes, but the test is not. For the nannofossil material, no clumped isotope vital effects are observed, consistent with previously published studies but at odds with strong vital effects in carbon and oxygen isotopes, often correlated with cell-size. In addition, we reveal that the <63 micron fraction of deep-sea ooze could constitute useful material for clumped isotope studies. An intriguing result of our study is that vital effects are mostly absent in clumped isotopes, even in phylums known for important isotopic effects. It remains to be explained why some parts of the echinoids show clear vital effects, notably enrichment in clumped isotopes of urchin tests. Mechanisms that could explain this include pH effects during calcification

  18. Stable isotopes in plant nutrition, soil fertility and environmental studies

    International Nuclear Information System (INIS)

    1991-01-01

    The individual contributions in these proceedings are indexed separately. Main topics covered include the measurement of biological nitrogen fixation, studies of soil organic matter, investigations of nutrient uptake and use by plants, studies of plant metabolism and new methodologies in the analysis of stable isotopes. Refs, figs and tabs

  19. Rubidium-strontium and uranium-lead isotopic age studies

    International Nuclear Information System (INIS)

    Loveridge, W.D.

    1981-01-01

    The results of five Rb-Sr isotopic age studies predominantly on whole-rock samples, and six U-Pb studies on zircon monazite concentrates are presented. Descriptions of the geological problems and interpretations of the measured ages are included. Laboratory age determination methods and techniques are described or referenced

  20. Tritium conductivity and isotope effect in proton-conducting perovskites

    International Nuclear Information System (INIS)

    Mukundan, R.; Brosha, E.L.; Birdsell, S.A.; Costello, A.L.; Garzon, F.H.; Willms, R.S.

    1999-01-01

    The tritium ion conductivities of SrZr 0.9 Yb 0.1 O 2.95 and BaCe 0.9 Yb 0.1 O 2.95 have been measured by ac impedance analysis. The high tritium conductivity of these perovskites could potentially lead to their application as an electrochemical membrane for the recovery of tritium from tritiated gas streams. The conductivities of these perovskites, along with SrCe 0.95 Yb 0.05 O 2.975 , were also measured in hydrogen- and deuterium-containing atmospheres to illustrate the isotope effect. For the strontium zirconate and barium cerate samples, the impedance plot consists of two clearly resolved arcs, a bulk and a grain boundary arc, in the temperature range 50--350 C. However, for the strontium cerate sample, the clear resolution of the bulk conductivity was not possible and only the total conductivity was measurable. Thus, the isotope effect was clearly established only for the strontium zirconate and barium cerate samples. The decrease in bulk conductivity with increasing isotope mass was found to be a result of an increase in the activation energy for conduction accompanied by a decrease in the pre-exponential factor. Since the concentration of the mobile species (H+, D+, or T+) should remain relatively constant at T < 350 C, this increase in activation energy is directly attributable to the increased activation energy for the isotope mobility

  1. Solvent isotope effect on the fluorescence of azoalkanes

    International Nuclear Information System (INIS)

    Mirbach, M.J.; Mirbach, M.F.; Cherry, W.R.; Turro, N.J.; Engel, P.

    1977-01-01

    A study of fluorescence quantum yields and fluorescence lifetimes of two cyclic azoalkanes reveal a striking dependence of phisub(F) and tausub(F) on solvent and on isotopic substitution (OH → OD). A mechanism involving specific deactivation of the fluorescent state from a hydrogen bonded complex is proposed to rationalize the data. (orig./HK) [de

  2. Structure of potassium isotopes studied with collinear laser spectroscopy

    CERN Document Server

    AUTHOR|(CDS)2082445

    By exploring the structure of different nuclei, one can learn about the interaction between the nucleons, their building blocks. In this field of research, there is a strong interplay between experiment and theory. In particular, theory has a crucial role in the interpretation of the experimental results, while new experimental results provide testing ground and directions for theorists. In the light- and mid-mass regions of the nuclear chart, the shell model is very successful and widely used for calculations of the ground- as well as excited- states properties. It is based on associated larger energy gaps between single particle energy levels for isotopes with certain proton (Z) and neutron (N) numbers, which are called "magic numbers". It was believed that these numbers (8, 20, 28, ...) are preserved for all nuclei throughout the nuclear chart. However, during the last decades studies of the isotopes with an unbalanced number of protons and neutrons revealed that in these isotopes the shell gaps could chan...

  3. Bibliographical study on photochemical separation of uranium isotopes

    International Nuclear Information System (INIS)

    Bougon, Roland

    1975-01-01

    The objective of this report is to propose an overview of knowledge and current works on isotopic separation of uranium by means of selective excitation where this excitation is obtained by a light source with a wave length corresponding to a selective or preferential absorption by a molecule or by the atom itself of one of the isotopes. After a brief overview of principles and requirements of isotopic separation by selective excitation, the author reviews compounds which can be used for this process. These compounds are mainly considered in terms of spectroscopy, and the study focuses on the most volatile among them, the uranium hexafluoride, its spectra, and possible processes for extraction. Some much less volatile uranium compounds are also mentioned with, when available, their spectroscopic properties. The uranium vapour excitation process is described, and some orientations for further researches are proposed [fr

  4. Study on the meat isotopic composition for origin identification

    Directory of Open Access Journals (Sweden)

    Irina Chernukha

    2018-03-01

    Full Text Available Russian consumer and governmental authorities are equally concerned to know where food products come from. This requires more accurate and specialized methods for the evaluation of geographical location. The following methods are used: chemometrics, histological and histochemical, genomic and proteomic, microbiological, immunochemical and mass spectrometric. Method of stable isotope analysis is becoming increasingly promising nowadays for the identification of meat and meat products' place of origin. The isotope ratios of the four elements - carbon, nitrogen, oxygen and hydrogen, are mainly determined. The method is successfully used to identify a country of origin of wines, juices and water. The aim of the research was to study the stable isotope ratios for pork and beef samples purchased in Moscow supermarkets (Russian Federation. The country of production of meat samples was determined according to specifications and/or labels. The geography of countries of meat samples origin includes Europe, both America continents and Australia. Databases collected by the All-Russian Scientific Research Institute of the Brewing, Non-Alcoholic and Wine Industrywere used for the analysis and interpretation of the results. Values of 13С/12С, δ13С, 18О/16О, δ18О, 2Н/1Н, δ2Н for 30 pork and beef samples from 13 countries were obtained. Differences in stable isotope ratios were found depending on place of origin. The data correlated with the oxygen isotope characteristics for wine, which were in the range from 2.5 to 4.5 ppm. According to the 13С/12С, δ13С results, the assumption was made about a false indication of the region for the beef sample. Despite the fact that beef was labeled as a product of Lithuania, the region of origin was most probably defined as Germany. The studies carried out showed the possibility to identify the region of raw meat origin by the stable isotope ratio.

  5. Modification of the isotope effect due to pair breaking

    International Nuclear Information System (INIS)

    Carbotte, J.P.; Greeson, M.; Perez-Gonzalez, A.

    1991-01-01

    We have calculated the effect of pair breaking on the isotope-effect coefficient (β) of a superconductor. We find that, as the pair-breaking scattering rate is increased, β also increases in absolute value. Values of β much larger than the canonical value of 1/2 can easily be achieved even in models where the electron-phonon interaction contributes only a very small amount to the value of the intrinsic critical temperature

  6. The study of multicomponent separation of Xe isotope by centrifugal method

    International Nuclear Information System (INIS)

    Jinyan Wu; Fu Zhuge

    1996-01-01

    The element Xe has nine isotopes in nature, the separation performance of each component mutually affects the others, so the binary separation theory can't be employed to study the multicomponent separation. Especially, when the molecular wight of a certain component is in the middle of its isotope components, the effect of the others on this component must be considered. In this paper, first, the multicomponent separation of Xe isotopes in a gas centrifuge is studied, with the consideration of the effect of the concentration on the diffusion coefficient and average molecular weight. The multicomponent diffusion equations are solved by the finite difference method. Second, the enrichment of Xe isotopes in a cascade is studied. On the basis of the study of a gas centrifuge, the simplified separation equations of a gas centrifuge for cascade calculation are obtained. Furthermore, the complete equations of the cascade separation are established according to the conservation of mass of each component and solved by a numerical method. The study of this paper can be extended for other isotope separation calculations. (author)

  7. Nitrogen and Oxygen Isotope Effects of Ammonia Oxidation by Thermophilic Thaumarchaeota from a Geothermal Water Stream.

    Science.gov (United States)

    Nishizawa, Manabu; Sakai, Sanae; Konno, Uta; Nakahara, Nozomi; Takaki, Yoshihiro; Saito, Yumi; Imachi, Hiroyuki; Tasumi, Eiji; Makabe, Akiko; Koba, Keisuke; Takai, Ken

    2016-08-01

    Ammonia oxidation regulates the balance of reduced and oxidized nitrogen pools in nature. Although ammonia-oxidizing archaea have been recently recognized to often outnumber ammonia-oxidizing bacteria in various environments, the contribution of ammonia-oxidizing archaea is still uncertain due to difficulties in the in situ quantification of ammonia oxidation activity. Nitrogen and oxygen isotope ratios of nitrite (δ(15)NNO2- and δ(18)ONO2-, respectively) are geochemical tracers for evaluating the sources and the in situ rate of nitrite turnover determined from the activities of nitrification and denitrification; however, the isotope ratios of nitrite from archaeal ammonia oxidation have been characterized only for a few marine species. We first report the isotope effects of ammonia oxidation at 70°C by thermophilic Thaumarchaeota populations composed almost entirely of "Candidatus Nitrosocaldus." The nitrogen isotope effect of ammonia oxidation varied with ambient pH (25‰ to 32‰) and strongly suggests the oxidation of ammonia, not ammonium. The δ(18)O value of nitrite produced from ammonia oxidation varied with the δ(18)O value of water in the medium but was lower than the isotopic equilibrium value in water. Because experiments have shown that the half-life of abiotic oxygen isotope exchange between nitrite and water is longer than 33 h at 70°C and pH ≥6.6, the rate of ammonia oxidation by thermophilic Thaumarchaeota could be estimated using δ(18)ONO2- in geothermal environments, where the biological nitrite turnover is likely faster than 33 h. This study extended the range of application of nitrite isotopes as a geochemical clock of the ammonia oxidation activity to high-temperature environments. Because ammonia oxidation is generally the rate-limiting step in nitrification that regulates the balance of reduced and oxidized nitrogen pools in nature, it is important to understand the biological and environmental factors underlying the regulation of

  8. Study of variations of stable isotopes in precipitation: case of Antananarivo

    International Nuclear Information System (INIS)

    Randrianarivola, M.

    2014-01-01

    The isotopic signature of precipitation is the input signal in any study of hydrological cycle. The scientific objective of this work is to better understand the isotopic variations in precipitation and identify their processes. We used the network of measurement GNIP (Global Network of Isotopes in Precipitation) in which data is acquired by the International Atomic Energy Agency through isotope hydrology laboratory at INSTN-Madagascar. Analyzes stable isotopes ( 18O and 2 H), were performed at a monthly time step. We were able to confirm the relative importance of different mechanisms governing the isotopic composition of precipitation. The spatial distribution of abundance ratios of Antananarivo rain is in fact dictated by the temperature which follow indirectly from the effects of altitude and seasonal variations. At the monthly scale, local meteoric water line δ 2 H versus δ 18 O shows the specificity of Antananarivo (deuterium excess of 17.5‰ ). Additionally, seasonal variations in precipitation is related to the temperature such that in summer (d=15‰) and winter (d=18‰) [fr

  9. Marginal-Fermi-liquid theory and the isotope effect

    International Nuclear Information System (INIS)

    Nicol, E.J.; Carbotte, J.P.

    1991-01-01

    In the marginal-Fermi-liquid model, the coupling between two electrons is via charge (attractive) and spin (repulsive) fluctuations, and so it does not exhibit an isotope effect. To include this effect, an additional phonon contribution must be introduced. Using the case of YBa 2 Cu 3 O 7 , for illustrative purposes, with a total isotope effect coefficient of β tot congruent 0.05 at a T c of 90 K, we find that the implied electron-phonon mass renormalization is very small for coupling to high-energy phonons but increases rapidly with decreasing phonon frequency or an increasing amount of spin fluctuations. Finally, we examine how β increases with decreasing T c when charge fluctuations are reduced or spin fluctuations augmented

  10. The Enriched Background Isotope Study (EBIS)

    Energy Technology Data Exchange (ETDEWEB)

    Hanson, Paul J. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Trumbore, Susan [Univ. of California, Irvine, CA (United States); Swanston, Chris [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Torn, Margaret [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Jastrow, Julie [Argonne National Lab. (ANL), Argonne, IL (United States); Parton, William A [Colorado State Univ., Fort Collins, CO (United States); Century Ecosystems, Inc. (United States); Post, Wilfred M. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Froberg, Mats J [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Hainsworth, Laura J [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Kleber, Markus [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Kramer, Christiane [Univ. of California, Irvine, CA (United States); Matamala-Paradeda, Roser [Argonne National Lab. (ANL), Argonne, IL (United States); Garten, Jr, Charles T. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

    2007-02-05

    A unique, large release of radiocarbon occurred near the Oak Ridge Reservation (ORR), Oak Ridge, TN in July/August 1999. Measurements of 14C in tree ring cellulose throughout the ORR area demonstrate that the 1999 release was unprecedented in its uptake by vegetation. We are taking advantage of the whole-ecosystem isotopic label generated by this release to address five outstanding issues in the terrestrial carbon cycle: (1) partitioning of soil respiration between autotrophic and heterotrophic sources, and quantification of that partitioning seasonally and inter-annually, (2) partitioning of heterotrophic respiration sources between above-ground litter decomposition and below-ground root detritus decomposition, (3) identification of pathways leading from leaf and root detritus to long-term stabilization of soil organic matter, including the role of soil fauna, (4) the role of dissolved organic carbon (DOC) transport in distributing carbon within the soil profile, and, (5) the longevity and turnover time of fine roots. The first four issues are being addressed through a reciprocal litter transplant experiment set up at four sites on the ORR encompassing two soil types and two levels of 14C exposure in 1999. The fifth issue, longevity and turnover of fine roots, is being addressed by tracing the radiocarbon label through the fine root pool over time. With a combination of incubation, soil surface chamber and soil CO2 profiles, and continuous measurements of soil temperature and moisture controls, we are tracking changes in soil respiration partitioning over several years. The nature and source of organic matter pools that reside in soils for years to decades are being tracked with differently labeled root and surface litter, and experiments to exclude soil fauna have been initiated to elucidate their role in vertical transport. Periodic sampling of soils and soil solutions and the use of inert tracers, allow us to investigate the chemical nature and form of DOC and

  11. Deuterium isotope effect on the intramolecular electron transfer in Pseudomonas aeruginosa azurin

    DEFF Research Database (Denmark)

    Farver, O.; Zhang, Jingdong; Chi, Qijin

    2001-01-01

    rather than negative. Isotope effects are, however, also inherent in the nuclear reorganization Gibbs free energy and in the tunneling factor for the electron transfer process. A slightly larger thermal protein expansion in H2O than in D2O (0.001 nm K-1) is sufficient both to account for the activation......Intramolecular electron transfer in azurin in water and deuterium oxide has been studied over a broad temperature range. The kinetic deuterium isotope effect, k(H)/k(D), is smaller than unity (0.7 at 298 K), primarily caused by the different activation entropies in water (-56.5 J K-1 mol(-1...

  12. Experimental study of xenon isotopes production by gas centrifuge

    International Nuclear Information System (INIS)

    Zhou Mingsheng; Liang Xiongwen; Zhang Yonggang; Dong Jinping

    2006-01-01

    The gas centrifuge technology is studied for the separation of Xe isotopes. The nature Xe is chosen as processing gas. A four-state cascade is designed to separate 124 Xe to a concentration of being greater than 65% in three separation runs. 124 Xe can be enriched to a concentration 99% in more separation runs using a cascade of more gas centrifuges. (authors)

  13. Applications of DNA-Stable Isotope Probing in Bioremediation Studies

    Science.gov (United States)

    Chen, Yin; Vohra, Jyotsna; Murrell, J. Colin

    DNA-stable isotope probing, a method to identify active microorganisms without the prerequisite of cultivation, has been widely applied in the study of microorganisms involved in the degradation of environmental pollutants. Recent advances and technique considerations in applying DNA-SIP in bioremediation are highlighted. A detailed protocol of a DNA-SIP experiment is provided.

  14. Gas cleaning with hot char beds studied by stable isotopes

    DEFF Research Database (Denmark)

    Egsgaard, Helge; Ahrenfeldt, Jesper; Ambus, Per

    2014-01-01

    The chemistry taking place in a high temperature char bed used for binding aromatic tar compounds has been studied in detail. 13C labelled tar compounds were used to trace the incorporation into the char bed using isotope ratio mass spectrometry (IRMS) and GC-MS. Furthermore, compounds labelled...

  15. Design study of fuel circulating system using Pd alloy membrane isotope separation method

    International Nuclear Information System (INIS)

    Naito, T.; Yamada, T.; Aizawa, T.; Kasahara, T.; Yamanaka, T.

    1981-01-01

    It is expected that the method of permeating through Pd-alloy membrances is effective for isotope separation and the refining of fuel gas. In this paper, the design study of the Fuel Circulating System (FCS) using Pb-alloy membranes is described. The study is mainly focused on the main vacuum, fuel gas refining, isotope separating, and tritium containment systems. In the fuel gas refining system, impurities are effectively removed by using Pd-alloy membranes. For the isotope separation system, the diffusion method through Pd-alloy membranes was adopted. From the standpoint of the safety and economy, a three-stage tritium containment system was adopted to control tritium release to the environment as low as possible. The principal conclusion drawn from the design study was as follows. In the FCS, while cryogenic distillation method appears to be practicable, Pd-alloy membrane method is attractive for isotope separation and the refining of fuel gas. For a large amount of tritium inventory, handling and control technologies should be completed by the experimental evaluation and development of the components and materials used for the FCS. A three-stage containment system was adopted to control tritium release to environment as low as possible. Consideration to prevent tritium escape will be necessary for fuel gas refiners and isotope separators. (Kato, T.)

  16. Stable isotope studies. Annual progress report, March 1, 1981-February 28, 1982

    International Nuclear Information System (INIS)

    Ishida, T.

    1981-01-01

    Our studies during the year consisted of cryogenic measurements of vapor pressure isotope effects (VPIE) in CHF 3 , CH 2 F 2 , CH 3 F, and ammonia, interpretations of the results of the VPIE studies of CHF 3 and CH 3 F by means of ab initio molecular orbital calculations and vibrational analyses, studies of nitrogen isotope fractionation by an exchange between nitric oxide and the liquid phase consisting of N 2 O 3 and N 2 O 4 under elevated pressures, an exploration of the concept of closed refluxer system for the Nitrox process for separating 15 N using a Fe(II)/Fe(III) system as reducing agent for nitric acid and the electrolysis for regeneration of Fe(II), and a theoretical study of approximation of the zero-point energy and its isotopic differences developed on the basis of Lanczos' tau-method

  17. Isotope effects in ion-exchange equilibria in aqueous and mixed solvent systems

    International Nuclear Information System (INIS)

    Gupta, A.R.

    1979-01-01

    Isotope effects in ion-exchange equilibria in aqueous and mixed solvents are analyzed in terms of the general features of ion-exchange equilibria and of isotope effects in chemical equilibria. The special role of solvent fractionation effects in ion-exchange equilibria in mixed solvents is pointed out. The various situations arising in isotope fractionation in ion exchange in mixed solvents due to solvent fractionation effects are theoretically discussed. The experimental data on lithium isotope effects in ion-exchange equilibria in mixed solvents are shown to conform to the above situations. The limitations of ion-exchange equilibria in mixed solvents for isotope fractionation are pointed out. 3 tables

  18. Dynamical barrier and isotope effects in the simplest substitution reaction via Walden inversion mechanism

    Science.gov (United States)

    Zhao, Zhiqiang; Zhang, Zhaojun; Liu, Shu; Zhang, Dong H.

    2017-02-01

    Reactions occurring at a carbon atom through the Walden inversion mechanism are one of the most important and useful classes of reactions in chemistry. Here we report an accurate theoretical study of the simplest reaction of that type: the H+CH4 substitution reaction and its isotope analogues. It is found that the reaction threshold versus collision energy is considerably higher than the barrier height. The reaction exhibits a strong normal secondary isotope effect on the cross-sections measured above the reaction threshold, and a small but reverse secondary kinetic isotope effect at room temperature. Detailed analysis reveals that the reaction proceeds along a path with a higher barrier height instead of the minimum-energy path because the umbrella angle of the non-reacting methyl group cannot change synchronously with the other reaction coordinates during the reaction due to insufficient energy transfer from the translational motion to the umbrella mode.

  19. Aerodynamic effects in isotope separation by gaseous diffusion

    International Nuclear Information System (INIS)

    Bert, L.A.; Prosperetti, A.; Fiocchi, R.

    1978-01-01

    The turbulent flow of an isotopic mixture in a porous-walled pipe is considered in the presence of suction through the wall. A simple model is formulated for the evaluation of aerodynamic effects on the separation efficiency. The predictions of the model are found to compare very favourably with experiment. In the limit of small suction velocities, results obtained by other investigators for diffusion in a turbulent steam are recovered. (author)

  20. Vapour pressure isotope effects in liquid hydrogen chloride

    Energy Technology Data Exchange (ETDEWEB)

    Lopes, J.N.C.; Calado, J.C.G. (Instituto Superior Tecnico, Lisbon (Portugal)); Jancso, Gabor (Hungarian Academy of Sciences, Budapest (Hungary). Central Research Inst. for Physics)

    1992-08-10

    The difference between the vapour pressures of HCl and DCl has been measured over the temperature range 170-203 K by a differential manometric technique in a precision cryostat. In this range the vapour pressure of HCl is higher than that of DCl by 3.2% at 170 K, decreasing to 0.9% at 200 K. The reduced partition function ratios f[sub l]/f[sub g] derived from the vapour pressure data can be described by the equation ln(f[sub l]/f[sub g]) = (3914.57[+-]10)/T[sup 2] - (17.730[+-]0.055)/T. The experimentally observed H-D vapour pressure isotope effect, together with the values on the [sup 35]Cl-[sup 37]Cl isotope effect available in the literature, is interpreted in the light of the statistical theory of isotope effects in condensed systems by using spectroscopic data of the vapour and liquid phases. The results indicate that the rotation in liquid hydrogen chloride is hindered. Temperature-dependent force constants for the hindered translational and rotational motions were invoked in order to obtain better agreement between the model calculation and experiment. (author).

  1. Isotopic hydrological studies carried out on the Karst water system

    International Nuclear Information System (INIS)

    Longinelli, A.

    1988-03-01

    The isotopic composition and temperature of many karst springs in the area of Trieste (Italy) have been measured for about three and a half years. During the same period the isotopic composition of precipitation has also been systematically studied. The isotopic composition of springs generally shows variations which are markedly shifted in time with respect to those of precipitation. In most of the springs the heavy isotope contents of winter samples are the highest of the whole year. On the contrary, summer samples normally show quite negative δ-values, the most negative of which often refer to the last summer months. The data obtained are explained in terms of variable mixing of waters from two main reservoirs. The less negative reservoir (in terms of δ) is recharged by ''local'' meteoric waters falling on the westernmost section of the karst area whose mean elevation is about 400 m a.s.l. The most negative reservoir is probably recharged by meteoric waters falling on the Slovenian section of the karst, whose mean elevation is about 800-900 m a.s.l. At least in the case of some of the northernmost karst springs, it is likely that a third water system, basically fed by the Isonzo river, flowing north of the karst area, could interfere with the previously mentioned reservoirs, partially controlling the outflow of some springs. 6 figs

  2. Critical overview on water - hydrogen isotopic exchange; a case study

    International Nuclear Information System (INIS)

    Peculea, Marius

    2002-01-01

    Water - hydrogen isotopic exchange process is attractive due to its high separation factor; it is neither corrosive or pollutant and, when used as a technological process of heavy water production, it requires water as raw material. Its efficiency depends strongly on the catalyst performance and geometry of the isotopic water - hydrogen exchange zone in which the isotopic transfer proceeds in two steps: liquid vapor distillation in the presence of an inert gas and a catalytic reaction in vapor - gas gaseous phase. An overview of the water hydrogen isotopic exchange is presented and technological details of the Trail - Canada facility as well as characteristics of the two pilots operated in Romania with Ni, Cr and hydrophobic catalysts are described. The mathematical approach of the successive water-water vapor-hydrogen isotopic exchange process given is based on a mathematical model worked out earlier by Palibroda. Discrepancies between computation and experimental results, lower than 11% for extreme cases and around 6% for the average range are explained as due to the ratio of the exchange potentials. Assumption is made in the theoretical approach that this ratio is positive and constant all long the column while the measurements showed that it varies within 0.7 and 1.1 at the upper end and within - 2.5 and - 4.4 at the lower end, what indicates a strong end effect. In conclusion it is stressed that a competing technological solution is emerging based on a monothermal electrolytic process or a bithermal - bibaric process both for heavy water and tritium separation process

  3. Kinetic secondary deuterium isotope effect in addition of nucleophile to m-bromobenzaldehyde

    International Nuclear Information System (INIS)

    Amaral, L. do; Rossi, M.H.

    1985-01-01

    The kinetic secondary deuterium isotope effects, KD/KH for hydrated proton catalyzed addition of semicarbazide, methoxyamine and hydroxylamine to m-bromobenzaldehyde is studied. The nature of the nucleophile, addition of the carbonyl group and the chemical reactions are evaluated. (M.J.C.) [pt

  4. Effect of Interband Interaction on Isotope Effect Coefficient of Mg B2 Superconductors

    International Nuclear Information System (INIS)

    Udomsamuthirun, P.; Kumvongsa, C.; Burakorn, A.; Changkanarth, P.; Maneeratanakul, S.

    2005-10-01

    In this research, the exact formula of Tc s equation and the isotope effect coefficient of two-band s-wave superconductors in weak-coupling limit are derived by considering the influence of interband interaction .In each band ,our model consist of two paring interactions : the electron-phonon interaction and non-electron-phonon interaction . According to the numerical calculation, we find that the isotope effect coefficient of MgB 2 , α=3 . 0 with T c 40 K can be found in the weak coupling regime and interband interaction of electron-phonon show more effect on isotope effect coefficient than interband interaction of non-phonon-electron

  5. Effect of Different Carbon Substrates on Nitrate Stable Isotope Fractionation During Microbial Denitrification

    DEFF Research Database (Denmark)

    Wunderlich, Anja; Meckenstock, Rainer; Einsiedl, Florian

    2012-01-01

    -labeled water and 18O-labeled nitrite were added to the microcosm experiments to study the effect of putative backward reactions of nitrite to nitrate on the stable isotope fractionation. We found no evidence for a reverse reaction. Significant variations of the stable isotope enrichment factor ε were observed......In batch experiments, we studied the isotope fractionation in N and O of dissolved nitrate during dentrification. Denitrifying strains Thauera aromatica and “Aromatoleum aromaticum strain EbN1” were grown under strictly anaerobic conditions with acetate, benzoate, and toluene as carbon sources. 18O...... of nitrate transport across the cell wall compared to the kinetics of the intracellular nitrate reduction step of microbial denitrification....

  6. Effect of complexing reagents on the ionization constant of boric acid and its relation to isotopic exchange separation factor

    International Nuclear Information System (INIS)

    Sharma, B.K.; Subramanian, R.; Mathur, P.K.

    1991-01-01

    The effect of change in concentration of complexing reagents having two or more hydroxyl groups, viz., ethylene glycol, propylene glycol, dextrose and mannitol on the ionization constant of boric acid has been studied by pH-metric titration method. The effect of increase in ionization constant of boric acid on isotopic exchange separation factor for the separation of isotopes of boron by ion exchange chromatography has been studied by the batch method. (author). 9 refs

  7. Mechanistic investigations of the hydrolysis of amides, oxoesters and thioesters via kinetic isotope effects and positional isotope exchange.

    Science.gov (United States)

    Robins, Lori I; Fogle, Emily J; Marlier, John F

    2015-11-01

    The hydrolysis of amides, oxoesters and thioesters is an important reaction in both organic chemistry and biochemistry. Kinetic isotope effects (KIEs) are one of the most important physical organic methods for determining the most likely transition state structure and rate-determining step of these reaction mechanisms. This method induces a very small change in reaction rates, which, in turn, results in a minimum disturbance of the natural mechanism. KIE studies were carried out on both the non-enzymatic and the enzyme-catalyzed reactions in an effort to compare both types of mechanisms. In these studies the amides and esters of formic acid were chosen because this molecular structure allowed development of methodology to determine heavy-atom solvent (nucleophile) KIEs. This type of isotope effect is difficult to measure, but is rich in mechanistic information. Results of these investigations point to transition states with varying degrees of tetrahedral character that fit a classical stepwise mechanism. This article is part of a special issue entitled: Enzyme Transition States from Theory and Experiment. Copyright © 2014 Elsevier B.V. All rights reserved.

  8. Effects of GC temperature and carrier gas flow rate on on-line oxygen isotope measurement as studied by on-column CO injection.

    Science.gov (United States)

    Chen, Zhi-Gang; Yin, Xi-Jie; Zhou, Youping

    2015-08-01

    Although deemed important to δ 18 O measurement by on-line high-temperature conversion techniques, how the GC conditions affect δ 18 O measurement is rarely examined adequately. We therefore directly injected different volumes of CO or CO-N 2 mix onto the GC column by a six-port valve and examined the CO yield, CO peak shape, CO-N 2 separation, and δ 18 O value under different GC temperatures and carrier gas flow rates. The results show the CO peak area decreases when the carrier gas flow rate increases. The GC temperature has no effect on peak area. The peak width increases with the increase of CO injection volume but decreases with the increase of GC temperature and carrier gas flow rate. The peak intensity increases with the increase of GC temperature and CO injection volume but decreases with the increase of carrier gas flow rate. The peak separation time between N 2 and CO decreases with an increase of GC temperature and carrier gas flow rate. δ 18 O value decreases with the increase of CO injection volume (when half m/z 28 intensity is rate. On average, the δ 18 O value of the injected CO is about 1‰ higher than that of identical reference CO. The δ 18 O distribution pattern of the injected CO is probably a combined result of ion source nonlinearity and preferential loss of C 16 O or oxygen isotopic exchange between zeolite and CO. For practical application, a lower carrier gas flow rate is therefore recommended as it has the combined advantages of higher CO yield, better N 2 -CO separation, lower He consumption, and insignificant effect on δ 18 O value, while a higher-than-60 °C GC temperature and a larger-than-100 µl CO volume is also recommended. When no N 2 peak is expected, a higher GC temperature is recommended, and vice versa. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.

  9. Carbon-13 isotope effects on 199Hg nuclear shielding

    International Nuclear Information System (INIS)

    Sebald, Angelika; Wrackmeyer, Bernd

    1985-01-01

    Secondary 13 C/ 12 C isotope effects on 199 Hg nuclear shielding (Δdeltasup(i)( 199 Hg)) are of interest because of the unusual shift to high frequency which has been observed for a few alkyl mercury compounds. Continuing interest in the NMR parameters of mercury compounds prompted a search for the values Δdeltasup(i)( 199 Hg) in a greater variety of organomercurials. This should help to find out about the range of Δdeltasup(i)( 199 Hg) and to obtain a firmer basis for the discussion of the high-frequency shifts. The data and experimental conditions are given for chemical shifts delta 199 Hg, coupling constants sup(n)J( 199 Hg 13 C) and 13 C/ 12 C isotope shifts Δdeltasup(i)( 199 Hg) of fourteen 199 Hg organomercury compounds. The results are discussed. (author)

  10. Kinetic isotope effects and how to describe them

    Directory of Open Access Journals (Sweden)

    Konstantin Karandashev

    2017-11-01

    Full Text Available We review several methods for computing kinetic isotope effects in chemical reactions including semiclassical and quantum instanton theory. These methods describe both the quantization of vibrational modes as well as tunneling and are applied to the ⋅H + H2 and ⋅H + CH4 reactions. The absolute rate constants computed with the semiclassical instanton method both using on-the-fly electronic structure calculations and fitted potential-energy surfaces are also compared directly with exact quantum dynamics results. The error inherent in the instanton approximation is found to be relatively small and similar in magnitude to that introduced by using fitted surfaces. The kinetic isotope effect computed by the quantum instanton is even more accurate, and although it is computationally more expensive, the efficiency can be improved by path-integral acceleration techniques. We also test a simple approach for designing potential-energy surfaces for the example of proton transfer in malonaldehyde. The tunneling splittings are computed, and although they are found to deviate from experimental results, the ratio of the splitting to that of an isotopically substituted form is in much better agreement. We discuss the strengths and limitations of the potential-energy surface and based on our findings suggest ways in which it can be improved.

  11. Isotopic effects in the neon fixed point: uncertainty of the calibration data correction

    Science.gov (United States)

    Steur, Peter P. M.; Pavese, Franco; Fellmuth, Bernd; Hermier, Yves; Hill, Kenneth D.; Seog Kim, Jin; Lipinski, Leszek; Nagao, Keisuke; Nakano, Tohru; Peruzzi, Andrea; Sparasci, Fernando; Szmyrka-Grzebyk, Anna; Tamura, Osamu; Tew, Weston L.; Valkiers, Staf; van Geel, Jan

    2015-02-01

    The neon triple point is one of the defining fixed points of the International Temperature Scale of 1990 (ITS-90). Although recognizing that natural neon is a mixture of isotopes, the ITS-90 definition only states that the neon should be of ‘natural isotopic composition’, without any further requirements. A preliminary study in 2005 indicated that most of the observed variability in the realized neon triple point temperatures within a range of about 0.5 mK can be attributed to the variability in isotopic composition among different samples of ‘natural’ neon. Based on the results of an International Project (EUROMET Project No. 770), the Consultative Committee for Thermometry decided to improve the realization of the neon fixed point by assigning the ITS-90 temperature value 24.5561 K to neon with the isotopic composition recommended by IUPAC, accompanied by a quadratic equation to take the deviations from the reference composition into account. In this paper, the uncertainties of the equation are discussed and an uncertainty budget is presented. The resulting standard uncertainty due to the isotopic effect (k = 1) after correction of the calibration data is reduced to (4 to 40) μK when using neon of ‘natural’ isotopic composition or to 30 μK when using 20Ne. For comparison, an uncertainty component of 0.15 mK should be included in the uncertainty budget for the neon triple point if the isotopic composition is unknown, i.e. whenever the correction cannot be applied.

  12. A Distinct Magnetic Isotope Effect Measured in Atmospheric Mercury in Epiphytes

    Science.gov (United States)

    Ghosh, S.; Odom, A. L.

    2007-12-01

    Due to the importance of Mercury as an environmental contaminant, mercury cycling in the atmosphere has been extensively studied. However, there still remain uncertainties in the relative amounts of natural and anthropogenic emissions, atmospheric deposition rates as well as the spatial variation of atmospheric mercury. Part of a study to determine the isotopic composition of mercury deposited from the atmosphere has involved the use of epiphytes as monitors. The greatest advantage of such natural monitors is that a widespread, high-density network is possible at low cost. One of the disadvantages at present is that these monitors likely contain different mercury species (for example both gaseous, elemental mercury trapped by adsorption and Hg (II) by wet deposition). The project began with the understanding that biochemical reactions involving metallothioneins within the epiphytes might have produced an isotopic effect. One such regional network was composed of samples of Tillandsia usenoides (common name: Spanish moss) collected along the eastern Coastal Plain of the U.S. from northern Florida to North Carolina. The isotopic composition of a sample is expressed as permil deviations from a standard. The deviations are defined as δAHg = \\left(\\frac{Rsample}{Rstd}-1 \\right)1000 ‰ , where A represents the atomic mass number. R=\\frac{AHg}{202Hg} were measured for the isotopes 198Hg, 199Hg, 200Hg, 201Hg, 202Hg and 204Hg relative to the mercury standard SRM NIST 3133, by a standard-sample bracketing technique. For all samples, the delta values of the even-N plotted against atomic mass numbers define a linear curve. For the odd-N isotopes, δ199Hg and δ201Hg deviate from this mass-dependent fractionation (MDF) relationship and indicate a mass-independent fractionation (MIF) effect and a negative anomaly, i.e. a depletion in 199Hg and 201Hg relative to the even-N isotopes. These deviations are expressed as Δ199Hg = δ199Hgtotal - δ199HgMDF. A Δ201Hg/Δ199Hg

  13. Isotopic incorporation and the effects of fasting and dietary lipid content on isotopic discrimination in large carnivorous mammals

    Science.gov (United States)

    Rode, Karyn D.; Stricker, Craig A.; Erlenbach, Joy; Robbins, Charles T.; Cherry, Seth; Newsome, Seth D.; Cutting, Amy; Jensen, Shannon; Stenhouse, Gordon; Brooks, Matt; Hash, Amy; Nicassio, Nicole

    2016-01-01

    There has been considerable emphasis on understanding isotopic discrimination for diet estimation in omnivores. However, discrimination may differ for carnivores, particularly species that consume lipid-rich diets. Here, we examined the potential implications of several factors when using stable isotopes to estimate the diets of bears, which can consume lipid-rich diets and, alternatively, fast for weeks to months. We conducted feeding trials with captive brown bears (Ursus arctos) and polar bears (Ursus maritimus). As dietary lipid content increased to ∼90%, we observed increasing differences between blood plasma and diets that had not been lipid extracted (∆13Ctissue-bulk diet) and slightly decreasing differences between plasma δ13C and lipid-extracted diet. Plasma Δ15Ntissue-bulk diet increased with increasing protein content for the four polar bears in this study and data for other mammals from previous studies that were fed purely carnivorous diets. Four adult and four yearling brown bears that fasted 120 d had plasma δ15N values that changed by <±2‰. Fasting bears exhibited no trend in plasma δ13C. Isotopic incorporation in red blood cells and whole blood was ≥6 mo in subadult and adult bears, which is considerably longer than previously measured in younger and smaller black bears (Ursus americanus). Our results suggest that short-term fasting in carnivores has minimal effects on δ13C and δ15N discrimination between predators and their prey but that dietary lipid content is an important factor directly affecting δ13C discrimination and indirectly affecting δ15N discrimination via the inverse relationship with dietary protein content.

  14. Isotope Fractionation in Methane Reactions Studied by Gas Chromatography and Liquid Scintillation

    DEFF Research Database (Denmark)

    Andersen, Bertel Lohmann; Bidoglio, G.; Leip, A.

    1997-01-01

    Determination of C-14-marked methane by gas chromatography and liquid scintillation counting is shown to be useful in studies of isotope effects. Data on the specific activity is used to separate the contributions of (CH4)-C-14, and (CH4)-C-12 to the gas-chromatographic peak area. As an application...

  15. Mixing effects on apparent reaction rates and isotope fractionation during denitrification in a heterogeneous aquifer

    Science.gov (United States)

    Green, Christopher T.; Böhlke, John Karl; Bekins, Barbara A.; Phillips, Steven P.

    2010-01-01

    Gradients in contaminant concentrations and isotopic compositions commonly are used to derive reaction parameters for natural attenuation in aquifers. Differences between field‐scale (apparent) estimated reaction rates and isotopic fractionations and local‐scale (intrinsic) effects are poorly understood for complex natural systems. For a heterogeneous alluvial fan aquifer, numerical models and field observations were used to study the effects of physical heterogeneity on reaction parameter estimates. Field measurements included major ions, age tracers, stable isotopes, and dissolved gases. Parameters were estimated for the O2 reduction rate, denitrification rate, O2 threshold for denitrification, and stable N isotope fractionation during denitrification. For multiple geostatistical realizations of the aquifer, inverse modeling was used to establish reactive transport simulations that were consistent with field observations and served as a basis for numerical experiments to compare sample‐based estimates of “apparent” parameters with “true“ (intrinsic) values. For this aquifer, non‐Gaussian dispersion reduced the magnitudes of apparent reaction rates and isotope fractionations to a greater extent than Gaussian mixing alone. Apparent and true rate constants and fractionation parameters can differ by an order of magnitude or more, especially for samples subject to slow transport, long travel times, or rapid reactions. The effect of mixing on apparent N isotope fractionation potentially explains differences between previous laboratory and field estimates. Similarly, predicted effects on apparent O2threshold values for denitrification are consistent with previous reports of higher values in aquifers than in the laboratory. These results show that hydrogeological complexity substantially influences the interpretation and prediction of reactive transport.

  16. Secondary partitioning isotope effects on solvolytic ion pair intermediates

    International Nuclear Information System (INIS)

    Abbey, K.J.

    1976-01-01

    The thermal decomposition of N-benzhydryl N-nitrosobenzamide (BNB) has been shown to produce an ion pair which either forms ester or reacts with the solvent. In ethanol, the fraction of ester produced, R, was much smaller than R values obtained from solvolysis or from the diphenyldiazomethane (DDM)-benzoic acid reaction, which was suggested to yield the same ion pair as solvolysis. This difference led to the conclusion that the ionic species for the nitrosamide decomposition is a nitrogen-separated ion pair. This study was initiated on the assumption that BNB led to solvolytic ion pairs, but that both the intimate and solvent-separated ion pairs were produced directly from the nitrosamide. The use of α-tritiated BNB for the study of partitioning isotope effects (PIE's) in this system led to activity ratios much lower than expected from other reported work. Results of studies of ''special'' salt effect were not consistent for all situations, but the results do suggest that the assumption that BNB leads to solvolytic ion pairs is probably valid. The investigation of the more stable p-methoxybenzhydryl benzoate system proved to be highly productive. The ester fraction produced, R, responded dramatically to the addition of common-ion as well as ''special'' salts. The functional relationship of R on salt concentration could be explained in terms of Winstein's solvolytic scheme where the intimate ion pair, the solvent-separated ion pair, and the dissociated ion were important. Tritium-labelled compounds were used for PIE studies on 3 different compounds, and three different methods of reaction are proposed

  17. Use of Isotopes for Studying Reaction Mechanisms

    Indian Academy of Sciences (India)

    their positions rapidly. This is especially true of carbocations and ... Several specific examples can be quoted. Ammonia is a ... All experimental studies on this system were ... rearrangement. Hence, the species will have a relatively simple 13C.

  18. Magnetic field and magnetic isotope effects on photochemical reactions

    International Nuclear Information System (INIS)

    Wakasa, Masanobu

    1999-01-01

    By at present exact experiments and the theoretical analysis, it was clear that the magnetic field less than 2 T affected a radical pair reaction and biradical reaction. The radical pair life and the dissipative radical yield showed the magnetic field effects on chemical reactions. The radical pair mechanism and the triplet mechanism were known as the mechanism of magnetic field effects. The radical pair mechanism consists of four mechanisms such as the homogeneous hyperfine interaction (HFC), the delta-g mechanism, the relaxation mechanism and the level cross mechanism. In order to observe the magnetic effects of the radical pair mechanism, two conditions need, namely, the recombination rate of singlet radical pair > the dissipation rate and the spin exchange rate > the dissipation rate. A nanosecond laser photo-decomposition equipment can observe the magnetic field effects. The inversion phenomena of magnetic field effect, isolation of the relaxation mechanism and the delta-g mechanism, the magnetic field effect of heavy metal radical reaction, the magnetic field effect in homogeneous solvent, saturation of delta-g mechanism are explained. The succeeded examples of isotope concentration by the magnetic isotope effect are 17 O, 19 Si, 33 S, 73 Ge and 235 U. (S.Y.)

  19. Isotopic tailoring with 59Ni to study the effect of helium on microstructural evolution and mechanical properties of neutron-irradiated Fe-Cr-Ni alloys

    International Nuclear Information System (INIS)

    Garner, F.A.; Hamilton, M.L.; Greenwood, L.R.; Stubbins, J.F.; Oliver, B.M.

    1992-03-01

    Tensile testing on three model Fe-Cr-Ni alloys removed from four discharges of the 59 Ni isotopic doping experiment in FFTF-MOTA indicates that helium/dpa ratios typical of fusion reactors do not produce changes in the yield strength or elongation that are significantly different from those at much lower helium generation rates. It also appears that tensile properties approach a saturation level that is dependent only on the final irradiation temperature, but not prior temperature history or thermomechanical starting condition. The saturation in mechanical properties reflects a similar saturation in microstructure that is independent of starting condition. The successful conduct of an isotopic doping experiment was found to require post-irradiation measurement of the helium levels in order to compensate for uncertainties in the cross sections for burn-out and burn-in of 59 Ni and for uncertainties in neutron flux and spectra in the vicinity of the edge of the core

  20. Isotopic and spin-nuclear effects in solid hydrogens (Review Article)

    Science.gov (United States)

    Freiman, Yuri A.; Crespo, Yanier

    2017-12-01

    The multiple isotopic family of hydrogens (H2, HD, D2, HT, DT, T2) due to large differences in the de Boer quantum parameter and inertia moments displays a diversity of pronounced quantum isotopic solid-state effects. The homonuclear members of this family (H2, D2, T2) due to the permutation symmetry are subjects of the constraints of quantum mechanics which link the possible rotational states of these molecules to their total nuclear spin giving rise to the existence of two spin-nuclear modifications, ortho- and parahydrogens, possessing substantially different properties. Consequently, hydrogen solids present an unique opportunity for studying both isotope and spin-nuclear effects. The rotational spectra of heteronuclear hydrogens (HD, HT, DT) are free from limitations imposed by the permutation symmetry. As a result, the ground state of these species in solid state is virtually degenerate. The most dramatic consequence of this fact is an effect similar to the Pomeranchuk effect in 3He which in the case of the solid heteronuclear hydrogens manifests itself as the reentrant broken symmetry phase transitions. In this review article we discuss thermodynamic and kinetic effects pertaining to different isotopic and spin-nuclear species, as well as problems that still remain to be solved.

  1. Isotope techniques in lake water studies

    International Nuclear Information System (INIS)

    Gourcy, L.

    1999-01-01

    Freshwater lakes are among the most easily exploitable freshwater resources. Lakes are also recognized as major sedimentological features in which stored material can be used to study recent climate and pollution evolution. To adequately preserve these important landscape features, and to use them as climatic archives, an improved understanding of processes controlling their hydrologic and bio-geochemical environments if necessary. This article briefly describes the IAEA activities related to the study of lakes in such areas as lake budget, lake dynamics, water contamination, and paleolimnological investigations

  2. Study of oxalic acid effect on equilibrium and kinetics of isotopic exchange between penta- and hexavalent neptunium in nitric acid solutions

    International Nuclear Information System (INIS)

    Nikitenko, S.I.; Ionnikova, N.I.

    1989-01-01

    Spectrophotometry at 25 deg C and ionic force μ=1.0 mol/l (KNO 3 +HNO 3 ) was used to show that at HNO 3 concentration 0.1-1.0 mol/l H 2 C 2 O 4 introduction to nitric acid solutions of Np 5+ in the presence of nitrite-ion resulted in the shift of equilibrium between Np 5+ and Np 6+ to the side of Np 6+ accumulation. The presence of H 2 C 2 O 4 at HNO 3 concentration > 1.0 mol/l doesn't affect the equilibrium position. The values of nominal equilibrium constant at different HNO 3 and H 2 C 2 O 4 concentrations were calculated. It was found that isotope exchange ( 239 Np/ 237 Np) between Np 5+ and Np 6+ in oxalate solutions proceeded more slowly than in oxalate absence. Rate constants of isotope exchange calculated at 9 deg C, μ=1.0 mol/l (KNO 3 ), H 2 C 2 O 4 concentration 0.01 mol/l and pH=2.2 and 3.5 are equal to 0.49x10 3 and 0.67x10 2 l/mol·min respectively. Mechanism of isotope exchange including electron transport between Np 5+ and Np 6+ oxalate complexes is suggested

  3. Isotope enrichment effect of gaseous mixtures in standing sound vibration

    International Nuclear Information System (INIS)

    Knesebeck, R.L.

    1984-01-01

    When standing acoustic waves are excited in a tube containing a mixture of two gases, a partial zonal fractioning of the components arises as consequence of mass transport by diffusion, driven by the thermal and pressure gradients which are associeted with the standing waves. This effect is present in each zone corresponding to a quarter wavelength, with the heavier component becoming enriched at the nodes fo the standing waves and deplected at the crests. The magnitude of the enrichment in one of the components of a binary gas mixture is given by Δω=ap 2 /lambda [b + (1-bω)] 2 . Where ω is the mass concentration of the component in the mixture, a and b are parameters which are related to molecular proprieties of the gases, p is the relative pressure amplitude of the standing wave and lambda is its wavelength. For a natural mixture of uranium hexafluorate, with 0.715% of the uranium isotope 340 an enrichment of about 2 x 10 -6 % in the concentration of this isotope is theorecticaly attainable per stage consisting of a quarter wavelenght, when a standing acoustical wave of relative pressure amplitude of 0,2 and wavelenght of 20 cm is used. Since standing acoustical waves are easely excited in gas columns, an isotope enrichment plant made of a cascade of tubes in which standing waves are excited, is presumably feasible with relatively low investment and operation costs. (Author) [pt

  4. Three New Offset {delta}{sup 11}B Isotope Reference Materials for Environmental Boron Isotope Studies

    Energy Technology Data Exchange (ETDEWEB)

    Rosner, M. [BAM Federal Institute for Materials Research and Testing, Berlin (Germany); IsoAnalysis UG, Berlin (Germany); Vogl, J. [BAM Federal Institute for Materials Research and Testing, Berlin (Germany)

    2013-07-15

    The isotopic composition of boron is a well established tool in various areas of science and industry. Boron isotope compositions are typically reported as {delta}{sup 11}B values which indicate the isotopic difference of a sample relative to the isotope reference material NIST SRM 951. A significant drawback of all of the available boron isotope reference materials is that none of them covers a natural boron isotope composition apart from NIST SRM 951. To fill this gap of required {delta}{sup 11}B reference materials three new solution boric acid reference materials were produced, which cover 60 per mille of the natural boron isotope variation (-20 to 40 per mille {delta}{sup 11}B) of about 100 per mille . The new reference materials are certified for their {delta}{sup 11}B values and are commercially available through European Reference Materials (http://www.erm-crm.org). The newly produced and certified boron isotope reference materials will allow straightforward method validation and quality control of boron isotope data. (author)

  5. Experimental investigation of nitrogen isotopic effects associated with ammonia degassing at 0-70 °C

    Science.gov (United States)

    Deng, Yuying; Li, Yingzhou; Li, Long

    2018-04-01

    Ammonia degassing is a common process in natural alkaline waters and in the atmosphere. To quantitatively assess the nitrogen cycle in these systems, the essential parameter of nitrogen isotope fractionation factors associated with ammonia degassing is required, but still not constrained yet. In this study, we carried out laboratory experiments to examine the nitrogen isotope behavior during ammonia degassing in alkaline conditions. The experiments started with ammonium sulfate solution with excess sodium hydroxide. The reaction can be described as: NH4+ + OH- (excess) → NH3·nH2O → NH3 (g)↑. Two sets of experiments, one with ammonia degassing under static conditions and the other with ammonia degassing by bubbling of N2 gas, were carried out at 2, 21, 50, and 70 °C. The results indicate that kinetic isotopic effects are dominated during efficient degassing of ammonia in the bubbling experiments, which yielded kinetic nitrogen isotope fractionation factors αNH3(g)-NH3(aq) of 0.9898 at 2 °C, 0.9918 at 21 °C, 0.9935 at 50 °C and 0.9948 at 70 °C. These values show a good relationship with temperature as 103lnαNH3(g)-NH3(aq) = 14.6 - 6.8 × 1000/T. In contrast, isotopic effects during less efficient degassing of ammonia in the static experiments are more complicated. The results do not match either kinetic isotope fractionation or equilibrium isotope fractionation but sit between these two. The most likely cause is that back dissolution of the degassed ammonia occurred in these experiments and consequently shifted kinetic isotope fractionation toward equilibrium isotope fractionation. Our experimental results highlight complicated isotopic effects may occur in natural environments, and need to be fully considered in the interpretation of field data.

  6. Isotopically modified nanoparticles for enhanced detection in bioaccumulation studies

    Science.gov (United States)

    Misra, S.K.; Dybowska, A.; Berhanu, D.; Croteau, M.-N.; Luoma, S.N.; Boccaccini, A.R.; Valsami-Jones, E.

    2012-01-01

    This work presents results on synthesis of isotopically enriched (99% 65Cu) copper oxide nanoparticles and its application in ecotoxicological studies. 65CuO nanoparticles were synthesized as spheres (7 nm) and rods (7 ?? 40 nm). Significant differences were observed between the reactivity and dissolution of spherical and rod shaped nanoparticles. The extreme sensitivity of the stable isotope tracing technique developed in this study allowed determining Cu uptake at exposure concentrations equivalent to background Cu concentrations in freshwater systems (0.2-30 ??g/L). Without a tracer, detection of newly accumulated Cu was impossible, even at exposure concentrations surpassing some of the most contaminated water systems (>1 mg/L). ?? 2011 American Chemical Society.

  7. A Tale of Two Gases: Isotope Effects Associated with the Enzymatic Production of H2 and N2O

    Science.gov (United States)

    Yang, H.; Gandhi, H.; Kreuzer, H. W.; Moran, J.; Hill, E. A.; McQuarters, A.; Lehnert, N.; Ostrom, N. E.; Hegg, E. L.

    2014-12-01

    Stable isotopes can provide considerable insight into enzymatic mechanisms and fluxes in various biological processes. In our studies, we used stable isotopes to characterize both enzyme-catalyzed H2 and N2O production. H2 is a potential alternative clean energy source and also a key metabolite in many microbial communities. Biological H2 production is generally catalyzed by hydrogenases, enzymes that combine protons and electrons to produce H2 under anaerobic conditions. In our study, H isotopes and fractionation factors (α) were used to characterize two types of hydrogenases: [FeFe]- and [NiFe]-hydrogenases. Due to differences in the active site, the α associated with H2 production for [FeFe]- and [NiFe]-hydrogenases separated into two distinct clusters (αFeFe > αNiFe). The calculated kinetic isotope effects indicate that hydrogenase-catalyzed H2 production has a preference for light isotopes, consistent with the relative bond strengths of O-H and H-H bonds. Interestingly, the isotope effects associated with H2 consumption and H2-H2O exchange reactions were also characterized, but in this case no specific difference was observed between the different enzymes. N2O is a potent greenhouse gas with a global warming potential 300 times that of CO2, and the concentration of N2O is currently increasing at a rate of ~0.25% per year. Thus far, bacterial and fungal denitrification processes have been identified as two of the major sources of biologically generated N2O. In this study, we measured the δ15N, δ18O, δ15Nα (central N atom in N2O), and δ15Nβ (terminal N atom in N2O) of N2O generated by purified fungal P450 nitric oxide reductase (P450nor) from Histoplasma capsulatum. We observed normal isotope effects for δ18O and δ15Nα, and inverse isotope effects for bulk δ15N (the average of Nα and Nβ) and δ15Nβ. The observed isotope effects have been used in conjunction with DFT calculations to provide important insight into the mechanism of P450nor. Similar

  8. Fundamental studies in isotope chemistry. Progress report, 1 August 1981-1 August 1982

    International Nuclear Information System (INIS)

    Bigeleisen, J.

    1982-01-01

    This research program is concerned with isotope chemistry and its applications. A summary of isotope separation activities during the past 5 years is included. Isotope effects are used as probes for chemical reactions, geochemistry, meteorology, and molecular biology, and this report also summarizes progress made in this area

  9. Coulomb excitation of neutron-deficient polonium isotopes studied at ISOLDE

    CERN Document Server

    Neven, Michiel

    The polonium isotopes represent an interesting region of the nuclear chart having only two protons outside the Z = 82 closed shell. These isotopes have already been extensively studied theoretically and experimentally. The heavier isotopes (A > 200) seem to follow a "regular seniority-type regime" while for the lighter isotopes (A < 200) a more collective behavior is observed. Many questions remain regarding the transition between these two regimes and the configuration mixing between quantum states. Experiments in the lighter polonium isotopes point to the presence of shape coexistence, however the phenomenon is not fully understood. A Coulomb excitation study of the polonium isotopes whereby the dynamic properties are investigated can provide helpful insights in understanding the shape coexistence phenomena. In this thesis $^{202}$Po was studied via Coulomb excitation. The $^{202}$Po isotope was part of an experimental campaign in which the $^{196,198,200,206}$Po isotopes were studied as well via Coulomb...

  10. Applications of C and N stable isotopes to ecological and environmental studies in seagrass ecosystems

    Energy Technology Data Exchange (ETDEWEB)

    Lepoint, Gilles [Centre MARE, Laboratoire d' Oceanologie, Institut de Chimie, B6, Universite de Liege, B-4000 Liege (Belgium)]. E-mail: g.lepoint@ulg.ac.be; Dauby, Patrick [Centre MARE, Laboratoire d' Oceanologie, Institut de Chimie, B6, Universite de Liege, B-4000 Liege (Belgium); Institut Royal des Sciences Naturelles de Belgique, rue Vautier, B1000 Brussels (Belgium); Gobert, Sylvie [Centre MARE, Laboratoire d' Oceanologie, Institut de Chimie, B6, Universite de Liege, B-4000 Liege (Belgium)

    2004-12-01

    Stable isotopes of carbon and nitrogen are increasingly used in marine ecosystems, for ecological and environmental studies. Here, we examine some applications of stable isotopes as ecological integrators or tracers in seagrass ecosystem studies. We focus on both the use of natural isotope abundance as food web integrators or environmental tracers and on the use of stable isotopes as experimental tools. As ecosystem integrators, stable isotopes have helped to elucidate the general structure of trophic webs in temperate, Mediterranean and tropical seagrass ecosystems. As environmental tracers, stable isotopes have proven their utility in sewage impact measuring and mapping. However, to make such environmental studies more comprehensible, future works on understanding of basic reasons for variations of N and C stable isotopes in seagrasses should be encouraged. At least, as experimental tracers, stable isotopes allow the study of many aspects of N and C cycles at the scale of a plant or at the scale of the seagrass ecosystem.

  11. Isotopic studies of the aquiferous of Lima

    International Nuclear Information System (INIS)

    Plata, A.; Rojas M, R.; Sebastian C, C.; Ruiz G, J.

    1993-01-01

    Filtrations from Rimac and Blanco rivers and Graton Tunnel (on the Rimac basin, 80 km from Lima city and 2500 m sea level) were studied using artificial tracers and superficial tracers and superficial water analysis. Graton tunnel has a 3 -5 m 3 /s volume. Domestic and industrial demand of Lima (7 millions inhabitants) is 22 m 3 /s . Preliminary results suggest that Graton tunnel filtrations do not originate on Rimac or Blanco rivers, but in regions at 4600 m sea level. Detected tritium suggests that water filtrated in Graton tunnel is modern. (authors) 10 refs., 2 figs

  12. Carbon isotope effects in carbohydrates and amino acids of photosynthesizing organisms

    International Nuclear Information System (INIS)

    Ivlev, A.A.; Kaloshin, A.G.; Koroleva, M.Ya.

    1982-01-01

    The analysis of the carbon isotope distribution in carbohydrates and amino acids of some photosynthesizing organisms revealed the close relationship between distribution and the pathways of biosynthesis of the molecules. This relationship is explained on the basis of the previously proposed mechanism of carbon isotope fractionation in a cell, in which the chief part is played by kinetic isotope effects in the pyruvate decarboxylation reaction progressively increased in the conjugated processes of gluconeogenesis. Isotope differences of C 2 and C 3 fragments arising in decarboxylation of pyruvate, as well as isotope differences of biogenic acceptor and environmental CO 2 appearing in assimilation are the main reasons of the observed intramolecular isotopic heterogeneity of biomolecules. The heterogeneity is preserved in metabolites owing to an incomplete mixing of carbon atoms in biochemical reactions. The probable existence of two pools of carbohydrates in photosynthesizing organisms different in isotopic composition is predicted. Two types of intramolecular isotope distribution in amino acids are shown. (author)

  13. On the Effect of Planetary Stable Isotope Compositions on Growth and Survival of Terrestrial Organisms.

    Directory of Open Access Journals (Sweden)

    Xueshu Xie

    Full Text Available Isotopic compositions of reactants affect the rates of chemical and biochemical reactions. Usually it is assumed that heavy stable isotope enrichment leads to progressively slower reactions. Yet the effect of stable isotopes may be nonlinear, as exemplified by the "isotopic resonance" phenomenon. Since the isotopic compositions of other planets of Solar system, including Mars and Venus, are markedly different from terrestrial (e.g., deuterium content is ≈5 and ≈100 times higher, respectively, it is far from certain that terrestrial life will thrive in these isotopic conditions. Here we found that Martian deuterium content negatively affected survival of shrimp in semi-closed biosphere on a year-long time scale. Moreover, the bacterium Escherichia coli grows slower at Martian isotopic compositions and even slower at Venus's compositions. Thus, the biological impact of varying stable isotope compositions needs to be taken into account when planning interplanetary missions.

  14. Isotopic Studies of O-O Bond Formation During Water Oxidation (SISGR)

    Energy Technology Data Exchange (ETDEWEB)

    Roth, Justine P. [Johns Hopkins Univ., Baltimore, MD (United States)

    2015-03-03

    Isotopic Studies of O-O Bond Formation During Water Oxidation (SISGR) Research during the project period focused primarily on mechanisms of water oxidation by structurally defined transition metal complexes. Competitive oxygen isotope fractionation of water, mediated by oxidized precursors or reduced catalysts together with ceric, Ce(IV), ammonium nitrate in aqueous media, afforded oxygen-18 kinetic isotope effects (O-18 KIEs). Measurement, calculation, and interpretation of O-18 KIEs, described in the accompanying report has important ramifications for the production of electricity and solar hydrogen (as fuel). The catalysis division of BES has acknowledged that understanding mechanisms of transition metal catalyzed water oxidation has major ramifications, potentially leading to transformation of the global economy and natural environment in years to come. Yet, because of program restructuring and decreased availability of funds, it was recommended that the Solar Photochemistry sub-division of BES would be a more appropriate parent program for support of continued research.

  15. Revisiting climate changes. Isotope studies open scientific windows to the past

    International Nuclear Information System (INIS)

    Gibson, John; Aggarwal, Pradeep

    2001-01-01

    present climate; Isotopes are being used to study the past climate from groundwater aquifers in Europe, Asia, Australia, Africa, and the Americas. Isotope-based research plays an important role in understanding past climate change. It is this understanding of past changes that holds the key to predicting future changes. These changes may not only influence global temperatures, but also energy needs, availability of drinking water, and adequate food supplies. In this sense, isotopes are invaluable tools that help scientists look 'back to the future' to develop options for minimizing adverse effects of the world's dynamic and changing climate

  16. Isotopic study of water exchange between atmosphere and biosphere at Changa Manga site in Pakistan

    International Nuclear Information System (INIS)

    Fazil, M.; Ali, M.; Latif, Z.; Butt, S.

    2012-01-01

    Study of water exchange between atmosphere and biosphere was initiated to understand the ties between these two spheres. Samples of leaves and stems of 23 woody plants along with soil from the surface and from the depth of 7 cm were collected from Changa Manga forest. Moisture content from these samples was extracted using the vacuum distillation method and analyzed for stable isotopes (/sup 18/O and /sup 2/H). Air moisture was also collected in the field. Isotopic data plotted long with the Local Meteoric Water Line (LMWL) indicates that /sup 18/O and /sup 2/H contents of moisture in the leaves of woody plants are higher than their respective stems. This behavior is due to the evaporative enrichment trend originating from the soil moisture in active root zone and also from the leaf surface. The stem samples did not show any significant variation in gamma /sup 18/O suggesting no significant evaporation from stems of big trees. Degree of enrichment of leave samples of woody plants indicated the species-specific effects in isotopes during transpiration. Pine and Eucalyptus leaves showed more variation in the isotopic contents as compared to other species. Temporal variations of /sup 18/O and /sup 2/H in the leaves indicated enriched isotopic values during hot and dry periods as compared to those during wet period (monsoon and winter rains) mainly due to higher transpiration rates at high temperature and low humidity. (orig./A.B.)

  17. Isotope effects in the non enzymic glycation of hemoglobin catalyzed by DPG

    International Nuclear Information System (INIS)

    Gil, Herminia; Uzcategui, Jorge

    1993-01-01

    The paradigmatic reaction of glucose with hemoglobin (Hb A o ) has been studied and is known to occur most rapidly at the N-terminal valine of the β-subunit. An initial, rapid imine formation is succeeded by slower Amadori rearrangement. Non enzymic glycation of Hb A o was studied in vitro in buffer Tris 10 mM in H 2 O and D 2 O, pH 7.3, pD 7.8 at 37 deg C at a fixed concentration of 2,3 diphosphoglycerate (DPG). The reaction exhibits identical rates in protium and deuterium oxides. When D-glucose-2-h is compared with D-glucose-2-d, the kinetic isotope effect for the DPG-dependent rate is 2.1 ± 0.3, while the DPG-independent rate constant shows no isotope effect (1.1 ± 0.1). The absence of a rate in isotopic water solvents shows that proton donation for solvent, lyons or DPG does not limit the rate. The substrate isotope effect of around 2 for the DPG kinetic term indicates that the proton abstraction step of the Amadori rearrangement by DPG is wholly or partially rate-limiting for this reaction. (author)

  18. Isotope effects in the non enzymic glycation of hemoglobin catalyzed by DPG

    Energy Technology Data Exchange (ETDEWEB)

    Gil, Herminia; Uzcategui, Jorge [Universidad de Los Andes, Merida (Venezuela). Dept. de Quimica

    1993-12-31

    The paradigmatic reaction of glucose with hemoglobin (Hb A{sub o}) has been studied and is known to occur most rapidly at the N-terminal valine of the {beta}-subunit. An initial, rapid imine formation is succeeded by slower Amadori rearrangement. Non enzymic glycation of Hb A{sub o} was studied in vitro in buffer Tris 10 mM in H{sub 2} O and D{sub 2} O, pH 7.3, pD 7.8 at 37 deg C at a fixed concentration of 2,3 diphosphoglycerate (DPG). The reaction exhibits identical rates in protium and deuterium oxides. When D-glucose-2-h is compared with D-glucose-2-d, the kinetic isotope effect for the DPG-dependent rate is 2.1 {+-} 0.3, while the DPG-independent rate constant shows no isotope effect (1.1 {+-} 0.1). The absence of a rate in isotopic water solvents shows that proton donation for solvent, lyons or DPG does not limit the rate. The substrate isotope effect of around 2 for the DPG kinetic term indicates that the proton abstraction step of the Amadori rearrangement by DPG is wholly or partially rate-limiting for this reaction. (author) 23 refs., 4 figs.

  19. Australis: AMS for ultra sensitive trace element and isotopic studies

    Energy Technology Data Exchange (ETDEWEB)

    Sie, S H; Suter, G F [Commonwealth Scientific and Industrial Research Organisation (CSIRO), North Ryde, NSW (Australia). Div. of Exploration Geoscience

    1994-12-31

    The accelerator mass spectrometer (AMS) at the CSIRO HIAF laboratory is being upgraded to enable in-situ measurements of ultratraces and isotopic-ratios in mineralogical applications. The upgraded system will include a microbeam Cs ion source which is designed to produce better than 50 micrometre diameter Cs beam to enable analyses of monomineralic grains. The Cs primary beam will be mass analysed in order to minimize contamination of the sample. The detection system will be upgraded to enable analyses of elements up to U, at 2 MV terminal voltage for charge states 4 and 5. The system will be known as AUSTRALIS: A.M.S. for Ultra Sensitive TRAce eLement and Isotopic Studies. An overview of the system and the anticipated applications in minerals exploration and mining research are presented. 4 refs., 1 fig.

  20. Australis: AMS for ultra sensitive trace element and isotopic studies

    Energy Technology Data Exchange (ETDEWEB)

    Sie, S.H.; Suter, G.F. [Commonwealth Scientific and Industrial Research Organisation (CSIRO), North Ryde, NSW (Australia). Div. of Exploration Geoscience

    1993-12-31

    The accelerator mass spectrometer (AMS) at the CSIRO HIAF laboratory is being upgraded to enable in-situ measurements of ultratraces and isotopic-ratios in mineralogical applications. The upgraded system will include a microbeam Cs ion source which is designed to produce better than 50 micrometre diameter Cs beam to enable analyses of monomineralic grains. The Cs primary beam will be mass analysed in order to minimize contamination of the sample. The detection system will be upgraded to enable analyses of elements up to U, at 2 MV terminal voltage for charge states 4 and 5. The system will be known as AUSTRALIS: A.M.S. for Ultra Sensitive TRAce eLement and Isotopic Studies. An overview of the system and the anticipated applications in minerals exploration and mining research are presented. 4 refs., 1 fig.

  1. Australis: AMS for ultra sensitive trace element and isotopic studies

    International Nuclear Information System (INIS)

    Sie, S.H.; Suter, G.F.

    1993-01-01

    The accelerator mass spectrometer (AMS) at the CSIRO HIAF laboratory is being upgraded to enable in-situ measurements of ultratraces and isotopic-ratios in mineralogical applications. The upgraded system will include a microbeam Cs ion source which is designed to produce better than 50 micrometre diameter Cs beam to enable analyses of monomineralic grains. The Cs primary beam will be mass analysed in order to minimize contamination of the sample. The detection system will be upgraded to enable analyses of elements up to U, at 2 MV terminal voltage for charge states 4 and 5. The system will be known as AUSTRALIS: A.M.S. for Ultra Sensitive TRAce eLement and Isotopic Studies. An overview of the system and the anticipated applications in minerals exploration and mining research are presented. 4 refs., 1 fig

  2. Excitation functions and isotopic effects in (n, p) reactions for stable nickel isotopes from reaction threshold to 20 MeV

    Energy Technology Data Exchange (ETDEWEB)

    Lalremruata, B. [Department of Physics, University of Pune, Ganeshkhind, Pune-411007, Maharashtra (India)], E-mail: marema@physics.unipune.ernet.in; Ganesan, S. [Reactor Physics Design Division, BARC, Mumbai 58 (India); Bhoraskar, V.N. [Department of Physics, University of Pune, Ganeshkhind, Pune-411007, Maharashtra (India)], E-mail: vnb@physics.unipune.ernet; Dhole, S.D. [Department of Physics, University of Pune, Ganeshkhind, Pune-411007, Maharashtra (India)], E-mail: sanjay@physics.unipune.ernet.in

    2009-05-01

    The excitation function for (n, p) reactions from reaction threshold to 20 MeV on five nickel isotopes viz; {sup 58}Ni, {sup 60}Ni, {sup 61}Ni, {sup 62}Ni and {sup 64}Ni were calculated using Talys-1.0 nuclear model code involving the fixed set of global parameters. A good agreement between the calculated and measured data is obtained with minimum effort on parameter fitting and only one free parameter called 'Shell damping factor'. This is of importance to the validation of nuclear model approaches with increased predictive power. The systematic decrease in (n, p) cross-sections with increasing neutron number in reactions induced by neutrons on isotopes of nickel is explained in terms of the proton separation energy and the pre-equilibrium model. The compound nucleus and pre-equilibrium reaction mechanism as well as the isotopic effects were also studied.

  3. Isotopes in oxidation reactions

    International Nuclear Information System (INIS)

    Stewart, R.

    1976-01-01

    The use of isotopes in the study of organic oxidation mechanisms is discussed. The help provided by tracer studies to demonstrate the two-equivalent path - hydride transfer, is illustrated by the examples of carbonium oxidants and the Wacker reaction. The role of kinetic isotope effects in the study of the scission of carbon-hydrogen bonds is illustrated by hydride abstraction, hydrogen atom abstraction, proton abstraction and quantum mechanical tunnelling. Isotopic studies on the oxidation of alcohols, carbonyl compounds, amines and hydrocarbons are discussed. The role of isotopes in the study of biochemical oxidation is illustrated with a discussion on nicotinamide and flavin coenzymes. (B.R.H.)

  4. Experimental study of hydrogen isotopes storage on titanium bed

    International Nuclear Information System (INIS)

    Vasut, Felicia; Zamfirache, Marius; Bornea, Anisia; Pearsica, Claudia; Bidica, Nicolae

    2002-01-01

    As known, the Nuclear Power Plant Cernavoda equipped with a Canadian reactor, of CANDU type, is the most powerful tritium source from Europe. On long term, due to a 6·10 16 Bq/year, Cernavoda area will be contaminated due to the increasing tritium quantity. Also, the continuous contamination of heavy water from the reactor, induces a reduction of moderation's capacity. Therefore, one considers that it is improperly to use heavy water if its activity level is higher than 40 Ci/kg in the moderator and 2 Ci/kg in the cooling fluid. For these reasons, we have developed a detritiation technology, based on catalytic isotopic exchange and cryogenic distillation. Tritium will be removed from the tritiated heavy water, so it appears the necessity of storage of tritium in a special vessel that can provide a high level of protection and safety of environment and personal. There several metals were tested as storage beds for hydrogen isotopes. One of the reference materials used for storage of hydrogen isotopes is uranium, a material with a great storage capacity, but unfortunately it is a radioactive metal and also can react with the impurities from the stored gas. Other metals and alloys as ZrCo, Ti, FeTi are also adequate as storage beds at normal temperature. The paper presents studies about the reaction between hydrogen and titanium used as storage bed for the hydrogen isotopes resulted after the detritiation of tritiated heavy water. The experiments that were carried out used protium and mixture of deuterium and protium at different storage parameters as process gas. (authors)

  5. Water isotopes and the Eocene. A tectonic sensitivity study

    Science.gov (United States)

    Legrande, A. N.; Roberts, C. D.; Tripati, A.; Schmidt, G. A.

    2009-04-01

    The early Eocene (54 Million years ago) is one of the warmest periods in the last 65 Million years. Its climate is postulated to have been the result of enhanced greenhouse gas concentration, with CO2 roughly 4 times pre-industrial and methane 7 times pre-industrial concentrations. One interesting feature of this period to emerge recently is the intermittent presence of fossilized Azolla, a type of freshwater fern, in the Arctic Ocean. Synchronous (within dating error) with this appearance were major changes in the restriction of the Arctic Ocean and the other global oceans. We investigate this time period using the Goddard Institute for Space Studies ModelE-R, a fully coupled atmosphere-ocean general circulation model that incorporates water isotopes throughout the hydrologic cycle, making it an ideal model to test hypotheses of past climate change and to compare to paleoclimate proxy data. We assess the impact of tectonic variability by using minimal and maximal levels of restriction for the Arctic Ocean seaways. We find that the modulation of connectivity of these basins dramatically alters global salinity distribution, leading to large changes in ocean circulation. Greater restriction of the Arctic Basin is associated with fresh and relatively warmer conditions. The same mechanisms responsible for this redistribution of salt also change the global distribution of water isotopes, and can alias (water isotope) proxy climate signals of warmth.

  6. Monopole Effect on Isotopes in Sn and Pb Regions

    Directory of Open Access Journals (Sweden)

    M. KHITER

    2016-11-01

    Full Text Available Abstract. When going toward in description of neutron-rich nuclei, the monopole field plays a determining role in the properties of the quasiparticle states and their interactions. Detailed theoretical in shell model calculations of the characteristics of the neutron-rich isotopes in 132Sn and 208Pb regions are performed using the monopole hamiltonien effect. Some modification mentioned in literatures of effectives interactions are introduced for evaluated the effective single-particle energies. Their effect show a successful and consistent description of excitation energies spectra of these nuclei.Keywords:Nuclear Structure, Monopole Hamiltonian, Odd-Odd Nuclei,Three body Effects, Similarity, 21.60.Cs; 27.60. +j; 21.30.Fe

  7. Study of hyperfine anomaly in 9,11Be isotopes

    International Nuclear Information System (INIS)

    Parfenova, Y.; Leclercq-Willain

    2005-01-01

    The study of the hyperfine anomaly of neutron rich nuclei, in particular, neutron halo nuclei, can give a very specific and unique way to measure their neutron distribution and confirm a halo structure. The hyperfine structure anomaly in Be + ions is calculated with a realistic electronic wave function, obtained as a solution of the Dirac equation. In the calculations, the Coulomb potential modified by the charge distribution of the clustered nucleus and three electrons in the configuration 1s 2 2s is used. The nuclear wave function for the 11 Be nucleus is obtained in the core + nucleon model, and that for the 9 Be nucleus is calculated in the three-cluster (α+α + n) model. The aim of this study is to test whether the hyperfine structure anomaly reflects an extended spatial structure of '1 1 Be. The results of the calculations are listed. ε BW is the hyperfine anomaly in the Bohr-Weisskopf effect and δ is the charge structure correction, μ is the calculated magnetic moment, and μ exp is the experimental value of the magnetic moment, Q and Q exp are the calculated and measured values of the quadrupole moment. The results for 9 Be are obtained with two different three-body wave functions (WF1 and WF2) showing the sensitivity of the calculations to the input parameters. The value of ε BW is sensitive to the weights of the states in the nuclear ground state wave function. The total hyperfine anomaly value εε BW +δ in 11 Be differs from that in 9 Be by 25%. This gives a measure of the accuracy of the hyperfine anomaly measurements needed to study the neutron distribution in the Be isotopes. (authors)

  8. Use of stable isotope techniques in soil organic matter studies

    International Nuclear Information System (INIS)

    Gerzabek, M.H.

    1998-01-01

    Plants differ distinctly in their C-isotopic composition. The largest differences occur between plant species with different photosynthetic pathways. C 3 - and C 4 -plants are differentiated by approximately 1.4% on the δ-scale (approx. -2.7% 13 C versus -1.3% 13 C). Modern elemental analyser - mass spectrometer combinations reach accuracies of at least 0.01% δ 13 C. Therefore, the difference between C 3 and C 4 plants is sufficient to be used for tracer studies. Several investigations of soil organic mater (SOM) turnover under field conditions were undertaken using the fact that the vegetation cover changed between C 3 and C 4 plants. The discrimination between SOM originating from indigenous vegetation (forest, C 3 ) and sugar cane (C 4 ) after 50 years of cropping introducing two SOM compartments of different stability was described. Another example is the change from prairie vegetation (C 4 ) to different C 3 -crops and the evaluation of the carbon origin at or near equilibrium. More recent studies use 15 N-labelled C 4 -plant residues or 13 C-labelled C 3 -plants to elucidate the fate of carbon and nitrogen in soils developed under C 3 -vegetation. Both in situ experiments and laboratory incubations were used to evaluate carbon and nitrogen fluxes from crop residues. Physical fractionation of bulk soil into particle sizes proved to be of advantage to follow short and long-term dynamics of crop residues within SOM. Changes in the natural abundance of 13 C and 15 N within soil profiles can elucidate leaching or mineralization of humic substances. Changes in the natural abundance of stable isotopes are also possible due to the application of organic manures, quantification, however is not easy because of the small isotopic differences between soil and manure carbon and nitrogen. 15 N labelling of soil nitrogen has been widely used in the last two decades to quantify biological nitrogen fixation. Considerable progress has been made due to the isotope dilution

  9. Dose formation and hematologic effects with prolonged internal exposure of rats by isotope 131I

    International Nuclear Information System (INIS)

    Sova, O.A.; Drozd, Yi.P.

    2013-01-01

    Processes in single dose formation and long-term domestic revenue 131 I in rats was investigated. Original method of estimating absorbed doses in hemacyte for macro-dosemeters indicators was proposed. Dose factors for hemacyte and the dynamics of the blood-forming organs doses for prolonged two cases of prolonged exposure was calculated. Hematologic effects were studied for two variants of entry of the isotope. Peculiarities of doses formation and identified hematological effects are discussed

  10. Molybdenum isotope variations in calc-alkaline lavas from the Banda arc, Indonesia: Assessing the effect of crystal fractionation in creating isotopically heavy continental crust

    NARCIS (Netherlands)

    Wille, Martin; Nebel, Oliver; Pettke, Thomas; Vroon, Pieter Z.; König, Stephan; Schoenberg, Ronny

    2018-01-01

    Recent studies report a large Mo isotope variability of up to 1‰ (expressed in δ98/95MoNIST3134) in convergent margin lavas. These isotopic variations have been associated with subduction zone processes and ultimately may account for heavy and variable isotope signatures in evolved continental

  11. Isotopic studies on oxidative methane coupling over samarium oxide

    International Nuclear Information System (INIS)

    Otsuka, Kiyoshi; Inaida, Masakatsu; Wada, Yuji; Komatsu, Takayuki; Morikawa, Akira

    1989-01-01

    The evident kinetic isotope effect was observed for the formations of ethylene and ethane through the oxidative coupling of methane on Sm 2 O 3 , when CH 4 and CD 4 were used as the reactants. Ethanes formed in the reaction of a mixture of CH 4 , CD 4 , and O 2 were C 2 H 6 , C 2 H 3 D 3 , and C 2 D 6 as major products. These results indicate that the rate-determining step of the reaction is abstraction of hydrogen from methane and that ethane is formed through the coupling of methyl intermediate. (author)

  12. Isotope study of groundwater in Beishan area, Gansu province

    International Nuclear Information System (INIS)

    Guo Yonghai; Liu Shufen; Yang Tianxiao

    2004-01-01

    Using the isotope techniques, the groundwater origin, evolution and circulation in the potential site of China's high-level waste repository are studied. The results indicate that both shallow groundwaters are and deep groundwaters in the site area are of meteoric origin. The shallow groundwaters are mainly recharged by modern and local precipitation, and the deep groundwaters are originated from regional history period with lower temperature. Through the study we can also understand that the deep underground is a very low-permeability system where the groundwater flow-rates are very low. (author)

  13. Contribution of isotopic data in cerebrospinal fluid (CSF) studies

    International Nuclear Information System (INIS)

    Askienazy, S.; Ducassou, D.

    The growing interest in isotopic CSF studies is explained by the fact that the mechanism and classification of hydrocephalus cases are based not only on anatomoclinical data but also on physiological information inaccessible by static image methods. This article shows the full importance of dynamic CSF research (ideal tracer: 111 In-DTPA); the possibilities of myeloscintigraphy to study the permeability of the medullary sub-arachnoid spaces (tracers used: sup(99m)Tc-DTPA in the liquid phase or xenon bubble technique in the gas phase); ventricular morphology; existence of meningeal gaps [fr

  14. Isotope effects in gas-phase chemical reactions and photodissociation processes: Overview

    International Nuclear Information System (INIS)

    Kaye, J.A.

    1992-01-01

    The origins of isotope effects in equilibrium and non-equilibrium chemical processes are reviewed. In non-equilibrium processes, attention is given to isotope effects in simple bimolecular reactions, symmetry-related reactions, and photodissociation processes. Recent examples of isotope effects in these areas are reviewed. Some indication of other scientific areas for which measurements and/or calculations of isotope effects are used is also given. Examples presented focus on neutral molecule chemistry and in many cases complement examples considered in greater detail in the other chapters of this volume

  15. Isotope exchange reactions on ceramic breeder materials and their effect on tritium inventory

    Energy Technology Data Exchange (ETDEWEB)

    Nishikawa, M; Baba, A [Kyushu Univ., Fukuoka (Japan). Faculty of Engineering; Kawamura, Y; Nishi, M

    1998-03-01

    Though lithium ceramic materials such as Li{sub 2}O, LiAlO{sub 2}, Li{sub 2}ZrO{sub 3}, Li{sub 2}TiO{sub 3} and Li{sub 4}SiO{sub 4} are considered as breeding materials in the blanket of a D-T fusion reactor, the release behavior of the bred tritium in these solid breeder materials has not been fully understood. The isotope exchange reaction rate between hydrogen isotopes in the purge gas and tritium on the surface of breeding materials have not been quantified yet, although helium gas with hydrogen or deuterium is planned to be used as the blanket purge gas in the recent blanket designs. The mass transfer coefficient representing the isotope exchange reaction between H{sub 2} and D{sub 2}O or that between D{sub 2} and H{sub 2}O in the ceramic breeding materials bed is experimentally obtained in this study. Effects of isotope exchange reactions on the tritium inventory in the bleeding blanket is discussed based on data obtained in this study where effects of diffusion of tritium in the grain, absorption of water in the bulk of grain, and adsorption of water on the surface of grain, together with two types of isotope exchange reactions are considered. The way to estimate the tritium inventory in a Li{sub 2}ZrO{sub 3} blanket used in this study shows a good agreement with data obtained in such in-situ experiments as MOZART, EXOTIC-5, 6 and TRINE experiments. (author)

  16. Shape coexistence in the lightest Tl isotopes studied by laser spectroscopy

    CERN Multimedia

    Herfurth, F; Antalic, S; Darby, I G; Venhart, M; Flanagan, K; Veselsky, M; Blaum, K; Radulov, D P; Beck, D; Kowalska, M; Schwarz, S; Chapman, R; Diriken, J V J; Lane, J; Rosenbusch, M

    This proposal aims at atomic spectroscopy studies of the very neutron-deficient isotopes $^{178-187}$Tl, at and far beyond the region of the neutron mid-shell at N=104, in which shape coexistence phenomena were investigated so far by particle and $\\gamma$-ray spectroscopy methods only. Our motivation for this proposal is as follows : \\\\\\\\ -These studies will provide direct data on magnetic dipole moment, spin, charge radii and deformations of these isotopes. The results will form a stringent test for our current understanding of the shape coexistence phenomena in the vicinity of the neutron mid-shell at N=104, where the relevant effects are expected to be the strongest (cf.shape staggering in the isotopes $^{181,183,185}$Hg). \\\\-The knowledge of the structure (configuration, spin, deformation) and whether one or two $\\beta$-decaying isomers are present in the parent isotopes $^{178,180,182}$Tl are crucial for understanding of the results of our recent studies of $\\beta$-delayed fission in the lightest thalli...

  17. Interim report on modeling studies of two-photon isotope separation

    International Nuclear Information System (INIS)

    Hwang, W.C.; Badcock, C.C.; Kamada, R.F.

    1975-01-01

    The two-photon or two-step dissociation method of laser induced isotope enrichment is being modeled for the HBrNO photochemical system. In the model, H 79 Br is selectively excited by resonance IR laser radiation and then dissociated by uv radiation. Selectively dissociated Br atoms are scavenged to form isotopically enriched BrNO and Br 2 . This model includes all kinetic and absorption processes found to be significant and the time-varying concentrations of any species involved in a significant process. Among these processes are vibrational energy transfer reactions (including isotopic exchange) involving HBr v = 0 - 3, rotational and translational (velocity) relaxation processes, dissociation of HBr in the v = 0 - 3 levels, and secondary chemical reactions of the dissociation products. The absorption and kinetic processes that are most important to 79 Br enrichment have been identified and the study of the effects on enrichment upon variation of external parameters (such as reactant pressure, ir or uv source intensity, and temperature) is in progress. Some preliminary results are: (1) intensity of the ir source is usually more important than the uv intensity; (2) chemical reactions are the dominant kinetic processes at lower pressures while energy transfer reactions dominate at higher pressures; (3) kinetic processes usually have greater effect on the absolute amount of enriched products; (4) isotopic abundance of 79 Br in the products can range from 0.55 to 0.80 for the conditions used in the model

  18. Aragonite-Calcite Inversion During Biogenic Carbonate Sampling: Considerations for Interpreting Isotopic Measurements in Paleoclimate Studies

    Science.gov (United States)

    Waite, A. J.; Swart, P. K.

    2011-12-01

    As aragonite is the metastable polymorph of calcium carbonate, it lends itself to monotropic inversion to the more stable polymorph, calcite. This inversion is possible through an increase in the temperature and pressure conditions to which the sample is exposed and, although first noted nearly a century ago, has been primarily discussed in the context of sample roasting prior to analyses in paleoclimatological studies. Over the last several decades, however, researchers have found evidence to suggest that the friction associated with the sampling of biogenic carbonates via milling/drilling also induces inversion. Furthermore, this inversion may be associated with a shift in measured oxygen isotopic values and ultimately have significant implications for the interpretation of paleoclimatic reconstructions. Despite this, the isotopic heterogeneity of biogenic aragonite skeletons makes the effects of inversion challenging to test and the subject remains underrepresented in the literature. Here we present a first order study into the effects of milling on both the mineralogy and isotopic compositions measured in sclerosponges, corals, and molluscs. X-Ray diffraction analysis of samples hand ground with a mortar and pestle reveal 100% aragonitic skeletons. Conversely, samples milled with a computerized micromill show measurable inversion to calcite. On average, percent inversion of aragonite to calcite for individual specimens was 15% for sclerosponges, 16% for corals, and 9% for molluscs. Isotopic data from these specimens show that the higher the percentage of aragonite inverted to calcite, the more depleted the measured oxygen isotopic values. In the largest of the datasets (sclerosponges), it is evident that the range of oxygen isotope values from milled samples (-0.02 to +0.84%) exceeds the range in values for those samples which were hand ground and showed no inversion (+0.53 to +0.90%). This, coupled with the strong correlation between the two variables

  19. Study of groundwater salinization in Chaj Doab using environmental isotopes

    International Nuclear Information System (INIS)

    Hussain, S.D.; Sajjid, M.I.; Akram, W.; Ahmad, M.; Rafiq, M.

    1991-09-01

    Environmental isotopes and chemical composition of water have been used to study the origin of groundwater salinity in Chaj Doab. Three important possible processes of salinization i.e. enrichment of salt content of water by evaopration, mixing with connate marine water and dissolution of salts from soil sediments have been investigated. No evidence for mixing with connate maine water could be found. The process of evaporation too does not seem to apply any significant role in salinization of groundwater. The dissolution of salts from soil sediments appears as dominant mechanism for increasing the salt content of water in this area. (author)

  20. Chemical and environmental isotopes study of precipitation in Syria

    International Nuclear Information System (INIS)

    Al-Charideh, A.; Abou Zakhem, B.

    2009-02-01

    Chemical and isotopic compositions of monthly precipitation were monitored at 12 stations distributed over the entire region in Syria for a period of 4 years from December 1999 to April 2003. Amount of precipitation and mean air temperature of rain monthly were also recorded. The conductivity of rain waters varies between 35 μ/cm in the mountainous stations and 336 μ/cm at Deir Az-Zor station. Excepted Tartous station, the mean value of Cl in the rainfall in all station is 3.8 mg/l. The seasonal variations in δ 18 O are smaller at west stations than to the east stations due to low seasonal temperature variations. All stations are characterized by water lines with slopes significantly lower than GMWL, except Bloudan, suggesting the influence of local factors on the isotopic composition of the precipitation. d-excess values decrease from 19% in the western part to 13% in the eastern part of Syria, indicating the influence of the precipitation generated by the air masses coming from the Mediterranean Sea over Syria. A reliable altitude effect represent by depletion of heavy stable isotopes of about -0.21, and -1.47, per 100 m elevation of 18 O and δ 2 H, respectively. Monthly tritium activity and seasonal variations pattern are low in the west stations than at the east stations. The weighted mean tritium values are between 3 to 9 TU during 2000-2003, and it is increasing with distance from the Syrian coast by 1 TU /100 Km. (author)

  1. Quantum tunneling observed without its characteristic large kinetic isotope effects.

    Science.gov (United States)

    Hama, Tetsuya; Ueta, Hirokazu; Kouchi, Akira; Watanabe, Naoki

    2015-06-16

    Classical transition-state theory is fundamental to describing chemical kinetics; however, quantum tunneling is also important in explaining the unexpectedly large reaction efficiencies observed in many chemical systems. Tunneling is often indicated by anomalously large kinetic isotope effects (KIEs), because a particle's ability to tunnel decreases significantly with its increasing mass. Here we experimentally demonstrate that cold hydrogen (H) and deuterium (D) atoms can add to solid benzene by tunneling; however, the observed H/D KIE was very small (1-1.5) despite the large intrinsic H/D KIE of tunneling (≳ 100). This strong reduction is due to the chemical kinetics being controlled not by tunneling but by the surface diffusion of the H/D atoms, a process not greatly affected by the isotope type. Because tunneling need not be accompanied by a large KIE in surface and interfacial chemical systems, it might be overlooked in other systems such as aerosols or enzymes. Our results suggest that surface tunneling reactions on interstellar dust may contribute to the deuteration of interstellar aromatic and aliphatic hydrocarbons, which could represent a major source of the deuterium enrichment observed in carbonaceous meteorites and interplanetary dust particles. These findings could improve our understanding of interstellar physicochemical processes, including those during the formation of the solar system.

  2. Charge exchange effect on laser isotope separation of atomic uranium

    International Nuclear Information System (INIS)

    Niki, Hideaki; Izawa, Yasukazu; Otani, Hiroyasu; Yamanaka, Chiyoe

    1982-01-01

    Uranium isotope separating experiment was performed using the two-step photoionization technique with dye laser and nitrogen laser by heating uranium metal with electron beam and producing atomic beam using generated vapour. The experimental results are described after explaining the two-step photoionization by laser, experimental apparatus, the selection of exciting wavelength and others. Enrichment factor depends largely on the spectrum purity of dye laser which is the exciting source. A large enrichment factor of 48.3 times was obtained for spectrum width 0.03A. To put the uranium isotope separation with laser into practice, the increase of uranium atomic density is considered to be necessary for improving the yield. Experimental investigation was first carried out on the charge exchange effect that seems most likely to affect the decrease of enrichment factor, and the charge exchange cross-section was determined. The charge exchange cross-section depends on the relative kinetic energy between ions and atoms. The experimental result showed that the cross-section was about 5 x 10 -13 cm 2 at 1 eV and 10 -13 cm 2 at 90 eV. These values are roughly ten times as great as those calculated in Lawrence Livermore Laboratory, and it is expected that they become the greatest factor for giving the upper limit of uranium atomic density in a process of practical application. (Wakatsuki, Y.)

  3. Introduction to chemistry and applications in nature of mass independent isotope effects special feature.

    Science.gov (United States)

    Thiemens, Mark H

    2013-10-29

    Stable isotope ratio variations are regulated by physical and chemical laws. These rules depend on a relation with mass differences between isotopes. New classes of isotope variation effects that deviate from mass dependent laws, termed mass independent isotope effects, were discovered in 1983 and have a wide range of applications in basic chemistry and nature. In this special edition, new applications of these effects to physical chemistry, solar system origin models, terrestrial atmospheric and biogenic evolution, polar paleo climatology, snowball earth geology, and present day atmospheric sciences are presented.

  4. Oxygen isotope fractionation effects in soil water via interaction with cations (Mg, Ca, K, Na) adsorbed to phyllosilicate clay minerals

    Science.gov (United States)

    Oerter, Erik; Finstad, Kari; Schaefer, Justin; Goldsmith, Gregory R.; Dawson, Todd; Amundson, Ronald

    2014-07-01

    In isotope-enabled hydrology, soil and vadose zone sediments have been generally considered to be isotopically inert with respect to the water they host. This is inconsistent with knowledge that clay particles possessing an electronegative surface charge and resulting cation exchange capacity (CEC) interact with a wide range of solutes which, in the absence of clays, have been shown to exhibit δ18O isotope effects that vary in relation to the ionic strength of the solutions. To investigate the isotope effects caused by high CEC clays in mineral-water systems, we created a series of monominerallic-water mixtures at gravimetric water contents ranging from 5% to 32%, consisting of pure deionized water of known isotopic composition with homoionic (Mg, Ca, Na, K) montmorillonite. Similar mixtures were also created with quartz to determine the isotope effect of non-, or very minimally-, charged mineral surfaces. The δ18O value of the water in these monominerallic soil analogs was then measured by isotope ratio mass spectrometry (IRMS) after direct headspace CO2 equilibration. Mg- and Ca-exchanged homoionic montmorillonite depleted measured δ18O values up to 1.55‰ relative to pure water at 5% water content, declining to 0.49‰ depletion at 30% water content. K-montmorillonite enriched measured δ18O values up to 0.86‰ at 5% water content, declining to 0.11‰ enrichment at 30% water. Na-montmorillonite produces no measureable isotope effect. The isotope effects observed in these experiments may be present in natural, high-clay soils and sediments. These findings have relevance to the interpretation of results of direct CO2-water equilibration approaches to the measurement of the δ18O value of soil water. The adsorbed cation isotope effect may bear consideration in studies of pedogenic carbonate, plant-soil water use and soil-atmosphere interaction. Finally, the observed isotope effects may prove useful as molecular scale probes of the nature of mineral

  5. Deuterium isotope effects on 13C chemical shifts of 10-Hydroxybenzo[h]quinolines

    DEFF Research Database (Denmark)

    Hansen, Poul Erik; Kamounah, Fadhil S.; Gryko, Daniel T.

    2013-01-01

    Deuterium isotope effects on 13C-NMR chemical shifts are investigated in a series of 10-hydroxybenzo[h]quinolines (HBQ’s) The OH proton is deuteriated. The isotope effects on 13C chemical shifts in these hydrogen bonded systems are rather unusual. The formal four-bond effects are found to be nega...

  6. Isotopic study of water exchange between atmosphere and biosphere at different sites in Pakistan

    International Nuclear Information System (INIS)

    Fazil, M.; Ali, M.; Ahmad, M.; Latif, Z.; Butt, S.; Choudhry, M.A.; Qureshiu, R.M.

    2009-11-01

    Study of Isotopic behavior of water exchange between atmosphere and biosphere was initiated to understand the ties between these two spheres. This report presents the isotopic data of delta/sup 18/O and delta /sup 2/H in the water contents of leaves and stems in different plant species along with soil moisture. Non woody plants of wheat and grass along with soil from the surface and from the depth of 7 cm were collected during January 2005 to April 2005. Woody plants of many species were sampled from two sites near Islamabad and Lahore. Air moisture was also collected in the field. Moisture contents from these samples were extracted using the vacuum distillation method and analyzed for /sup 18/O and /sup 2/H Data depicts that the /sup 18/O and /sup 2/H of moisture in the leaves of non- woody and woody plants are much more enriched than their respective stems. This behavior is due to the evaporative enrichment trend originating from the soil moisture in the active root zone and also from the surface of the leaf. Degree of enrichment depends on the size of leaves, temperature, wind speed, stomatal resistance, soil chemistry and humidity. Significant evaporation effects in the moisture of grass stems are due to photosynthesis. Reflection of typical isotopic values of individual rain events is also observed in soil, plant water and atmospheric moisture, which can be used for studying water-use efficiency. Leaves of woody plants have relatively depleted/sup 18/O values during wet (monsoon) period mainly due to retardation of fractionation resulting from higher humidity. The stem samples do not show any significant variation in delta/sup 18/O indicating no evaporation from stems of big trees. Degree of enrichment of leave samples of woody plants also indicates the species- specific effects in oxygen and hydrogen isotopes during transpiration. Pine and Eucalyptus leaves show more variation in the isotopic contents as compared to other species. (author)

  7. Microscopic study of neutron-rich dysprosium isotopes

    International Nuclear Information System (INIS)

    Vargas, Carlos E.; Velazquez, Victor; Lerma, Sergio

    2013-01-01

    Microscopic studies in heavy nuclei are very scarce due to large valence spaces involved. This computational problem can be avoided by means of the use of symmetry-based models. Ground-state, γ and β bands, and their B(E2) transition strengths in 160-168 Dy isotopes, are studied in the framework of the pseudo-SU(3) model which includes the preserving symmetry Q . Q term and the symmetry-breaking Nilsson and pairing terms, systematically parametrized. Additionally, three rotor-like terms are considered, whose free parameters, fixed for all members of the chain, are used to fine tune the moment of inertia of rotational bands and the band head of γ and β bands. The model succesfully describes in a systematic way rotational features in these nuclei and allows to extrapolate toward the midshell nucleus 170 Dy. The results presented show that it is possible to study a full chain of isotopes or isotones in the region with the present model. (orig.)

  8. Microscopic study of neutron-rich dysprosium isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Vargas, Carlos E. [Universidad Veracruzana, Facultad de Fisica e Inteligencia Artificial, Xalapa (Mexico); Universidad Nacional Autonoma de Mexico, Facultad de Ciencias, Apartado Postal 70-542, Mexico D.F. (Mexico); Velazquez, Victor [Universidad Nacional Autonoma de Mexico, Facultad de Ciencias, Apartado Postal 70-542, Mexico D.F. (Mexico); Lerma, Sergio [Universidad Veracruzana, Facultad de Fisica e Inteligencia Artificial, Xalapa (Mexico)

    2013-01-15

    Microscopic studies in heavy nuclei are very scarce due to large valence spaces involved. This computational problem can be avoided by means of the use of symmetry-based models. Ground-state, {gamma} and {beta} bands, and their B(E2) transition strengths in {sup 160-168}Dy isotopes, are studied in the framework of the pseudo-SU(3) model which includes the preserving symmetry Q . Q term and the symmetry-breaking Nilsson and pairing terms, systematically parametrized. Additionally, three rotor-like terms are considered, whose free parameters, fixed for all members of the chain, are used to fine tune the moment of inertia of rotational bands and the band head of {gamma} and {beta} bands. The model succesfully describes in a systematic way rotational features in these nuclei and allows to extrapolate toward the midshell nucleus {sup 170}Dy. The results presented show that it is possible to study a full chain of isotopes or isotones in the region with the present model. (orig.)

  9. Utilizing Stable Isotopes and Isotopic Anomalies to Study Early Solar System Formation Processes

    Science.gov (United States)

    Simon, Justin

    2017-01-01

    Chondritic meteorites contain a diversity of particle components, i.e., chondrules and calcium-, aluminum-rich refractory inclusions (CAIs), that have survived since the formation of the Solar System. The chemical and isotopic compositions of these materials provide a record of the conditions present in the protoplanetary disk where they formed and can aid our understanding of the processes and reservoirs in which solids formed in the solar nebula, an important step leading to the accretion of planetesimals. Isotopic anomalies associated with nucleosynthetic processes are observed in these discrete materials, and can be compared to astronomical observations and astrophysical formation models of stars and more recently proplyds. The existence and size of these isotopic anomalies are typically thought to reflect a significant state of isotopic heterogeneity in the earliest Solar System, likely left over from molecular cloud heterogeneities on the grain scale, but some could also be due to late stellar injection. The homogenization of these isotopic anomalies towards planetary values can be used to track the efficiency and timescales of disk wide mixing,

  10. Isotopic shifts in chemical exchange systems. 1. Large isotope effects in the complexation of Na+ isotopes by macrocyclic polyethers

    International Nuclear Information System (INIS)

    Knoechel, A.; Wilken, R.D.

    1981-01-01

    The complexation of 24 Na + and 22 Na + by 18 of the most widely used macrocyclic polyethers (crown ethers and monocyclic and bicyclic aminopolyethers) has been investigated in view of possible equilibrium isotope shifts. Solvated salts and polyether complexes were distributed differently into two phases and isotope ratios determined in both phases. Chloroform/water systems were shown to be particularly suitable to the investigations allowing favorable distribution for Na + and 13 of the 18 polyethers employed. With crown ethers 24 Na + enrichment varied from nonsignficant values (for large crown ethers) up to 3.1 +- 0.4% (18-crown-6). In the case of bicyclic aminopolyethers, ligands with cages of optimum size to accommodate Na + showed 24 Na + enrichment between O (nonsignificant) (2.2/sub B/2./sub B/) and 5.2 +- 1.8% (2.2.1). In contrast, for 2.2.2. and its derivatives, being too large for Na + , 22 Na + enrichment varying from O (nonsignificant) (2.2.2.p) up to 5.4 +- 0.5% (2.2.2.) has been observed. These values are remarkably high. They are explained by different bonding in solvate structure and polyether complex by using the theoretical approach of Bigeleisen

  11. Chemical and environmental isotope study of precipitation in Syria

    International Nuclear Information System (INIS)

    Kattan, Z.

    1999-01-01

    Waters from a network of rainfall collection covering mine meteorological stations distributed mainly in the western part of Syria have been assayed using chemical and environmental isotope techniques for a period of 5 months from Dec. 1989 to Apr. 1990. The chemistry of rain waters falling over the mountainous stations shows a low solute concentration (20-105 mg 1 -1 ) compared with those falling over the coastal and anterior stations (50-210 mg 1 -1 ). The rain waters was generally characterized by a high deuterium excess (d=19%) compared with that of typical global meteoric waters (d=10%). The estimated deuterium excess is lower than that for the eastern Mediterranean meteoric waters (d=22%). The altitude effect is shown up by a depletion of heavy stable isotopes of about - 0.23% and -1.65% per 100 m elevation of δ 1 8 O and δD, respectively. The spatial distribution pattern of tritium contents shows a gradual build up with increasing distance from the Syrian coast. The weighted mean tritium content in rain waters falling over the country is estimated to amount to 9.5 tritium units (TU) during the period of observation. (author)

  12. Tungsten isotopic compositions of iron meteorites: Chronological constraints vs. cosmogenic effects

    Science.gov (United States)

    Markowski, A.; Quitté, G.; Halliday, A. N.; Kleine, T.

    2006-02-01

    High-precision W isotopic compositions are presented for 35 iron meteorites from 7 magmatic groups (IC, IIAB, IID, IIIAB, IIIF, IVA, and IVB) and 3 non-magmatic groups (IAB, IIICD, and IIE). Small but resolvable isotopic variations are present both within and between iron meteorite groups. Variations in the 182W/ 184W ratio reflect either time intervals of metal-silicate differentiation, or result from the burnout of W isotopes caused by a prolonged exposure to galactic cosmic rays. Calculated apparent time spans for some groups of magmatic iron meteorites correspond to 8.5 ± 2.1 My (IID), 5.1 ± 2.3 My (IIAB), and 5.3 ± 1.3 My (IVB). These time intervals are significantly longer than those predicated from models of planetesimal accretion. It is shown that cosmogenic effects can account for a large part of the W isotopic variation. No simple relationship exists with exposure ages, compromising any reliable method of correction. After allowance for maximum possible cosmogenic effects, it is found that there is no evidence that any of the magmatic iron meteorites studied here have initial W isotopic compositions that differ from those of Allende CAIs [ ɛ182W = - 3.47 ± 0.20; [T. Kleine, K. Mezger, H. Palme, E. Scherer and C. Münker, Early core formation in asteroids and late accretion of chondrite parent bodies: evidence from 182Hf- 182W in CAIs, metal-rich chondrites and iron meteorites, Geochim. Cosmochim. Acta (in press)]. Cosmogenic corrections cannot yet be made with sufficient accuracy to obtain highly precise ages for iron meteorites. Some of the corrected ages nevertheless require extremely early metal-silicate segregation no later than 1 My after formation of CAIs. Therefore, magmatic iron meteorites appear to provide the best examples yet identified of material derived from the first planetesimals that grew by runaway growth, as modelled in dynamic simulations. Non-magmatic iron meteorites have a more radiogenic W isotopic composition than magmatic

  13. Carnivore specific bone bioapatite and collagen carbon isotope fractionations: Case studies of modern and fossil grey wolf populations

    Science.gov (United States)

    Fox-Dobbs, K.; Wheatley, P. V.; Koch, P. L.

    2006-12-01

    Stable isotope analyses of modern and fossil biogenic tissues are routinely used to reconstruct present and past vertebrate foodwebs. Accurate isotopic dietary reconstructions require a consumer and tissue specific understanding of how isotopes are sorted, or fractionated, between trophic levels. In this project we address the need for carnivore specific isotope variables derived from populations that are ecologically well- characterized. Specifically, we investigate the trophic difference in carbon isotope values between mammalian carnivore (wolf) bone bioapatite and herbivore (prey) bone bioapatite. We also compare bone bioapatite and collagen carbon isotope values collected from the same individuals. We analyzed bone specimens from two modern North American grey wolf (Canis lupus) populations (Isle Royale National Park, Michigan and Yellowstone National Park, Wyoming), and the ungulate herbivores that are their primary prey (moose and elk, respectively). Because the diets of both wolf populations are essentially restricted to a single prey species, there were no confounding effects due to carnivore diet variability. We measured a trophic difference of approximately -1.3 permil between carnivore (lower value) and herbivore (higher value) bone bioapatite carbon isotope values, and an average inter-tissue difference of 5.1 permil between carnivore bone collagen (lower value) and bioapatite (higher value) carbon isotope values. Both of these isotopic differences differ from previous estimates derived from a suite of African carnivores; our carnivore-herbivore bone bioapatite carbon isotope spacing is smaller (-1.3 vs. -4.0 permil), and our carnivore collagen-bioapatite carbon difference is larger (5.1 vs. 3.0 permil). These discrepancies likely result from comparing values measured from a single hypercarnivore (wolf) to average values calculated from several carnivore species, some of which are insectivorous or partly omnivorous. The trophic and inter

  14. Mechanism of the flame ionization detector. II. Isotope effects and heteroatom effects

    DEFF Research Database (Denmark)

    Holm, Torkil

    1997-01-01

    The relative molar flame ionization detecton (FID) response (RMR) for a hydrocarbon does not change when deuterium is substituted for hydrogen. The exception is methane for which an inverse deuterium effect of 3..5% is observed for tetradeuteriomethane. [13C]Methane shows an inverse isotope effect...... of 2%. The reason for the small or non-existent isotope effects is that H/2H exchange takes place in the pre-combustion hydrogenolysis in the flame. This was shown by taking samples from the lower part of the flame by means of a fused silica capillary probe. By the same technique the hydrogenolytic...

  15. NMR spectroscopic determination of an equilibrium isotope effect on the hydration of cobalt(II)

    International Nuclear Information System (INIS)

    Evilia, R.F.; Saunders, M.

    1985-01-01

    A recently reported NMR method for the measurement of deuterium equilibrium isotope effects is applied to the hydration of the paramagnetic cobalt(II) ion. An isotope effect of about 1.3% is measured. A substantial difference between the intrinsic shift of H 2 O and D 2 O when coordinated to cobalt is also measured

  16. Electrochemical H-D isotope effect at metal-perovskite proton conductor interfaces

    DEFF Research Database (Denmark)

    Kek, D.; Bonanos, N.

    1999-01-01

    The H-D isotope effect on the electrode kinetics of a metal-proton conductor interface has been investigated. The current-voltage behaviour depends on the nature of the electrode (Ni, Ag), the atmosphere (H(2), D(2)), the partial pressures of the gases, and the temperature. The isotope effect was...

  17. Intra-event isotope and raindrop size data of tropical rain reveal effects concealed by event averaged data

    Science.gov (United States)

    Managave, S. R.; Jani, R. A.; Narayana Rao, T.; Sunilkumar, K.; Satheeshkumar, S.; Ramesh, R.

    2016-08-01

    Evaporation of rain is known to contribute water vapor, a potent greenhouse gas, to the atmosphere. Stable oxygen and hydrogen isotopic compositions (δ18O and, δD, respectively) of precipitation, usually measured/presented as values integrated over rain events or monthly mean values, are important tools for detecting evaporation effects. The slope ~8 of the linear relationship between such time-averaged values of δD and δ18O (called the meteoric water line) is widely accepted as a proof of condensation under isotopic equilibrium and absence of evaporation of rain during atmospheric fall. Here, through a simultaneous investigation of the isotopic and drop size distributions of seventeen rain events sampled on an intra-event scale at Gadanki (13.5°N, 79.2°E), southern India, we demonstrate that the evaporation effects, not evident in the time-averaged data, are significantly manifested in the sub-samples of individual rain events. We detect this through (1) slopes significantly less than 8 for the δD-δ18O relation on intra-event scale and (2) significant positive correlations between deuterium excess ( d-excess = δD - 8*δ18O; lower values in rain indicate evaporation) and the mass-weighted mean diameter of the raindrops ( D m ). An estimated ~44 % of rain is influenced by evaporation. This study also reveals a signature of isotopic equilibration of rain with the cloud base vapor, the processes important for modeling isotopic composition of precipitation. d-excess values of rain are modified by the post-condensation processes and the present approach offers a way to identify the d-excess values least affected by such processes. Isotope-enabled global circulation models could be improved by incorporating intra-event isotopic data and raindrop size dependent isotopic effects.

  18. Water uptake in woody riparian phreatophytes of the southwestern United States: a stable isotope study

    International Nuclear Information System (INIS)

    Busch, D.E.; Ingraham, N.L.; Smith, S.D.

    1992-01-01

    Alluvial forest associations are often dominated by woody phreatophytes, plants that are tightly linked to aquifers for water uptake. Anthropogenic hydrological alterations (e.g., water impoundment or diversion) are of clear importance to riparian ecosystem function. Because decreased frequency of flooding and depression of water tables may, in effect, sever riparian plants from their natural water sources, research was undertaken to determine water uptake patterns for the dominant native and introduced woody taxa of riparian plant communities of the southwestern United States. At floodplain study sites along the Bill Williams and lower Colorado Rivers (Arizona, USA), naturally occurring D and 18 O were used to distinguish among potential water sources. Isotopic ratios from potential uptake locations were compared to water extracted from the dominant woody taxa of the study area (Populus fremontii, Salix gooddingii, and Tamarix ramosissima) to elucidate patterns of water absorption. Isotopic composition of water obtained from sapwood cores did not differ significantly from heartwood or branch water, suggesting that heartwood water exchange, stem capacitance, and phloem sap mixing may be inconsequential in actively transpiring Salix and Populus. There was evidence for close hydrologic linkage of river, ground, and soil water during the early part of the growing season. Surface soils exhibited D enrichment due to cumulative exposure to evaporation as the growing season progressed. Isotopic ratios of water extracted from Populus and Salix did not exhibit isotopic enrichment and were not significantly different from groundwater or saturated soil water sources, indicating a phreatophytic uptake pattern. Associations of isotopic ratios with water relations parameters indicated high levels of canopy evaporation and possible use of moisture from unsaturated alluvial soils in addition to groundwater in Tamarix. (author)

  19. Application of isotopic techniques for study of ground water from karstic areas. 1. Origin of waters

    International Nuclear Information System (INIS)

    Feurdean, Victor; Feurdean, Lucia

    2000-01-01

    Environmental stable isotope method was used for study of ground water from karst of NE Dobrogea. Study area is in the vicinity of Danube Delta (declared in 1990 by UNESCO the Reserve of Biosphere) and presents scientific and ecological interest. Measurements of deuterium content of ground water show that waters are meteoric in origin, but at the same time the results showed that the water from two sampling points could not originate from local ground water and have their recharge area at high altitude and a considerable distance. According to the δD values the following categories of waters were established: - waters depleted in deuterium (δD 0 / 00 ) relative to δD values of surface and ground water in the geographic area from which they were collected. They represent most probably the intrusion of isotopically light water from high altitude sites (higher than 1000 m) through network of highly permeable karst channels. The discharge of this component of aquifer occurs both by conduct flow and by diffuse flow; - Waters tributaries to the Danube River (δD > -75 0 / 00 ) that have a small time variability of δD values; - Local infiltration waters, situated in the West side of the investigated area towards the continental platform of the Dobrogea (δD > -70 0 / 00 ). They present high time variability of δD values, due to distinct seasonal effects; - Waters originated in mixing processes between the waters with different isotopic content. The endmember one is heavier isotopic water that belongs to local recharged waters (local infiltration waters and waters tributary to Danube river) while the other endmember is the isotopically light water. (authors)

  20. Delayed Particle Study of Neutron Rich Lithium Isotopes

    CERN Multimedia

    Marechal, F; Perrot, F

    2002-01-01

    We propose to make a systematic complete coincidence study of $\\beta$-delayed particles from the decay of neutron-rich lithium isotopes. The lithium isotopes with A=9,10,11 have proven to contain a vast information on nuclear structure and especially on the formation of halo nuclei. A mapping of the $\\beta$-strength at high energies in the daughter nucleus will make possible a detailed test of our understanding of their structure. An essential step is the comparison of $\\beta$-strength patterns in $^{11}$Li and the core nucleus $^{9}$Li, another is the full characterization of the break-up processes following the $\\beta$-decay. To enable such a measurement of the full decay process we will use a highly segmented detection system where energy and emission angles of both charged and neutral particles are detected in coincidence and with high efficiency and accuracy. We ask for a total of 30 shifts (21 shifts for $^{11}$Li, 9 shifts $^{9}$Li adding 5 shifts for setting up with stable beam) using a Ta-foil target...

  1. Modeling study of vibrational photochemical isotope enrichment. [HBr + Cl/sub 2/; HCl + Br/sub 2/

    Energy Technology Data Exchange (ETDEWEB)

    Badcock, C.C.; Hwang, W.C.; Kalsch, J.F.

    1978-09-29

    Chemical kinetic modeling studies of vibrational-photochemical isotope enrichment have been performed on two systems: Model (I), H/sup 79/Br(H/sup 81/Br) + Cl/sub 2/ and, Model (II), H/sup 37/Cl(H/sup 35/Cl) + Br. Pulsed laser excitation was modeled to the first excited vibrational level of H/sup 79/Br in Model I and the first and second excited vibrational levels of both HCl isotopes in Model II. These are prototype systems of exoergic (Model I) and endoergic (Model II) reactions. The effects on enrichment of varying the external parameters (pressure, laser intensity) and the internal parameters (rate constants for V-V exchange and excited-state reactions) were examined. Studies of these prototype systems indicate that a favorable reaction for enrichment, with isotopically-specific excitation and a significantly accelerated vibrationally-excited-state reaction should have the following properties: the reaction from v = 0 should be only moderately exoergic, and the most favorable coreactant should be a polyatomic species, such as alkyl radical. Direct excitation of the reacting vibrational level is at least an order of magnitude more favorable for enrichment than is population by energy transfer. Enrichment of the minor isotope by these processes is more effective than is major isotope enrichment. Within limits, increased laser intensity is beneficial. However, for sequential excitation of a second vibrational level, major isotope enrichment can be diminished by high populations of the first vibrational level.

  2. Effect of density of state on isotope effect exponent of two-band superconductors

    International Nuclear Information System (INIS)

    Udomsamuthirun, P.; Kumvongsa, C.; Burakorn, A.; Changkanarth, P.; Yoksan, S.

    2005-01-01

    The exact formula of T c 's equation and the isotope effect exponent of two-band s-wave superconductors in weak-coupling limit are derived by considering the influence of two kinds of density of state: constant and van Hove singularity. The paring interaction in each band consisted of two parts: the electron-phonon interaction and non-electron-phonon interaction are included in our model. We find that the interband interaction of electron-phonon show more effect on isotope exponent than the intraband interaction and the isotope effect exponent with constant density of state can fit to experimental data, MgB 2 and high-T c superconductor, better than van Hove singularity density of state

  3. Study on the flow state of groundwater by isotope tracer

    International Nuclear Information System (INIS)

    Lin Tong; Chen Jiansheng; Chen Liang

    2008-01-01

    Radioisotope logging technique is an effective method to evaluate groundwater movement. Moving with the water, the isotope tracer distributes differently in different flow states. According to the depth and time distribution of radioactivity, flow state of the groundwater can be determined. In this paper, different flow states, i.e. laminar flow, turbulent flow and mixing flow, are analyzed, and calculation of the flow velocity is discussed. Also, we discuss how to distinguish the laminar flow part and turbulent part in a mixing flow. If one judges the flow state incorrectly, the error of flow velocity will be huge, hence the importance of flow state analysis. Finally, some problems in the practical projects and measuring methods are concluded. (authors)

  4. Isotope effect and deuterium excess parameter revolution in ice and snow melt

    International Nuclear Information System (INIS)

    Yin Guan; Ni Shijun; Fan Xiao; Wu Hao

    2003-01-01

    The change of water isotope composition actually is a integrated reaction depending on the change of environment. The ice and snow melt of different seasons in high mountain can obviously influence the change of isotope composition and deuterium excess parameter of surface flow and shallow groundwater. To know the isotopic fractionation caused by this special natural background, explore its forming and evolvement, is unusually important for estimating, the relationship between the environment, climate and water resources in an area. Taking the example of isotope composition of surface flow and shallow groundwater in Daocheng, Sichuan, this paper mainly introduced the changing law of isotope composition and deuterium excess parameter of surface flow and hot-spring on conditions of ice and snow melt with different seasons in high mountain; emphatically discussed the isotope effect and deuterium excess parameter revolution in the process of ice and snow melting and its reason. (authors)

  5. Isotope labeling for NMR studies of macromolecular structure and interactions

    International Nuclear Information System (INIS)

    Wright, P.E.

    1994-01-01

    Implementation of biosynthetic methods for uniform or specific isotope labeling of proteins, coupled with the recent development of powerful heteronuclear multidimensional NMR methods, has led to a dramatic increase in the size and complexity of macromolecular systems that are now amenable to NMR structural analysis. In recent years, a new technology has emerged that combines uniform 13 C, 15 N labeling with heteronuclear multidimensional NMR methods to allow NMR structural studies of systems approaching 25 to 30 kDa in molecular weight. In addition, with the introduction of specific 13 C and 15 N labels into ligands, meaningful NMR studies of complexes of even higher molecular weight have become feasible. These advances usher in a new era in which the earlier, rather stringent molecular weight limitations have been greatly surpassed and NMR can begin to address many central biological problems that involve macromolecular structure, dynamics, and interactions

  6. Use of isotopes in root activities and distribution studies

    International Nuclear Information System (INIS)

    Nario M, Adriana; Pino N, Ines; Albornoz G, Maria Paz; Baherle V, Pedro

    2003-01-01

    Several studies shown the relevance of the plant's root activity pattern knowledge, across the profile, to determine the suitable zone to apply the nutrients and irrigation to the plant. In Chile, the studies with the isotopes 15 N and 32 P had been used to carry out applications in solution across the soil profile and in lateral distances from the plant in fruit trees and prairies to determine root activity pattern. In peaches, under furrow irrigation, the major root concentration was found at 20 cm depth and 1 m lateral distance from the trunk. Table grapes, under drip irrigation, presented more root activity at 40 cm depth and under the dripper line in lateral distance. In prairies, the root activity was found between 10 to 40 cm depth, depending on the root capacity to explore the profile (author)

  7. Stable isotope studies. Progress report, March 1, 1985-October 1985

    International Nuclear Information System (INIS)

    Ishida, T.

    1985-01-01

    The studies of last year have been continued in three experimental and two theoretical areas. A closed recycle process for SO 2 /H 2 SO 4 has been developed. The phase ratios of the isotopic reduced partition function ratios for solid and liquid 14 NH 3 / 14 ND 3 and 14 NH 3 / 15 NH 3 and for 12 CH 2 F 2 / 12 CD 2 F 2 and 12 CH 2 F 2 / 13 CH 2 F 2 have been obtained from differential vapor pressure data, and F matrices for each phase of each chemical species have been calculated. A concept of combining chemically modified electrodes and supported catalysts has been investigated. Results of ab initio MO calculations on various clusters of methylene fluoride are compared to those on the clusters of methyl fluoride and fluoroform. An MO study on clusters of ammonia molecules has been started. 29 refs., 3 figs., 10 tabs

  8. Isotope labeling for NMR studies of macromolecular structure and interactions

    Energy Technology Data Exchange (ETDEWEB)

    Wright, P.E. [Scripps Research Institute, La Jolla, CA (United States)

    1994-12-01

    Implementation of biosynthetic methods for uniform or specific isotope labeling of proteins, coupled with the recent development of powerful heteronuclear multidimensional NMR methods, has led to a dramatic increase in the size and complexity of macromolecular systems that are now amenable to NMR structural analysis. In recent years, a new technology has emerged that combines uniform {sup 13}C, {sup 15}N labeling with heteronuclear multidimensional NMR methods to allow NMR structural studies of systems approaching 25 to 30 kDa in molecular weight. In addition, with the introduction of specific {sup 13}C and {sup 15}N labels into ligands, meaningful NMR studies of complexes of even higher molecular weight have become feasible. These advances usher in a new era in which the earlier, rather stringent molecular weight limitations have been greatly surpassed and NMR can begin to address many central biological problems that involve macromolecular structure, dynamics, and interactions.

  9. Hydrodynamic influence on reservoir sustainability in semi-arid climate: A physicochemical and environmental isotopic study.

    Science.gov (United States)

    Ammar, Rawaa; Kazpard, Véronique; El Samrani, Antoine G; Amacha, Nabil; Saad, Zeinab; Chou, Lei

    2017-07-15

    Water scarcity and increasing water demand require the development of water management plans such as establishing artificial lakes and dams. Plans to meet water needs are faced by uprising challenges to improve water quality and to ensure the sustainability of hydro-projects. Environmental isotopes coupled to water physicochemical characteristics were investigated over a biennial cycle to assess both geomorphological and environmental impacts on the water quality of a reservoir situated in an intensively used agricultural watershed under a Mediterranean semi-arid climate. The particularity of the semi-arid climate and the diverse topography generate a continental and orographic rain effect on the isotopic composition of precipitation and the water recharged sources. The studied reservoir responds quickly to land-use activities and climatic changes as reflected by temporal and spatial variations of water chemistry and isotopic composition. Increasing changes in precipitation rate and dry periods significantly modified the water isotopic composition in the reservoir. During the first year, hydrogen (δD) and oxygen (δ 18 O) isotopes are depleted by 6 and 2‰ between dry and wet season, respectively. While a shift of -2‰ for δD and -1‰ for δ 18 O was detected during the second annual cycle. Environmental isotopic compositions demonstrate for the first time the occurrence of groundwater inflow to the central (Cz) and dam (Dz) zones of the Qaraaoun reservoir. The Cz and Dz can be considered as open water bodies subjected to dilution by groundwater inflow, which induces vertical mixing and reverse isotopic stratification of the water column. In the contrary, the river mouth zone acts as a closed system without groundwater intrusion, where heavy water accumulates and may act as a sink for contaminants during dry season. Groundwater influx acts as a dilution factor that renews the hypolimnion, and minimizes the perturbations induced by both internal

  10. Silver diffusion and isotope effect in silver rubidium iodide

    International Nuclear Information System (INIS)

    Arzigian, J.S.

    1980-01-01

    The diffusion coefficient of silver in RbAg 4 I 5 was measured in both superionic phases using radiotracer Ag-110m and serial sectioning with a low temperature sectioning apparatus. The activation energies for diffusion in alpha-RbAg 4 I 5 and beta-RbAg 4 I 5 , respectively, are 0.11 +- 0.01 eV and 0.20 +- 0.04 eV. An isotope effect for diffusion was also measured in both superionic phases. Ag-105 and Ag-110m radioisotopes were used with gamma spectroscopy and energy discrimination. The effect is small, with no significant temperature variation, with the value at 333 0 K being 0.12 +- 0.01. The second-order phase transition at 208 0 K has a small effect, if any, on the magnitude of the effect. The data suggest that a highly cooperative transport mechanism is responsible for the unusually high values of both the conductivity and diffusion coefficient. Although it is not possible to deduce the particular mechanism involved, theories inolving ionic polarons, or cooperative motion, such as crowdions or solitons, seem consistent with the observed results

  11. Oxygen isotopes in tree rings record variation in precipitation δ18O and amount effects in the south of Mexico.

    Science.gov (United States)

    Brienen, Roel J W; Hietz, Peter; Wanek, Wolfgang; Gloor, Manuel

    2013-12-01

    [1] Natural archives of oxygen isotopes in precipitation may be used to study changes in the hydrological cycle in the tropics, but their interpretation is not straightforward. We studied to which degree tree rings of Mimosa acantholoba from southern Mexico record variation in isotopic composition of precipitation and which climatic processes influence oxygen isotopes in tree rings ( δ 18 O tr ). Interannual variation in δ 18 O tr was highly synchronized between trees and closely related to isotopic composition of rain measured at San Salvador, 710 km to the southwest. Correlations with δ 13 C, growth, or local climate variables (temperature, cloud cover, vapor pressure deficit (VPD)) were relatively low, indicating weak plant physiological influences. Interannual variation in δ 18 O tr correlated negatively with local rainfall amount and intensity. Correlations with the amount of precipitation extended along a 1000 km long stretch of the Pacific Central American coast, probably as a result of organized storm systems uniformly affecting rainfall in the region and its isotope signal; episodic heavy precipitation events, of which some are related to cyclones, deposit strongly 18 O-depleted rain in the region and seem to have affected the δ 18 O tr signal. Large-scale controls on the isotope signature include variation in sea surface temperatures of tropical north Atlantic and Pacific Ocean. In conclusion, we show that δ 18 O tr of M . acantholoba can be used as a proxy for source water δ 18 O and that interannual variation in δ 18 O prec is caused by a regional amount effect. This contrasts with δ 18 O signatures at continental sites where cumulative rainout processes dominate and thus provide a proxy for precipitation integrated over a much larger scale. Our results confirm that processes influencing climate-isotope relations differ between sites located, e.g., in the western Amazon versus coastal Mexico, and that tree ring isotope records can help in

  12. Isotope Fractionation Studies in Prestellar Cores: The Case of Nitrogen

    Science.gov (United States)

    Milam, Stefanie N.; Charnley, Steven B.

    2011-01-01

    Isotopically fractionated material is found in many solar system objects, including meteorites and comets. It is considered, in some cases, to trace interstellar material that was incorporated into the solar system without undergoing significant processing, thus preserving the fractionation. In interstellar molecular clouds, ion-molecule chemistry continually cycles nitrogen between the two main reservoirs - N and N2 - leading to only minor N-15 enrichments. Charnley and Rodgers showed that depletion of CO removes oxygen from the gas and weakens this cycle such that significant N-15 fractionation can occur for N2 and other N-bearing species in such cores. Observations are being conducted at millimeter and submillimeter wavelengths employing various facilities in order to both spatially and spectrally, resolve emission from these cores. A preliminary study to obtain the N-14/N-15 ratio in nitriles (HCN and HNC) was conducted at the Arizona Radio Observatory's 12m telescope on Kitt Peak, AZ. Spectra were obtained at high resolution (0.08 km/s) in order to resolve dynamic properties of each source as well as to resolve hyperfine structure present in certain isotopologues. This study included four dark cloud cores, observed to have varying levels of molecular depletion: L1521E, L1498, L1544, and L1521F. Previous studies of the N-14/N-15 ratio towards LI544 were obtained with N2H+ and NIH3, yielding ratios of 446 and >700, respectively. The discrepancy observed in these two measurements suggests a strong chemical dependence on the fractionation of nitrogen. Ratios (C,N, and D) obtained from isotopologues for a particular molecule are likely tracing the same chemical heritage and are directly comparable within a given source. Results and comparisons between the protostellar evolutionary state and isomer isotope fractionation as well as between other N-bearing species will be presented.

  13. Diffusion related isotopic fractionation effects with one-dimensional advective–dispersive transport

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Bruce S. [Civil Engineering Department, University of Toronto, 35 St George Street, Toronto, ON M5S 1A4 (Canada); Lollar, Barbara Sherwood [Earth Sciences Department, University of Toronto, 22 Russell Street, Toronto, ON M5S 3B1 (Canada); Passeport, Elodie [Civil Engineering Department, University of Toronto, 35 St George Street, Toronto, ON M5S 1A4 (Canada); Chemical Engineering and Applied Chemistry Department, University of Toronto, 200 College Street, Toronto, ON M5S 3E5 (Canada); Sleep, Brent E., E-mail: sleep@ecf.utoronto.ca [Civil Engineering Department, University of Toronto, 35 St George Street, Toronto, ON M5S 1A4 (Canada)

    2016-04-15

    Aqueous phase diffusion-related isotope fractionation (DRIF) for carbon isotopes was investigated for common groundwater contaminants in systems in which transport could be considered to be one-dimensional. This paper focuses not only on theoretically observable DRIF effects in these systems but introduces the important concept of constraining “observable” DRIF based on constraints imposed by the scale of measurements in the field, and on standard limits of detection and analytical uncertainty. Specifically, constraints for the detection of DRIF were determined in terms of the diffusive fractionation factor, the initial concentration of contaminants (C{sub 0}), the method detection limit (MDL) for isotopic analysis, the transport time, and the ratio of the longitudinal mechanical dispersion coefficient to effective molecular diffusion coefficient (D{sub mech}/D{sub eff}). The results allow a determination of field conditions under which DRIF may be an important factor in the use of stable carbon isotope measurements for evaluation of contaminant transport and transformation for one-dimensional advective–dispersive transport. This study demonstrates that for diffusion-dominated transport of BTEX, MTBE, and chlorinated ethenes, DRIF effects are only detectable for the smaller molar mass compounds such as vinyl chloride for C{sub 0}/MDL ratios of 50 or higher. Much larger C{sub 0}/MDL ratios, corresponding to higher source concentrations or lower detection limits, are necessary for DRIF to be detectable for the higher molar mass compounds. The distance over which DRIF is observable for VC is small (less than 1 m) for a relatively young diffusive plume (< 100 years), and DRIF will not easily be detected by using the conventional sampling approach with “typical” well spacing (at least several meters). With contaminant transport by advection, mechanical dispersion, and molecular diffusion this study suggests that in field sites where D{sub mech}/D{sub eff} is

  14. Diffusion related isotopic fractionation effects with one-dimensional advective–dispersive transport

    International Nuclear Information System (INIS)

    Xu, Bruce S.; Lollar, Barbara Sherwood; Passeport, Elodie; Sleep, Brent E.

    2016-01-01

    Aqueous phase diffusion-related isotope fractionation (DRIF) for carbon isotopes was investigated for common groundwater contaminants in systems in which transport could be considered to be one-dimensional. This paper focuses not only on theoretically observable DRIF effects in these systems but introduces the important concept of constraining “observable” DRIF based on constraints imposed by the scale of measurements in the field, and on standard limits of detection and analytical uncertainty. Specifically, constraints for the detection of DRIF were determined in terms of the diffusive fractionation factor, the initial concentration of contaminants (C_0), the method detection limit (MDL) for isotopic analysis, the transport time, and the ratio of the longitudinal mechanical dispersion coefficient to effective molecular diffusion coefficient (D_m_e_c_h/D_e_f_f). The results allow a determination of field conditions under which DRIF may be an important factor in the use of stable carbon isotope measurements for evaluation of contaminant transport and transformation for one-dimensional advective–dispersive transport. This study demonstrates that for diffusion-dominated transport of BTEX, MTBE, and chlorinated ethenes, DRIF effects are only detectable for the smaller molar mass compounds such as vinyl chloride for C_0/MDL ratios of 50 or higher. Much larger C_0/MDL ratios, corresponding to higher source concentrations or lower detection limits, are necessary for DRIF to be detectable for the higher molar mass compounds. The distance over which DRIF is observable for VC is small (less than 1 m) for a relatively young diffusive plume (< 100 years), and DRIF will not easily be detected by using the conventional sampling approach with “typical” well spacing (at least several meters). With contaminant transport by advection, mechanical dispersion, and molecular diffusion this study suggests that in field sites where D_m_e_c_h/D_e_f_f is larger than 10, DRIF

  15. Decay studies of neutron-deficient lawrencium isotopes

    International Nuclear Information System (INIS)

    Antalic, S.; Saro, S.; Streicher, B.; Venhart, M.; Hessberger, F.P.; Ackermann, D.; Heinz, S.; Kindler, B.; Kojouharov, I.; Lommel, B.; Mann, R.; Hofmann, S.; Kuusiniemi, P.; Leino, M.; Nishio, K.; Sulignano, B.

    2008-01-01

    The radioactive decay of the isotopes 254-256 Lr and their daughter products was investigated by means of α, prompt α-γ and delayed conversion electron-γ coincidence spectroscopy. The isotopes were produced using the reaction 48 Ca+ 209 Bi. (orig.)

  16. Isotopic study of water origin in salt mines in Poland

    International Nuclear Information System (INIS)

    Dulinski, M.; Grabczak, J.; Garlicki, A.; Zuber, A.

    1998-01-01

    The most important results of isotopic analyses carried out so far in salt mines in Wieliczka, Bochnia, Klodawa, Wapno and Inowroclaw are presented. Discussion of these results for individual leakages proofs that isotopic methods are fully useful in determining of the origin of water appearing in salt mines. (author)

  17. Isotope study in the Alpine karst region of Rawil (Switzerland)

    International Nuclear Information System (INIS)

    Schotterer, U.; Siegenthaler, U.; Oeschger, H.; Wildberger, A.; Nabholz, W.

    1978-01-01

    An isotope study in the karst of the high Alps in Switzerland is described. From 1973 to 1978 discharge, 3 H, delta 18 O, conductivity and temperature were measured in representative springs. The springs are influenced by snowmelt in late spring and summer, by rain in late summer and autumn, and in the winter period, when infiltration stops, by reservoir water. Since tritium in precipitation in the last years scattered irregularly in time and space, the residence time of winter baseflow (2-4 years) could not be determined very precisely. The pronounced difference in delta 18 O between several springs allowed us to estimate the difference in mean altitude of their recharge areas. (orig.) [de

  18. Isotopes to Study the coastal aquifer plain, Cap Bon, Tunisia

    International Nuclear Information System (INIS)

    Ben Hamouda, M. F.; Zouari, Kamel; Tarhouni, J.; Gaye, C.B.; Oueslati, M.N.

    2005-01-01

    The study area is located in the northeastern part of Tunisia about 60 km south of the Tunis city. It is bounded by the Gulf of Haematite in the East, Djebel Sidi Aberahmane in the West, The town of Nabeul in the south and the area of the town Kelibia in the north. The landscape is a coastal plain slightly sloping (3%) towards the sea. The groundwater of the Oriental coast aquifer system occurs mainly at two levels, a shallow aquifer up to depths of about 50 m whose reservoir is consisted by sediments of the Plio quaternary and a deep aquifer between about 150 and 400 m located in the sand stone formations of Miocene of the anticline of Djebel Sidi Abderrahmene. The climate of the region is semi-arid to sub-humid and of Mediterranean type. There are no perennial rivers in this region; but intense storms occasionally cause surface runoff, which is discharged by the oueds. The study is related to a technical cooperation project with the International Atomic Energy Agency, Vienna, Austria, aimed at the use of isotope techniques to study the seawater intrusion into the coastal aquifers of Cap Bon in Tunisia. In this regard, a better understanding of the recharge and flow regime as well as the origin or salinity of the groundwater was required. To reach this goal, isotope and geochemical investigations were carried out. Water samples were taken from wells, boreholes from deep and shallow aquifer of the Oriental coastal aquifer located between Beni Khiar in the south and Kelibia in the north. The samples were analysed for their chemical and isotopic compositions (18O, 2H, 3H, 13C, 14C, 34S). In the following, the results of these analyses are presented and discussed in terms of the recharge and flow regime of the groundwater and the origin and evolution of its salinity. The results of geochemical and isotopic studies have shown that the groundwater is very eterogeneous and suggest the aquifer is replenished by recent water coming from direct infiltration from rain. At

  19. Groundwater salinity study in the Mekong Delta using isotope techniques

    International Nuclear Information System (INIS)

    Le Van Khoi, Nguyen Kien Chinh; Do Tien Hung

    2002-01-01

    Environmental isotopes D, 18 O and chemical composition were used for study of recharge and salinization of groundwater in the are located between Bassac and Mekong Rivers. The results showed that: (a) Pleistocene aquifers are recharged through flood plains and outcrops located at the same altitude. The sanility of groundwater in these aquifers is mostly due to dissolution of the aquifer material, (b) Pliocene and Miocene aquifers receive recharge through outcrops located at the higher altitude on the northeast extension of the Delta and Cambodia. The salinity of groundwater in the coastal region of the aquifer is attributable to sea water intrusion. There appears to be significant retention of sea water in the coastal sediment during intrusion. (Author)

  20. A study of Cirus heavy water system isotopic purity

    International Nuclear Information System (INIS)

    Thomas, Shibu; Sahu, A.K.; Unni, V.K.P.; Pant, R.C.

    2000-01-01

    Cirus uses heavy water as moderator and helium as cover gas. Approximately one tonne of heavy water was added to the system every year for routine make up. Isotopic purity (IP) of this water used for addition was always higher than that of the system. Though this should increase IP of heavy water in the system, it has remained almost at the same level, over the years. A study was carried out to estimate the extent of improvement in IP of heavy water in the system that should have occurred because of this and other factors in last 30 years. Reasons for non-occurrence of such an improvement were explored. Ion exchange resins used for purification of heavy water and air ingress into helium cover gas system appear to be the principal sources of entry of light water into heavy water system. (author)

  1. Study of isotopic exchange reactions of azidothymidine with tritium

    International Nuclear Information System (INIS)

    Sidorov, G.V.; Zverkov, Yu.B.; Myasoedov, N.F.

    2003-01-01

    Different reactions of isotopic exchange of azidothymidine (3 - azido-3 - desoxythymidine) with tritium, such as solid- and liquid-phase catalytic isotopic exchange with gaseous tritium and isotopic exchange in solution with tritium water, are investigated. It is determined that catalytic reactions of azidothymidine with gaseous tritium in solution lead to practically full reduction of azido group up to amino group. In reactions of solid-phase catalytic hydrogenation this process takes place too and 3 - azido-3 - desoxythymidine yield is from 20 to 70 %. Molar radioactivity of labelled with tritium azidothymidine prepared in reactions of solid-phase catalytic isotopic exchange with gaseous tritium and so by isotopic exchange in solution with tritium water does not exceed 0.5 Cu/mmol [ru

  2. Determination of the variation of mercury isotope concentration based on spectral-phase effects

    International Nuclear Information System (INIS)

    Ganeev, A.A.; Man', D.D.; Turkin, Yu.I.

    1988-01-01

    A method of isotopic atomic-absorption analysis, based on spectral-phase effects in which there is no need to use several sources of radiation with pure isotopes of the analyte element, was developed. The method made it possible to simplify the analysis and to determine the variation of the concentration of mercury isotopes from one deposit to another with an accuracy several times higher that of traditional methods of spectral isotopic analysis. The method was tested on mercury 198 and mercury 202. The isotopic analyzer is diagramed and described. The mechanism of spectral-phase effects was determined by the difference in effective photon lifetimes, corresponding to different components of the hyperfine structure of the resonance line of mercury at 254 nm

  3. Evaluating cleansing effects on trace elements and stable isotope values in feathers of oiled birds.

    Science.gov (United States)

    Valladares, Sonia; Moreno, Roćio; Jover, Lluis; Sanpera, Carola

    2010-01-01

    Feathers of seabirds are widely used as a nondestructive tissue for pollution monitoring of trace elements, as well as convenient samples for trophic ecology studies by means of stable isotope analysis (SIA). Nevertheless, feathers can be occasionally impregnated with oil from deliberate ship discharges and from massive oil spill accidents. The feather structure makes them effective traps for particles and are subject to external contamination. It is unknown to what extent the oil adhered to feathers can change trace element concentrations or stable isotope signatures. This study has two primary objectives: (1) to assess if there are differences between trace element concentrations and stable isotope signatures of oiled and clean feathers, and (2) to determine if the cleansing of oiled feathers using commonly applied techniques such as sodium hydroxide (NaOH) washes in combination with an organic solvent (hexane) is more effective than using NaOH alone. In order to do this, we analysed trace elements (Se, Hg, Pb, Cu and Zn) and stable isotopes (delta(13)C and delta(15)N) of individual feathers of yellow-legged gulls (Larus michahellis) which were affected by the 2002 Prestige oil spill in Galicia (NW Spain). Two sets of feathers were analysed, one group were oil-free (Control group) and the other had oil adhered to its surface (Oiled group). We expected to find differences between control and oiled feathers when cleaning exclusively with NaOH and no differences when using hexane. Our results did not show significant differences between Control and Oiled groups as a consequence of the cleansing method used. Unexpectedly, the additional cleansing with hexane resulted in decreasing selenium concentrations and increasing zinc and delta(15)N values in all groups of feathers.

  4. Isotopic spin effect in three-pion Bose-Einstein correlations

    International Nuclear Information System (INIS)

    Suzuki, N.

    1998-01-01

    Bose-Einstein (BE) correlations of identical particles in multiple production processes are extensively studied last years because they give an information on the space-time region of interaction. The basic effect is analogous to Hanbury-Brown - Twiss (HBT) interferometry in optics and suggests statistical production of the particles (mainly π mesons). The possible presence of coherent pionic component (for example, in the case of disoriented chiral condensate formation) modifies the HBT effect. On the other hand, the pions (contrary to photons) are subject to isotopic spin (and electric charge) conservation and so they can not be emitted independently. While the corresponding change of the statistical part is not essential for large multiplicities, the coherent part changes substantially when isotopic spin conservation is taken into account. BE correlations of the pions in the presence of both statistical and coherent components are reconsidered taking into account isotopic spin conservation in the coherent part. That will result in appearance of additional contribution to pionic correlation function. (author)

  5. Isotope exchange study of nickel xanthate in presence of aniline and isomeric toluidines

    International Nuclear Information System (INIS)

    Naidu, G.R.K.; Naidu, P.R.

    1982-01-01

    Isotopic exchange behaviour of nickel xanthate is studied in the presence of aniline and three isomeric toluidines at 18degC. The effect of base concentration is also studied on the exchange rate. The results show that the complex is labile in the kinetic sense in the presence of aniline meta and para toluidines. The rate of exchange increases with and para toluidines. The rate of exchange increases with increase in concentration of the base. The complex displays inert behaviour in the presence of o-toluidine and it is ascribed to dominant steric effect. (author)

  6. Isotope-edited proton NMR study on the structure of a pepsin/inhibitor complex

    International Nuclear Information System (INIS)

    Fesik, S.W.; Luly, J.R.; Erickson, J.W.; Abad-Zapatero, C.

    1988-01-01

    A general approach is illustrated for providing detailed structural information on large enzyme/inhibitor complexes using NMR spectroscopy. The method involves the use of isotopically labeled ligands to simplify two-dimensional NOE spectra of large molecular complexes by isotope-editing techniques. With this approach, the backbone and side-chain conformations (at the P 2 and P 3 sites) of a tightly bound inhibitor of porcine pepsin have bene determined. In addition, structural information on the active site of pepsin has been obtained. Due to the sequence homology between porcine pepsin and human renin, this structural information may prove useful for modeling renin/inhibitor complexes with the ultimate goal of designing more effective renin inhibitors. Moreover, this general approach can be applied to study other biological systems of interest such as other enzyme/inhibitor complexes, ligands bound to soluble receptors, and enzyme/substrate interactions

  7. Uses of stable isotopes

    International Nuclear Information System (INIS)

    Axente, Damian

    1998-01-01

    The most important fields of stable isotope use with examples are presented. These are: 1. Isotope dilution analysis: trace analysis, measurements of volumes and masses; 2. Stable isotopes as tracers: transport phenomena, environmental studies, agricultural research, authentication of products and objects, archaeometry, studies of reaction mechanisms, structure and function determination of complex biological entities, studies of metabolism, breath test for diagnostic; 3. Isotope equilibrium effects: measurement of equilibrium effects, investigation of equilibrium conditions, mechanism of drug action, study of natural processes, water cycle, temperature measurements; 4. Stable isotope for advanced nuclear reactors: uranium nitride with 15 N as nuclear fuel, 157 Gd for reactor control. In spite of some difficulties of stable isotope use, particularly related to the analytical techniques, which are slow and expensive, the number of papers reporting on this subject is steadily growing as well as the number of scientific meetings organized by International Isotope Section and IAEA, Gordon Conferences, and regional meeting in Germany, France, etc. Stable isotope application development on large scale is determined by improving their production technologies as well as those of labeled compound and the analytical techniques. (author)

  8. Water stable isotopes: application to the water cycle and climate variations study

    International Nuclear Information System (INIS)

    Risi, C.

    2009-12-01

    The stable isotopic composition of water (H 2 16 , HDO, H 2 18 , H 2 17 ) is a promising tracer of the present day water cycle and past climates. While the isotopic composition recorded in polar ice core have long been used to reconstruct past temperatures, however, what controls the isotopic composition of the tropical precipitation is more complex. The goal of this thesis is thus to better understand the processes that affect the isotopic composition of tropical precipitation and atmospheric water, more particularly in the tropics. Since most of the tropical precipitation arises from atmospheric convection, and most isotopic archives are on land, we focus more particularly on the impact of convective and land surface processes. In turn, what can be learned about convection and land surface processes using isotopic measurements? Can they help constrain their representation in models? At the inter-annual to climate change scale, what information about the tropical climate variability is recorded in isotopic signals observed in archives? First, we investigate the influence of convection on water stable isotopes. We use both (1) numerical modeling, with a hierarchy of models (single column model, two-dimensional model of squall lines, general circulation model) and (2) data analysis, using isotopic data from rain collected in the Sahel during the African Monsoon Multidisciplinary Analysis campaign, at the event and intra-event scales. These studies highlight the strong impact of convection on the precipitation composition, and stress the importance of rain evaporation and convective or meso-scale subsidence in controlling the rain isotopic composition. Convection also plays an important role on isotopic profiles in the upper troposphere-lower stratosphere. Second, we study what information about climatic variability is recorded by water stable isotopes in precipitation. We analyze simulations of present day and past climates with LMDZ, and evaluate to what extent

  9. Isotope effect of impurity diffusion of cadmium in silver

    International Nuclear Information System (INIS)

    Rockosch, H.J.; Herzig, C.

    1984-01-01

    The isotope effect of impurity diffusion of cadmium in silver single crystals was measured with the radioisotopes 115 Cd/ 109 Cd by gamma spectrometry. As a mean value E = 0.37 at T = 1060 K was obtained. The correlation factor f /SUB Cd/ = 0.41 is in disagreement with previous results of other investigators due to their unfavourable experimental approach. The present value of f /SUB Cd/ , however, is consistent with those of In and Sn in Ag. A comparison with the corresponding correlation factors in the copper solvent reveals a distinct influence of lattice perturbations because of the different atomic volumes of the solvents. Since the size effect is neglected in the electrostatic diffusion model, the agreement with this model is only qualitative. The frequency ratios for vacancy jumps were calculated. The free binding enthalpy of the vacancy-impurity complex was estimated to be Δg /SUB Cd/ = -0.064 eV. This value is smaller than those for In and Sn in Ag and complies with the relative diffusivities of these impurities in Ag

  10. Nuclear structure studies of rare francium isotopes using Collinear Resonance Ionization Spectroscopy (CRIS)

    CERN Document Server

    AUTHOR|(CDS)2084441

    It was known for many years that nuclei possessing certain numbers of protons (Z) and neutrons (N), called the magic numbers (8,20,28,50,82,126...), exhibit characteristic behavior and are in general more stable than their neighboring isotopes. As the capabilities of producing isotopes with more extreme values of Z and N increased, it was realized that those spherical nuclei only represent a small fraction of the total number of isotopes and that most isotopes are deformed. In order to study exotic isotopes and their deformation, it was necessary to develop new experimental techniques that would be powerful enough to be able to cope with very small production yields, but precise enough to measure the nuclear properties (such as radii and moments) with relatively small uncertainties. One technique that can measure nuclear properties of scarcely produced isotopes is in-source resonant ionization, but this technique does not allow for sufficient precision to deduce nuclear quadrupole moments. Furthermore, this t...

  11. Isotope tracers in global water and climate studies of the past and present

    International Nuclear Information System (INIS)

    Edwards, T.W.D.; Birks, S.J.; Gibson, J.J.

    2002-01-01

    To date the global distribution of isotopes in modern precipitation has been characterized almost exclusively from the IAEA/WMO GNIP database, although patchiness of GNIP station records in both time and space has limited the potential of isotope hydrology and climate applications in some areas. Herein, we discuss the prospect of utilizing GCMs for simulating global isotope distributions as a supplementary tool for modern and paleoclimate isotope studies to bridge this gap. Such models currently generate reliable zonal isotope fields, and it is anticipated that future enhancements in finescale resolution of GCMs, and incorporation of land-surface feedbacks and topography will allow for future development of a global reanalysis data set ground-truthed by GNIP. Compilation of time-slice maps of past isotope distribution in precipitation from archival records of meteoric waters also offers significant potential to ground-truth paleoclimate simulations extending back tens to hundreds of thousands of years. (author)

  12. Effect of interband interaction on isotope effect exponent of MgB2 ...

    Indian Academy of Sciences (India)

    The interband interaction of the electron–phonon interaction shows more effect on the isotope exponent than on the non-phonon interaction. Acknowledgement. The authors would like to thank Thailand Research Fund for financial support and the University of the Thai Chamber of Commerce for partial financial support and.

  13. Photon strength functions in Gd isotopes studied from radiative capture of resonance neutrons

    Directory of Open Access Journals (Sweden)

    Kroll J.

    2014-04-01

    Full Text Available The experimental spectra of γ rays following radiative neutron capture on isolated resonances of stable 152,154–158Gd targets were measured by the DANCE calorimeter installed at the Los Alamos Neutron Scattering Center in New Mexico, USA. These spectra were analyzed within the extreme statistical model to get new information on the photon strength functions. Special emphasis was put on study of the scissors vibrational mode present in these isotopes. Our data show that the scissors-mode resonances are built not only on the ground states but also on the excited levels of all studied Gd isotopes. The scissors mode strength observed in 157,159Gd products is significantly higher than in neighboring even-even nuclei 156,158Gd. Such a difference indicates the existence of an odd-even effect in the scissors mode strength. Moreover, there exists no universal parameter-free model of the electric dipole photon strength function describing the experimental data in all of the Gd isotopes studied. The results for the scissors mode are compared with the (γ, γ′ data for the ground-state transitions and with the results from 3He-induced reactions.

  14. Isotopic studies of Yucca Mountain soil fluids and carbonate pedogenesis

    International Nuclear Information System (INIS)

    McConnaughey, T.A.; Whelan, J.F.; Wickland, K.P.; Moscati, R.J.

    1994-01-01

    Secondary carbonates occurring within the soils, faults, and subsurface fractures of Yucca Mountain contain some of the best available records of paleoclimate and palehydrology for the potential radioactive waste repository site. This article discusses conceptual and analytical advances being made with regard to the interpretation of stable isotope data from pedogenic carbonates, specifically related to the 13 C content of soil CO 2 , CaCO 3 , precipitation mechanisms, and isotopic fractionations between parent fluids and precipitating carbonates. The 13 C content of soil carbon dioxide from Yucca Mountain and vicinity shows most of the usual patterns expected in such contexts: Decreasing 13 C content with depth decreasing 13 C with altitude and reduced 13 C during spring. These patterns exist within the domain of a noisy data set; soil and vegetational heterogeneities, weather, and other factors apparently contribute to isotopic variability in the system. Several soil calcification mechanisms appear to be important, involving characteristic physical and chemical environments and isotopic fractionations. When CO 2 loss from thin soil solutions is an important driving factor, carbonates may contain excess heavy isotopes, compared to equilibrium precipitation with soil fluids. When root calcification serves as a proton generator for plant absorption of soil nutrients, heavy isotope deficiencies are likely. Successive cycles of dissolution and reprecipitation mix and redistribute pedogenic carbonates, and tend to isotopically homogenize and equilibrate pedogenic carbonates with soil fluids

  15. Experimental study of relationship between average isotopic fractionation factor and evaporation rate

    Directory of Open Access Journals (Sweden)

    Tao Wang

    2010-12-01

    Full Text Available Isotopic fractionation is the basis of tracing the water cycle using hydrogen and oxygen isotopes. Isotopic fractionation factors in water evaporating from free water bodies are mainly affected by temperature and relative humidity, and vary significantly with these atmospheric factors over the course of a day. The evaporation rate (E can reveal the effects of atmospheric factors. Therefore, there should be a certain functional relationship between isotopic fractionation factors and E. An average isotopic fractionation factor (α* was defined to describe isotopic differences between vapor and liquid phases in evaporation with time intervals of days. The relationship between α* and E based on the isotopic mass balance was investigated through an evaporation pan experiment with no inflow. The experimental results showed that the isotopic compositions of residual water were more enriched with time; α* was affected by air temperature, relative humidity, and other atmospheric factors, and had a strong functional relation with E. The values of α* can be easily calculated with the known values of E, the initial volume of water in the pan, and isotopic compositions of residual water.

  16. Structure of Li, Be And B isotopes studied with quantum molecular dynamic model

    International Nuclear Information System (INIS)

    Abdel-Hafiez, A.; Saleh, Z.A.

    2000-01-01

    Quantum molecular dynamics (QMD) is applied to study the ground state properties of Li, Be and B isotopes. The model Hamiltonian includes both two-and three-body density dependent interactions, a Coulomb term, and a momentum dependent Pauli potential. With parameters which guarantee the infinite nuclear matter properties, the QMD model can only reproduce the binding energies for Be and B isotopes. The experimental root mean square radii of the Li, Be and B isotopes are not sufficiently reproduced by these parameters. It is shown, however, that the binding energies and root mean square radii of these isotopes can simultaneously be reproduced in the lower density limit of the potential parameters

  17. Hydrogen isotope effect through Pd in hydrogen transport pipe

    International Nuclear Information System (INIS)

    Tamaki, Masayoshi

    1992-01-01

    This investigation concerns hydrogen system with hydrogen transport pipes for transportation, purification, isotope separation and storage of hydrogen and its isotopes. A principle of the hydrogen transport pipe (heat pipe having hydrogen transport function) was proposed. It is comprised of the heat pipe and palladium alloy tubes as inlet, outlet, and the separation membrane of hydrogen. The operation was as follows: (1) gas was introduced into the heat pipe through the membrane in the evaporator; (2) the introduced gas was transported toward the condenser by the vapor flow; (3) the transported gas was swept and compressed to the end of the condenser by the vapor pressure; and (4) the compressed gas was exhausted from the heat pipe through the membrane in the condenser. The characteristics of the hydrogen transport pipe were examined for various working conditions. Basic performance concerning transportation, evacuation and compression was experimentally verified. Isotopic dihydrogen gases (H 2 and D 2 ) were used as feed gas for examining the intrinsic performance of the isotope separation by the hydrogen transport pipe. A simulated experiment for hydrogen isotope separation was carried out using a hydrogen-helium gas mixture. The hydrogen transport pipe has a potential for isotope separation and purification of hydrogen, deuterium and tritium in fusion reactor technology. (author)

  18. Matrix effects in laser ablation molecular isotopic spectrometry

    Energy Technology Data Exchange (ETDEWEB)

    Brown, Staci, E-mail: staci.brown@cepast.famu.edu [Department of Physics, Florida A and M University, 2077 E. Paul Dirac Drive, Tallahassee, FL 32310 (United States); Ford, Alan, E-mail: alan.ford@alakaidefense.com [Alakai Defense Systems, 197 Replacement Ave, Suite 102, Fort Leonard Wood, MO 65473 (United States); Akpovo, Charlemagne C., E-mail: charlemagne.akpovo@cepast.famu.edu [Department of Physics, Florida A and M University, 2077 E. Paul Dirac Drive, Tallahassee, FL 32310 (United States); Martinez, Jorge, E-mail: jmartinez@cepast.famu.edu [Department of Physics, Florida A and M University, 2077 E. Paul Dirac Drive, Tallahassee, FL 32310 (United States); Johnson, Lewis, E-mail: lewis@cepast.famu.edu [Department of Physics, Florida A and M University, 2077 E. Paul Dirac Drive, Tallahassee, FL 32310 (United States)

    2014-11-01

    Recently, it has been shown that laser-induced breakdown spectroscopy (LIBS) can be used for the detection of isotopes of elements via isotopic shifts in diatomic species in a technique known as laser ablation molecular isotopic spectrometry (LAMIS). While LAMIS works quite well for isotopic analysis of pure compounds under optimal conditions, it is desirable for it to be applicable for a variety of compounds and matrices. However, the LIBS plasma emission associated with LAMIS depends on several parameters, including the applied electric field of the laser pulse, the physical properties of the material being investigated, and the presence of additional elements other than the element of interest. In this paper, we address some of the pitfalls arising from these dependencies when using LAMIS for the determination of the relative isotopic abundance of boron-containing materials with varying chemical matrices. - Highlights: • LAMIS usually determines isotopic composition of boron compounds within 3 percent. • LaBO{sub 3} and some boron-containing mixtures yield inaccurate LAMIS results. • Higher laser energy reduces variability but does not remedy poor LAMIS outcomes.

  19. A first isotopic dietary study of the Greenlandic Thule Culture

    DEFF Research Database (Denmark)

    Nelson, D.E.; Lynnerup, Niels; Arneborg, J.

    2012-01-01

    The isotopic dietary method has been applied to samples of some 65 Thule Culture individuals from existing archaeological collections of Greenlandic human skeletal material. The aim was to use the Greenlandic Thule Culture as a test of the isotopic method, in that we know they were heavily...... was used as the basis for analysis. As expected, the results indicate that these people were almost entirely dependent on the marine biosphere for their protein. An exception is those from Northeast Greenland, whose isotopic signatures show evidence for consumption of terrestrial protein as well....... Not expected were the observed differences at the regional and local levels....

  20. Investigation of the feeding effect on the 13C/12C isotope ratio of the hormones in bovine urine using gas chromatography/combustion isotope ratio mass spectrometry

    NARCIS (Netherlands)

    Balizs, Gabor; Jainz, Annett; Horvatovich, Peter

    2005-01-01

    The effect of the feeding on the 13C/12C isotope ratio of four endogenous steroid hormones testosterone (T), epi-testosterone (epi-T), dehydroepiandrosterone (DHEA) and etiocholanolone (ETIO) in bovine urine was investigated. An analytical method to determine the accurate isotope ratio was developed

  1. Ion beam production and study of radioactive isotopes with the laser ion source at ISOLDE

    Science.gov (United States)

    Fedosseev, Valentin; Chrysalidis, Katerina; Day Goodacre, Thomas; Marsh, Bruce; Rothe, Sebastian; Seiffert, Christoph; Wendt, Klaus

    2017-08-01

    At ISOLDE the majority of radioactive ion beams are produced using the resonance ionization laser ion source (RILIS). This ion source is based on resonant excitation of atomic transitions by wavelength tunable laser radiation. Since its installation at the ISOLDE facility in 1994, the RILIS laser setup has been developed into a versatile remotely operated laser system comprising state-of-the-art solid state and dye lasers capable of generating multiple high quality laser beams at any wavelength in the range of 210-950 nm. A continuous programme of atomic ionization scheme development at CERN and at other laboratories has gradually increased the number of RILIS-ionized elements. At present, isotopes of 40 different elements have been selectively laser-ionized by the ISOLDE RILIS. Studies related to the optimization of the laser-atom interaction environment have yielded new laser ion source types: the laser ion source and trap and the versatile arc discharge and laser ion source. Depending on the specific experimental requirements for beam purity or versatility to switch between different ionization mechanisms, these may offer a favourable alternative to the standard hot metal cavity configuration. In addition to its main purpose of ion beam production, the RILIS is used for laser spectroscopy of radioisotopes. In an ongoing experimental campaign the isotope shifts and hyperfine structure of long isotopic chains have been measured by the extremely sensitive in-source laser spectroscopy method. The studies performed in the lead region were focused on nuclear deformation and shape coexistence effects around the closed proton shell Z = 82. The paper describes the functional principles of the RILIS, the current status of the laser system and demonstrated capabilities for the production of different ion beams including the high-resolution studies of short-lived isotopes and other applications of RILIS lasers for ISOLDE experiments. This article belongs to the Focus on

  2. Intramolecular kinetic isotope effect in gas-phase proton-transfer reactions

    International Nuclear Information System (INIS)

    Wellman, K.M.; Victoriano, M.E.; Isolani, P.C.; Riveros, J.M.

    1979-01-01

    The k/sub H//k/sub D/ isotope effects were determined by ICR for the reaction of substituted toluenes with several alkoxides. The results showed a definite trend for k/sub H//k/sub D/ starting as a normal isotope effect for appreciably exothermic reaction (> 3 kcal mol -1 ) and proceeding smoothly toward an inverse isotope effect as the reaction approached thermoneutrality or becomes endothermic. These observations were explained by a reaction which involved a double minima potential with a central energy barrier

  3. Transient competitive complexation in biological kinetic isotope fractionation explains non-steady isotopic effects: Theory and application to denitrification in soils

    Energy Technology Data Exchange (ETDEWEB)

    Maggi, F.M.; Riley, W.J.

    2009-06-01

    The theoretical formulation of biological kinetic reactions in isotopic applications often assume first-order or Michaelis-Menten-Monod kinetics under the quasi-steady-state assumption to simplify the system kinetics. However, isotopic e ects have the same order of magnitude as the potential error introduced by these simpli cations. Both formulations lead to a constant fractionation factor which may yield incorrect estimations of the isotopic effect and a misleading interpretation of the isotopic signature of a reaction. We have analyzed the isotopic signature of denitri cation in biogeochemical soil systems by Menyailo and Hungate [2006], where high {sup 15}N{sub 2}O enrichment during N{sub 2}O production and inverse isotope fractionation during N{sub 2}O consumption could not be explained with first-order kinetics and the Rayleigh equation, or with the quasi-steady-state Michaelis-Menten-Monod kinetics. When the quasi-steady-state assumption was relaxed, transient Michaelis-Menten-Monod kinetics accurately reproduced the observations and aided in interpretation of experimental isotopic signatures. These results may imply a substantial revision in using the Rayleigh equation for interpretation of isotopic signatures and in modeling biological kinetic isotope fractionation with first-order kinetics or quasi-steady-state Michaelis-Menten-Monod kinetics.

  4. Effect of amino acids on the precipitation kinetics and Ca isotopic composition of gypsum

    Science.gov (United States)

    Harouaka, Khadouja; Kubicki, James D.; Fantle, Matthew S.

    2017-12-01

    frequency calculations of clusters derived from DFT structures vary by as much as 1.4‰. This suggests that the equilibrium fractionation factor for the bulk crystal can vary substantially, and that surface sorption can induce changes in αeq associated with gypsum precipitation. While we do not rule out the influence of kinetic isotope effects, our results clearly demonstrate that the mode of crystal growth can have a sizeable effect on the bulk fractionation factor (αs-f). Ultimately, our results suggest that the same mechanism by which organic molecules affect the morphology of a mineral can also impact the isotopic composition of the mineral. The results of our study provide valuable insight into the mechanism of Ca isotopic fractionation during gypsum precipitation. Our results are also important for establishing a framework for accurate interpretations of mineral-hosted Ca isotope records of the past, as we demonstrate a mechanistic pathway by which the biological and chemical environment can impact Ca isotopic fractionation during mineral precipitation.

  5. Soil drying effects on the carbon isotope composition of soil respiration

    Science.gov (United States)

    Stable isotopes are used widely as a tool for determining sources of carbon (C) fluxes in ecosystem C studies. Environmental factors that change over time, such as moisture, can create dynamic changes in the isotopic composition of C assimilated by plants, and offers a unique opp...

  6. Covariance of oxygen and hydrogen isotopic composition in plant water: Species effects

    Energy Technology Data Exchange (ETDEWEB)

    Cooper, L.W.; DeNiro, M.J. (Univ. of California, Los Angeles (United States))

    1989-12-01

    Leaf water becomes enriched in the heavy isotopes of oxygen and hydrogen during evapotranspiration. The magnitude of the enrichment has been shown to be influenced by temperature and humidity, but the effects of species-specific factors on leaf water enrichment of D and {sup 18}O have not been studied for different plants growing together. To learn whether leaf water enrichment patterns and processes for D and {sup 18}O are different for individual species growing under the same environmental conditions the authors tested the proposal that leaf waters in plants with crassulacean acid metabolism (CAM) show high sloped (m in the leaf water equation {delta}D = m {delta}{sup 18}O + b) than in C{sub 3} plants. They determined the relationships between the stable hydrogen ({delta}D) and oxygen ({delta}{sup 18}O) isotope ratios of leaf waters collected during the diurnal cycle of evapotranspiration for Yucca schidigera, Ephedra aspera, Agave deserti, Prunus ilicifolia, Yucca whipplei, Heteromeles arbutifolia, Dyckia fosteriana, Simmondsia chinensis, and Encelia farinosa growing at two sites in southern California. The findings indicate that m in the aforementioned equation is related to the overall residence time for water in the leaf and proportions of water subjected to repeated evapotranspiration enrichments of heavy isotopes.

  7. The effect of natural weathering on the chemical and isotopic composition of biotites

    International Nuclear Information System (INIS)

    Clauer, N.; Bonnot-Courtois, C.

    1982-01-01

    The effect of progressive natural weathering on the isotopic (Rb-Sr, K-Ar, deltaD, delta 18 O) and chemical (REE, H 2 O + ) compositions of biotite has been studied on a suite of migmatitic biotites from the Chad Republic. During the early stages of weathering the Rb-Sr system is strongly affected, the hydrogen and oxygen isotope compositions change markedly, the minerals are depleted in light REE, the water content increases by a factor of two, and the K-Ar system is relatively little disturbed. During intensive weathering the K-Ar system is more strongly disturbed than the Rb-Sr system. Most of the isotopic and chemical modifications take place under nonequilibrium conditions and occur before newly formed kaolinite and/or smectite can be detected. These observations suggest that (a) 'protominerals' may form within the biotite structure during the initial period of weathering, and (b) only when chemical equilibrium is approached in the weathering profile are new minerals able to form. (author)

  8. Stable carbon and oxygen isotope study on benthic foraminifera ...

    Indian Academy of Sciences (India)

    Ajoy K Bhaumik

    2017-07-24

    Jul 24, 2017 ... of a species for isotopic analysis has forced us to select multiple species from down-core samples. Thus ... microhabitat, climatic variability, bottom and pore ...... Trends, rhythms, and aberrations in global climate 65 Ma.

  9. Triple Isotope Water Analyzer for Extraplanetary Studies, Phase II

    Data.gov (United States)

    National Aeronautics and Space Administration — Los Gatos Research (LGR) proposes to employ Off-Axis ICOS to develop triple-isotope water analyzers for lunar and other extraplanetary exploration. This instrument...

  10. Isotopic study of some fossil and actual hydrothermal systems

    International Nuclear Information System (INIS)

    Demont, J.M.

    1981-07-01

    Oxygen and hydrogen isotopic compositions of rocks from the INAG no 1 drillhole provide evidence of a fossil hydrothermal system in the Ceyssat region of the Massif Central. Oxygen isotope temperatures for the mineral paragenesis are about 275 0 C and the water is of marine origin. Measurements have also been made of delta 13 C values of dissolved carbon and gaseous CO 2 from several hot springs in the Pyrenees and Massif Central. The carbon isotopic composition of the total systems have been calculated from the gas-liquid ratios at the emergence sites and these results are discussed in terms of the origin of the carbon. Most of the hydrothermal carbon is of deep origin. The observed variations in isotopic compositions may be explained by the behavior of the fluids during their ascent to the surface [fr

  11. Coordinated Isotopic and TEM Studies of Presolar Graphites from Murchison

    Science.gov (United States)

    Croat, T. K.; Stadermann, F. J.; Zinner, E.; Bernatowicz, T. J.

    2004-03-01

    TEM and NanoSIMS investigations of the same presolar Murchison KFC graphites revealed high Zr, Mo, and Ru content in refractory carbides within the graphites. Along with isotopically light carbon, these suggest a low-metallicity AGB source.

  12. Effect of Calcium Oxide Microstructure on the Diffusion of Isotopes

    CERN Document Server

    Fernandes Ramos, João Pedro; Stora, T

    2012-01-01

    Calcium oxide (CaO) powder targets have been successfully used at CERN-ISOLDE to produce neutron deficient exotic argon and carbon isotopes under proton irradiation at high temperatures (>1000°C). These targets outperform the other related targets for the production of the same beams. However, they presented either slow release rates (yields) from the beginning or a rapid decrease over time. This problem was believed to come from the target microstructure degradation, justifying the material investigation. In order to do so, the synthesis, reactivity in ambient air and sintering kinetics of CaO were studied, through surface area determination by N2 adsorption, X-ray diffraction for crystalline phase identification and crystallite size determination, and scanning and transmission electron microscopy to investigate the microstructure. The synthesis studies revealed that a nanometric material is obtained from the decarbonation of CaCO3 in vacuum at temperatures higher than 550°C, which is very reactive in air....

  13. Covariance of oxygen and hydrogen isotopic compositions in plant water: species effects

    International Nuclear Information System (INIS)

    Cooper, L.W.; DeNiro, M.J.

    1989-01-01

    Leaf water becomes enriched in the heavy isotopes of oxygen and hydrogen during evapotranspiration. The magnitude of the enrichment has been shown to be influenced by temperature and humidity, but the effects of species—specific factors on leaf water enrichment of D and 18 O have not been studied for different plants growing together. Accordingly, to learn whether leaf water enrichment patterns and processes for D and 18 O are different for individual species growing under the same environmental conditions we tested the proposal that leaf waters in plants with crassulacean acid metabolism (CAM) show higher slopes (m in the leaf water equation °D = m ° 18 O + b) than in C 3 plants. We determined the relationships between the stable hydrogen (°D) and oxygen (° 18 O) isotope ratios of leaf waters collected during the diurnal cycle of evapotranspiration for Yucca schidigera, Ephedra aspera, Agave deserti, Prunus ilicifolia, Yucca whipplei, Heteromeles arbutifolia, Dyckia fosteriana, Simmondsia chinensis, and Encelia farinosa growing at two sites in southern California. Slopes (m in the above leaf water equation) ranged from 1.50 to 3.21, compared to °8 for meteoric water, but differences in slope could not be attributed to carboxylation pathway (CAM vs. C 3 ) nor climate (coastal California vs. Sonoran Desert). Higher slopes were correlated with greater overall ranges of leaf water enrichment of D and 18 O. Water in plants with higher slopes also differed most from unaltered meteoric water. Leaf water isotope ratios in plants with lower slopes were better correlated with temperature and humidity. The findings indicate that m in the aforementioned equation is related to the overall residence time for water in the leaf and proportions of water subjected to repeated evapotranspiration enrichments of heavy isotopes

  14. Isotopic studies of nitrogen balance in a cracking clay

    International Nuclear Information System (INIS)

    Craswell, E.T.; Martin, A.E.

    1975-01-01

    The stable isotope 15 N was used to study the fate of nitrogen fertilizers applied to a black earth growing wheat. In a glasshouse experiment using soil packed at 56 per cent moisture (pF 2) into pots, added nitrate was almost completely recovered (mean, 98.8 +- 2.3 per cent) by soil and plant analysis. This experiment was repeated using 15 N-labelled ammonium as well as nitrate; mean recoveries at 15 weeks were 96.8 and 97 per cent respectively (+- 2.2 per cent at P 15 N measured, 97 and 96.8 per cent at 56 and 63 per cent moisture respectively. Fallow and planted systems were then studied in a gas lysimeter. During experiments lasting up to 14 weeks, gaseous losses as 15 N-labelled denitrification products were less than the equivalent of 0.2 μg nitrogen/g soil (the lower limit of detection with a mass spectrometer). Although analysis of plant and soil from the lysimeter in two experiments showed virtually quantitative recovery (99.7 and 97.05 per cent), small (0.16 per cent) losses of labelled ammonia into the lysimeter atmosphere were detected. The significance of these results is discussed in relation to the common finding of large deficits in nitrogen balance studies. (author)

  15. Carbon isotope effects in carbohydrates and amino acids of photosynthesizing organisms

    Energy Technology Data Exchange (ETDEWEB)

    Ivlev, A.A.; Kaloshin, A.G.; Koroleva, M.Ya. (Ministerstvo Geologii SSR, Moscow)

    1982-02-10

    The analysis of the carbon isotope distribution in carbohydrates and amino acids of some photosynthesizing organisms revealed the close relationship between distribution and the pathways of biosynthesis of the molecules. This relationship is explained on the basis of the previously proposed mechanism of carbon isotope fractionation in a cell, in which the chief part is played by kinetic isotope effects in the pyruvate decarboxylation reaction progressively increased in the conjugated processes of gluconeogenesis. Isotope differences of C/sub 2/ and C/sub 3/ fragments arising in decarboxylation of pyruvate, as well as isotope differences of biogenic acceptor and environmental CO/sub 2/ appearing in assimilation are the main reasons of the observed intramolecular isotopic heterogeneity of biomolecules. The heterogeneity is preserved in metabolites owing to an incomplete mixing of carbon atoms in biochemical reactions. The probable existence of two pools of carbohydrates in photosynthesizing organisms different in isotopic composition is predicted. Two types of intramolecular isotope distribution in amino acids are shown.

  16. ISOTOPE METHODS IN HOMOGENEOUS CATALYSIS.

    Energy Technology Data Exchange (ETDEWEB)

    BULLOCK,R.M.; BENDER,B.R.

    2000-12-01

    The use of isotope labels has had a fundamentally important role in the determination of mechanisms of homogeneously catalyzed reactions. Mechanistic data is valuable since it can assist in the design and rational improvement of homogeneous catalysts. There are several ways to use isotopes in mechanistic chemistry. Isotopes can be introduced into controlled experiments and followed where they go or don't go; in this way, Libby, Calvin, Taube and others used isotopes to elucidate mechanistic pathways for very different, yet important chemistries. Another important isotope method is the study of kinetic isotope effects (KIEs) and equilibrium isotope effect (EIEs). Here the mere observation of where a label winds up is no longer enough - what matters is how much slower (or faster) a labeled molecule reacts than the unlabeled material. The most careti studies essentially involve the measurement of isotope fractionation between a reference ground state and the transition state. Thus kinetic isotope effects provide unique data unavailable from other methods, since information about the transition state of a reaction is obtained. Because getting an experimental glimpse of transition states is really tantamount to understanding catalysis, kinetic isotope effects are very powerful.

  17. Effect of the magnetic isotope of magnesium, 25Mg, on post-radiation recovery of Saccharomyces cerevisiae

    International Nuclear Information System (INIS)

    Grodzinskij, D.M.; Evstyukhina, T.A.; Kol'tover, V.K.; Korolev, V.G.; Kutlakhmedov, Yu.A.; Grodzinskij, D.M.; Evstyukhina, T.A.; Kol'tover, V.K.; Korolev, V.G.; Kutlakhmedov, Yu.A.; Grodzinskij, D.M.; Evstyukhina, T.A.; Kol'tover, V.K.; Korolev, V.G.; Kutlakhmedov, Yu.A.

    2011-01-01

    Among three stable magnesium isotopes, 24 Mg, 25 Mg, and 26 Mg with natural abundance 79, 10, and 11%, only 25 Mg has the nuclear spin (I=5/2) and, therefore, the nuclear magnetic moment. Two other isotopes are spinless (I=0) and, hence, have no magnetic moment. We have revealed that magnetic isotope 25 Mg, by comparison to nonmagnetic isotope 24 Mg, essentially stimulates the recovery process in the yeast cells, Saccharomyces cerevisiae, after UV irradiation. Thus, we have first documented the magnetic isotope effect in radiation biology. This finding opens up the way to the development of novel radio-protectors based on the stable magnetic isotopes.

  18. On depth profiling of hydrogen and helium isotopes and its application to ion-implantation studies

    International Nuclear Information System (INIS)

    Boettiger, J.

    1979-01-01

    The thesis is divided into two parts, the first being a general review of the experimental methods for depth profiling of light isotopes, where ion beams are used. In the second part, studies of ion implantation of hydrogen and helium isotopes, applying the techniques discussed in the first part, are described. The paper summarizes recent experimental results and discusses recent developments. (Auth.)

  19. Advisory group meeting on stable isotope labelled compounds in biomedical studies

    International Nuclear Information System (INIS)

    Vera Ruiz, H.; Parr, R.M.

    1985-11-01

    The programme of the meeting was restricted to topics involving applications of stable isotopes of the lighter elements (H, C, N, O). The current status of stable isotope techniques and applications in nutritional and biomedical studies, the applicability of these techniques in developing countries and the IAEA's future programmes on this topic were discussed

  20. Contribution of stable isotopes to the study of pharmacokinetics of magnesium salts

    International Nuclear Information System (INIS)

    Benech, H.

    1999-01-01

    The use of stable isotopes as labels is becoming an attractive tool for the study of magnesium behavior in humans. It has been used two stable isotopes of magnesium, 25 Mg and 26 Mg, to measure the absolute bioavailability of a pharmaceutical form of magnesium. (N.C.)

  1. Multi-column chromatography and the use of isotopes in the study of steroid metabolism

    International Nuclear Information System (INIS)

    Sayegh, J.F.; Vestergaard, P.

    1978-01-01

    Multi-column liquid chromatography is demonstrated to be a technique well suited for isotope experiments involving administration of labelled cortisol. It has potential for secretion rate determinations, for dynamic studies of cortisol metabolism and for work with stable isotopes. (author)

  2. Stable isotope studies. Progress report, August 1, 1974--July 31, 1975

    International Nuclear Information System (INIS)

    Flynn, G.W.; Hsu, D.S.Y.; Preses, J.M.; Spindel, W.; Weston, R.E.

    1975-01-01

    Progress is reported in the following studies: selective two-step laser-induced photodissociation, unimolecular processes induced by multiple-photon absorption, and vibrational energy transfer processes involving isotopic species of sulfur dioxide. These laser-induced chemical reactions can possibly be applied to isotope separation

  3. Variable temperature ion trap studies of CH4+ + H2, HD and D2: negative temperature dependence and significant isotope effect

    International Nuclear Information System (INIS)

    Asvany, O.; Savic, I.; Schlemmer, S.; Gerlich, D.

    2004-01-01

    Reactions of methane cations, CH 4 + , with H 2 , HD and D 2 have been studied in a variable temperature 22-pole ion trap from room temperature down to 15 K. The formation of CH 5 + in collisions with H 2 is slow at 300 K, but it becomes faster by at least one order of magnitude when the temperature is lowered to 15 K. This behavior is tentatively explained with a longer complex lifetime at low temperatures. However, since tunneling is most probably not responsible for product formation, other dynamical or statistical restrictions must be responsible for the negative temperature dependence. In collisions of CH 4 + with HD, the CH 5 + product ion (68% at 15 K) prevails over CH 4 D + (32%). Reaction of CH 4 + with D 2 is found to be much slower than with H 2 or HD. The rate coefficient for converting CH 4 + into CH 3 D + by H-D exchange has been determined to be smaller than 10 -12 cm 3 /s, indicating that scrambling in the CH 6 + complex is very unlikely

  4. Variable temperature ion trap studies of CH{sub 4}{sup +} + H{sub 2}, HD and D{sub 2}: negative temperature dependence and significant isotope effect

    Energy Technology Data Exchange (ETDEWEB)

    Asvany, O.; Savic, I.; Schlemmer, S.; Gerlich, D

    2004-03-08

    Reactions of methane cations, CH{sub 4}{sup +}, with H{sub 2}, HD and D{sub 2} have been studied in a variable temperature 22-pole ion trap from room temperature down to 15 K. The formation of CH{sub 5}{sup +} in collisions with H{sub 2} is slow at 300 K, but it becomes faster by at least one order of magnitude when the temperature is lowered to 15 K. This behavior is tentatively explained with a longer complex lifetime at low temperatures. However, since tunneling is most probably not responsible for product formation, other dynamical or statistical restrictions must be responsible for the negative temperature dependence. In collisions of CH{sub 4}{sup +} with HD, the CH{sub 5}{sup +} product ion (68% at 15 K) prevails over CH{sub 4}D{sup +} (32%). Reaction of CH{sub 4}{sup +} with D{sub 2} is found to be much slower than with H{sub 2} or HD. The rate coefficient for converting CH{sub 4}{sup +} into CH{sub 3}D{sup +} by H-D exchange has been determined to be smaller than 10{sup -12} cm{sup 3}/s, indicating that scrambling in the CH{sub 6}{sup +} complex is very unlikely.

  5. Stable isotope study of thermal and other waters in Fiji

    International Nuclear Information System (INIS)

    Cox, M.E.; Hulston, J.R.

    1980-01-01

    The O-18/O-16, D/H ratios and chloride concentrations of 79 thermal spring, subsurface, and surface waters from the two main islands of Fiji have been measured to determine the origin of the thermal waters and the characteristics of the geothermal activity. The meteoric waters generally fall along the Meteoric Water Line with a slope of 8, and best fit a line of this slope with a delta D intercept of +13 per mill. The delta O-18/delta D ratios of the thermal waters indicate low magnitude subsurface temperatures and a negligible enrichment in O-18. In one coastal locality in which higher temperature conditions exist, up to 50% seawater is shown to be mixing within the system, probably at shallow depths. The isotopic characteristics of the thermal waters reflect those of the local meteoric water, indicating localised recharge and an essentially meteoric origin. The effects of prevailing wind conditions and topography of these islands cause a depletion of deuterium in both precipitation and surface meteoric water from windward to leeward coasts (auth)

  6. Oxygen isotope studies of the Salton Sea geothermal field

    International Nuclear Information System (INIS)

    Olson, E.R.

    1978-01-01

    Interbedded shales and sandstones were drilled to a depth of 1588 metres in Sinclair Number Four Well, Salton Sea Geothermal Field. Bottom hole temperatures are approximately 290 0 C. The oxygen dels of hydrothermal and detrital calcite have a systematic relationship at any depth in the geothermal reservoir. Typical values are: vein calcite, +6 0 / 00 ; calcite in white sandstone, +10 0 / 00 ; calcite in dark gray shale, +11 0 / 00 ; calcite in light gray shale, +17 0 / 00 ; calcite in red-brown shale, +20 0 / 00 . This succession represents decreasing water-rock interaction that is also indicated by the clay mineralogy of the shales. Permeability has a marked effect on the equilibration of water and rocks at any given temperature. Original differences in permeability have resulted in partial preservation of original detrital sedimentary compositions. The fluids in the Salton Sea Geothermal Field are probabaly partially evaporated Colorado River water, and their oxygen del values vary as much as 4 0 / 00 throughout the field. Truesdell's (1974) data suggest that dissolved salts may make the water oxygen activity del as much as 6 0 / 00 greater than the concentration del in the geothermal reservoir. Such an uncertainty is a serious impediment to precise isotope geothermometry in this system.(auth.)

  7. Effect of leaf litter degradation and seasonality on D/H isotope ratios of n-alkane biomarkers

    NARCIS (Netherlands)

    Zech, M.; Pedentchouk, N.; Buggle, B.; Leiber, K.; Kalbitz, K.; Markovic, S.B.; Glaser, B.

    2011-01-01

    During the last decade, compound-specific hydrogen isotope analysis of plant leaf-wax and sedimentary n-alkyl lipids has become a promising tool for paleohydrological reconstructions. However, with the exception of several previous studies, there is a lack of knowledge regarding possible effects of

  8. Secondary isotope effects and tunneling in elimination reaction of quaternary ammonium salts

    International Nuclear Information System (INIS)

    Lin, S.

    1993-01-01

    In order to gain more experimental evidence of the tunneling effect on the non-transferred isotopically-substituted hydrogen in the rate determining step and to investigate in more detail concerning the variable nature of the E2 transition state, tritium tracer-labeled β- and/or α-phenyl substituted ethyltrimethylammonium ions in the elimination reaction and their 2,2-d 2 analogues were studied. The three different substrates are 2-(p-trifluoromethylphenyl)ethyltrimethylammonium bromide (I), 1-phenylethyltrimethylammonium bromide (II) and 1-phenyl- 2-p-chlorophenylethyltrimethylammonium bromide (III). The reactions were found to proceed via a concerted E2 process. The proton is more than one-half transferred to the base at the transition state, especially for case I and III. There is more C beta -H and less C alpha -N bond rupture at the transition state when an electron-withdrawing group is introduced on the β-phenyl ring, i.e., more carbonion character in the transition state. The secondary tritium isotope effects were measured and they were found larger than the maximum value. (1.17) for rehybridization. It was found that these values were strongly temperature dependent. They increase as the temperature goes down. The Arrenhius pre-exponential factors were below unity and the exponential factor to convert the isotope effect of D/T to H/T were much greater than predicted for zero-point energy effects alone (3.26). Tunneling turns to be the only plausible explanation. By reviewing this evidence, one may conclude that the contribution of tunneling is indeed a common occurrence in proton transfer processes. For elimination of compound I, the tunneling effect is greatest while it is less for the other two, which are about the same, but the nature of their transition states is quite different. The variable nature of the transition states for the three eliminations are discussed in terms of the More O'Ferral-Jencks diagram

  9. Heavy-atom isotope effects on binding of reactants to lactate dehydrogenase and pyruvate kinase

    International Nuclear Information System (INIS)

    Gawlita, E.

    1993-04-01

    18 O and 13 C kinetic isotope effects have been measured on the reaction of pyruvate kinase with phospho-enol-pyruvate and ADP using a remote label technique. The magnitude of both investigated isotope effects showed a dependence on the concentration of ADP. However, while the carbon effect was simply 'washed out' to unity at high ATP concentration, the oxygen effect becomes inverse and reached 0.9928 at the highest used concentration of ADP. Such a result testifies that the assumption of the negligible effect of isotopic substitution on enzyme-substrate associations remains correct only for carbon effects. An equilibrium 18 O isotope effect on association of oxalate with lactate dehydrogenase in the presence of NADHP has been evaluated by both experimental and theoretical means. Experimental methods, which involved equilibrium dialysis and gas chromatographic/mass spectrometric measurement of isotopic ration, yielded an inverse value of 0.9840. Semiempirical methods involved vibrational analysis of oxalate in two different environments. The comparison of calculated values with the experimentally determined isotope effect indicated that the AM 1 Hamiltonian proved superior to its PM 3 counterpart in this modelling. 160 refs, 8 figs, 18 tabs

  10. Mechanistic positron emission tomography studies: demonstration of a deuterium isotope effect in the monoamine oxidase-catalyzed binding of (/sup 11/C)L-deprenyl in living baboon brain

    Energy Technology Data Exchange (ETDEWEB)

    Fowler, J.S.; Wolf, A.P.; MacGregor, R.R.; Dewey, S.L.; Logan, J.; Schlyer, D.J.; Langstrom, B.

    1988-11-01

    The application of positron emission tomography (PET) to the study of biochemical transformations in the living human and animal body requires the development of highly selective radiotracers whose concentrations in tissue provide a record of a discrete metabolic process. L-N-(11C-methyl)Deprenyl ((11C)L-deprenyl), a suicide inactivator of monoamine oxidase (MAO) type B, has been developed as a radiotracer for mapping MAO B in the living human and animal brain. In this investigation, (11C)L-deprenyl (1) and (11C)L-deprenyl-alpha, alpha-2H2 (2) have been compared in three different baboons by PET measurement of carbon-11 uptake and retention in the brain and the measurement of the amount of unchanged tracer in the arterial plasma over a 90-min time interval. For one baboon, N-(11C-methyl-2H3)L-deprenyl (3) was also studied. Kinetic parameters calculated using a three-compartment model revealed a deuterium isotope effect of 3.8 +/- 1.1. Comparison of the two tracers (1 and 2) in mouse brain demonstrated that deuterium substitution significantly reduced the amount of radioactivity bound to protein. HPLC and GLC analysis of the soluble radioactivity in mouse brain after injection of (11C)L-deprenyl showed the presence of (11C)methamphetamine as a major product along with unidentified labeled products. Sodium dodecyl sulfate-polyacrylamide electrophoresis with carbon-14-labeled L-deprenyl showed that a protein of molecular weight 58,000 was labeled. These results establish that MAO-catalyzed cleavage of the alpha carbon-hydrogen bond on the propargyl group is the rate limiting (or a major rate contributing) step in the retention of carbon-11 in brain and that the in vivo detection of labeled products in brain after the injection of (11C)L-deprenyl provides a record of MAO activity.

  11. Limits on the expression of enzyme-mediated solvent isotope effects

    International Nuclear Information System (INIS)

    Northrop, D.B.

    1981-01-01

    Steady-state analysis of primary solvent isotope effects on enzyme-catalyzed reactions, mediated by solvent-shielded di- or triprotic groups on the enzyme, yields equations describing the upper limit of intramolecular isotopic discrimation. For diprotic groups [P/sub H]/[P/sub D/] = 3k/sub H//k/sub D/ + 3), and for triprotic groups [P/sub H/]/[P/sub D/] = [7(k/sub H//k/sub D/ 2 = 10k/sub H/k/sub D/ + 1]/[(k/sub H//k/sub D/) 2 + 10k/sub H//k/sub D/ + 7]. Given a normal intrinsic isotope effect of k/sub H//k/sub D/ = 7, maximal isotopic discrimation in 50:50 H 2 O:D 2 O is therefore 2.2 and 3.3, respectively, versus 1.0 for a monoprotic group. Intermediate values of isotope discrimination may be interpreted with respect to distinguishing enzyme-mediated catalytic mechanisms from those of direct transfer between solvent and substrate, and to identifying mediating groups, by comparisons of isotopic discrimination at high and low concentrations of substrates and by reference to intrinsic and intermolecular isotope effects

  12. Solvent-dependent deuterium isotope effects in the 15N NMR spectra of an ammonium ion

    International Nuclear Information System (INIS)

    Wielogorska, E.; Jackowski, K.

    2000-01-01

    Deuterium isotope effects on 15 N NMR chemical shifts and spin-spin coupling constants have been investigated for the 15 N enriched ammonium chloride (conc. 15 NH 4 + ion has been observed in water, methanol, ethanol and dimethylsulfoxide, while the 15 ND 4 + has been monitored in the analogous deuterated liquids. It is shown that the isotope effect in nitrogen chemical shifts ( 1 Δ 15 N( 2/1 H)), significantly different in various solvents, changes from -1.392 ppm in dimethylsulfoxide to -0.071 ppm in ethanol. The 1 J(N,H) and 1 J(N,D) coupling constants have been measured for acidic solutions under conditions of slow proton (or deuterium) exchange. The reduced coupling constants have been estimated to present isotope effects in the spin-spin coupling constants. The latter isotope effects are fairly small. (author)

  13. Sulfur isotope study of a modern intertidal environment, and the interpretation of ancient sulfides

    International Nuclear Information System (INIS)

    Chambers, L.A.

    1982-01-01

    Extensive sulfur isotope distribution data for sulfides precipitated in an intertidal environment show no distinctive features when compared with isotope values for other marine, sedimentary sulfides. The fractionation ranges from α = 1.030 to α = 1.048. The pattern is characteristic for a system essentially open to sulfate, and isotope analyses of interstitial sulfates are corroborative. A population of sulfate-reducing bacteria of the order of 10 9 organisms per cc of interstitial water is indicated. Seasonal variation of the isotope distribution reflects a transient sulfide composition and a bacterial population in which the fractionation effect is indirectly controlled by temperature. The data presented for this modern shallow water environment are at variance with an earlier assessment of isotopic distributions in ancient sulfides which linked shallow water environments with limited fractionation (α =< 1.025) in a closed system. (author)

  14. Sulfur isotope study of a modern intertidal environment, and the interpretation of ancient sulfides

    Energy Technology Data Exchange (ETDEWEB)

    Chambers, L.A. (Baas Becking Geobiological Lab., Canberra City (Australia))

    1982-05-01

    Extensive sulfur isotope distribution data for sulfides precipitated in an intertidal environment show no distinctive features when compared with isotope values for other marine, sedimentary sulfides. The fractionation ranges from ..cap alpha.. = 1.030 to ..cap alpha.. = 1.048. The pattern is characteristic for a system essentially open to sulfate, and isotope analyses of interstitial sulfates are corroborative. A population of sulfate-reducing bacteria of the order of 10/sup 9/ organisms per cc of interstitial water is indicated. Seasonal variation of the isotope distribution reflects a transient sulfide composition and a bacterial population in which the fractionation effect is indirectly controlled by temperature. The data presented for this modern shallow water environment are at variance with an earlier assessment of isotopic distributions in ancient sulfides which linked shallow water environments with limited fractionation (..cap alpha.. =< 1.025) in a closed system.

  15. Comparative study on ion-isotopic exchange reaction kinetics by application of tracer technique

    International Nuclear Information System (INIS)

    Lokhande, R.S.; Singare, P.U.

    2007-01-01

    The radioactive isotopes 131 I and 82 Br were used to trace the ion-isotopic exchange reactions using industrial grade ion exchange resins Amberlite IRA-400. The experiments were performed to understand the effect of temperature and concentration of ionic solution on kinetics of exchange reactions. Both the exchange reactions were greatly influenced by rise in temperature, which result in higher percentage of ions exchanged. For bromide ion-isotopic exchange reactions, the calculated values of specific reaction rate/min -1 , and amount of ions exchanged/mmol were obtained higher than that for iodide ion-isotopic exchange reactions under identical experimental conditions. The observed variation in the results for two ion-isotopic exchange reactions was due to the difference in the ionic size of bromide and iodide ions. (orig.)

  16. Surface studies of water isotopes in Antarctica for quantitative interpretation of deep ice core data

    Science.gov (United States)

    Landais, Amaelle; Casado, Mathieu; Prié, Frédéric; Magand, Olivier; Arnaud, Laurent; Ekaykin, Alexey; Petit, Jean-Robert; Picard, Ghislain; Fily, Michel; Minster, Bénédicte; Touzeau, Alexandra; Goursaud, Sentia; Masson-Delmotte, Valérie; Jouzel, Jean; Orsi, Anaïs

    2017-07-01

    Polar ice cores are unique climate archives. Indeed, most of them have a continuous stratigraphy and present high temporal resolution of many climate variables in a single archive. While water isotopic records (δD or δ18O) in ice cores are often taken as references for past atmospheric temperature variations, their relationship to temperature is associated with a large uncertainty. Several reasons are invoked to explain the limitation of such an approach; in particular, post-deposition effects are important in East Antarctica because of the low accumulation rates. The strong influence of post-deposition processes highlights the need for surface polar research programs in addition to deep drilling programs. We present here new results on water isotopes from several recent surface programs, mostly over East Antarctica. Together with previously published data, the new data presented in this study have several implications for the climatic reconstructions based on ice core isotopic data: (1) The spatial relationship between surface mean temperature and mean snow isotopic composition over the first meters in depth can be explained quite straightforwardly using simple isotopic models tuned to d-excess vs. δ18O evolution in transects on the East Antarctic sector. The observed spatial slopes are significantly higher (∼ 0.7-0.8‰·°C-1 for δ18O vs. temperature) than seasonal slopes inferred from precipitation data at Vostok and Dome C (0.35 to 0.46‰·°C-1). We explain these differences by changes in condensation versus surface temperature between summer and winter in the central East Antarctic plateau, where the inversion layer vanishes in summer. (2) Post-deposition effects linked to exchanges between the snow surface and the atmospheric water vapor lead to an evolution of δ18O in the surface snow, even in the absence of any precipitation event. This evolution preserves the positive correlation between the δ18O of snow and surface temperature, but is

  17. Kinetic isotope effects in the OH and Cl reactions of the clumped methane species 13CH3D

    DEFF Research Database (Denmark)

    Joelsson, Magnus

    . As is proven in the current research project, the clumped isotopes are removed by oxidation mechanisms at a slower rate. The residual methane pool is therefore enriched in clumped isotopes compared to the methane from the sources. In order to construct a top-down budget of methane, the clumped kinetic effect...... of the sinkmechanisms must be taken into account. The clumped kinetic effect in atmospheric oxidation of methane has been studied experimentally and theoretically in the three current papers: In Paper I the effect of oxidation by the chlorine radical at roomtemperature (25 ±C) was studied, in Paper II the effect...... of oxidation by the hydroxyl radical over a range of temperatures (5 ±C–40 ±C) was studied, and in Paper III the effect of both the chlorine and the hydroxyl radical at room temperature was studied. All the experiments were conducted in the smog chamber of the Department of Chemistry, University of Copenhagen...

  18. Application of carbon and oxygen stable isotopes to the study of Brazilian precambrian

    International Nuclear Information System (INIS)

    Torquato, J.R.F.

    1980-01-01

    Samples of carbonated rocks of precambrian age are studied. The stable carbon and oxygen isotopes are applied to the study of terrestrial materials considering the variations of some element isotopic composition in function of the environment of sedimentation. The isotopic analysis was done using mass spectrometers. The analytical results and the description of region geology of the site of each sample are presented. The isotopic data are interpreted aiming to the environment of sedimentation. New techniques for better improvement of carbon and oxygen ratios, are proposed, such as: to use the analysis of surface trend and the isotopic logging in mapping of surface and subsurface. A new method for approximated determination of the ages of precambrian carbonated rocks, considering the limitations of their new technique, is also presented. (M.C.K.) [pt

  19. Isotope effects associated with the anaerobic oxidation of sulfide by the purple photosynthetic bacterium, Chromatium vinosum

    International Nuclear Information System (INIS)

    Fry, B.; Gest, H.; Hayes, J.M.

    1984-01-01

    Small inverse isotope effects of 1-3 per thousand were consistently observed for the oxidation of sulfide to elemental sulfur during anaerobic photometabolism by Chromatium vinosum. The inverse fractionation can be accounted for by an equilibrium isotope effect between H 2 S and HS - , and may indicate that C. vinosum (and other photosynthetic bacteria) utilizes H 2 S rather than HS - as the substrate during sulfide oxidation. (Auth.)

  20. Isotope pattern deconvolution as a tool to study iron metabolism in plants.

    Science.gov (United States)

    Rodríguez-Castrillón, José Angel; Moldovan, Mariella; García Alonso, J Ignacio; Lucena, Juan José; García-Tomé, Maria Luisa; Hernández-Apaolaza, Lourdes

    2008-01-01

    Isotope pattern deconvolution is a mathematical technique for isolating distinct isotope signatures from mixtures of natural abundance and enriched tracers. In iron metabolism studies measurement of all four isotopes of the element by high-resolution multicollector or collision cell ICP-MS allows the determination of the tracer/tracee ratio with simultaneous internal mass bias correction and lower uncertainties. This technique was applied here for the first time to study iron uptake by cucumber plants using 57Fe-enriched iron chelates of the o,o and o,p isomers of ethylenediaminedi(o-hydroxyphenylacetic) acid (EDDHA) and ethylenediamine tetraacetic acid (EDTA). Samples of root, stem, leaves, and xylem sap, after exposure of the cucumber plants to the mentioned 57Fe chelates, were collected, dried, and digested using nitric acid. The isotopic composition of iron in the samples was measured by ICP-MS using a high-resolution multicollector instrument. Mass bias correction was computed using both a natural abundance iron standard and by internal correction using isotope pattern deconvolution. It was observed that, for plants with low 57Fe enrichment, isotope pattern deconvolution provided lower tracer/tracee ratio uncertainties than the traditional method applying external mass bias correction. The total amount of the element in the plants was determined by isotope dilution analysis, using a collision cell quadrupole ICP-MS instrument, after addition of 57Fe or natural abundance Fe in a known amount which depended on the isotopic composition of the sample.

  1. Isotope pattern deconvolution as a tool to study iron metabolism in plants

    Energy Technology Data Exchange (ETDEWEB)

    Rodriguez-Castrillon, Jose A.; Moldovan, Mariella; Garcia Alonso, J.I. [University of Oviedo, Department of Physical and Analytical Chemistry, Oviedo (Spain); Lucena, Juan J.; Garcia-Tome, Maria L.; Hernandez-Apaolaza, Lourdes [Autonoma University of Madrid, Department of Agricultural Chemistry, Madrid (Spain)

    2008-01-15

    Isotope pattern deconvolution is a mathematical technique for isolating distinct isotope signatures from mixtures of natural abundance and enriched tracers. In iron metabolism studies measurement of all four isotopes of the element by high-resolution multicollector or collision cell ICP-MS allows the determination of the tracer/tracee ratio with simultaneous internal mass bias correction and lower uncertainties. This technique was applied here for the first time to study iron uptake by cucumber plants using {sup 57}Fe-enriched iron chelates of the o,o and o,p isomers of ethylenediaminedi(o-hydroxyphenylacetic) acid (EDDHA) and ethylenediamine tetraacetic acid (EDTA). Samples of root, stem, leaves, and xylem sap, after exposure of the cucumber plants to the mentioned {sup 57}Fe chelates, were collected, dried, and digested using nitric acid. The isotopic composition of iron in the samples was measured by ICP-MS using a high-resolution multicollector instrument. Mass bias correction was computed using both a natural abundance iron standard and by internal correction using isotope pattern deconvolution. It was observed that, for plants with low {sup 57}Fe enrichment, isotope pattern deconvolution provided lower tracer/tracee ratio uncertainties than the traditional method applying external mass bias correction. The total amount of the element in the plants was determined by isotope dilution analysis, using a collision cell quadrupole ICP-MS instrument, after addition of {sup 57}Fe or natural abundance Fe in a known amount which depended on the isotopic composition of the sample. (orig.)

  2. Grain size effect on Sr and Nd isotopic compositions in eolian dust. Implications for tracing dust provenance and Nd model age

    International Nuclear Information System (INIS)

    Feng Jinliang; Zhu Liping; Zhen Xiaolin; Hu Zhaoguo

    2009-01-01

    Strontium (Sr) and neodymium (Nd) isotopic compositions enable identification of dust sources and reconstruction of atmospheric dispersal pathways. The Sr and Nd isotopic compositions in eolian dust change systematically with grain size in ways not yet fully understood. This study demonstrates the grain size effect on the Sr and Nd isotopic compositions in loess and 2006 dust fall, based on analyses of seven separated grain size fractions. The analytical results indicate that Sr isotopic ratios strongly depend on the grain size fractions in samples from all types of eolian dust. In contrast, the Nd isotopic ratios exhibit little variation in loess, although they vary significantly with grain size in samples from a 2006 dust fall. Furthermore, Nd model ages tend to increase with increasing grain size in samples from all types of eolian dust. Comparatively, Sr isotopic compositions exhibit high sensitively to wind sorting, while Nd isotopic compositions show greater sensitively to dust origin. The principal cause for the different patterns of Sr and Nd isotopic composition variability with grain size appears related to the different geochemical behaviors between rubidium (Rb) and Sr, and the similar geochemical behaviors between samarium (Sm) and Nd. The Nd isotope data indicate that the various grain size fractions in loess have similar origins for each sample. In contrast, various provenance components may separate into different grain size fractions for the studied 2006 dust fall. The Sr and Nd isotope compositions further confirm that the 2006 dust fall and Pleistocene loess in Beijing have different sources. The loess deposits found in Beijing and those found on the Chinese Loess Plateau also derive from different sources. Variations between Sr and Nd isotopic compositions and Nd model ages with grain size need to be considered when directly comparing analyses of eolian dust of different grain size. (author)

  3. The effects of the 'key' molar mass on the design of a cascade handling a multi-isotopic mixture

    International Nuclear Information System (INIS)

    Raichura, R.C.; Al-Janabi, M.A.M.

    1991-01-01

    The parameters required for describing the characteristics of separating units and cascades handling a multi-isotope mixture are first reviewed from previous work and then expressed in terms of a newly defined parameter called the 'Key' molar mass. The effects of the latter on the operating and economic parameters of a gas centrifuge cascade handling a multi-isotopic mixture are studied. Only cascades of the 'primitive' type, i.e. those in which the feed of a stage is made up of the light and heavy fractions of neighbouring stages, are considered. The costs incurred in obtaining outputs with specified concentrations are then discussed. (author)

  4. Numerical simulation of bellows effect on flow and separation of uranium isotopes in a supercritical gas centrifuge

    International Nuclear Information System (INIS)

    Borisevich, V.D.; Morozov, O.E.; Godisov, O.N.

    2000-01-01

    Numerical solving of the Navier-Stokes and convection-diffusion equations by the finite difference technique has been applied to study the influence of bellows on the flow and separation of uranium isotopes in a single supercritical gas centrifuge. Dependence of the separative power of a gas centrifuge on geometric parameters and position of a bellows on a rotor wall as well as the effect of scoop drag and feed flow on isotope separation in a gas centrifuge with a bellows have been obtained in computing experiments. It was demonstrated that increase of the separative power with increase of the gas centrifuge length is less considerable than predicted by the Dirac's law

  5. Feasibility study of medical isotope production at Sandia National Laboratories

    International Nuclear Information System (INIS)

    Massey, C.D.; Miller, D.L.; Carson, S.D.

    1995-12-01

    In late 1994, Sandia National Laboratories in Albuquerque, New Mexico, (SNL/NM), was instructed by the Department of Energy (DOE) Isotope Production and Distribution Program (IPDP) to examine the feasibility of producing medically useful radioisotopes using the Annular Core Research Reactor (ACRR) and the Hot Cell Facility (HCF). Los Alamos National Laboratory (LANL) would be expected to supply the targets to be irradiated in the ACRR. The intent of DOE would be to provide a capability to satisfy the North American health care system demand for 99 Mo, the parent of 99m Tc, in the event of an interruption in the current Canadian supply. 99m Tc is used in 70 to 80% of all nuclear medicine procedures in the US. The goal of the SNL/NM study effort is to determine the physical plant capability, infrastructure, and staffing necessary to meet the North American need for 99 Mo and to identify and examine all issues with potential for environmental impact

  6. Isotope hydrology study of Kato Nevrokopi of Dramas

    International Nuclear Information System (INIS)

    Leontiadis, I.L.; Payne, B.R.; Letsios, A.; Papagianni, N.; Kakarelis, D.; Chadjiagorakis, D.

    1984-01-01

    The isotopic composition of the water was used in order to define the mechanism of recharge of the high plateau of Kato Nevrokopi of Dramas. The results of this study indicate that there are two main sources of recharge to groundwater. One is infiltration of water from the network of irrigation canals which carry water from the Vathitopos stream. The other source of recharge originates in the mountains to the east of the plain. Infiltration from the Nevrokopi stream does occur, but is believed to be minor in this part of the plain. Recharge by infiltration of local precipitation is considered to be minor in comparison with the two main sources of recharge. An underground barrier prevents draining of the groundwater through the sinkhole, resulting in a very big reservoir under the whole central and southern parts of the high plateau. The exploitation of the groundwater of this reservoir very probably offers a low-cost solution to satisfy all needs of the area for irrigation water. (author)

  7. Isotope hydrology study of Molai area in Laconia

    International Nuclear Information System (INIS)

    Leontiadis, J.L.

    1981-04-01

    The isotopic composition of the groundwater was used in order to investigate the mechanism of recharge of the Molai plain (Laconia) and of the coastal brackish springs of the area. The results of this study have shown that the Tripolitza carbonates, northeast of the plain, do not form a unique aquifer nor contribute to the recharge of the plain which is mainly fed by the local rainwater. The brackish springs at Glyfada are fed by the Tripolitza carbonates, northeast of the Mavrovouni-Koupia fault, through an isolated from the neogene aquifer of the plain conduit. The water content of the corresponding reservoir is estimated in the range of 2318 to 3091 hm 3 . The brackish springs at Plytra are fed by the marbles of Chavallas and Skardolakka mountains through the bedrock of Assopos river and the neogene aquifer of that part of the plain. The water content of the corresponding reservoir is estimated to be more than 284 hm 3 . The brackish coastal springs between Palea Monemvasia and Hierax are fed by the Tripolitza limestones southeast of the Mavrovouni-Koupia fault. (T.A.)

  8. Sr isotopic tracer study of the Samail ophiolite, Oman

    International Nuclear Information System (INIS)

    Lanphere, M.A.; Coleman, R.G.; Hopson, C.A.

    1981-01-01

    We have measured Rb and Sr concentrations and Sr isotopic compositions in 41 whole-rock samples and 12 mineral separates from units of the Samail ophiolite, including peridotite, gabbro, plagiogranite diabase dikes, and gabbro and websterite dikes within the metamorphic peridotite. Ten samples of cummulate gabbro from the Wadir Kadir section and nine samples from the Wadi Khafifah section have mean 87 Sr/ 86 Sr ratios and standard deviations of 0.70314 +- 0.00030 and 0.70306 +- 0.00034, respectively. The dispersion in Sr isotopic composition may reflect real heterogeneities in the magma source region. The average Sr isotopic composition of cumulate gabbro falls in the range of isotopic compositions of modern midocean ridge basalt. The 87 Sr/ 86 Sr ratios of noncumulate gabbro, plagiogranite, and diabase dikes range from 0.7034 to 0.7047, 0.7038 to 0.7046, and 0.7037 to 0.7061, respectively. These higher 87 Sr/ 86 Sr ratios are due to alteration of initial magmatic compositions by hydrothermal exchange with seawater. Mineral separates from dikes that cut harzburgite tectonite have Sr isotopic compositions which agree with that of cumulate gabbro. These data indicate that the cumulate gabbro and the different dikes were derived from partial melting of source regions that had similar long-term histories and chemical compositions

  9. Contribution of stable isotopes to the study of pharmacokinetics of magnesium salts; Apport des isotopes stables a l'etude de la pharmacocinetique de sels de magnesium

    Energy Technology Data Exchange (ETDEWEB)

    Benech, H

    1999-05-28

    The use of stable isotopes as labels is becoming an attractive tool for the study of magnesium behavior in humans. It has been used two stable isotopes of magnesium, {sup 25}Mg and {sup 26}Mg, to measure the absolute bioavailability of a pharmaceutical form of magnesium. (N.C.)

  10. Contribution of stable isotopes to the study of pharmacokinetics of magnesium salts; Apport des isotopes stables a l'etude de la pharmacocinetique de sels de magnesium

    Energy Technology Data Exchange (ETDEWEB)

    Benech, H

    1999-05-28

    The use of stable isotopes as labels is becoming an attractive tool for the study of magnesium behavior in humans. It has been used two stable isotopes of magnesium, {sup 25}Mg and {sup 26}Mg, to measure the absolute bioavailability of a pharmaceutical form of magnesium. (N.C.)

  11. Effects of inorganic anions on carbon isotope fractionation during Fenton-like degradation of trichloroethene

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Yunde [State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074 (China); School of Environmental Studies, China University of Geosciences, Wuhan 430074 (China); Laboratory of Basin Hydrology and Wetland Eco-restoration, China University of Geosciences, Wuhan 430074 (China); Zhou, Aiguo, E-mail: aiguozhou@cug.edu.cn [State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074 (China); School of Environmental Studies, China University of Geosciences, Wuhan 430074 (China); Gan, Yiqun; Li, Xiaoqian [State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074 (China); School of Environmental Studies, China University of Geosciences, Wuhan 430074 (China)

    2016-05-05

    Highlights: • The effect of inorganic anions on carbon isotope fractionation was evaluated. • The enrichment factors was independent concentration of NO{sub 3}{sup −}, or SO{sub 4}{sup 2−}. • Cl{sup −} significantly influenced the carbon isotope fractionation. - Abstract: Understanding the magnitude and variability in isotope fractionation with respect to specific processes is crucial to the application of stable isotopic analysis as a tool to infer and quantify transformation processes. The variability of carbon isotope fractionation during Fenton-like degradation of trichloroethene (TCE) in the presence of different inorganic ions (nitrate, sulfate, and chloride), was investigated to evaluate the potential effects of inorganic anions on carbon isotope enrichment factor (ε value). A comparison of ε values obtained in deionized water, nitrate solution, and sulfate solution demonstrated that the ε values were identical and not affected by the presence of nitrate and sulfate. In the presence of chloride, however, the ε values (ranging from −6.3 ± 0.8 to 10 ± 1.3‰) were variable and depended on the chloride concentration, indicating that chloride could significantly affect carbon isotope fractionation during Fenton-like degradation of TCE. Thus, caution should be exercised in selecting appropriate ε values for the field application of stable isotope analysis, as various chloride concentrations may be present due to naturally present or introduced with pH adjustment and iron salts during Fenton-like remediation. Furthermore, the effects of chloride on carbon isotope fractionation may be able to provide new insights about reaction mechanisms of Fenton-like processes.

  12. Effects of inorganic anions on carbon isotope fractionation during Fenton-like degradation of trichloroethene

    International Nuclear Information System (INIS)

    Liu, Yunde; Zhou, Aiguo; Gan, Yiqun; Li, Xiaoqian

    2016-01-01

    Highlights: • The effect of inorganic anions on carbon isotope fractionation was evaluated. • The enrichment factors was independent concentration of NO_3"−, or SO_4"2"−. • Cl"− significantly influenced the carbon isotope fractionation. - Abstract: Understanding the magnitude and variability in isotope fractionation with respect to specific processes is crucial to the application of stable isotopic analysis as a tool to infer and quantify transformation processes. The variability of carbon isotope fractionation during Fenton-like degradation of trichloroethene (TCE) in the presence of different inorganic ions (nitrate, sulfate, and chloride), was investigated to evaluate the potential effects of inorganic anions on carbon isotope enrichment factor (ε value). A comparison of ε values obtained in deionized water, nitrate solution, and sulfate solution demonstrated that the ε values were identical and not affected by the presence of nitrate and sulfate. In the presence of chloride, however, the ε values (ranging from −6.3 ± 0.8 to 10 ± 1.3‰) were variable and depended on the chloride concentration, indicating that chloride could significantly affect carbon isotope fractionation during Fenton-like degradation of TCE. Thus, caution should be exercised in selecting appropriate ε values for the field application of stable isotope analysis, as various chloride concentrations may be present due to naturally present or introduced with pH adjustment and iron salts during Fenton-like remediation. Furthermore, the effects of chloride on carbon isotope fractionation may be able to provide new insights about reaction mechanisms of Fenton-like processes.

  13. The Effect of Phytase on the Oxygen Isotope Composition of Phosphate

    Science.gov (United States)

    von Sperber, C.; Tamburini, F.; Bernasconi, S. M.; Frossard, E.

    2013-12-01

    Plants and microorganisms under phosphorus (P) stress release extracellular phosphatases as a strategy to acquire inorganic phosphate (Pi) (1-2). These enzymes catalyze the hydrolysis of phosphoesters leading to a release of Pi. The enzymatic hydrolysis leads, via a nucleophilic attack, to the incorporation of one oxygen atom from the water into the newly formed Pi molecule. During the incorporation, an isotopic fractionation occurs, which might be used to identify the origin of Pi in the environment (3-6). While the effect of phosphomonoesterases and phosphodiesterases on the oxygen isotope composition of phosphate has been examined, there are, so far, no studies dealing with the effect of phytases (4-6). Phytases catalyze the hydrolysis of myo-inositol-hexakis-phosphate (IP6), which is an important component of organic P in many ecosystems (7). Enzymatic assays with phytase from wheat germ and Aspergillus niger were prepared under sterile and temperature controlled conditions in order to determine the effect of phytases on the oxygen isotope composition of phosphate, which has been liberated from IP6 via enzymatic hydrolysis. Assays with phytase from wheat germ lead to a turnover of the substrate close to 100%, while assays with phytase from Aspergillus niger lead to a turnover of the substrate close to 80%. In the case of the assays with phytase from wheat germ, our results indicate that one sixth of the total 24 oxygen which are associated to the phosphates in IP6 are exchanged with oxygen from water. From this we conclude that the incorporation of one oxygen atom from water occurs only at four phosphate molecules of IP6, while two phosphate molecules do not experience an incorporation of oxygen. This suggests that during the enzymatic hydrolysis, four P-O bonds and two C-O bonds are broken. Provided that, the isotopic fractionation can be calculated with an isotopic mass balance resulting in -8.4‰ (×3.6 SD). This is a value very similar to those reported

  14. NMR studies of two spliced leader RNAs using isotope labeling

    Energy Technology Data Exchange (ETDEWEB)

    Lapham, J.; Crothers, D.M. [Yale Univ., New Haven, CT (United States)

    1994-12-01

    Spliced leader RNAs are a class of RNA molecules (<200 nts) involved in the trans splicing of messenger RNA found in trypanosomes, nematodes, and other lower eukaryotes. The spliced leader RNA from the trypanosome Leptomonas Collosoma exists in two alternate structural forms with similar thermal stabilities. The 54 nucleotides on the 5{prime} end of the SL molecule is structurally independent from the 3{prime} half of the RNA, and displays the two structural forms. Furthermore, the favored of the two structures was shown to contain anomalous nuclease sensitivity and thermal stability features, which suggests that there may be tertiary interactions between the splice site and other nucleotides in the 5{prime} end. Multidimensional NMR studies are underway to elucidate the structural elements present in the SL RNAs that give rise to their physical properties. Two spliced leader sequences have been studied. The first, the 54 nucleotides on the 5{prime} end of the L. Collosoma sequence, was selected because of earlier studies in our laboratory. The second sequence is the 5{prime} end of the trypanosome Crithidia Fasciculata, which was chosen because of its greater sequence homology to other SL sequences. Given the complexity of the NMR spectra for RNA molecules of this size, we have incorporated {sup 15}N/{sup 13}C-labeled nucleotides into the RNA. One of the techniques we have developed to simplify the spectra of these RNA molecules is isotope labeling of specific regions of the RNA. This has been especially helpful in assigning the secondary structure of molecules that may be able to adopt multiple conformations. Using this technique one can examine a part of the molecule without spectral interference from the unlabeled portion. We hope this approach will promote an avenue for studying the structure of larger RNAs in their native surroundings.

  15. Isotope effects in interstellar molecules by chemical hyperfine interaction

    International Nuclear Information System (INIS)

    Haberkorn, R.; Michel-Beyerle, M.E.

    1977-01-01

    If free radicals recombine on grain surfaces, not only the different masses of isotopes but also their differing nuclear spin moments (e.g. 12 C/ 13 C, 14 N/ 15 N, 17 O/ 18 O) may imply variations in the recombination probability due to hyperfine interaction. This mechanism has not been accounted for so far. (orig.) [de

  16. Isotope study of impact of climatic changes on hydrological cycle in Central Asian and Caspian arid region

    International Nuclear Information System (INIS)

    Ferronsky, V.I.; Polyakov, V.A.; Lobov, A.L.; Batov, V.I.

    2001-01-01

    The problem of replenishment of groundwater and lakes in the Central Asian and Caspian and region during the Late Pleistocene-Holocene transition time on the basis of isotope studies is discussed. Interpretation of the oxygen and carbon isotope record from the palaeogroundwaters and lake sediments shows that during climate cooling over the Eurasian continent its humid zone was extended towards the and regions. In addition, voluminous glaciers were accumulated in the northern and southern mountain regions. Intensive melting of the glaciers during the transition time provided effective replenishment of the aquifers and lakes in the and zone by fresh water. (author)

  17. Lead isotopic studies of the Samail ophiolite, Oman

    Energy Technology Data Exchange (ETDEWEB)

    Chen, J.H.; Pallister, J.S.

    1981-04-10

    The isotopic composition of Pb and the concentrations of U, Th, and Pb have been determined for samples from various lithologic units and massive sulfides of the Samail ophiolite. The observed /sup 206/Pb//sup 204/Pb ratios range from 17.90 to 19.06, /sup 207/Pb//sup 204/Pb ratios from 15.43 to 15.63, and /sup 208/Pb//sup 204/Pb from 37.66 to 38.78. In Pb isotopic evolution diagrams, the initial Pb isotopic compositions of most of the samples from the Samail ophiolite plot within the field of oceanic basalt, clearly distinct from island arc data, and define some of the least radiogenic Pb observed from oceanic rocks. Lead data from the Samail are compatible with a model involving magma generation from an oceanic mantle source and formation of the ophiolite at an oceanic spreading center. U--Th--Pb isotopic systematics demonstrate that vertical heterogeneity in the oceanic crust can be created through differential concentration of U, Th, and Pb during crystal fractionation and alteration at, or near, the spreading ridge. Calcite form amygdules in the ophiolite basalt has similar Pb isotopic composition to the igneous rocks, suggesting precipitation of the calcite from seawater which contained Pb derived mostly from the oceanic crust. Lead isotopic data on Fe--Cu sulfides are also similar to the results from the igneous suite suggesting that the source of the sulfides is predominently from the oceanic crust. Lead data from serpentinized peridotite and a galena sample from below the ophiolite suggest that part of the serpentinization process and the formation of galena could involve addition of radiogenic Pb from either a continental source or from oceanic sediments.

  18. Radioactive isotope and isomer separation with using light induced drift effect

    International Nuclear Information System (INIS)

    Hradecny, C.; Slovak, J.; Tethal, T.; Ermolaev, I.M.; Shalagin, A.M.

    1991-01-01

    The isotope separation with using light induced drift (LID) is discussed. The basic theoretical characteristics of the method are deduced: separation simultaneously with an arbitrary high enrichment and without significant losses; separation productivity up to 100 μg/h. These characteristics are sufficient and very convenient for separation of expensive radioactive isotopes and isomers which are applied in medicine and science. The first experimental separation of the radioactive isotopes ( 22,24 Na) by using the LID effect is reported. 13 refs.; 5 figs

  19. 13C Kinetic isotopic effect of polymerization on monomers with multiple bond

    International Nuclear Information System (INIS)

    Berman, E.L.; Polyakov, V.B.; Makovetskij, K.L.; Golenko, T.G.; Galimov, Eh.M.; AN SSSR, Moscow. Inst. Organicheskoj Khimii; AN SSSR, Moscow. Inst. Geokhimii i Analiticheskoj Khimii)

    1988-01-01

    13 C kinetic isotopic effect (KIE) of anionic and radical polymerization and metathesis reaction of monomers with multiple bonds are studied and correlation between the found KIE values of polymerization and the structure of transition state is established. 13 C KIE of polymerization reactions are investigated using monomers with natural content of the isotope. Polymerization was carried out using high-vacuum equipment: radical polymerization of methyl acrylate (MA) and vinyl acetate in benzene solution under the effect of benzoyl peroxide (60 deg C); anionic polymerization of MA, initiated by potassium butyl cellosolvolate, was realized in mass at 25 deg C; cyclopentene metathesis reaction was conducted in benzene under the effect of initiating system WCl 6 - (C 3 H 5 ) 2 Si(CH 3 ) 2 at -30 deg C; phenylacetylene polymers were prepared by polymerization in benzene solution at 20 deg C under the effect of WCl 6 . It is ascertained that 13 C KIE of radical and anionic polymerization of olefins and cycloolefin metathesis constitutes 2.0 -2.4%. Polymerization of compound with ternary bond is accompanied by a lower value of 13 C KIE (<1%), which is explained by double bond of reacting bond in transition state

  20. The oxygen isotope effect on the in-plane penetration depth in cuprate superconductors

    International Nuclear Information System (INIS)

    Khasanov, R; Shengelaya, A; Morenzoni, E; Conder, K; Savic, I M; Keller, H

    2004-01-01

    Muon spin rotation (μSR) studies of the oxygen isotope ( 16 O/ 18 O) effect (OIE) on the in-plane magnetic field penetration depth λ ab in cuprate high-temperature superconductors (HTS) are presented. First, the doping dependence of the OIE on the transition temperature T c in various HTS is briefly discussed. It is observed that different cuprate families show similar doping dependences of the OIE on T c . Then, bulk μSR, low-energy μSR, and magnetization studies of the total and site-selective OIE on λ ab are described in some detail. A substantial OIE on λ ab was observed in various cuprate families at all doping levels, suggesting that cuprate HTS are non-adiabatic superconductors. The experiments clearly demonstrate that the total OIE on T c and λ ab arise from the oxygen sites within the superconducting CuO 2 planes, demonstrating that the phonon modes involving the movement of planar oxygen are dominantly coupled to the supercarriers. Finally, it is shown that the OIE on T c and λ ab exhibit a relation that appears to be generic for different families of cuprate HTS. The observation of these unusual isotope effects implies that lattice effects play an essential role in cuprate HTS and have to be considered in any realistic model of high-temperature superconductivity

  1. The oxygen isotope effect on the in-plane penetration depth in cuprate superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Khasanov, R [Physik-Institut der Universitaet Zuerich, CH-8057 Zurich (Switzerland); Shengelaya, A [Physik-Institut der Universitaet Zuerich, CH-8057 Zurich (Switzerland); Morenzoni, E [Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen PSI (Switzerland); Conder, K [Laboratory for Neutron Scattering, ETH Zuerich and PSI Villigen, CH-5232 Villigen PSI (Switzerland); Savic, I M [Faculty of Physics, University of Belgrade, 11001 Belgrade (Serbia and Montenegro); Keller, H [Physik-Institut der Universitaet Zuerich, CH-8057 Zurich (Switzerland)

    2004-10-13

    Muon spin rotation ({mu}SR) studies of the oxygen isotope ({sup 16}O/{sup 18}O) effect (OIE) on the in-plane magnetic field penetration depth {lambda}{sub ab} in cuprate high-temperature superconductors (HTS) are presented. First, the doping dependence of the OIE on the transition temperature T{sub c} in various HTS is briefly discussed. It is observed that different cuprate families show similar doping dependences of the OIE on T{sub c}. Then, bulk {mu}SR, low-energy {mu}SR, and magnetization studies of the total and site-selective OIE on {lambda}{sub ab} are described in some detail. A substantial OIE on {lambda}{sub ab} was observed in various cuprate families at all doping levels, suggesting that cuprate HTS are non-adiabatic superconductors. The experiments clearly demonstrate that the total OIE on T{sub c} and {lambda}{sub ab} arise from the oxygen sites within the superconducting CuO{sub 2} planes, demonstrating that the phonon modes involving the movement of planar oxygen are dominantly coupled to the supercarriers. Finally, it is shown that the OIE on T{sub c} and {lambda}{sub ab} exhibit a relation that appears to be generic for different families of cuprate HTS. The observation of these unusual isotope effects implies that lattice effects play an essential role in cuprate HTS and have to be considered in any realistic model of high-temperature superconductivity.

  2. The mechanism of oxygen isotopic fractionation during fungal denitrification - A pure culture study

    Science.gov (United States)

    Wrage-Moennig, Nicole; Rohe, Lena; Anderson, Traute-Heidi; Braker, Gesche; Flessa, Heinz; Giesemann, Annette; Lewicka-Szczebak, Dominika; Well, Reinhard

    2014-05-01

    Nitrous oxide (N2O) from soil denitrification originates from bacteria and - to an unknown extent - also from fungi. During fungal denitrification, oxygen (O) exchange takes place between H2O and intermediates of the denitrification process as in bacterial exchange[1,2]. However, information about enzymes involved in fungal O exchanges and the associated fractionation effects is lacking. The objectives of this study were to estimate the O fractionation and O exchange during the fungal denitrifying steps using a conceptual model[2] adapted from concepts for bacterial denitrification[3], implementing controls of O exchange proposed by Aerssens, et al.[4] and using fractionation models by Snider et al.[5] Six different pure fungal cultures (five Hypocreales, one Sordariales) known to be capable of denitrification were incubated under anaerobic conditions, either with nitrite or nitrate. Gas samples were analyzed for N2O concentration and its isotopic signatures (SP, average δ15N, δ18O). To investigate O exchange, both treatments were also established with 18O-labelled water as a tracer in the medium. The Hypocreales strains showed O exchange mainly at NO2- reductase (Nir) with NO2- as electron acceptor and no additional O exchange at NO3- reductase (Nar) with NO3- as electron acceptor. The only Hypocreales species having higher O exchange with NO3- than with NO2- also showed O exchange at Nar. The Sordariales species tested seems capable of O exchange at NO reductase (Nor) additionally to O exchange at Nir with NO2-. The data will help to better interpret stable isotope values of N2O from soils. .[1] D. M. Kool, N. Wrage, O. Oenema, J. Dolfing, J. W. Van Groenigen. Oxygen exchange between (de)nitrification intermediates and H2O and its implications for source determination of NO?3- and N2O: a review. Rapid Commun. Mass Spec. 2007, 21, 3569. [2] L. Rohe, T.-H. Anderson, B. Braker, H. Flessa, A. Giesemann, N. Wrage-Mönnig, R. Well. Fungal Oxygen Exchange between

  3. Kinetic isotope effects in the CH4 + H→CH3 + H2 system. Predictions of the LMR six-body potential-energy reaction hypersurface

    International Nuclear Information System (INIS)

    Marriott, T.D.

    1976-01-01

    Scope of Study: The purpose of this study was two-fold. First, it served to test, in part, the usefulness of the LMR six-body potential-energy surface (LMR-PES) for transition-state theory predictions of the kinetic isotope effects for both the forward and reverse reactions of CH 4 + H reversible CH 3 + H 2 . In this regard the agreement between experimental and theoretical isotope effects, assuming the former to be accurate, provides information about the accuracy of the curvature of the potential energy surface for motion both parallel and perpendicular to the reaction coordinate. Second, these isotope effects were used to assess the validity of a number of qualitative and semi-quantitative interpretations of kinetic isotope effects developed in physical organic chemistry with regard to this reaction system. The force constants and geometries obtained numerically from the LMR-PES were found to produce reasonable harmonic approximations to the reactant normal mode frequencies. Neglecting tunneling, the LMR-PES reasonably reproduces the experimental k/sub H//k/sub D/ values for the reactions CH 4 + H(D), CH 3 + HD(DH) and CD 2 + HD(DH). Since previous theoretical treatments of primary deuterium kinetic isotope effects have neglected the bending normal mode frequencies, a semi-quantitative study of the effect of neglecting bending frequencies on the VP, EXC, and ZPE elements as well as the transition-state theory kinetic isotope effects was performed. The Swain-Schaad relationship between primary deuterium and tritium kinetic isotope effects was shown to hold to a reasonable degree of accuracy for the LMR-PES reaction system. A relationship between 13-carbon and 14-carbon kinetic isotope effects similar to the Swain-Schaad relationship was derived

  4. Effects of alkalinity and salinity at low and high light intensity on hydrogen isotope fractionation of long-chain alkenones produced by Emiliania huxleyi

    Directory of Open Access Journals (Sweden)

    G. M. Weiss

    2017-12-01

    Full Text Available Over the last decade, hydrogen isotopes of long-chain alkenones have been shown to be a promising proxy for reconstructing paleo sea surface salinity due to a strong hydrogen isotope fractionation response to salinity across different environmental conditions. However, to date, the decoupling of the effects of alkalinity and salinity, parameters that co-vary in the surface ocean, on hydrogen isotope fractionation of alkenones has not been assessed. Furthermore, as the alkenone-producing haptophyte, Emiliania huxleyi, is known to grow in large blooms under high light intensities, the effect of salinity on hydrogen isotope fractionation under these high irradiances is important to constrain before using δDC37 to reconstruct paleosalinity. Batch cultures of the marine haptophyte E. huxleyi strain CCMP 1516 were grown to investigate the hydrogen isotope fractionation response to salinity at high light intensity and independently assess the effects of salinity and alkalinity under low-light conditions. Our results suggest that alkalinity does not significantly influence hydrogen isotope fractionation of alkenones, but salinity does have a strong effect. Additionally, no significant difference was observed between the fractionation responses to salinity recorded in alkenones grown under both high- and low-light conditions. Comparison with previous studies suggests that the fractionation response to salinity in culture is similar under different environmental conditions, strengthening the use of hydrogen isotope fractionation as a paleosalinity proxy.

  5. Effects of alkalinity and salinity at low and high light intensity on hydrogen isotope fractionation of long-chain alkenones produced by Emiliania huxleyi

    Science.gov (United States)

    Weiss, Gabriella M.; Pfannerstill, Eva Y.; Schouten, Stefan; Sinninghe Damsté, Jaap S.; van der Meer, Marcel T. J.

    2017-12-01

    Over the last decade, hydrogen isotopes of long-chain alkenones have been shown to be a promising proxy for reconstructing paleo sea surface salinity due to a strong hydrogen isotope fractionation response to salinity across different environmental conditions. However, to date, the decoupling of the effects of alkalinity and salinity, parameters that co-vary in the surface ocean, on hydrogen isotope fractionation of alkenones has not been assessed. Furthermore, as the alkenone-producing haptophyte, Emiliania huxleyi, is known to grow in large blooms under high light intensities, the effect of salinity on hydrogen isotope fractionation under these high irradiances is important to constrain before using δDC37 to reconstruct paleosalinity. Batch cultures of the marine haptophyte E. huxleyi strain CCMP 1516 were grown to investigate the hydrogen isotope fractionation response to salinity at high light intensity and independently assess the effects of salinity and alkalinity under low-light conditions. Our results suggest that alkalinity does not significantly influence hydrogen isotope fractionation of alkenones, but salinity does have a strong effect. Additionally, no significant difference was observed between the fractionation responses to salinity recorded in alkenones grown under both high- and low-light conditions. Comparison with previous studies suggests that the fractionation response to salinity in culture is similar under different environmental conditions, strengthening the use of hydrogen isotope fractionation as a paleosalinity proxy.

  6. Effects of preservation methods of muscle tissue from upper-trophic level reef fishes on stable isotope values (δ (13)C and δ (15)N).

    Science.gov (United States)

    Stallings, Christopher D; Nelson, James A; Rozar, Katherine L; Adams, Charles S; Wall, Kara R; Switzer, Theodore S; Winner, Brent L; Hollander, David J

    2015-01-01

    Research that uses stable isotope analysis often involves a delay between sample collection in the field and laboratory processing, therefore requiring preservation to prevent or reduce tissue degradation and associated isotopic compositions. Although there is a growing literature describing the effects of various preservation techniques, the results are often contextual, unpredictable and vary among taxa, suggesting the need to treat each species individually. We conducted a controlled experiment to test the effects of four preservation methods of muscle tissue from four species of upper trophic-level reef fish collected from the eastern Gulf of Mexico (Red Grouper Epinephelus morio, Gag Mycteroperca microlepis, Scamp Mycteroperca phenax, and Red Snapper Lutjanus campechanus). We used a paired design to measure the effects on isotopic values for carbon and nitrogen after storage using ice, 95% ethanol, and sodium chloride (table salt), against that in a liquid nitrogen control. Mean offsets for both δ (13)C and δ (15)N values from controls were lowest for samples preserved on ice, intermediate for those preserved with salt, and highest with ethanol. Within species, both salt and ethanol significantly enriched the δ (15)N values in nearly all comparisons. Ethanol also had strong effects on the δ (13)C values in all three groupers. Conversely, for samples preserved on ice, we did not detect a significant offset in either isotopic ratio for any of the focal species. Previous studies have addressed preservation-induced offsets in isotope values using a mass balance correction that accounts for changes in the isotope value to that in the C/N ratio. We tested the application of standard mass balance corrections for isotope values that were significantly affected by the preservation methods and found generally poor agreement between corrected and control values. The poor performance by the correction may have been due to preferential loss of lighter isotopes and

  7. Study of hydrogen isotopes super permeation through vanadium membrane on 'Prometheus' setup

    International Nuclear Information System (INIS)

    Musyaev, R. K.; Yukhimchuk, A. A.; Lebedev, B. S.; Busnyuk, A. O.; Notkin, M. E.; Samartsev, A. A.; Livshits, A. I.

    2008-01-01

    To develop the membrane pumping technology by means of superpermeable membranes at RFNC-VNIIEF in the 'Prometheus' setup, the experiments on superpermeation of hydrogen isotopes through metal membranes were carried out. The experimental results on superpermeation of thermal atoms of hydrogen isotopes including tritium through a cylindrical vanadium membrane are presented. The possibility of effective pumping, compression and recuperation of hydrogen isotopes by means of superpermeable membrane was demonstrated. The evaluation of membrane pumping rates and asymmetry degree of pure vanadium membrane was given. The work was performed under the ISTC-2854 project. (authors)

  8. Neutronic and thermal-hydraulic studies of aqueous homogeneous reactor for medical isotopes production

    International Nuclear Information System (INIS)

    Perez, Daniel Milian; Lorenzo, Daniel E. Milian; Lira, Carlos A. Brayner de Oliveira; Garcia, Lorena P. Rodríguez; Universidade Federal de Pernambuco

    2017-01-01

    The use of Aqueous Homogenous Reactors (AHR) is one of the most promissory alternatives to produce medical isotopes, mainly "9"9Mo. Compare to multipurpose research reactors, an AHR dedicated for "9"9Mo production has advantages because of their low cost, small critical mass, inherent passive safety, and simplified fuel handling, processing, and purification characteristics. This article presents the current state of research in our working group on this topic. Are presented and discussed the group validation efforts with benchmarking exercises that include neutronic and thermal-hydraulic results of two solution reactors, the SUPO and ARGUS reactors. Neutronic and thermal-hydraulic results of 75 kWth AHR based on the ARGUS reactor LEU configuration are presented. The neutronic studies included the determination of parameters such as reflector thickness, critical height, medical isotopes production and others. Thermal-hydraulics studies were focused on demonstrating that sufficient cooling capacity exists to prevent fuel overheating. In addition, the effects of some calculation parameters on the computational modeling of temperature, velocity and gas volume fraction during steady-state operation of an AHR are discussed. The neutronic and thermal-hydraulics studies have been performed with the MCNPX version 2.6e computational code and the version 14 of ANSYS CFX respectively. Our group studies and the results obtained contribute to demonstrate the feasibility of using AHR for the production of medical isotopes, however additional studies are still necessary to confirm these results and contribute to development and demonstration of their technical, safety, and economic viability. (author)

  9. Neutronic and thermal-hydraulic studies of aqueous homogeneous reactor for medical isotopes production

    Energy Technology Data Exchange (ETDEWEB)

    Perez, Daniel Milian; Lorenzo, Daniel E. Milian; Lira, Carlos A. Brayner de Oliveira; Garcia, Lorena P. Rodríguez, E-mail: milianperez89@gmail.com, E-mail: dmilian@instec.cu, E-mail: lorenapilar1109@gmail.com, E-mail: cabol@ufpe.br [Higher Institute of Technologies and Applied Sciences (InSTEC), Havana (Cuba); Universidade Federal de Pernambuco (UFPE), Recife, PE (Brazil). Departamento de Energia Nuclear

    2017-11-01

    The use of Aqueous Homogenous Reactors (AHR) is one of the most promissory alternatives to produce medical isotopes, mainly {sup 99}Mo. Compare to multipurpose research reactors, an AHR dedicated for {sup 99}Mo production has advantages because of their low cost, small critical mass, inherent passive safety, and simplified fuel handling, processing, and purification characteristics. This article presents the current state of research in our working group on this topic. Are presented and discussed the group validation efforts with benchmarking exercises that include neutronic and thermal-hydraulic results of two solution reactors, the SUPO and ARGUS reactors. Neutronic and thermal-hydraulic results of 75 kWth AHR based on the ARGUS reactor LEU configuration are presented. The neutronic studies included the determination of parameters such as reflector thickness, critical height, medical isotopes production and others. Thermal-hydraulics studies were focused on demonstrating that sufficient cooling capacity exists to prevent fuel overheating. In addition, the effects of some calculation parameters on the computational modeling of temperature, velocity and gas volume fraction during steady-state operation of an AHR are discussed. The neutronic and thermal-hydraulics studies have been performed with the MCNPX version 2.6e computational code and the version 14 of ANSYS CFX respectively. Our group studies and the results obtained contribute to demonstrate the feasibility of using AHR for the production of medical isotopes, however additional studies are still necessary to confirm these results and contribute to development and demonstration of their technical, safety, and economic viability. (author)

  10. Calcium Isotope Analysis by Mass Spectrometry

    Science.gov (United States)

    Boulyga, S.; Richter, S.

    2010-12-01

    The variations in the isotopic composition of calcium caused by fractionation in heterogeneous systems and by nuclear reactions can provide insight into numerous biological, geological, and cosmic processes, and therefore isotopic analysis finds a wide spectrum of applications in cosmo- and geochemistry, paleoclimatic, nutritional, and biomedical studies. The measurement of calcium isotopic abundances in natural samples has challenged the analysts for more than three decades. Practically all Ca isotopes suffer from significant isobaric interferences, whereas low-abundant isotopes can be particularly affected by neighboring major isotopes. The extent of natural variations of stable isotopes appears to be relatively limited, and highly precise techniques are required to resolve isotopic effects. Isotope fractionation during sample preparation and measurements and instrumental mass bias can significantly exceed small isotope abundance variations in samples, which have to be investigated. Not surprisingly, a TIMS procedure developed by Russell et al. (Russell et al., 1978. Geochim Cosmochim Acta 42: 1075-1090) for Ca isotope measurements was considered as revolutionary for isotopic measurements in general, and that approach is used nowadays (with small modifications) for practically all isotopic systems and with different mass spectrometric techniques. Nevertheless, despite several decades of calcium research and corresponding development of mass spectrometers, the available precision and accuracy is still not always sufficient to achieve the challenging goals. This presentation discusses figures of merits of presently used analytical methods and instrumentation, and attempts to critically assess their limitations. Additionally, the availability of Ca isotope reference materials will be discussed.

  11. Isotope studies of UK tufa deposits and associated source waters

    International Nuclear Information System (INIS)

    Thorpe, P.M.

    1981-12-01

    Tufa is a secondary deposit of calcium carbonate precipitated from springs and streams. Previous attempts to date tufa deposits directly with 14 C have had limited success. The major problem is to quantify the amount of carbon incorporated in tufa, derived from the dissolution of carbonate bedrock, essentially free of 14 C. The isotopic composition of tufa-depositing streamwaters is similar to that of water recharging aquifers. The 14 C levels of recent tufa layers, at three sites, were similar to those of the source waters. 14 C dates from tufa at these sites suggested a Postglacial origin when corrected for bedrock carbon dilution of 16 to 24%. This dilution was overestimated by consideration of carbon mass balance using characteristic stable carbon isotope compositions (delta 13 C) for the biogenic and bedrock components. This method of correction is often applied to 14 C dates from groundwaters. The carbon isotope composition of spring waters supplying the tufa-depositing streams was realistically explained by a two stage process of carbonate dissolution under open and then closed conditions with respect to gaseous carbon dioxide. Seasonal variations in the 14 C and delta 13 C composition of stream and spring waters, downstream increases in 14 C and delta 13 C and seasonal variations in the oxygen and hydrogen isotopic composition of rainfall are explained. (author)

  12. Groundwater regimes and isotopic studies, Ranger mine area, Northern Territory

    Energy Technology Data Exchange (ETDEWEB)

    Ahmad, M; Green, D C

    1986-12-01

    Three types of groundwater occur in the area of the Ranger mine. Type A groundwater occurs in the loose sands and gravels occupying the present day stream channels, Type B in the weathering profile and Type C occurs in relatively fresh fractured bedrock occupying open fractures and other cavities. The three types of groundwater can be distinguished both chemically and isotopically. Light stable isotope data suggest that most early rains are lost by evapotranspiration and have no imprint on the groundwater. Later in the wet season, the ground is saturated and groundwater recharge occurs on a regional scale. This younger groundwater sits on the older waters. Mixing is probably minimal as before any large scale mixing could occur, most younger waters are lost by evapotranspiration. Stable isotope data suggest that Type B groundwater in certain areas has some connection with evaporated surface water bodies. Stable isotope measurements for the pollution monitoring bores around the tailings dam do not indicate any connection with the polluted pond waters at the time of sample collection.

  13. Heating Isotopically Labeled Bernal Stacked Graphene: A Raman Spectroscopy Study

    Czech Academy of Sciences Publication Activity Database

    Ek Weis, Johan; da Costa, Sara; Frank, Otakar; Kalbáč, Martin

    2014-01-01

    Roč. 5, č. 3 (2014), s. 549-554 ISSN 1948-7185 R&D Projects: GA MŠk LL1301 Institutional support: RVO:61388955 Keywords : Bernal * graphene * isotopic labeling Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 7.458, year: 2014

  14. Hydrologic and isotopic study of the Quito aquifer

    International Nuclear Information System (INIS)

    Villalba, Fabio; Benalcazar, Julio; Garcia, Marco; Altamirano, Cesar; Altamirano, Homero; Sarasti, Santiago; Mancero, Maria; Leiva, Eduardo; Pino, Jose; Alulema, Rafael; Cedeno, Alberto; Burbano, Napoleon; Paquel, Efren; Becerra, Simon; Andrade, Graciela

    2000-10-01

    The dynamics of the Quito basin and surrounding area aquifers were determined through the use of stable and radioactive isotopes, and the monitoring of the freatic levels and of the bacteriological and physico-chemical quality of the water. A conceptual hydrodynamic model of the Quito aquifer was also proposed in order to establish in the future a sustainable management system

  15. Normal coordinate treatment of liquid water and calculation of vapor pressure isotope effects

    International Nuclear Information System (INIS)

    Gellai, B.; Van Hook, W.A.

    1983-01-01

    A vibrational analysis of liquid water is reported, assuming a completely hydrogen-bonded network with continuously varying strengths of the hydrogen bonds. Frequency distribution calculations are made for intramolecular stretching and bending modes and for the intramolecular frequency region. The calculated distributions are compared with the experimental spectroscopic ones. As another test, vapor pressure isotope effects are calculated from the theoretical distributions for some isotopic water molecules. Results are compared with those of other authors obtained from a mixture model. (author)

  16. Isotope mixtures of hydrogen in vanadium

    International Nuclear Information System (INIS)

    Mecking-Schloetensack, P.

    1982-03-01

    The properties of isotope-mixtures of Protium and Deuterium stored in Vanadium have been studied. Protium and Deuterium are existing as interstitial-atoms on tetrahedral sites as well as on octahedral sites in this system. This feature leads to large isotopic-effects between the two isotopes. The dependence of the thermodynamic functions like heat of solution, nonconfigurational entropy, specific heat and ordering temperatures from the composition of the isotope-mixture has been determined. (orig.)

  17. Utility of stable isotope analysis in studying foraging ecology of herbivores: Examples from moose and caribou

    Science.gov (United States)

    Ben-David, Merav; Shochat, Einav; Adams, Layne G.

    2001-01-01

    Recently, researchers emphasized that patterns of stable isotope ratios observed at the individual level are a result of an interaction between ecological, physiological, and biochemical processes. Isotopic models for herbivores provide additional complications because those mammals consume foods that have high variability in nitrogen concentrations. In addition, distribution of amino acids in plants may differ greatly from that required by a herbivore. At northern latitudes, where the growing season of vegetation is short, isotope ratios in herbivore tissues are expected to differ between seasons. Summer ratios likely reflect diet composition, whereas winter ratios would reflect diet and nutrient recycling by the animals. We tested this hypothesis using data collected from blood samples of caribou (Rangifer tarandus) and moose (Alces alces) in Denali National Park and Preserve, Alaska, USA. Stable isotope ratios of moose and caribou were significantly different from each other in late summer-autumn and winter. Also, late summer-autumn and winter ratios differed significantly between seasons in both species. Nonetheless, we were unable to evaluate whether differences in seasonal isotopic ratios were a result of diet selection or a response to nutrient recycling. We believe that additional studies on plant isotopic ratios as related to ecological factors in conjunction with investigations of diet selection by the herbivores will enhance our understanding of those interactions. Also, controlled studies investigating the relation between diet and physiological responses in herbivores will increase the utility of isotopic analysis in studying foraging ecology of herbivores.

  18. International conference on isotopes in environmental studies - Aquatic Forum 2004. Book of extended synopses

    International Nuclear Information System (INIS)

    2004-01-01

    The International Conference on Isotopes in Environmental Studies: AQUATIC FORUM 2004, organized by the International Atomic Energy Agency (IAEA) was held in Monte-Carlo, Monaco, 25-29 October 2004. The principal objective of the Conference was to review recent achievements in the use of isotopic techniques to study marine and terrestrial environmental processes, transport of contaminants in the aquatic environment, climate change, computer modelling of environmental processes, present state of the art of isotopic techniques, data validation and syntheses, and the development of geographical information systems. This publication contains the extended synopses of presentations at the Conference

  19. International conference on isotopes in environmental studies - Aquatic Forum 2004. Book of extended synopses

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2004-07-01

    The International Conference on Isotopes in Environmental Studies: AQUATIC FORUM 2004, organized by the International Atomic Energy Agency (IAEA) was held in Monte-Carlo, Monaco, 25-29 October 2004. The principal objective of the Conference was to review recent achievements in the use of isotopic techniques to study marine and terrestrial environmental processes, transport of contaminants in the aquatic environment, climate change, computer modelling of environmental processes, present state of the art of isotopic techniques, data validation and syntheses, and the development of geographical information systems. This publication contains the extended synopses of presentations at the Conference.

  20. Study of the stability of the gallium isotopes beyond the N = 50 neutron shell closure

    CERN Multimedia

    We propose to study the stability of the nuclear structure beyond N = 50 and Z = 28 with beams of neutron-rich gallium isotopes at the CRIS experiment at ISOLDE. The study of their hyperne structure and isotope shift will provide spins, magnetic dipole moments, electric quadrupole moments and changes in the mean-square charge radii. The $\\beta$-decay of $^{80}$Ga will be unambiguously measured using the technique of Laser Assisted Nuclear Decay Spectroscopy (LANDS). The half-lives of the very neutron-rich isotopes with N > 54 will be measured for their impact on the astrophysical ${r}$-process.

  1. Environmental isotope study of a groundwater supply project in the Kalahari of Gordonia

    International Nuclear Information System (INIS)

    Verhagen, B.T.

    1984-01-01

    A feasibility study for a central fresh groundwater supply scheme in the Kalahari of the Gordonia district, South Africa, provided the opportunity to study fresh and saline water occurrences in detail with environmental isotopes. The isotopic and chemical signals show a clear contrast among groundwaters below a river bed, an extended fresh groundwater body and saline groundwaters in close proximity to the river. Carbon-14, tritium and stable-isotope data lead to a vertical rain recharge model rather than a regional flow mechanism for an understanding of the various water occurrences, their interrelationships and varied hydrochemistry. (author)

  2. High flux isotope reactor cold source preconceptual design study report

    International Nuclear Information System (INIS)

    Selby, D.L.; Bucholz, J.A.; Burnette, S.E.

    1995-12-01

    In February 1995, the deputy director of Oak Ridge National Laboratory (ORNL) formed a group to examine the need for upgrades to the High Flux Isotope Reactor (HFIR) system in light of the cancellation of the Advanced Neutron Source Project. One of the major findings of this study was that there was an immediate need for the installation of a cold neutron source facility in the HFIR complex. The anticipated cold source will consist of a cryogenic LH 2 moderator plug, a cryogenic pump system, a refrigerator that uses helium gas as a refrigerant, a heat exchanger to interface the refrigerant with the hydrogen loop, liquid hydrogen transfer lines, a gas handling system that includes vacuum lines, and an instrumentation and control system to provide constant system status monitoring and to maintain system stability. The scope of this project includes the development, design, safety analysis, procurement/fabrication, testing, and installation of all of the components necessary to produce a working cold source within an existing HFIR beam tube. This project will also include those activities necessary to transport the cold neutron beam to the front face of the present HFIR beam room. The cold source project has been divided into four phases: (1) preconceptual, (2) conceptual design and research and development (R and D), (3) detailed design and procurement, and (4) installation and operation. This report marks the conclusion of the preconceptual phase and establishes the concept feasibility. The information presented includes the project scope, the preliminary design requirements, the preliminary cost and schedule, the preliminary performance data, and an outline of the various plans for completing the project

  3. Therapeutic use of radioactive isotopes

    CERN Document Server

    Caroline Duc

    2013-01-01

    In December, researchers from ISOLDE-CERN, the Paul Scherrer Institute (PSI) and the Institut Laue-Langevin (ILL) published the results of an in vivo study which successfully proved the effectiveness of four terbium isotopes for diagnosing and treating cancerous tumours.   Four terbium isotopes suitable for clinical purposes. “ISOLDE is the only installation capable of supplying terbium isotopes of such purity and intensity in the case of three out of the four types used in this study,” explains Karl Johnson, a physicist at ISOLDE.  “Producing over a thousand different isotopes, our equipment offers the widest choice of isotopes in the world!” Initially intended for fundamental physics research, ISOLDE has diversified its activities over time to invest in various projects in the materials science, biochemistry and nuclear medicine fields. The proof-of-concept study has confirmed that the four terbium isotopes 149Tb, 152Tb, 155Tb produ...

  4. Crystal-plastic deformation of zircon : effects on microstructures, textures, microchemistry and the retention of radiogenic isotopes

    International Nuclear Information System (INIS)

    Kovaleva, E.

    2015-01-01

    Dating of deep-crustal deformation events potentially can be achieved by using plastically-deformed accessory minerals found in high-temperature shear zones. Deformation microstructures, such as dislocations and low-angle boundaries, form due to plastic deformation in the crystal lattice and act as fluid migration pathways and trace element (e.g. Pb, Ti, U, Th, REE) diffusion pathways through so-called “pipe diffusion”. Deformation microstructures can alter the chemical and isotopic composition of certain grain parts and may lead to complete or partial isotopic resetting of certain geochronometers (e.g. U/Th/Pb, K/Ar, Rb/Sr) in the mineral domains. This work aims to better understand the processes of crystal-plastic deformation and associated trace element redistribution and the resetting of isotopic systems in zircon. This study finds that: a) there are three general finite deformation patterns in deformed zircons; b) suggests that it is possible to reconstruct the macroscopic kinematic framework of the shear zone based on the orientation of deformed zircon grains and the operating misorientation axes; c) and demonstrates the effect of deformation microstructures on trace elements and Pb isotopes in zircon. The final goal of this project is to develop a tool for isotopic dating of high-temperature deformation events in the deep crust. In addition to these results, zircon grains with planar deformation bands have been discovered in paleo-seismic zones; these deformation features have been described in detail and a possible mechanism of their origin and formation is suggested. The effect of planar deformation bands on trace element and isotopic behavior has also been investigated. (author) [de

  5. Temperature dependence of carbon kinetic isotope effect for the oxidation reaction of ethane by OH radicals under atmospherically relevant conditions

    Science.gov (United States)

    Piansawan, Tammarat; Saccon, Marina; Laumer, Werner; Gensch, Iulia; Kiendler-Scharr, Astrid

    2015-04-01

    Modeling of the global distribution of atmospheric ethane sources and sinks by using the 13C isotopic composition requires accurate knowledge of the carbon kinetic isotope effect (KIE) of its atmospheric removal reactions. The quantum mechanical prediction implies the necessity to elucidate the temperature dependence of KIE within atmospherically relevant temperature range by experiment. In this study, the KIE and its temperature dependence for ethane oxidation by OH radicals was investigated at ambient pressure in a temperature range of 243 K to 303 K. The chemical reactions were carried out in a 15 L PFE reaction chamber, suspended in a thermally controlled oven. The isotope ratios of the gas phase components during the course of the reactions were measured by Thermal Desorption -- Gas Chromatography -- Isotope Ratio Mass Spectrometry (TD-GC-IRMS). For each temperature, the KIE was derived from the temporal evolution of the concentration and stable carbon isotope ratio (δ13C) of ethane using a method adapted from the relative reaction rate concept. The room temperature KIE of the ethane reaction with OH radicals was found to be 6.85 ± 0.32 ‰. This value is in agreement with the previously reported value of 8.57 ± 1.95 ‰ [Anderson et al. 2004] but has a substantially lower uncertainty. The experimental results will be discussed with the KIE temperature dependence predicted by quantum mechanical calculations. Reference: Rebecca S. Anderson, Lin Huang, Richard Iannone, Alexandra E. Thompson, and Jochen Rudolph (2004), Carbon Kinetic Isotope Effects in the Gas Phase Reactions of Light Alkanes and Ethene with the OH Radical at 296 ± 4 K, J. Phys. Chem. A, 108, 11537--11544

  6. The effective management of medical isotope production in research reactors

    International Nuclear Information System (INIS)

    Drummond, D.T.

    1993-01-01

    During the 50-yr history of the use of radioisotopes for medical applications, research reactors have played a pivotal role in the production of many if not most of the key products. The marriage between research reactors and production operations is subject to significant challenges on two fronts. The medical applications of the radioisotope products impose some unique constraints and requirements on the production process. In addition, the mandates and priorities of a research reactor are not always congruent with the demands of a production environment. This paper briefly reviews the historical development of medical isotope production, identifies the unique challenges facing this endeavor, and discusses the management of the relationship between the isotope producer and the research reactor operator. Finally, the key elements of a successful relationship are identified

  7. Lithium isotope effect in the extraction systems of polyethers: effect of salt concentration

    International Nuclear Information System (INIS)

    Fang Shengqiang; Fu Lian

    1991-01-01

    Separation factors of lithium isotopes at 20 deg C were determined in the extraction systems of B15C5-CHCl 3 /LiBr-H 2 O. The initial concentration of LiBr was controlled in the extent of more than 2 mol/l. It may be established that the increase of LiBr concentration causes a remarkable increase of the separation factor. The essence of this effect due to the change in salt concentration was discussed in connection with examination of relevant phenomena in literature. It can be concluded that the relationship between α and Cm, the concentration of lithium salt, is dependent on K Q and K P express respectively, lithium isotope exchange equilibrium constants between Li-crownether complex and hydrated lithium ion for lithium concentration less than 1-2 mol/l, and between lithium salt ion pair and hydrated lithium ion for lithium concentration more than 2 mol/l in aqueous phase

  8. Isotope effect in the photochemical decomposition of CO{sub 2} (ice) by Lyman-{alpha} radiation

    Energy Technology Data Exchange (ETDEWEB)

    Yuan Chunqing; Yates, John T. Jr. [Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904 (United States)

    2013-04-21

    The photochemical decomposition of CO{sub 2}(ice) at 75 K by Lyman-{alpha} radiation (10.2 eV) has been studied using transmission infrared spectroscopy. An isotope effect in the decomposition of the CO{sub 2} molecule in the ice has been discovered, favoring {sup 12}CO{sub 2} photodecomposition over {sup 13}CO{sub 2} by about 10%. The effect is caused by electronic energy transfer from the excited CO{sub 2} molecule to the ice matrix, which favors quenching of the heavier electronically-excited {sup 13}CO{sub 2} molecule over {sup 12}CO{sub 2}. The effect is similar to the Menzel-Gomer-Redhead isotope effect in desorption from adsorbed molecules on surfaces when electronically excited. An enhancement of the rate of formation of lattice-trapped CO and CO{sub 3} species is observed for the photolysis of the {sup 12}CO{sub 2} molecule compared to the {sup 13}CO{sub 2} molecule in the ice. Only 0.5% of the primary photoexcitation results in O-CO bond dissociation to produce trapped-CO and trapped-CO{sub 3} product molecules and the majority of the electronically-excited CO{sub 2} molecules return to the ground state. Here either vibrational relaxation occurs (majority process) or desorption of CO{sub 2} occurs (minority process) from highly vibrationally-excited CO{sub 2} molecules in the ice. The observation of the {sup 12}C/{sup 13}C isotope effect in the Lyman-{alpha} induced photodecomposition of CO{sub 2} (ice) suggests that over astronomical time scales the isotope enrichment effect may distort historical information derived from isotope ratios in space wherever photochemistry can occur.

  9. Disentangling effects of growth and nutritional status on seabird stable isotope ratios

    Science.gov (United States)

    Sears, J.; Hatch, Shyla A.; O'Brien, D. M.

    2009-01-01

    A growing number of studies suggest that an individual's physiology affects its carbon and nitrogen stable isotope signatures, obscuring a signal often assumed to be only a reflection of diet and foraging location. We examined effects of growth and moderate food restriction on red blood cell (RBC) and feather ??15N and ??13C in rhinoceros auklet chicks (Cerorhinca monocerata), a piscivorous seabird. Chicks were reared in captivity and fed either control (75 g/day; n = 7) or ~40% restricted (40 g/day; n = 6) amounts of high quality forage fish. We quantified effects of growth on isotopic fractionation by comparing ??15N and ??13C in control chicks to those of captive, non-growing subadult auklets (n = 11) fed the same diet. To estimate natural levels of isotopic variation, we also collected blood from a random sample of free-living rhinoceros auklet adults and chicks in the Gulf of Alaska (n = 15 for each), as well as adult feather samples (n = 13). In the captive experiment, moderate food restriction caused significant depletion in ??15N of both RBCs and feathers in treatment chicks compared to control chicks. Growth also induced depletion in RBC ??15N, with chicks exhibiting lower ??15N when they were growing the fastest. As growth slowed, ??15N increased, resulting in an overall pattern of enrichment over the course of the nestling period. Combined effects of growth and restriction depleted ??15N in chick RBCs by 0.92???. We propose that increased nitrogen-use efficiency is responsible for 15N depletion in both growing and food-restricted chicks. ??15N values in RBCs of free-ranging auklets fell within a range of only 1.03???, while feather ??15N varied widely. Together, our captive and field results suggest that both growth and moderate food restriction can affect stable isotope ratios in an ecologically meaningful way in RBCs although not feathers due to greater natural variability in this tissue. ?? 2008 Springer-Verlag.

  10. Geological, Geochemical 1 and Rb-Sr isotopic studies on tungsten 2 ...

    Indian Academy of Sciences (India)

    37

    Geological, Geochemical and Rb-Sr isotopic studies on tungsten. 1 mineralised ..... From the field relations it is demonstrated that SG (biotite-bearing granitic gneiss) and. 120 ..... cases Ba) and vice-versa for the low concentration. 291.

  11. Application of Environmental Isotopes in Hydrological Studies Along the River Nile Valley, Egypt

    Energy Technology Data Exchange (ETDEWEB)

    Nada, A. A. [Site and Environmental Dept. NCNSRC, Atomic Energy Authority, Cairo (Egypt)

    2013-07-15

    This paper reviews some of the contributions of isotope techniques to better understanding hydrological problems in Egypt and the Nile basin. The stable isotope composition of precipitation shows considerable variations both in time and space since it is controlled by climatic factors. Surface waters became enriched in deuterium and oxygen-18 relative to their initial isotopic composition as losses by evaporation occur. The GNIP sampling stations at Entebbe and Addis Ababa, which are located at the source of the Nile River, present relatively depleted isotopic contents. Assuming that the central Africa runoff (White Nile downstream from Sudan) represents 30% of the natural discharge of Egypt, and the remaining 70% is derived from Ethiopia (Blue Nile), we obtain a composite depleted stable isotope composition of the river Nile reaching upper Egypt under natural conditions (before the construction of the Aswan High Dam). Stable isotopes were used to estimate the evaporation rate from Lake Nasser, based on the isotopic content of the lake water. The lake can be divided into two sectors: the first sector, with remarkable vertical gradient in O-18 and deuterium, and a second sector, characterized by a lower vertical isotopic gradient. In order to detect this effect, surface Nile water samples have been collected at Cairo after a heavy storm event covering all Egypt at the beginning of November 1994, characterized by very negative deuterium and oxygen-18 contents. The isotopic content of Nile water samples fluctuated and slightly changed with time. The variation of the bomb tritium response of the Nile has been reconstructed using a model based on the contents in the catchment areas of the Nile. Pre-bomb tritium content in the Nile was about 5 TU, reaching a maximum level during the early sixties of about 500 TU. At present the tritium level content of the Nile is about 6 TU. (author)

  12. Application of stable isotope analysis to study temporal changes in foraging ecology in a highly endangered amphibian.

    Directory of Open Access Journals (Sweden)

    J Hayley Gillespie

    Full Text Available Understanding dietary trends for endangered species may be essential to assessing the effects of ecological disturbances such as habitat modification, species introductions or global climate change. Documenting temporal variation in prey selection may also be crucial for understanding population dynamics. However, the rarity, secretive behaviours and obscure microhabitats of some endangered species can make direct foraging observations difficult or impossible. Furthermore, the lethality or invasiveness of some traditional methods of dietary analysis (e.g. gut contents analysis, gastric lavage makes them inappropriate for such species. Stable isotope analysis facilitates non-lethal, indirect analysis of animal diet that has unrealized potential in the conservation of endangered organisms, particularly amphibians.I determined proportional contributions of aquatic macroinvertebrate prey to the diet of an endangered aquatic salamander Eurycea sosorum over a two-year period using stable isotope analysis of (13/12C and (15/14N and the Bayesian stable isotope mixing model SIAR. I calculated Strauss' dietary electivity indices by comparing these proportions with changing relative abundance of potential prey species through time. Stable isotope analyses revealed that a previously unknown prey item (soft-bodied planarian flatworms in the genus Dugesia made up the majority of E. sosorum diet. Results also demonstrate that E. sosorum is an opportunistic forager capable of diet switching to include a greater proportion of alternative prey when Dugesia populations decline. There is also evidence of intra-population dietary variation.Effective application of stable isotope analysis can help circumvent two key limitations commonly experienced by researchers of endangered species: the inability to directly observe these species in nature and the invasiveness or lethality of traditional methods of dietary analysis. This study illustrates the feasibility of stable

  13. Parameter study on Japanese proposal of ITER hydrogen isotope separation system

    International Nuclear Information System (INIS)

    Yoshida, Hiroshi; Enoeda, Mikio; Tanaka, Shigeru; Ohokawa, Yoshinao; Ohara, Atsushi; Nagakura, Masaaki; Naito, Taisei; Nagashima, Kazuhiro.

    1991-01-01

    As part of Japanese design contribution in the ITER activity, conceptual design of an entire ITER tritium system and their safety analysis have been carried out through the three-year period since 1988. The tritium system includes the following subsystems; - Fuelling (gas puffing and pellet injection) subsystem, - Torus vacuum pumping subsystem, - Plasma exhaust gas purification subsystem, - Hydrogen isotope separation subsystem, - NBI gas processing subsystem, - Blanket tritium recovery subsystem, - Tritiated water processing subsystem, - Tritium safety subsystem. Hydrogen isotope separation system is a key subsystem in the ITER tritium system because it is connected to all above subsystems. This report describes an analytical study on the Japanese concept of hydrogen isotope separation system. (author)

  14. Isotopic studies of rare gases in terrestrial samples and in natural nucleosynthesis

    International Nuclear Information System (INIS)

    Reynolds, J.H.

    1988-08-01

    This project is concerned with research in rare gas mass spectrometry. The broad objective is to read the natural record that isotopes of the rare gases comprise as trace constituents of natural gases, rocks, and meteorites. In past years, these interests have led to the study of such diverse problems as the dating of rocks, the early chronology and isotopic structure of the solar system as revealed by extinct radioactivities, and the elemental and isotopic composition of trapped primordial rare gases in meteorites. In recent years, the project has focused progressively more on terrestrial problems

  15. Isotopic studies of rare gases in terrestrial samples and in natural nucleosynthesis

    International Nuclear Information System (INIS)

    1987-07-01

    This project is concerned with research in rare gas mass spectrometry. The broad objective is to read the natural record that isotopes of the rare gases comprise as trace constituents of natural gases, rocks, and meteorites. In past years, these interests have led to the study of such diverse problems as the dating of rocks, the early chronology and isotopic structure of the solar system as revealed by extinct radioactivities, and the elemental and isotopic composition of trapped primordial rare gases in meteorites. In recent years, the project has focused progressively more on terrestrial problems

  16. Investigations on the heterogenous catalytic hydrogenation using isotope effect and gamma- and neutron radiation

    Energy Technology Data Exchange (ETDEWEB)

    Kudlacek, R; Cabicar, J [Ceske Vysoke Uceni Technicke, Prague (Czechoslovakia). Katedra Jaderne Chemie

    1976-01-01

    The kinetic and solvent isotope effects during the maleic acid heterogeneous catalytic hydrogenation and deuteration in light and heavy water have been studied. Also the effect of the gamma and neutron irradiation on the Ni-ZnO catalysts (with various ratios of components) on the reaction kinetics and mechanism has been measured, as well as the effect of pH on the adsorption behaviour of maleic acid and the temperature dependence of the reaction rate. Existence of different adsorption centers for hydrogen and maleic acid could be deduced from these experiments. A reaction mechanism based on the two-dimensional diffusion of components in the surface is proposed. The catalyst is formed from Ni and ZnO-microspheres. Hydrogen is bound to nickel and maleic acid is adsorbed on the ZnO-microspheres. The reaction takes place on the boundary layers of these microspheres.

  17. Insights into iron sources and pathways in the Amazon River provided by isotopic and spectroscopic studies

    Science.gov (United States)

    Mulholland, Daniel Santos; Poitrasson, Franck; Boaventura, Geraldo Resende; Allard, Thierry; Vieira, Lucieth Cruz; Santos, Roberto Ventura; Mancini, Luiz; Seyler, Patrick

    2015-02-01

    The present study investigated the weathering and transport mechanisms of Fe in the Amazon River. A particular emphasis was placed on Fe partitioning, speciation, and isotopic fractionation in the contrasting waters of the Solimões and Negro rivers and their mixing zone at the beginning of the Amazon River. Samples collected in the end-member rivers and thirteen sites distributed throughout the mixing zone were processed through frontal vacuum filtration and tangential-flow ultrafiltration to separate the different suspended solid fractions, i.e., particulate (P > 0.45 μm and P > 0.22 μm), colloidal (0.22 μm > C > 5 kDa) and truly dissolved elements (TD particulate fractions yielded light isotopic compositions of -0.344‰ for P > 0.22 μm and -0.104‰ for P > 0.45 μm fractions). The mineral particulate-rich waters of the Solimões River had dissolved and colloidal fractions with light isotopic composition (-0.532‰ and -0.176‰, respectively), whereas the particulate fractions yielded δ57Fe values close to those of the continental crust (i.e., -0.029‰ for P > 0.22 μm and 0.028‰ for P > 0.45 μm). Ten kilometers downstream from the Negro and Solimões junction, the concentrations of colloidal and dissolved Fe species deviate markedly from conservative mixing. A maximum Fe loss of 43 μg/L (i.e., 50% of the dissolved and colloidal Fe) is observed 110 km downstream from the rivers junction. The contrasting Negro and Solimões Rivers isotopic compositions along the pore-sized water fractions is attributable to the biogeochemical processes involving different types of upland soils and parental materials. For instance, the isotopic composition of colloidal and dissolved Fe from the Negro River are consistent with Fe oxidation and complexation mechanisms at the interface between waterlogged podzols and river networks, as supported by strong organo-Fe complexes signals observed by EPR. Conversely, the particulate and colloidal fractions from the Solim

  18. Radioactive Emissions from Fission-Based Medical Isotope Production and Their Effect on Global Nuclear Explosion Detection

    International Nuclear Information System (INIS)

    Bowyer, T.; Saey, P.

    2015-01-01

    The use of medical isotopes, such as Tc-99m, is widespread with over 30 million procedures being performed every year, but the fission-based production of isotopes used for medical procedures causes emissions into the environment. This paper will show that gaseous radioactive isotopes of xenon, such as Xe-133, are released in high quantities, because they have a high fission cross section and they are difficult to scrub from the processes used to produce the medical isotopes due to their largely unreactive nature. Unfortunately, the reasons that large amounts of radioactive xenon isotopes are emitted from isotope production are the same as those that make these isotopes the most useful isotopes for the detection of underground nuclear explosions. Relatively recently, the nuclear explosion monitoring community has established a provisional monitoring network for the Comprehensive Nuclear-Test-Ban Treaty (CTBT) that includes radioactive xenon monitoring as a major component. This community has discovered that emissions from medical isotope production present a more serious problem to nuclear explosion monitoring than thought when the network was first conceived. To address the growing problem, a group of scientists in both the monitoring and the isotope production communities have come together to attempt to find scientific and pragmatic ways to address the emissions problems, recognizing that medical isotope production should not be adversely affected, while monitoring for nuclear explosions should remain effective as isotope production grows, changes, and spreads globally. (author)

  19. Stable isotope variations in benthic primary producers along the Bosphorus (Turkey): A preliminary study

    International Nuclear Information System (INIS)

    Calizza, Edoardo; Aktan, Yelda; Costantini, Maria Letizia; Rossi, Loreto

    2015-01-01

    Highlights: • Nitrogen pollution along the Bosphorus Strait was investigated. • C and N isotopic and elemental analyses on benthic primary producers were performed. • δ 15 N decreased, while δ 13 C and N% increased from north to south along the Strait. • Ulva lactuca was more useful than epiphytes as indicator of nitrogen pollution. • Preliminary isotopic analyses on resident organisms are useful monitoring tools. - Abstract: The Bosphorus Strait is a dynamic and complex system. Recent evidences showed nitrogen and heavy metal concentrations to follow opposite patterns across the Strait, suggesting a complex spatial organisation of the anthropogenic disturbance in this system. Here, we provide isotopic information on the origin and transportation of dissolved nitrogen along the Bosphorus. C and N isotopic and elemental analyses were performed on specimens of Ulva lactuca and associated epiphytes sampled in five locations across the Strait. Variations in C and N isotopic signatures were observed in U. lactuca, pointing to a decrease in the availability of anthropogenic organic dissolved nitrogen along a north-south direction. Conversely, epiphytes did not show isotopic or elemental patterns across the Strait. These results suggest that preliminary stable isotope surveys in extended costal systems basing on U. lactuca can represent a valuable tool to focus meaningful targets and hypotheses for pollution studies in the Mediterranean region

  20. Lead isotope ratios as a tracer for lead contamination sources: A lake Andong case study

    Directory of Open Access Journals (Sweden)

    Kim Y. H

    2013-04-01

    Full Text Available The objective of this study was to evaluate stable Pb isotope signatures as a tracer for Pb contamination in Lake Andong. For Pb isotope analysis, we collected water and sediment from Lake Andong, particles in the air, soils, and stream water, mine tailings, sludge and wastewater from zinc smelting around lake Andong watershed. The results showed that Pb isotope ratios (206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb for zinc concentrate were 18.809 ± 0.322, 15.650 ± 0.062, and 38.728 ± 0.421, respectively. In wastewater, isotopic ratio values (206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb were 17.363 ± 0.133, 15.550 ± 0.025, and 37.217 ± 0.092, respectively. Additionally, isotopic ratio values (206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb for sludge were 17.515 ± 0.155, 15.537 ± 0.018, and 37.357 ± 0.173, respectively. These values were similar to those in zinc and lead concentrate originated from Canada and South America. In contrast, Pb isotope ratios of soil, tailings and sediment from Lake Andong were similar to those of Korean ore. Atmospheric particles showed different patterns of Pb isotope ratios from sediments, soils, and zinc smelting and this needs further investigation in order to identify atmospheric Pb sources.

  1. Prediction of isotope effects for anticipated intermediate structures in the course of bacterial denitrification

    International Nuclear Information System (INIS)

    Morgenstern, M.A.; Schowen, R.L.

    1989-01-01

    Vibrational-analysis methods have been used to estimate the equilibrium 14 N/ 15 N isotope effects to be expected for conversion of nitrite anion to thirteen possible intermediate-state and product-state structures [HONO, NO + , NO, NO - , FeNO, ON * NO 2 , O * NNO 2 , O 2 NNO 2 , ONO * N, O * NON, ONNO, * NNO, N * NO] in the reduction of nitrite ion to nitrous oxide denitrifying bacteria. The results, taken in combination with previous experimental isotope-effect and tracer studies of the Pseudomonas stutzeri and related systems, are consistent with a suggestion that a second nitrite anion enters the enzyme-catalytic cycle at the stage of a nitrosyl-ion intermediate but re-emerges after entry of the reducing electrons; the product nitrous oxide is then formed by disproportionation of enzymically generated hyponitrous acid. The calculations are consistent with contributions, under different experimental conditions, of several different transition states to limiting the rate of the enzymic reaction. These transition states (and the corresponding experimental conditions) are the transition states for N-O fission in the generation of a mononitrogen electrophilic species from nitrite anion (high reductant, high nitrite concentrations), for attack of nitrite on this electrophile (high reductant, low nitrite concentrations) and for electron transfer to a dinitrogen-trioxide-like species (low reductant concentration). (orig.)

  2. Study of polonium isotopes ground state properties by simultaneous atomic- and nuclear-spectroscopy

    CERN Multimedia

    Koester, U H; Kalaninova, Z; Imai, N

    2007-01-01

    We propose to systematically study the ground state properties of neutron deficient $^{192-200}$Po isotopes by means of in-source laser spectroscopy using the ISOLDE laser ion source coupled with nuclear spectroscopy at the detection setup as successfully done before by this collaboration with neutron deficient lead isotopes. The study of the change in mean square charge radii along the polonium isotope chain will give an insight into shape coexistence above the mid-shell N = 104 and above the closed shell Z = 82. The hyperfine structure of the odd isotopes will also allow determination of the nuclear spin and the magnetic moment of the ground state and of any identifiable isomer state. For this study, a standard UC$_{x}$ target with the ISOLDE RILIS is required for 38 shifts.

  3. Groundwater Inputs to Rivers: Hydrological, Biogeochemical and Ecological Effects Inferred by Environmental Isotopes

    Energy Technology Data Exchange (ETDEWEB)

    Stellato, L. [Centre for Isotopic Research on Cultural and Environmental heritage (CIRCE), Seconda Universita degli Studi di Napoli, Caserta (Italy); Newman, B. D. [Isotope Hydrology Section, International Atomic Energy Agency, Vienna (Austria)

    2013-05-15

    In an effort to improve river management, numerous studies over the past two decades have supported the concept that river water and groundwater need to be considered together, as part of a hydrologic continuum. In particular, studies of the interface between surface water and groundwater (the hyporheic zone) have seen the tight collaboration of catchment hydrologists and stream ecologists in order to elucidate processes affecting stream functioning. Groundwater and surface waters interact at different spatial and temporal scales depending on system hydrology and geomorphology, which in turn influence nutrient cycling and in-stream ecology in relation to climatic, geologic, biotic and anthropogenic factors. In this paper, groundwater inputs to rivers are explored from two different and complementary perspectives: the hydrogeological, describing the generally acknowledged mechanisms of streamflow generation and the main factors controlling stream-aquifer interactions, and the ecologic, describing the processes occurring at the hyporheical and the riparian zones and their possible effects on stream functioning and on nutrient cycling, also taking into consideration the impact of human activities. Groundwater inflows to rivers can be important controls on hot moment/hot spot type biogeochemical behaviors. A description of the common methods used to assess these processes is provided emphasizing tracer methods (including physical, chemical and isotopic). In particular, naturally occurring isotopes are useful tools to identify stream discharge components, biogeochemical processes involved in nutrient cycling (such as N and P dynamics), nutrient sources and transport to rivers, and subsurface storage zones and residence times of hyporheic water. Several studies which have employed isotope techniques to clarify the processes occurring when groundwater enters the river,are reported in this chapter, with a view to highlighting both the advantages and limitations of these

  4. Isotope labeling strategies for NMR studies of RNA

    International Nuclear Information System (INIS)

    Lu, Kun; Miyazaki, Yasuyuki; Summers, Michael F.

    2010-01-01

    The known biological functions of RNA have expanded in recent years and now include gene regulation, maintenance of sub-cellular structure, and catalysis, in addition to propagation of genetic information. As for proteins, RNA function is tightly correlated with structure. Unlike proteins, structural information for larger, biologically functional RNAs is relatively limited. NMR signal degeneracy, relaxation problems, and a paucity of long-range 1 H- 1 H dipolar contacts have limited the utility of traditional NMR approaches. Selective isotope labeling, including nucleotide-specific and segmental labeling strategies, may provide the best opportunities for obtaining structural information by NMR. Here we review methods that have been developed for preparing and purifying isotopically labeled RNAs, as well as NMR strategies that have been employed for signal assignment and structure determination.

  5. Studies of neutron-deficient mendelevium isotopes at SHIP

    Energy Technology Data Exchange (ETDEWEB)

    Antalic, S.; Saro, S. [Comenius University, Department of Nuclear Physics and Biophysics, Bratislava (Slovakia); Hessberger, F.P.; Ackermann, D.; Heinz, S.; Kindler, B.; Kojouharov, I.; Lommel, B.; Mann, R. [GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, Darmstadt (Germany); Hofmann, S. [GSI Helmholtzzentrum fuer Schwerionenforschung GmbH, Darmstadt (Germany); Goethe-Universitaet, Institut fuer Kernphysik, Frankfurt am Main (Germany); Kuusiniemi, P. [University of Oulu, Centre for Underground Physics in Pyhaesalmi (CUPP), Oulu (Finland); Leino, M. [University of Jyvaeskylae, Department of Physics, Jyvaeskylae (Finland)

    2010-01-15

    The radioactive decay of the isotopes {sup 247}Md, {sup 246}Md and their daughter products was investigated by means of {alpha}-{alpha} and {alpha}-{gamma} coincidence spectroscopy. The isotopes were produced using the fusion reaction {sup 40}Ar + {sup 209}Bi. Decay schemes are suggested for {sup 247}Md and {sup 243}Es. A new isomeric state in {sup 246}Md with a half-life of (4.4{+-}0.8) s was observed. Previous data of electron-capture delayed fission of {sup 246}Md and {sup 242}Es were confirmed. The probability for this decay branch in {sup 246}Md was measured to be P{sub ECDF}>0.10. The probability for electron-capture delayed fission in the case of {sup 242}Es was determined to be P{sub ECDF}=0.013{sup +0.012} {sub -0.007}. (orig.)

  6. Measurement of boron isotope ratios in groundwater studies

    International Nuclear Information System (INIS)

    Porteous, N.C.; Walsh, J.N.; Jarvis, K.E.

    1995-01-01

    Boron is present at low levels in groundwater and rainfall in the UK, ranging between 2 and 200 ng ml -1 . A sensitive technique has been developed using inductively coupled plasma mass spectrometry (ICP-MS) to measure boron isotope ratios at low concentrations with a precision (s r ) of between 0.1 and 0.2%. Samples were evaporated to increase elemental boron concentrations to 200 ng ml -1 and interfering matrix elements were removed by an adapted cation-exchange separation procedure. The validity of measuring boron isotopic ratios by ICP-MS at this concentration level is discussed in relation to the theoretical instrument precision attainable based on counting statistics. (author)

  7. Thermal Conductivity of Nanotubes Revisited: Effects of Chirality, Isotope Impurity, Tube Length, and Temperature

    OpenAIRE

    Zhang, Gang; Li, Baowen

    2004-01-01

    We study the dependence of thermal conductivity of single walled nanotubes (SWNT) on chirality, isotope impurity, tube length and temperature by nonequilibrium molecular dynamics method with accurate potentials. It is found that, contrary to electronic conductivity, the thermal conductivity is insensitive to the chirality. The isotope impurity, however, can reduce the thermal conductivity up to 60% and change the temperature dependence behavior. We also found that the tube length dependence o...

  8. Coordinated programme on isotopic tracer-aided studies of the biological side effects of foreign chemical residues in food and agriculture. Study of sulfur dioxide effects on phosphorus metabolism in plants using 32-P as indicator

    International Nuclear Information System (INIS)

    Plesnicar, M.

    1977-07-01

    Exposure of bean plants to low sulphur dioxide concentrations (0.02-0.32 ppm, up to 72 hours) stimulated the incorporation of 32 P into RNA, DNA, phospholipids and the acid soluble fraction, without altering the total phosphorus content. Statistically significant 32 P increases were only observed with RNA. Uptake of 35 SO 2 (14 ppm) by bean leaves was shown to be fairly rapid and the radioactivity was translocated in the roots within 1 to 6 hours following exposure. Subcellular leaf fractions showed that the supernatant contained 60-90% of the absorbed radioactivity. The chloroplasts and microsomes showed higher 35 S content than the mitochondrial fraction. In vitro studies on pea-derived chloroplasts included photosynthetic phosphorylation and electron transport. Phosphorylation was found to be inhibited in presence of SO 2 (I 50 =3.7 mM). The nature of inhibition seems to be of the reversible-competitive type with an apparent inhibitor constant (Ki) of 1.5 mM. The electron transport system remained unaffected. It is maintained that the identification of some lesions in this study would contribute to a better understanding of the nature of the complex interactions between cultivated plants and sulphur dioxide

  9. Ab initio calculations of the Fe(II) and Fe(III) isotopic effects in citrates, nicotianamine, and phytosiderophore, and new Fe isotopic measurements in higher plants

    Science.gov (United States)

    Moynier, Frédéric; Fujii, Toshiyuki; Wang, Kun; Foriel, Julien

    2013-05-01

    Iron is one of the most abundant transition metal in higher plants and variations in its isotopic compositions can be used to trace its utilization. In order to better understand the effect of plant-induced isotopic fractionation on the global Fe cycling, we have estimated by quantum chemical calculations the magnitude of the isotopic fractionation between different Fe species relevant to the transport and storage of Fe in higher plants: Fe(II)-citrate, Fe(III)-citrate, Fe(II)-nicotianamine, and Fe(III)-phytosiderophore. The ab initio calculations show firstly, that Fe(II)-nicotianamine is ˜3‰ (56Fe/54Fe) isotopically lighter than Fe(III)-phytosiderophore; secondly, even in the absence of redox changes of Fe, change in the speciation alone can create up to ˜1.5‰ isotopic fractionation. For example, Fe(III)-phytosiderophore is up to 1.5‰ heavier than Fe(III)-citrate2 and Fe(II)-nicotianamine is up to 1‰ heavier than Fe(II)-citrate. In addition, in order to better understand the Fe isotopic fractionation between different plant components, we have analyzed the iron isotopic composition of different organs (roots, seeds, germinated seeds, leaves and stems) from six species of higher plants: the dicot lentil (Lens culinaris), and the graminaceous monocots Virginia wild rye (Elymus virginicus), Johnsongrass (Sorghum halepense), Kentucky bluegrass (Poa pratensis), river oat (Uniola latifolia), and Indian goosegrass (Eleusine indica). The calculations may explain that the roots of strategy-II plants (Fe(III)-phytosiderophore) are isotopically heavier (by about 1‰ for the δ56Fe) than the upper parts of the plants (Fe transported as Fe(III)-citrate in the xylem or Fe(II)-nicotianamine in the phloem). In addition, we suggest that the isotopic variations observed between younger and older leaves could be explained by mixing of Fe received from the xylem and the phloem.

  10. Use of water stable isotopes in climatology and paleoclimatology illustrated from polar ice cores studies

    International Nuclear Information System (INIS)

    Jouzel, J.; Lorius, C.

    1994-01-01

    The isotopic content of ancient waters (deuterium and oxygen 18) gives a key access to past climatic changes. An essentially linear relationship exists between the isotopic content of a precipitation and the temperature of the site (at least for medium and high latitudes). This link between water isotope atmospheric cycle and climate is presented through various isotopic models and illustrated from the deuterium profile obtained along the Vostok ice core in East Antarctica. This 2 km record which covers a full glacial-interglacial cycle (160000 years) confirms the existence of a link between insolation changes and climate (Milankovitch theory). It shows also that the greenhouse effect has played a role in glacial-interglacial changes in amplifying this orbital forcing. (authors). 10 figs., 23 refs

  11. Lead (Pb) isotopic fingerprinting and its applications in lead pollution studies in China: a review.

    Science.gov (United States)

    Cheng, Hefa; Hu, Yuanan

    2010-05-01

    As the most widely scattered toxic metal in the world, the sources of lead (Pb) observed in contamination investigation are often difficult to identify. This review presents an overview of the principles, analysis, and applications of Pb isotopic fingerprinting in tracing the origins and transport pathways of Pb in the environment. It also summarizes the history and current status of lead pollution in China, and illustrates the power of Pb isotopic fingerprinting with examples of its recent applications in investigating the effectiveness of leaded gasoline phase-out on atmospheric lead pollution, and the sources of Pb found in various environmental media (plants, sediments, and aquatic organisms) in China. The limitations of Pb isotopic fingerprinting technique are discussed and a perspective on its development is also presented. Further methodological developments and more widespread instrument availability are expected to make isotopic fingerprinting one of the key tools in lead pollution investigation. Copyright 2009 Elsevier Ltd. All rights reserved.

  12. Stable isotope probing to study functional components of complex microbial ecosystems.

    Science.gov (United States)

    Mazard, Sophie; Schäfer, Hendrik

    2014-01-01

    This protocol presents a method of dissecting the DNA or RNA of key organisms involved in a specific biochemical process within a complex ecosystem. Stable isotope probing (SIP) allows the labelling and separation of nucleic acids from community members that are involved in important biochemical transformations, yet are often not the most numerically abundant members of a community. This pure culture-independent technique circumvents limitations of traditional microbial isolation techniques or data mining from large-scale whole-community metagenomic studies to tease out the identities and genomic repertoires of microorganisms participating in biological nutrient cycles. SIP experiments can be applied to virtually any ecosystem and biochemical pathway under investigation provided a suitable stable isotope substrate is available. This versatile methodology allows a wide range of analyses to be performed, from fatty-acid analyses, community structure and ecology studies, and targeted metagenomics involving nucleic acid sequencing. SIP experiments provide an effective alternative to large-scale whole-community metagenomic studies by specifically targeting the organisms or biochemical transformations of interest, thereby reducing the sequencing effort and time-consuming bioinformatics analyses of large datasets.

  13. Metabolism and transport studies of exogenous compounds thanks to 13C uniform isotopic enrichment

    International Nuclear Information System (INIS)

    Bravin, F.

    2008-12-01

    The study of many exogenous compounds does not raise difficulties when they are isolated, purified and in quantities sufficient for the usual detection methods used in biology (Chromatography, NMR, Mass Spectrometry, etc). When they are found in a biological fluid (blood, urines,..), they are often in infinitesimal amount such as the effect of their biological matrices or the background noise that make their detection and their quantification very delicate. The use of internal standards uniformly enriched with carbon 13 and/or nitrogen 15 makes it possible to obtain a signal more easily recognizable and identifiable thanks to the presence of the isotopes (peaks shifted in a mass spectrum for example). This is why, complementary to the analytical and biochemical studies of zearalenone (ZEN) metabolism, we were interested in building mass spectra of molecules enriched (rates between 0 and 1) by various isotopes ( 13 C, 15 N, 18 O and 2 H). In parallel we studied the influence of the 13 C enrichment on the reactivity of a given molecule, from a theoretical and an experimental point of view. (author)

  14. Aspartate beta-decarboxylase from Alcaligenes faecalis: carbon-13 kinetic isotope effect and deuterium exchange experiments

    International Nuclear Information System (INIS)

    Rosenberg, R.M.; O'Leary, M.H.

    1985-01-01

    The authors have measured the 13 C kinetic isotope effect at pH 4.0, 5.0, 6.0, and 6.5 and in D 2 O at pH 5.0 and the rate of D-H exchange of the alpha and beta protons of aspartic acid in D 2 O at pH 5.0 for the reaction catalyzed by the enzyme aspartate beta-decarboxylase from Alcaligenes faecalis. The 13 C kinetic isotope effect, with a value of 1.0099 +/- 0.0002 at pH 5.0, is less than the intrinsic isotope effect for the decarboxylation step, indicating that the decarboxylation step is not entirely rate limiting. The authors have been a