Fractionation of nitrogen stable isotopes by ion exchange chromatography

The ion exchange chromatography displacement technique was used for the enrichment of ¹⁵N. The runs were conducted in laboratory and bench scales using two systems of columns filled with Wofatit KPS ion exchange resin (medium porosity type). Ammonia NH₄ ⁺/NH₃ aq. was chosen as the isotopic exchange system. The ammonium bands formed in the columns were eluted by means of sodium hydroxide solution. Hydrodynamic patterns in the column beds was evaluated in terms of dimensionless Reynolds number. The results show that separation process can be performed in the turbulent or laminar flow regime.     

Measurement of activation cross sections of the proton induced nuclear reactions on palladium

Excitation functions of proton induced reactions on Pd are important for medical radioisotope production, for activation analysis, for development of low activation materials and other purposes. No experimental data exist in the literature for low and medium energy range protons. A detailed study of the excitation functions was performed up to 80 MeV proton energy by using the stacked foil irradiation technique and gamma-ray spectrometry. The irradiations were carried out at the external beam lines of the AVF cyclotron at the Tohoku University. Japan (80 and 70 MeV) and the CGR 560 cyclotron at the Vrije Universiteit Brussels (38, 29 and 17 MeV). The beam intensity, the incident energy and the energy degradation were controlled by a method based on flux constancy via normalization to the parallel measured excitation functions of ^natAl(p,x)^22,24Na and ^natCu(p,x)^56,58Co, ^62,65Zn monitor reactions. Excitation functions for direct and cumulative cross sections have been measured for the production of ^{105mg,106m,110m}Ag, ¹⁰¹Pd, ^101mRh and ⁹⁷Ru radionuclei. Calculations for the excitation functions using the Alice-IPPE code were performed with a view to estimate the weight of the different contributing reactions and to check the trend and the magnitude of the obtained experimental data.     

Determination of the half-lives of transactinium isotopes by relative activity method

Relative activity method offers the potentiality of providing half-life values over a wide range in a short time for different -emitting transactinium isotopes. The method involves the preparation of a synthetic mixture using another isotope of the same element followed by the determination of atom ratio and -activity ratio by thermal ionization mass spectrometry and -spectrometry, respectively. A double dilution technique is described which helps in maintaining the atom ratios as well as -activity ratios close to unity so that these could be determined with high precision and accuracy. Results obtained on the half-lives of²³²U,²³⁸Pu,²⁴²Pu and²⁴³Am using double dilution technique in relative activity method are summarized. Requirements, advantages and applications of this technique for determining the half-lives of other transactinium isotopes are presented.     

Sputtering induced recombination of nitrogen isotopes on tungsten

Adsorbed isotopic mixtures of ¹⁴N₂ and ¹⁵N₂ at low coverages on polycrystalline tungsten have been used as model systems for studying sputtering induced recombination during secondary ion mass spectrometry (SIMS). Earlier studies have shown that N₂ is completely dissociated on a W surface at low coverage. Thermal desorption spectroscopy (TDS) has been employed here to confirm this fact; our results show that complete isotopic mixing occurs. Adsorbed nitrogen can be sputtered as both atoms and molecules and sputtering induced recombination of adsorbate atoms increases as primary ion energy increases. Sputtering induced recombination is detected through isotopic mixing in SIMS. The data show that the dominant mechanism for sputtering of dimers (N₂) is not direct emission from the surface but rather a sputtering induced recombination mechanism.     

Determination of molecular nitrogen by electron-impact induced fluorescence

When a sample of nitrogen gas is bombarded by 100-eV electrons, fluorescent emission from the nitrogen molecular ion, N(+)(2), is observed. The intensity of this fluorescence can be related to the pressure (or molar concentration) of the parent molecule, N(2). The limit of detection for N(2) by means of electron-impact induced fluorescence is 5.0 x 10(-8)mmHg (1.6 x 10(9) molecules/cm(3) or 2.7 x 10(-12) mole/l.). The fluorescence signal is linearly related to N(2) pressure over a range of four orders of magnitude, and relative standard deviations of less than 2% are observed for replicate measurements.     

Determination of inorganic chlorine stable isotopes by continuous flow isotope ratio mass spectrometry

Chlorine stable isotope analyses of inorganic samples were conducted using continuous flow isotope ratio mass spectrometry (CF-IRMS) coupled with gas chromatography (GC). Inorganic chloride was precipitated in the form of silver chloride (AgCl) by using silver nitrate in a standard methodology. Chlorine stable isotope analysis was carried out on methyl chloride (CH3Cl) after converting AgCl into CH3Cl by reacting it with methyl iodide (CH3I). The reaction between AgCl and CH3I took place in 20 mL size vials. Addition of CH3I was performed in a glove bag under helium flow. An Agilent 6890 gas chromatograph equipped with a CTC Analytics CombiPAL autosampler and a DB-5MS 60 m column was used to separate CH3Cl from CH3I. This new technique uses samples as small as 0.2 mg of AgCl (1.4 micromol of Cl-). The chlorine stable isotope analysis using continuous flow technology showed excellent precision and accuracy. The internal precision using pure CH3Cl gas is better than +/-0.04 per thousand (+/-STDV). The external precision using seawater standard is better than +/-0.07 per thousand (+/-STDV) for n=12. Moreover, the sample analysis time is much shorter and many more samples can be analyzed in one day than by using the conventional off-line techniques.     

Metabolic turnover rates of carbon and nitrogen stable isotopes in captive juvenile snakes

Metabolic turnover rates (m) of δ¹⁵N and δ¹³C were assessed in different tissues of newly hatched captive‐raised corn snakes (Elaphe guttata guttata) fed maintenance diets consisting of earthworms (Eisenia foetida) that varied substantially in δ¹⁵N (by 644‰) and δ¹³C (by 5.0‰). Three treatments were used during this 144 day experiment that consisted of the same diet throughout (control), shifting from a depleted to an enriched stable isotope signature diet (uptake), and shifting from an enriched to depleted stable isotope signature diet (elimination). Values of δ¹³C in the liver, blood, and muscle of the control snakes reached equilibrium with and were, respectively, 1.73, 2.25 and 2.29 greater than in their diet, this increase is called an isotopic discrimination factor (Δδ¹³C = δ¹³C_snake ? δ¹³C_food). Values of δ¹⁵N in snake tissues did not achieve equilibrium with the diets in any of the exposures and thus Δ¹⁵N could not be estimated. Values of metabolic turnover rates (m) for δ¹³C and δ¹⁵N were greater in liver than in muscle and blood, which were similar, and relative results remained the same if the fraction of ¹⁵N and ¹³C were modeled. Although caution is warranted because equilibrium values of stable isotopes in the snakes were not achieved, values of m were greater for δ¹³C than δ¹⁵N, resulting in shorter times to dietary equilibrium for δ¹³C upon a diet shift, and for both stable isotopes in all tissues, greater during an elimination than in an uptake shift in diet stable isotope signature. Multiple explanations for the observed differences between uptake and elimination shifts raise new questions about the relationship between animal and diet stable isotope concentrations. Based on this study, interpretation of feeding ecology using stable isotopes is highly dependent on the kind of stable isotope, tissue, direction of diet switch (uptake versus elimination), and the growth rate of the animal. Copyright © 2009 John Wiley & Sons, Ltd.     

Optical isotope shifts and changes in nuclear charge radii of stable Ti isotopes

Isotope shifts and hyperfine structures in three optical transitions of TiI have been investigated by using laser induced resonance fluorescence in a collimated atomic beam. From the isotope shifts data, changes of the mean square charge radii of the stable titanium isotopes have been determined for the first time. Using a combined analysis with muonic atom data on root mean square nuclear charge radii, improved model independent r ^21/2 values for the odd-even Ti isotopes have been obtained.     

The effects induced by proton irradiation on structural characteristics of nuclear graphite

A grade TSX graphite was irradiated by a 2.5 MeV proton and a dose of 1.47 × 10¹⁸ ion cm⁻² at 330 K. The displacement per atom under this irradiation condition was about 0.02. The lattice parameter, crystallite size and the vacancies density in the graphite was measured before and after irradiation. It was found that the proton irradiation led to an increase in the volume of the sample. The volume change in the irradiated sample was confirmed by atomic force and scanning electron microscopes observations as increased roughness and pore size. Also, FTIR results showed that graphite is slightly oxidized by irradiation.

     

Fractionation and metabolic turnover of carbon and nitrogen stable isotopes in black fly larvae

Diet-tissue fractionation factors and metabolic turnover rates of delta15N and delta13C were assessed in laboratory-reared black fly (Simulium vittatum IS-7) larvae fed isotopically distinct diets. Five treatments consisted of using food with different delta15N signatures throughout the experiments (19-26 days), a sixth shifted from a low to high delta15N signature diet (uptake) on day 14, and the last shifted from a high to low delta15N signature diet (elimination) on day 14. In the larvae, diet-tissue fractionation factors for delta13C, which were in steady state with food, ranged from -0.61 to 2.0, with a median of 1.87. The delta15N diet-tissue fractionation factors were mostly negative, ranging from +2.85 to -24.96 per thousand, with a single positive value from the elimination treatment in which larval delta15N did not achieve steady state with the food. Diet-tissue fractionation factors also had a significant negative relationship (r2 = 0.98) with delta15N values in the food suggesting that nitrogen diet-tissue fractionation factors are 15N concentration-dependent. The delta15N of shed head capsules and feces were enriched in 15N and could be mechanisms for elimination of 15N by the larvae. For delta15N, metabolic turnover values based on the Hesslein model were highly consistent (0.40 to 0.43 delta15N*day(-1)) between uptake and elimination phases and across experiments and were an order of magnitude greater than growth rates. The rapid turnover of nitrogen in black fly larvae, which was orders of magnitude greater than measured in vertebrates, makes them an excellent indicator of short-term changes in nitrogen inputs to aquatic systems.     

Determination of actinide and fission-product isotopes in very-high-burnup spent nuclear fuel

The purpose of this study was to examine the nail response to concurrent intake of methyl mercury (MeHg) and Se. Weanling male Long Evans rats were fed diets containing Se and MeHg. The Se concentration in the nail was well correlated (r ²>0.90) with dietary Se in every MeHg supplementation group. Good correlation was observed between dietary MeHg and nail Hg concentration in every Se group. Exposure to high levels of MeHg resulted in a lower (p<0.03) measured nail Se concentration in the highest Se experimental group relative to control.     

Source identification of nitrate by means of stable nitrogen isotopes in the river Daugava and loads of nitrogen to the Gulf of Riga

Nitrogen isotope ratio of nitrate provides a powerful tool to investigate nitrate sources and cycling mechanisms. Although the use of an isotope ratio method for ¹⁵N/¹⁴N allows identifying the nitrate sources in rivers by estimating a seasonal variation of N-NO₃ concentration, however, there are some restrictions. Nitrification, the conversion of NH₄⁺ to NO₃-, can proceed with significant nitrogen isotope fractionation, preferentially accumulating ¹⁴N in the produced NO₃-, and can make it difficult to identify the nitrate source with a high proportion of the isotope δ¹⁵N. However, the uptake and assimilation of NH₄⁺ and NO₃- have the capability of affecting isotopic compositions of riverine nitrogen compounds, and this may hinder the determination of whether the impact of the nitrate source with a high proportion of the isotope δ¹⁵N reduces. In addition, this study demonstrates that nitrate nitrogen concentration may correlate with δ¹⁵N_NO3 values both positively and negatively. Such correlations are the result of isotope effects during nitrogen transformation processes (e.g. nitrification and assimilation) and isotopic variability in the various nitrate sources. A comparison of NO₃- concentration and δ¹⁵N_NO3 can be used to further distinguish mixing from biological processing. However, in order to get a more precise answer regarding the nitrate sources, it would be useful to take both the data of nitrogen isotopes and data of oxygen isotopes present in nitrates.     

Determination of the absolute configuration of peptide natural products by using stable isotope labeling and mass spectrometry

Structure elucidation of natural products including the absolute configuration is a complex task that involves different analytical methods like mass spectrometry, NMR spectroscopy, and chemical derivation, which are usually performed after the isolation of the compound of interest. Here, a combination of stable isotope labeling of Photorhabdus and Xenorhabdus strains and their transaminase mutants followed by detailed MS analysis enabled the structure elucidation of novel cyclopeptides named GameXPeptides including their absolute configuration in crude extracts without their actual isolation.     

Simultaneous determination of 14N and 15N isotopes in opium by proton induced γ-ray emission technique

The paper describes the simultaneous determination of ¹⁴N and ¹⁵N isotopes in opium by proton induced γ-ray emission (PIGE) technique. The isotopic ratio of ¹⁴N and ¹⁵N is a useful parameter for assigning provenance of (seized) illicit drugs. The measurement, non-destructive in nature, is performed on pellets made up of opium powders and is based on the prompt detection of 2.313 and 4.4 MeV γ-rays emanating from ¹⁴N(p,p′γ)¹⁴N and ¹⁵N(p,αγ)¹²C nuclear reactions respectively, induced simultaneously by 3.6–3.8 MeV proton beam. Positive as well as negative deviations from the natural isotopic abundance (99.63:0.37) were observed in the samples. The precision of the measurements is about 4%. The methodology provides an easy and rapid approach to determine the isotopic ratio of ¹⁴N and ¹⁵N and has been used for the first time in the analysis of opium.     

Quantitative problems in using nuclear reactions and dielectric detectors for the detection of stable isotopes (6Li and10B) in biological samples

The methodology of the detection of (n, ) nuclear reactions by means of cellulose nitrate detectors is discussed with special reference to the reliability of the quantitative estimates. The discrimination of¹⁰B and⁶Li from the other isotopes is possible by using thin coloured detectors. The ratio of the number of tracks found at the level of a¹⁰B or⁵Li-enriched calibrating sample, and the number expected from theoretical calculation, i.e. the detection efficiency, P is generally below 1. P is fairly sensitive to the experimental conditions, and for precise quantitative measurements it must be determined separately for each different experiment. The gelatin, used for solidification of liquid samples is boron contaminated (almost 1 mol natural B per g). It has been observed, especially with¹⁰B-enriched liquid samples, that part of the stable tracer under study is lost during sample preparation.⁶Li extra tracks appear at the rear face of thick, non-plastic-supported detectors. Boron diffuses in the cellulose-nitrate detectors with the diffusion coefficient of the order of 10^–8 cm²·s^–1. Therefore it requires rapid operations for microlocation of boron with high resolving power.     

Formation of236Pu,237Pu and238Pu isotopes by3He-induced nuclear reactions on uranium

The reaction U(³He, xn)Pu was studied by irradiating enriched²³⁵U (50.3%) and enriched²³⁸U (99.7%) targets with³He ions at the Åbo Akademi cyclotron (Turku, Finland). The incident³He ion energy in the irradiations was 27.0, 24.5 and 21.9 MeV. Plutonium was separated from the thin uranium targets by ion exchange. From the ion exchange fractions obtained, plutonium was electrodeposited on steel plates for alpha and X-ray counting. The activity of²³⁷Pu in the steel plates was determined with a Ge(Li) detector and the activity of²³⁶Pu and²³⁸Pu with a Si surface barrier detector. The cross sections of the reactions and the yields of plutonium isotopes are given.