Determination Of Isotopic Abundances Research Articles

Two-photon resonant three-photon ionization of Be applied to the determination of isotopic abundances

We show that when more than one photons are involved in bound-bound transitions by a broad-band laser for the determination of isotopic abundances, the ac Stark shift may cause the discrimination on ionization between different isotopes for a given atomic species. As an example, we present specific numerical calculations with Be atom in terms of the determination of isotopic abundances.

Early History and Future Outlook for the X-ray Crystal Density Method

It is useful to recall that the (late nineteenth-century) Baltimore Lectures of Lord Kelvin indicated that the likely sizes of atomic particles spanned almost two decades. Yet in the early years of the present century, Sir William Bragg's ansatz, together with the oil-drop e, gave the first reliable estimate of the scale of crystal interplanar spacings. The converse process of using an XRCD approach to obtain a value for the Avogadro constant was, prior to the advent of x-ray interferometry, limited by the need to connect optical and x-ray wavelengths before using the latter to estimate unit cell dimensions in crystals. Other limitations of these early measurements included the use of water as a density standard and the assignment of molar masses to individual specimens based on geochemical abundance averages. All these difficulties were overcome, in principle, with the application of x-ray/optical interferometry to the determination of lattice periods, the use of solid object density standards, and the determination of densities and isotopic abundances on individual monocrystalline specimens. While the present-day situation is addressed in other contributions to this workshop, the present essay attempts to place some of the early work in context and to look also to the future.

Recovery of submilligram quantities of carbon dioxide from gas streams by molecular sieve for subsequent determination of isotopic carbon-13 and carbon-14 natural abundances

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTRecovery of submilligram quantities of carbon dioxide from gas streams by molecular sieve for subsequent determination of isotopic carbon-13 and carbon-14 natural abundancesJames E. Bauer, Peter M. Williams, and Ellen R. M. DruffelCite this: Anal. Chem. 1992, 64, 7, 824–827Publication Date (Print):April 1, 1992Publication History Published online1 May 2002Published inissue 1 April 1992https://doi.org/10.1021/ac00031a024RIGHTS & PERMISSIONSArticle Views203Altmetric-Citations52LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (537 KB) Get e-Alerts Get e-Alerts

Determination of uranium element concentration and235U isotope abundance by neutron activation analysis

A new neutron activation technique has been developed for the determination of uranium element concentration and235U isotope abundance in nuclear safeguards and reference material samples based on the activation of bare and cadmium-covered samples with different thermal to epithermal neutron flux ratios and on the combination of the two corre-sponding delayed-fission neutron measurements. The principle of the new technique can be applied also to improve multi-element neutron activation analysis.

Determination of radium isotope ratios and abundances in geological samples by thermal ionization mass spectrometry

We describe chemical separation and mass spectrometric procedures for the measurement of radium isotopes in geologic samples. These methods provide 226Ra/228Ra ratio measurements for 1 g or less of rock sample containing subpicogram amounts of radium with precision better than 1.5% (95% confidence level). Radium-226 concentrations were measured by isotope dilution for smaller sample sizes (100-500 mg) containing as little as 1-10 fg of total 226Ra with similar high precision.

Isotopic abundance determination by inductively coupled plasma high- resolution laser excited atomic and ionic fluorescence spectroscopy

Inductively coupled plasma-laser excited atomic fluorescence spectroscopy (ICP-LEAFS) has been successfully applied to isotopic analysis for the first time. The criteria for selecting useful excitation/fluorescence line pairs are presented and applied to the determination of uranium isotope concentration. Calculations of the ICP-LEAFS line profiles for U II 286.57 and 288.96 nm excitation are presented and suggest that the first transition should be useful for isotopic analysis using the ICP source, with a multi-mode dye laser, whereas the second should not. These results were confirmed by experiment. The detection limit for U via ICP-LEAFS using the 286.57/288.96 nm excitation/fluorescence line pair was estimated to be ~2 μg ml . The non-resonance fluorescence determination of U dissolved in a very complex matrix was shown to be independent of spectral line interferences from the matrix elements.

Theory of doubly resonant ionization by broad-band radiation applied to the determination of isotopic abundances.

We present a theoretical study of doubly resonant three-photon ionization with radiation of sufficiently broad bandwidth to overlap all hyperfine levels of the resonant intermediate states. We demonstrate that isotopic selectivity in ionization is apt to occur under a variety of circumstances, although the degree may vary from negligible to quite significant, depending on the relative values of atomic and radiation parameters. Our theory provides a satisfactory quantitative interpretation of recent experimental data in Sn.

Theory of resonant ionization by broad-band radiation in the determination of isotopic abundances.

We present a theory for resonant ionization by broad-band laser radiation with emphasis on the role of laser bandwidth. It is shown that under certain conditions, often encountered in experiments of this type, the amount of ionization will depend on an intricate interplay between atomic and radiation parameters. The theory is discussed in the context of an application to Sn, which enables us to provide quantitative comparison with recent experimental data.

Fast-Pulse Detection for Isotopic Abundance Determination By Resonance Ionization, Time-Of-Flight Mass Spectrometry

ABSTRACT A linear time-of-flight mass spectrometer with static electrode voltages was developed for isotopic abundance measurements and showed good resolving power (620) for atomic ions. Positive ions, produced by multiphoton excitations, were detected by a microchannel plate detector that featured low noise and good pulse height distribution. Signal pulses were too fast for precise quantification by currently available transient digitizers. A gated pulse counter, which used AND logic circuitry to direct pulses for different isotopes into separate channels of a counter, was developed for quantification of the signal pulses and results for isotopic ratio measurements showed good precision, 0.3% to 1% relative standard deviation. The time-of-flight mass spectrometer with gated pulse counter was particularly well matched to pulsed laser ionization, because it could detect all isotopes of the selected element ionized in each laser pulse, and it did not impose a limit on the laser pulse repetition rate.

Isotopes and Atomic Absorption Spectrometry. Computer Simulations, Part I: Evaluation of the Simulation Model Using the Flame Atomic Absorption Determination of Lithium Isotope Abundances

An evaluation of a computer model developed to calculate absorbances involving multi-isotopic elements is presented. With the use of the model, an independently performed flame atomic absorption experiment to determine isotope abundances of lithium is simulated. The necessity of having accurate values of the critical model parameters (damping constant, isotope shift, fine structure separation, and collisional shift) is demonstrated. The ability of the model to reveal experimental relationships which would be difficult to observe unless the experiments were performed with extreme care is shown. Further, the potential of the model to simulate isotope effects in AAS and its use as an aid in the evaluation of experimental results are demonstrated.

New method for the measurement of osmium isotopes applied to a New Zealand Cretaceous/Tertiary boundary shale

The determination of osmium content and isotopic abundances in geological materials has received increasing attention in recent years following the proposal of Alvarez et al.1 that mass extinctions at the end of the Cretaceous period were caused by the impact of a large (∼10km) meteorite which left anomalously high iridium levels as a geochemical signature in the boundary shales. Here we report a new and simple method for measuring osmium in geological materials, involving fusion of the sample with sodium peroxide, distillation of the osmium as the tetroxide using perchloric acid, extraction into chloroform, and absorption of the chloroform extract onto graphite powder before instrumental neutron activation analysis. In a variant of this technique, the chloroform extract is back-extracted into an aqueous phase and the osmium isotopes are determined by plasma-source mass spectrometry (ICPMS). We have used this method on the Woodside Creek (New Zealand) Cretaceous/Tertiary boundary clay and have obtained the first osmium content (6g ng g−1) for this material. The 187Os/186Os ratio is 1.12±0.16, showing a typical non-crustal signature. This combined distillation–extraction–ICPMS method will prove to be useful for measuring osmium isotopes in other geological materials.

Gas chromatographic-mass spectrometric determination of isotopic enrichment of 6- 15NH 2 in adenine nucleotides

A gas chromatographic-mass spectrometric method for the determination of isotopic abundance in [6- 15NH 2]adenine nucleotides is described. The method involves formation of the di-t-butyldimethylsilyl (TBDMS) derivative of adenine following isolation of the nucleotide fraction with solid-phase ion-exchange chromatography and subsequent acid hydrolysis of nucleotides to free base. Mass spectra for both adenine-diTBDMS and [6- 15NH 2]adenine-diTBDMS were obtained to identify those ions containing the 6-NH 2 moiety. The base peak ( m z 306) was formed by loss of C 4H 9 (57) and constitutes approximately one-third of the total ion current. Using selected ion monitoring of the m z 306/ m/z 307 ratio, levels of isotopic abundance of 1.0–50.0 mol% excess could be measured reproducibly with the injection of 10–20 pmol of the adenine-diTBDMS derivative obtained from isolated rat hepatocytes. Confirmation that measured isotopic abundance was referable to labeling of the 6- 15NH 2 group was obtained by oxidation of adenine to hypoxanthine and determination of enrichment in the hypoxanthine-diTBDMS derivative. The method was used to study the formation of [6- 15NH 2]adenine nucleotides during the incubation of isolated rat hepatocytes with [ 15N]alanine. A level of approximately 6.0 mol% excess was observed at 60 min incubation.

Precise determination of low isotopic nitrogen-15 abundances by emission spectrometry

Improvements in the determination of low nitrogen-15 abundances by emission spectrometry are described. Stronger emission is observed if a capillary constriction is formed at the centre of the discharge tube, and the background under the 14N15N peak is greatly reduced. The relative error normally caused by problems in estimating the background is thus decreased. The overall precision is better than 1% in the range from natural abundance to 1.0 atom-% nitrogen-15.

A rapid method of extraction of uranium and thorium from granite for alpha spectrometry

The lithium metaborate fusion technique for analysis of rock samples has been adapted for the alpha spectrometric determination of uranium and thorium isotope abundances in granite. Powdered granite is spiked with a solution of a uranium-thorium isotope tracer, mixed with LiBO 2 in a 1:3 ratio and fused at 950°C in a graphite crucible. The mixture is poured into 1 M HNO 3 and stirred until dissolved. Uranium and thorium are simultaneously extracted with 10% tributylphosphate (TBP) in amyl acetate using Al(NO 3) 3 as the salting agent, and then back-extracted into 1 M H 2SO 4. Uranium is separated from thorium using anion exchange resin and, after further purification, each is plated onto steel discs for alpha counting. Overall chemical yields are adequate at present (generally 20 to 60%). Preliminary tests show the TBP extraction step to be almost quantitative for both elements, in spite of the presence of silicon and high concentrations of aluminium. This procedure is much faster than the usual acid digestion technique, and uranium and thorium discs for counting can be prepared in approximately eight hours, starting from rock powder.

Double-comparison method for mass spectrometric determination of hydrogen isotopic abundances

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDouble-comparison method for mass spectrometric determination of hydrogen isotopic abundancesD. A. Schoeller, D. W. Peterson, and J. M. HayesCite this: Anal. Chem. 1983, 55, 6, 827–832Publication Date (Print):May 1, 1983Publication History Published online1 May 2002Published inissue 1 May 1983https://doi.org/10.1021/ac00257a005RIGHTS & PERMISSIONSArticle Views59Altmetric-Citations8LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (784 KB) Get e-Alerts Get e-Alerts

The Determination of Osmium Isotope Abundances by High Resolution Laser Spectroscopy

The Determination of Osmium Isotope Abundances by High Resolution Laser Spectroscopy

The atomic absorption spectrometric determination of lithium isotope abundances by direct measurement of the absorbance ratio

A specially designed amplifier allows direct measurement of the absorbance ratio. The unit simultaneously monitors the attenuation of both a natural-lithium and a 6Li-enriched hollow-cathode lamp, which are aligned in the optical axis of the instrument. The attenuations are converted to absorbances, the ratio of which is proportional to the relative isotope abundance. The stable signals obtained permit rapid determinations at natural abundance levels, with a relative standard deviation of 3%.

The Mass Spectrometric Determination of Uranium-235 in Uranium Hexafluoride

If different laboratories using thermionic mass spectrometry determine in routine operation a /sup 235/U concentration of approx. 0.7% in the same sample material, their measurement results deviate by at least 0.8% (relative) in approx. 50% of the cases. The application of gas mass spectrometry reduces this deviation to 0.1 or 0.05%, the more favorable value being obtained by measurements in which the same reference material is used by all laboratories. These results were obtained by application of an empirical evaluation procedure that, contrary to the usual statistical tools, is not restricted to homogeneous data material. The data were taken from two interlaboratory evaluation programs performed recently on the isotopic abundance determination of /sup 235/U in uranium hexafluoride by mass spectrometry.

The determination of lithium isotope abundances with a dual-beam atomic absorption spectrometer

The direct determination of lithium isotope abundances by atomic absorption spectrometry with a dual-beam instrument is described. A natural lithium hollow-cathode lamp and an enriched lithium-6 hollow-cathode lamp are both aligned on the optical axis. When a solution of lithium is nebulized into an air-acetylene flame, the difference in absorbance of the outputs of the two lamps, obtained in a single measurement and computed electronically, is proportional to the isotopic abundance. This relationship has been used as a basis for carrying out abundance measurements of 0–100 atom % lithium-6. The method is simple and rapid and compares favourably with the atomic absorption procedure based on absorbance ratios. The precision is ± 0.5 atom % lithium-6. The method is dependent on concentration with respect to total lithium content.

Electronic system for high sensitivity and high stability mass spectrometry Part III: New electronic arrangement for high precision in the determination of isotopic abundances

Electronic system for high sensitivity and high stability mass spectrometry Part III: New electronic arrangement for high precision in the determination of isotopic abundances