IRMM-3100a: A new certified isotopic reference material with equal abundances of 233U, 235U, 236U and 238U

The new so-called Quad-IRM (“Quadruple Isotope Reference Material”) was prepared from highly enriched ²³³U, ²³⁵U, ²³⁶U and ²³⁸U isotopic materials using an optimized combination of gravimetrical mixing and mass spectrometry. Within the mixing process the isotope ratios were adjusted to about n(²³³U)/n(²³⁵U)/n(²³⁶U)/n(²³⁸U) = 1/1/1/1 and certified with expanded relative uncertainties of 0.0054% per mass unit (coverage factor k = 2). This new isotope reference material is ideal for verifying the inter-calibration of multi-detector systems in isotope mass spectrometry.The certified n(²³³U)/n(²³⁶U) ratio of IRMM-3100a was derived from the mass metrology data of the gravimetrical mixing of highly enriched ²³³U and ²³⁶U materials. It was verified by thermal ionization mass spectrometry (TIMS) measurements using the classical total evaporation (TE) and modified total evaporation (MTE) methods. The n(²³⁴U)/n(²³⁶U), n(²³⁵U)/n(²³⁶U) and n(²³⁸U)/n(²³⁶U) ratios were then determined by TIMS using the n(²³³U)/n(²³⁶U) ratio for internal normalization and using a multi-dynamic measurement procedure in order to circumvent any possible influence and uncertainties from Faraday cup efficiencies and amplifier gain factors. The certified n(²³⁵U)/n(²³⁶U) and n(²³⁸U)/n(²³⁶U) ratios were additionally verified using the classical and modified total evaporation methods using two TIMS instruments at IRMM and one TIMS instrument at IAEA-SGAS. The verification data can be regarded as results obtained at three independent instruments at two different nuclear safeguards laboratories.     

Preparation of targets for nuclear chemistry experiments at DANCE

In this paper, we describe the separation chemistry and electrodepositions conducted for the preparation of ²⁴¹Am, ²⁴³Am and ²³³U targets used for cross-section measurements at DANCE. Thick, adherent deposits were prepared using molecular plating from isopropyl alcohol solutions. Improved yields and thicknesses were observed for ²⁴¹Am electrodeposition after the material was purified using TRU resin from Eichrom. Similarly, ²³³U deposits were improved after purification with an anion exchange column in 9 M HBr followed by purification using UTEVA resin from Eichrom.     

Cd3(P3O9)2 · 14H2O. II—ETUDE DE L'EAU AU MOYEN DE LA RESONANCE MAGNETIQUE PROTONIQUE SUR POUDRE

Abstract

Cadmium trimetaphosphate tetradecahydrate powder has been studied by ¹H nuclear magnetic resonance between ?191 and 60°C. The spectra includes one contribution from molecular water and one contribution from H atoms belonging to “OH” groups. The formula which agrees with these results is Cd₃(OH) _n (P₃O₉)₂H _n · (14- _n )H₂O; it seems that n increases with increasing values of temperature.

L'étude par résonance magnétique du proton du trimétaphosphate de cadmium tetradécahydraté en poudre a été faite entre ?191 et +60°C. Le spectre comporte une contribution d'eau moléculaire et une contribution d'atomes H appartenant à des groupes OH. La formule en accord avec ces résultats est Cd₃(OH) _n (P₃O₉)₂H _n · (14- _n )H₂O, o[ugrave] n croit vraisemblablement avec la température.     

Measurement of non-separated U/Pu samples: optimization of TIMS procedures for safeguards purposes at Rokkasho on-site laboratory

The on-site laboratory (OSL) at Rokkasho Reprocessing Plant (RRP) is jointly operated by the Japanese authority Nuclear Material Control Centre and the International Atomic Energy Agency (IAEA) and provides, together with the Nuclear Material Laboratory (NML) at Seibersdorf, analytical services to the IAEA’s inspectorate. OSL deals with a variety of samples typical to a reprocessing plant including pure product solutions of uranium and plutonium but also mixed U/Pu solutions originating from various stages of the chemical process. For a significant proportion of the samples, the requirement on measurement accuracy and precision from the Inspectorate makes the use of thermal ionization mass spectrometry (TIMS) indispensible. Until recently, all samples intended for TIMS had to undergo time-consuming U/Pu separation before isotope dilution measurement. The need for rapid reporting of analytical results for certain safeguards samples evoked the idea of performing TIMS measurements without prior U/Pu separation for mixed U/Pu products as they are obtained from the PUREX process at RRP. For this purpose, a systematic study was initiated to probe the figure of merits and limitations of conducting TIMS analyses on mixed U/Pu samples and, in particular, whether the accuracy and precision of the main ratios of interest, n(²³⁵U)/n(²³⁸U) and n(²⁴⁰Pu)/n(²³⁹Pu), are influenced by the presence of larger amounts of the other element. A series of synthetic mixtures with U/Pu ratios ranging from 1:10 up to 100:1 were prepared and measured in both laboratories—OSL and NML—using ThermoFisher TRITON multi-collector TIMS instruments. For the n(²³⁵U)/n(²³⁸U) ratio, interference due to ²³⁸Pu was observed which can be significant depending on the U/Pu ratio and the ²³⁸Pu abundance. However, for the n(²⁴⁰Pu)/n(²³⁹Pu) ratio, which is of premier importance for safeguarding RRP, no significant interference arising from the concomitant U was detected independently of enrichment. Even in samples with an excess of U (U/Pu ratio of 100:1), compliance with International Target Values (ITV2010) was demonstrated for n(²⁴⁰Pu)/n(²³⁹Pu) results with a relative difference to certified not exceeding 0.01 %.     

Determination of <Superscript>241</Superscript>Am/<Superscript>243</Superscript>Am ratios

Determination of ²⁴¹Am/²⁴³Am ratios is required for vanous purposes including assay of Am by isotope dilution techniques. Alpha-spectrometry on electrodeposited sources is a preferred technique for this determination. However, there is an inherent problem of tail contribution which necessitates the use of suitable algorithms to account for the same. Recently, in the frame of a Coordinated Research Program (CRP) of the International Atomic Energy Agency (IAEA), WinALPHA software has been developed which is a combination of an asymmetrical Gaussian for the main part of the peak and a low energy function. Therefore, it was of interest to compare the use of this algorithm with the routinely used method, in our laboratory, based on geometric progression (G. P.) decrease. Since, there are no reference materials available commercially for ²⁴¹Am/²⁴³Am ratios, synthetic mixtures covening a wide range (0.3 to 2.0) of ²⁴¹Am/²⁴³Am α-activity ratios were used and un-ignited electrodeposited sources were prepared for α-spectrometry. The α-spectra obtained using PIPS detector, were evaluated using the two algonthms The ²⁴¹Am/²⁴³Am α-activity ratios obtained were also compared with those determined by thermal ionization mass spectrometry (TIMS). An agreement of about 1% was obtained in the ²⁴¹Am/²⁴³Am ratios determined by the two methods and also by using the two algorithms for α-spectrum evaluation.     

Creatinine determination in urine from the point of view of reference values

In this paper, the creation of a certified reference material for urinary creatinine is described. We used the Jaffe method and HPLC method for establishment of the certified value. Homogeneity tests are also described. We obtained material with sufficient homogeneity, stability, and with certified value (expanded uncertainty, k=2 for CI 95%) (7.77±0.27) mmol·L⁻¹. This material was consequently used for the interlaboratory comparison (EQA Czech Republic for clinical chemistry). Twenty-nine percent of the participants obtained measurement results within the interval of the certified value ± expanded uncertainty, while 85% of the participants obtained values inside the interval of the certified value ± target measurement uncertainty. Direct use of the certified reference materials for method evaluation in EQA programs means a significant advance for monitoring and documentation traceability of results in routine measurements.     

EQRAIN: uranium and plutonium interlaboratory exercises from 1997 to 2016—comparison to ITVs-2010

Since 1987, the CEA’s Committee for the establishment of analysis methods (CETAMA) has regularly implemented interlaboratory comparisons, entitled “evaluation of the quality results of analysis in the nuclear industry” (EQRAIN). Notably, the EQRAIN U and EQRAIN Pu interlaboratory comparisons assess proficiency in measuring a mass content of uranium or plutonium in reference solutions. This paper presents the results of measurement uncertainty assessments from EQRAIN U and EQRAIN Pu comparisons over 20 years of exercises (1997–2016). The mathematical approach developed in this work allowed to estimate the impact of short-term systematic and random errors to the overall uncertainty of each analytical method used in the interlaboratory comparison program. This statistical analysis shows a good consistency between measurement uncertainty values from EQRAINs and the measurement uncertainty target values established by the International Atomic Energy Agency for nuclear material balances (ITVs-2010).

     

Develop dissipative particle dynamics method to study the fluid flow and heat transfer of Ar and O2 flows in the micro- and nanochannels with precise atomic arrangement versus molecular dynamics approach

Fluid atomic behavior is an important factor for industrial applications. Computer simulations based on simple models predict Poiseuille flow for these atomic structures with the presence of external force. In this work, we describe the dynamical properties of Ar and O₂ flows with precise atomic arrangement via dissipative particle dynamics (DPD) and molecular dynamics (MD) simulation approaches. In these methods, each model is represented by using Large-scale Atomic/Molecular Massively Parallel Simulator package. Simulation results show that maximum rate for velocity of Ar flow in platinum and copper microchannels is 0.100 (unit less)/0.091 Å ps^?1 and 0.121 (unit less)/0.105 Å ps^?1 by using DPD/MD approach. This atomic parameter changes to 0.111 (unit less)/0.102 Å ps^?1 and 0.125 (unit less)/0.108 Å ps^?1 for O₂ fluid with mentioned approaches. By decreasing the microchannel size, the maximum rate of velocity reaches to 0.101 (unit less)/0.099 Å ps^?1 and maximum temperature rate decreases to 485 (unit less)/440 K with DPD/MD approaches. These calculated parameters can be used in industrial application designing for some processes such as heat transfer in structures. It was seen that the developed DPD approach was able to simulate the fluid flow and heat transfer of various types of fluids at micro- and nanoscales with suitable accuracy versus MD.

     

Determination of butoxyacetic acid (biomarker of ethylene glycol monobutyl ether exposure) in human urine candidate reference material

Ethylene glycol monobutyl ether (EGBE), an industrial solvent, is absorbed by the body not only by inhalation but also by dermal absorption (liquid or vapour). EGBE is metabolized to butoxyacetic acid (BAA). Pooled freeze-dried urine candidate reference material (RM) was prepared from urine obtained from persons occupationally exposed to EGBE. This material has the advantage of containing butoxyacetic acid in both the free and conjugated (glutamine and glycine) forms, as found in native urine. In all GC method modifications used, acid hydrolysis was used to release BAA from its conjugated form. The amount of butoxyacetic acid in homogeneity and stability testing was measured by GC after derivatisation with N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide. Detection was by MS in EI mode, in the authors’ laboratory. For interlaboratory comparison of the reference material GC methods with MS, FID, and ECD were used. Different extraction solvents (dichloromethane–isopropanol 2:1, ethyl acetate, or dichloromethane) and derivatisation reagents (trimethylsilyldiazomethane, N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide) were used. Using ANOVA (at the statistical level α = 0.05) no changes were found in the concentration of butoxyacetic acid during fifteen month isochronous stability testing, or in homogeneity testing. The uncertainty contributions were u _h = 8.8 mg L⁻¹ and u _s = 6.5 mg L⁻¹. The concentration of butoxyacetic acid in freeze-dried urine RM was evaluated from the results of eight laboratory data sets within an interlaboratory comparison by use of the interactive statistical software IPECA. The contribution to total uncertainty derived from interlaboratory comparison was u _i = 12.7 mg L⁻¹. The reference value (c = 273 ± 33 mg L⁻¹) is an unweighted arithmetic average of accepted results. The value is traceable to the pure butoxyacetic acid (98% w/w; Acros Organic #257760010) used as calibrant. The uncertainty given is combined expanded uncertainty derived from the results from interlaboratory comparison, and from homogeneity and stability tests (k = 2). The reference material will be used to verify method performance in the biological monitoring of occupational exposure to EGBE.     

Distribution behavior of U(VI), Am(III) and Eu(III) on diglycolamide based extraction chromatographic resin in perchloric acid medium

An attempt has been made in the present work to investigate the role of anion for the uptake of Am(III)/Eu(III)/U(VI) by extraction chromatography (EXC) resin incorporating tetra-n-octyl-3-oxapentanediamide, commonly referred to as tetra-octyl diglycolamide (TODGA). In contrast to the nitric acid, perchloric acid medium favors extraction of trivalent metal ions even at low acidity (pH 2) and is almost insensitive to the acidity up to 5 M. Exceptionally large distribution coefficients (10⁵–10⁶) in the wide range of perchlorate concentration (10^?2–5 M) is quite unusual and is by far the largest reported in the literature for Am(III)/Eu(III). Thermodynamic data suggests the possibility of inner sphere/cation exchange mechanism involving TODGA aggregates at higher acidity but outer sphere/cation exchange mechanism at low acidity for Eu(III). There is a possibility of employing TODGA based EXC resin for the remediation of liquid waste (contaminated with long lived transuranics like ^241/243Am and ²⁴⁵Cm) in the wide range of acidity.     

Fit for purpose validated method for the determination of the strontium isotopic signature in mineral water samples by multi-collector inductively coupled plasma mass spectrometry

A robust method allowing the routine determination of n(⁸⁷Sr)/n(⁸⁶Sr) with at least five significant decimal digits for large sets of mineral water samples is described. It is based on 2 consecutive chromatographic separations of Sr associated to multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) measurements. Separations are performed using commercial pre-packed columns filled with “Sr resin” to overcome isobaric interferences affecting the determination of strontium isotope ratios. The careful method validation scheme applied is described. It included investigations on all parameters influencing both chromatographic separations and MC-ICPMS measurements, and also the test on a synthetic sample made of an aliquot of the NIST SRM 987 certified reference material dispersed in a saline matrix to mimic complex samples. Correction for mass discrimination was done internally using the n(⁸⁸Sr)/n(⁸⁶Sr) ratio. For comparing mineral waters originating from different geological backgrounds or identifying counterfeits, calculations involved the well known consensus value (1/0.1194) ± 0 as reference. The typical uncertainty budget estimated for these results was 40 ‘ppm’ relative (k = 2). It increased to 150 ‘ppm’ (k = 2) for the establishment of stand alone results, taking into account a relative difference of about 126 ‘ppm’ systematically observed between measured and certified values of the NIST SRM 987. In case there was suspicion of a deviation of the n(⁸⁸Sr)/n(⁸⁶Sr) ratio (worst case scenario) our proposal was to use the NIST SRM 987 value 8.37861 ± 0.00325 (k = 2) as reference, and assign a typical relative uncertainty budget of 300 ‘ppm’ (k = 2). This method is thus fit for purpose and was applied to eleven French samples.     

A new technique for differentiating between 2J(C,H) and 3/4J(C,H) connectivities

We present a new pulse sequence that yields two simultaneously detected types of long‐range correlation spectra. The one spectrum is to show all ⁿJ(C,H) connectivities and the other is to show exclusively ²J(C,H) connectivities. The method is demonstrated by using strychnine as a test sample. A comparison with HMBC shows that the ²J(C,H)/ⁿJ(C,H) experiment supplies a ⁿJ(C,H) spectrum that is of equal standard with regard to sensitivity and spectral information. The additional ²J(C,H) spectrum allows the disentanglement of ²J(C,H) and ⁿJ(C,H) signals (n > 2) in HMBC type spectra, which greatly simplifies signal assignment and structure elucidation in general. Copyright © 2003 John Wiley & Sons, Ltd.     

Die Bestimmung von Uran und Plutonium im Rahmen der Ausscheidungsanalyse

Zusammenfassung Eine in der Praxis angewandte Analysenmethode zur Bestimmung von Plutonium in Harnproben wurde mit Hilfe von Tracerversuchen mit²³⁶Pu,²³³U und²⁴¹Am hinsichtlich ihrer radiochemischen Ausbeute und ihrer Trenneffizienz überprüft. Dabei zeigte sich, daß die Pu-Bestimmung mit einer Ausbeute von 95% praktisch quantitativ erfolgt. Im allgemeinen ist es nicht notwendig, vom Restgehalt an Uran, der 25% beträgt, weiter abzutrennen. Bei Uranmengen bis zu 100g U (nat.) sind die Meßproben alphaspektrometrisch zur qualitativen und zur quantitativen Auswertung geeignet. Auf diese Weise kann neben der Pu-Bestimmung aus demselben Alphaspektrum einer Harnprobe auch eine Aussage über die Isotopenzusammensetzung des Urangehaltes und eine mengenmäßige Abschätzung getroffen werden.Die Abtrennung des²⁴¹Am erfolgt dagegen vollständig. Der Restgehalt an²⁴¹Am in der durch Elektrodeposition hergestellten Pu-Meßprobe wurde mit weniger als 0,3% ermittelt und ermöglicht eine Auswertung des Alphaspektrums auch auf²³⁸Pu.Die Ergebnisse von Routinemessungen im Rahmen der Personenüberwachung zeigten einen normalen Urangehalt im Harn von <0,3g U/l und einen normalen Plutoniumgehalt von 0,05 pCi²³⁹Pu/24 h-Harn.

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The determination of uranium and flutonium in excretion analysis

Summary A routine method for the determination of Pu in urine samples was tested with tracer amounts of²³⁶Pu,²³³U and²⁴¹Am for its recovery and for efficiency of radiochemical separation. Pu recovery was 95%, uranium about 25%, which in generally does not need to be separated for-spectrometric determination of Pu. With uranium content up to 100g U_(nat.) counting sources are suitable for qualitative and quantitative evaluation of-spectra. In this way additionally information about the isotopic composition and the amount of uranium in the urine sample can be achieved from the same measurement.Separation from²⁴¹Am, however, can be assumed quantitatively. The activity of²⁴¹Am in such counting sources prepared by electrodeposition was less than 0,3% which enables evaluation of²³⁸Pu too. Results of routine determinations in personnel monitoring show normal background levels of uranium concentration in urine samples of less than 0,3g U (nat.)/l and for plutonium of 0,05 pCi²³⁹Pu/24-hr urine samples.

     

The role of kinetic energy in chemical binding

The wavefunctions and various partitions of the energy are examined for a variety of small molecules (H₂, H₃, H₄, HeH, HeH₂, He₂, LiH, and BH) in order to isolate the factors crucial for bond formation. We find that a natural partition of the energy leads to the conclusion that the crucial factor is the exchange, or nonclassical, part of the kinetic energy, T ^x. The change in T ^xupon pushing the atoms towards one another is the dominant term in the binding energy; it is negative when the resulting molecule is stable and positive when it is unstable. We show that T ^x is related to the interference kinetic energy considered by Ruedenberg.

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Zusammenfassung Die Wellenfunktionen und verschiedene Zerlegungen der Energie werden für eine Reihe kleiner Moleküle untersucht (H₂, H₃, H₄, HeH, HeH₂, He₂, LiH und BH), um die Faktoren zu finden, die für die Bindungsbildung ausschlaggebend sind. Die natürliche Zerlegung der Energie läßt die Folgerung zu, daß der bestimmende Faktor der Austauschanteil T ^x(oder nichtklassische Anteil) der kinetischen Energie ist. Die Änderung von T ^xbeim Zusammenführen der Atome ist der dominierende Term für die Bindungsenergie; er ist negativ, wenn das resultierende Molekül stabil ist, und positiv, falls es instabil ist. Es wird gezeigt, daß T ^x im Zusammenhang zum Wechselwirkungsanteil der kinetischen Energie nach Ruedenberg steht.

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Partially supported by a grant (GP-15423) from the National Science Foundation. This paper is based on a portion of the PhD thesis (California Institute of Technology, 1970) by CWW.

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National Science Foundation Predoctoral Trainee.

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Alfred P. Sloan Foundation Research Fellow.

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Contribution No. 3917.     

Electrostatic,sequential bond energies and structures of Li+·(N2)n complexes: computational study

The MP2 and CCSD calculations of the geometries and binding energies of the Li⁺·(N₂)_n (n?=?1–4) complexes are obtained. The potential energy surface showed that these complexes exhibit one minimum state and one transition state. The mono- and di-ligated complexes exhibit linear configurations with a binding energy of 11.1 and 21.2 kcal mol^?1, respectively. Trigonal planar and tetrahedral configurations are obtained for tri- and tetra-ligated complexes, respectively. The computed sequential bond dissociation energies (BDEs) of Li⁺·(N₂)_n (n?=?1–4) complexes are also calculated in which the mono-ligated complex has the largest BDE value. The obtained trend is mainly dependent on the variation in the ion-quadrupole interaction of these ion complexes. These calculations predict that these complexes are of purely electrostatic nature.

     

Preparation and calibration of a 231Pa reference material

A ²³¹Pa reference material has been characterized for amount of protactinium. This reference material is primarily intended for calibration of ²³³Pa tracers produced for ²³⁵U–²³¹Pa model age measurements associated with nuclear forensics and nuclear safeguards. Primary measurements for characterization were made by isotope dilution mass spectrometry of a purified ²³¹Pa solution using a ²³³Pa isotopic spike. The spike was calibrated by allowing multiple aliquots of the ²³³Pa spike solution to decay to ²³³U and then measuring the ingrown ²³³U by isotope dilution mass spectrometry using a certified uranium assay and isotopic standard as a reverse-spike. The new ²³¹Pa reference material will simplify calibration of the ²³³Pa isotope dilution spikes, provide metrological traceability, and potentially reduce the overall measurement uncertainty of model ages.

     

Monotonicity properties of the atomic charge density function

The present knowledge of the monotonicity properties of the spherically averaged electron density ρ(r) and its derivatives, which comes mostly from Roothan-Hartree-Fock calculations, is reviewed and extended to all Hartree-Fock ground-state atoms from hydrogen (Z = 1) to uranium (Z = 92). In looking for electron functions with universal (i.e., valid in the whole periodic table) monotonicity properties, it is found that there exist positive values of α so that the function g_o(r; α) = ρ(r)/r^α is convex, and g₁(r;α) = −ρ′(r)/r^α is not only monotonically decreasing from the origin but also convex. This is, however, not the case for the function g₂(r; α) = ρ′(r)/r^α. Additionally, the conditions which specify values for β such that the function g_n(r; β) = (−1) ′ρ⁽ⁿ⁾(r)/r^β is logarithmically convex are obtained and numerically calculated for n = 0,1 in all neutral atoms below uranium. The last property is used to obtain inequalities of general validity involving three radial expectation values which generalize all the similar ones known to date, as well as other relationships among these quantities and the values of the electron density and its derivatives at the nucleus. © 1996 John Wiley & Sons, Inc.     

Isotopic “fingerprints” for natural uranium ore samples

A set of six samples, collected worldwide from various uranium ore mining facilities, was analysed for uranium isotopic composition by high accuracy isotope mass spectrometry. The goal of this article was twofold: to measure isotopic variations between samples of different geographical origin and to produce calibrated isotope ratios with the smallest achievable uncertainty (as defined according to the ISO Guide to the Expression of Uncertainty in Measurement). In the first step, the molar ratio of the isotopes ²³⁵U and ²³⁸U, n(²³⁵U)/n(²³⁸U), was measured using a UF₆-gas-inlet isotope mass spectrometer (VARIAN MAT 511). This instrument was calibrated against gravimetrically prepared synthetic isotope mixtures thus allowing SI-traceable measurements to be made. The ratios of the “minor isotopes” to ²³⁸U [n(²³⁴U)/n(²³⁸U) and n(²³⁶U)/n(²³⁸U)] were determined in a second step using a thermal ionisation mass spectrometer with high abundance sensitivity (Finnigan MAT262-RPQ-PLUS). The mass-fractionation correction was done internally using the result of the n(²³⁵U)/n(²³⁸U) measurement. As a result, the complete measured uranium isotopic composition is traceable to the SI system. For all ratios n(²³⁴U)/n(²³⁸U), n(²³⁵U)/n(²³⁸U), and n(²³⁶U)/n(²³⁸U) significant differences for samples of different origin were found. Regarding the n(²³⁶U)/n(²³⁸U) results, only two samples, one of them from the Oklo reactor in Gabon, showed significant presence of ²³⁶U. For all other samples an upper limit for n(²³⁶U)/n(²³⁸U) of about 6 × 10⁻¹⁰, mainly dependent on the instrumentation, was found. As a result of this study we propose values for the isotope abundances of natural uranium for the “Best Measurement from a Single Terrestrial Source” and the “Range of Natural Variations” in the IUPAC-table of the “Isotopic Composition of the Elements.”     

Preparation and certification of new thorium isotopic reference materials

Preparation of two Isotopic Reference Materials of thorium has been performed, starting from highly enriched ²³²Th (99.99%) and ²³⁰Th (99.8%). After full characterization (chemical and isotopic) of these purified base materials the thorium nitrate was transformed to thorium dioxide. Accurately weighed amounts of the two isotopes in the dioxide form were subsequently dissolved in nitric acid and resulted in solutions with amount ratios n(²³⁰Th)/n(²³²Th) close to 10^–5 (IRMM-035) and 3 · 10^–6 (IRMM-036). These gravimetrically prepared ratios were finally verified by means of Thermal Ionization Mass Spectrometry (TIMS). The purpose of the Reference Materials is to calibrate thorium isotope amount ratio measurements. Received: 7 July 1997 / Revised: 1 December 1997 / Accepted: 7 December 1997     

Preparation and certification of new thorium isotopic reference materials

Preparation of two Isotopic Reference Materials of thorium has been performed, starting from highly enriched ²³²Th (99.99%) and ²³⁰Th (99.8%). After full characterization (chemical and isotopic) of these purified base materials the thorium nitrate was transformed to thorium dioxide. Accurately weighed amounts of the two isotopes in the dioxide form were subsequently dissolved in nitric acid and resulted in solutions with amount ratios n(²³⁰Th)/n(²³²Th) close to 10^–5 (IRMM-035) and 3 · 10^–6 (IRMM-036). These gravimetrically prepared ratios were finally verified by means of Thermal Ionization Mass Spectrometry (TIMS). The purpose of the Reference Materials is to calibrate thorium isotope amount ratio measurements. Received: 7 July 1997 / Revised: 1 December 1997 / Accepted: 7 December 1997