Hélène Isnard

Determination of 93Zr decay scheme and half-life

This study describes a new determination of the decay scheme and half-life of (93)Zr. A pure (93)Zr solution was obtained after chemical separation from the dissolution of an irradiated zircaloy sample. The concentration of (93)Zr in the solution was measured by mass spectrometry, with an isotopic dilution technique. The activity of the solution was measured by liquid scintillation counting, using an efficiency tracing method. The measurement of the activity concentration of (93)Nb(m) by X-ray spectrometry, allowed the determination of the (93)Zr decay scheme and the calculation of the (93)Zr detection efficiency. This leads to the calculation of the decay probability of (93)Zr toward (93)Nb(m) of (0.73+/-0.06) and to a half-life of (93)Zr of (1.64+/-0.06)x10(6) years. These values are discussed in comparison with the evaluated values available in the literature.

Multi-elemental Gd, Eu, Sm, Nd isotope ratio measurements by liquid chromatography coupled to MC-ICPMS with variable Faraday cup configurations during elution

The high-precision isotopic characterization of actinides and fission products in nuclear samples is fundamental for various applications such as the management of spent nuclear fuel or the validation of neutronic calculation codes. However multi-elemental isotope ratio measurements by mass spectrometric techniques are hampered by the presence of both spectral and non-spectral interferences as complex sample matrices are encountered in such topics, but also due to the lack of high precision mass spectrometers able to cover the entire mass spectrum. This work describes a new LC-MC-ICPMS approach allowing simultaneous high-precision and multi-elemental isotope ratio measurements of four fission products of interest for nuclear issues (Nd, Sm, Eu, Gd) within a single elution run. Variable motorized Faraday cup configurations were successively used during a specifically designed elution procedure in order to take into account the non-natural Nd, Sm, Eu, Gd isotopic compositions encountered in irradiated nuclear samples. This new method, involving the relevant isotopic reference standard injection timings for on-line mass bias corrections, was validated by the analysis of a simulated fission product fraction from a 235U-irradiated target. Reproducibilities better than 2‰ (k=2), comparable to those obtained by off-line measurements and the classic sample-standard bracketing mass bias correction approach, were obtained for all isotope ratios, except those involving isotopes with a transient signal peak apex lower than 100mV, for which the reproducibilities were comprised between 2‰ and 6‰.

Results of the EURAMET.RI(II)-K2.Ho-166m activity comparison

In 2013, five laboratories took part in the EURAMET.RI(II)-K2.Ho-166m comparison of activity concentration measurements of 166m Ho. The activity measurements of this comparison are part of the joint research project “Metrology for Radioactive Waste Management” of the European Metrology Research Programme (EMRP). One aim of this project is a new determination of the 166m Ho half-life.The results were found to be in good agreement and no outlier could be identified. A comparison reference value (CRV) has been calculated as the power-moderated mean (PMM) of all final laboratory results and was found to be 119.27(10) kBq g –1 . Preliminary degrees of equivalence based on the Comparison Refeence Value were also calculated for each reporting laboratory. The Key Comparison Reference Value and final degrees of equivalence will be calculated by the BIPM from the data contained herein and data from measurements made in the International Reference System (SIR).

A new procedure for high precision isotope ratio determinations of U, Cu and Zn at nanogram levels in cultured human cells: What are the limiting factors?

The monitoring of isotopic fractionations in in vitro cultured human cell samples is a very promising and under-exploited tool to help identify the metabolic processes leading to disease-induced isotopic fractionations or decipher metabolic pathways of toxic metals in these samples. One of the limitations is that the analytes are often present at small amounts, ranging from tens to hundreds of ng, thus making challenging low-uncertainty isotope ratio determinations. Here we present a new procedure for U, Cu and Zn purification and isotope ratio determinations in cultured human neuron-like cells exposed to natural U. A thorough study of the influence of the limiting factors impacting the uncertainty of δ238U, δ66Zn and δ65Cu is also carried out. These factors include the signal intensity, which determines the within-day measurement reproducibility, the procedural blank correction and the matrix effects, which determine the accuracy of the mass bias correction models. Given the small Cu and U amounts in the cell samples, 15-30 and 20ng respectively, a highly efficient sample introduction system was employed in order to improve the analyte transport to the plasma and, hence, the signal intensity. With this device, the procedural blanks became the main uncertainty source of δ238U and δ65Cu values, accounting over 65% of the overall uncertainty. The matrix effects gave rise to inaccuracies in the mass bias correction models for samples finally dissolved in the minimal volumes required for the analysis, 100-150µL, leading to biases for U and Cu. We will show how these biases can be cancelled out by dissolving the samples in volumes of at least 300µL for Cu and 450µL for U. Using our procedure, expanded uncertainties (k = 2) of around 0.35‰ for δ238U and 0.15‰ for δ66Zn and δ65Cu could be obtained. The analytical approach presented in this work is also applicable to other biological microsamples and can be extended to other elements and applications.

Deconvolution of the isotopic drift in LC-MC-ICPMS coupling: a new tool for studying isotope fractionation induced by sample introduction techniques

On-line hyphenated methods between Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) and a variety of introduction techniques (liquid and gas chromatography, laser ablation…) provide transient signals with specific time-windows. It is now well-known that the isotope ratio drift which is observed during transient signal acquisition is generated from the MC-ICPMS detection system, the introduction techniques, or a combination of both parameters. In this work, the Nd isotope ratios were investigated through a coupling of MC-ICPMS with Liquid Chromatography (LC). The purpose was to dissociate the isotopic drift coming from the detection system from the drift caused by the introduction technique by using raw isotope data. To this end, the time constants of the MC-ICPMS amplifiers were used, and the isotope drift generated by the detection system was successfully corrected. After this correction, the isotope drift coming exclusively from the LC was highlighted. The use of the Method of Internal Signal Synchronization (MISS) allowed the correction of the chromatographic drift and the calculation of a time lag between the Nd isotopes of 0.0036 s amu−1. This is the first time that for an isotope fractionation caused by a specific physicochemical process the time lag between the isotopes was calculated. We believe that the calculation of time lag values between the isotopes could be a simple and robust method opening up new possibilities for the study of isotope fractionations generated by different introduction techniques directly coupled with MC-ICPMS.

Accurate measurements of 129I concentration by isotope dilution using MC-ICPMS for half-life determination

Abstract Determining the 129I concentration, a long-lived radionuclide present in spent nuclear fuel, is a major issue for nuclear waste disposal purpose. 129I also has to be measured in numerous environmental, nuclear and biological samples. To be able to accurately determine the 129I concentration, an analytical method based on the use of a multicollector-inductively coupled plasma mass spectrometer (MC-ICPMS) combined with an isotope dilution technique using an 127I spike, was developed. First, the influence of different media (HNO3, NaOH and TMAH) on natural 127I signal intensity and stability and on memory effects was studied. Then an analytical procedure was developed by taking into account the correction of blanks and interferences. Tellurium was chosen for instrumental mass bias correction, as no certified standards with suitable 127I/129I ratio are available. Finally, the results, reproducibility and uncertainties obtained for the 129I concentration determined by isotope dilution with a 127I spike are presented and discussed. The final expanded relative uncertainty obtained for the iodine-129 concentration was lower than 0.7% (k = 1). This precise 129I determination in association with further activity measurements of this nuclide on the same sample will render it possible to determine a new value of the 129I half-life with a reduced uncertainty (0.76%, k = 1).

Multi-elemental Nd, Sm, Eu, Gd isotope ratio measurements by stop-flow isotachophoresis coupled to MC-ICPMS

In this study, a new analytical procedure based on isotachophoresis (ITP) coupled to a multi collector inductively coupled plasma mass spectrometer named Stop-Flow-ITP-MC-ICPMS is developed for exhaustive and high-precision multi-elemental isotopic characterization. We demonstrate that Stop-Flow-ITP makes it possible to stop the analytes migration several times for a duration compatible with the detector configuration changes without losing the separation performance. With this procedure, isotope ratio measurements of four lanthanides of interest for nuclear applications (Nd, Sm, Eu and Gd) were obtained with a reproducibility better than 0.4% in a single analysis with only 20ng of each element. A nebulization interface between ITP and MC-ICPMS composed of a dual inlet spray chamber and a multiple flow stream valve made it possible to perform isotopic reference standard injections for on-line mass bias correction by the sample standard bracketing approach. The flexibility of the Stop-Flow-ITP-MC-ICPMS procedure opens the way to online determination of isotope ratio measurements of multiple analytes present in a sample in a single analysis.

The half-life of 129I

The radionuclide 129I is a long-lived fission product that decays to 129Xe by beta-particle emission. It is an important tracer in geological and biological processes and is considered one of the most important radionuclides to be assessed in studies of global circulation. It is also one of the major contributors to radiation dose from nuclear waste in a deep geological repository. Its half-life has been obtained by a combination of activity and mass concentration measurements in the frame of a cooperation of 6 European metrology institutes. The value obtained for the half-life of 129I is 16.14 (12) × 106 a, in good agreement with recommended data but with a significant improvement in the uncertainty.

Precise U and Pu isotope ratio measurements in nuclear samples by hyphenating capillary electrophoresis and MC-ICPMS

Precise isotopic and elemental characterization of spent nuclear fuel is a major concern for the validation of the neutronic calculation codes and waste management strategy in the nuclear industry. Generally, the elements of interest, particularly U and Pu which are the two major elements present in spent fuel, are purified by ion exchange or extractant resins before off-line measurements by thermal ionization mass spectrometry. The aim of the present work was to develop a new analytical approach based on capillary electrophoresis (CE) hyphenated to a multicollector inductively coupled plasma mass spectrometer (MC-ICPMS) for online isotope ratio measurements. An electrophoretic separation protocol of U, Pu, and the fraction containing fission products and minor actinides (Am and Cm) was developed using acetic acid as the electrolyte and complexing agent. The instrumentation for CE was designed to be used in a glovebox, and a laboratory-built interface was developed for hyphenation with MC-ICPMS. The separation was realized with only a few nL of a solution of spent nuclear fuel, and the reproducibilities obtained on the U and Pu isotope ratios were on the order of a few ‰ which is comparable to those obtained by thermal ionization mass spectrometry (TIMS). This innovative protocol allowed a tremendous reduction of the analyte masses from μg to ng and also a drastic reduction of the liquid waste production from mL to μL. In addition, the time of analysis was shorted by at least a factor of three. All of these improved parameters are of major interest for nuclear applications.

Neodymium isotope ratio measurements by CE-MC-ICPMS: investigation of isotopic fractionation and evaluation of analytical performances

Precise isotope ratio measurements in the nuclear field often require hyphenation of separation techniques with multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). Among these separation techniques, electrokinetic methods are very interesting as they use the lowest sample volumes and produce the least amount of radioactive waste. The objectives of this study were to evaluate the performances when coupling electrokinetic techniques with MC-ICPMS for measuring isotope ratios of Nd, an element of interest for nuclear purposes. During data acquisition along the elution peak, an isotope ratio drift was observed and studied. In order to discriminate the drift induced by the MC-ICPMS detectors, the raw data of the isotope signals were corrected by taking into account the difference of time response of the Faraday cup amplifiers. An isotopic mass-dependent fractionation induced by the electrokinetic separation was then highlighted. Some of the parameters were modified (i.e., the length of the capillary and the external pressure) to evaluate their impact on the amplitude of fractionation. Finally, the measurement performances were evaluated for all the isotope ratios. The reproducibility obtained was lower than 0.2‰ regardless of the considered Nd isotope ratio with only 0.5 ng of injected Nd.