X-ray absorption spectroscopy systematics at the tungsten L-edge

A series of mononuclear six-coordinate tungsten compounds spanning formal oxidation states from 0 to +VI, largely in a ligand environment of inert chloride and/or phosphine, has been interrogated by tungsten L-edge X-ray absorption spectroscopy. The L-edge spectra of this compound set, comprised of [W<sup>0</sup>(PMe<sub>3</sub>)<sub>6</sub>], [W<sup>II</sup>Cl<sub>2</sub>(PMePh<sub>2</sub>)<sub>4</sub>], [W<sup>III</sup>Cl<sub>2</sub>(dppe)<sub>2</sub>][PF<sub>6</sub>] (dppe = 1,2-bis(diphenylphosphino)ethane), [W<sup>IV</sup>Cl<sub>4</sub>(PMePh<sub>2</sub>)<sub>2</sub>], [W<sup>V</sup>(NPh)Cl<sub>3</sub>(PMe<sub>3</sub>)<sub>2</sub>], and [W<sup>VI</sup>Cl<sub>6</sub>] correlate with formal oxidation state and have usefulness as references for the interpretation of the L-edge spectra of tungsten compounds with redox-active ligands and ambiguous electronic structure descriptions. The utility of these spectra arises from the combined correlation of the estimated branching ratio (EBR) of the L<sub>3,2</sub>-edges and the L<sub>1</sub> rising-edge energy with metal Z<sub>eff</sub>, thereby permitting an assessment of effective metal oxidation state. An application of these reference spectra is illustrated by their use as backdrop for the L-edge X-ray absorption spectra of [W<sup>IV</sup>(mdt)<sub>2</sub>(CO)<sub>2</sub>] and [W<sup>IV</sup>(mdt)<sub>2</sub>(CN)<sub>2</sub>]<sup>2–</sup> (mdt<sup>2–</sup> = 1,2-dimethylethene-1,2-dithiolate), which shows that both compounds are effectively W<sup>IV</sup> species. Use of metal L-edge XAS to assess a compound of uncertain formulation requires: 1) Placement of that data within the context of spectra offered by unambiguous calibrant compounds, preferably with the same coordination number and similar metal ligand distances. Such spectra assist in defining upper and/or lower limits for metal Z<sub>eff</sub> in the species of interest; 2) Evaluation of that data in conjunction with information from other physical methods, especially ligand K-edge XAS; 3) Increased care in interpretation if strong π-acceptor ligands, particularly CO, or π-donor ligands are present. The electron-withdrawing/donating nature of these ligand types, combined with relatively short metal-ligand distances, exaggerate the difference between formal oxidation state and metal Z<sub>eff</sub> or, as in the case of [W<sup>IV</sup>(mdt)<sub>2</sub>(CO)<sub>2</sub>], add other subtlety by modulating the redox level of other ligands in the coordination sphere

Agile manufacturing practices: the role of big data and business analytics with multiple case studies

The purpose of this study was to examine the role of big data and business analytics (BDBA) in agile manufacturing practices. Literature has discussed the benefits and challenges related to the deployment of big data within operations and supply chains, but there has not been a study of the facilitating roles of BDBA in achieving an enhanced level of agile manufacturing practices. As a response to this gap, and drawing upon multiple qualitative case studies undertaken among four U.K. organizations, we present and validate a framework for the role of BDBA within agile manufacturing. The findings show that market turbulence has negative universal effects and that agile manufacturing enablers are being progressively deployed and aided by BDBA to yield better competitive and business performance objectives. Further, the level of intervention was found to differ across companies depending on the extent of deployment of BDBA, which accounts for variations in outcomes

Accurate determination of Curium and Californium isotopic ratios by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS) in 248Cm samples for transmutation studies

The French Atomic Energy Commission has carried out several experiments including the mini-INCA (INcineration of Actinides) project for the study of minor-actinide transmutation processes in high intensity thermal neutron fluxes, in view of proposing solutions to reduce the radiotoxicity of long-lived nuclear wastes. In this context, a Cm sample enriched in {sup 248}Cm ({approx}97 %) was irradiated in thermal neutron flux at the High Flux Reactor (HFR) of the Laue-Langevin Institute (ILL). This work describes a quadrupole ICP-MS (ICP-QMS) analytical procedure for precise and accurate isotopic composition determination of Cm before sample irradiation and of Cm and Cf after sample irradiation. The factors that affect the accuracy and reproducibility of isotopic ratio measurements by ICP-QMS, such as peak centre correction, detector dead time, mass bias, abundance sensitivity and hydrides formation, instrumental background, and memory blank were carefully evaluated and corrected. Uncertainties of the isotopic ratios, taking into account internal precision of isotope ratio measurements, peak tailing, and hydrides formations ranged from 0.3% to 1.3%. This uncertainties range is quite acceptable for the nuclear data to be used in transmutation studies

Bk and Cf chromatographic separation and 249^{249}Bk/248^{248}Cm and 249^{249}Cf/248^{248}Cm elemental ratios determination by inductively coupled plasma quadrupole mass spectrometry

International audienceThe French Atomic Energy Commission has carried out several experiments for the study of minor-actinide transmutation processes in high intensity thermal neutron flux. In this context a Cm sample enriched in $^{248}$Cm (∼97%) was irradiated in a thermal neutron flux at the High Flux Reactor (HFR) of the Laue–Langevin Institute (ILL). The precise and accurate determination of Cf isotope ratios and of $^{249}$Bk/$^{248}$Cm and $^{249}$Cf/$^{248}$Cm elemental ratios in the 248Cm irradiated sample is crucial for the calculation of actinide neutron capture cross-sections. This work describes an analytical procedure for the separation and the isotope ratio measurement of Bk and Cf in the irradiated sample. The Bk and Cf separation is based on a lanthanides separation protocol previously developed by the laboratory. Well-defined retention times for Bk and Cf were obtained by coupling the Ionic Chromatography (IC) with an ICP-QMS. All conditions of element separation by IC and the different steps of the analytical protocol in order to obtain the isotopic and elemental ratios are presented. Relative uncertainties of Cf isotopic ratios range from 0.3% to 0.5% and the uncertainty of the $^{249}$Bk/$^{248}$Cm and $^{249}$Cf/$^{248}$Cm elemental ratios are respectively 6.1% and 3.2%. This level of uncertainty for both isotopic and elemental ratios is in perfect agreement with the requirement for transmutation studies

Quasi-Absolute Neutron-Induced Fission Cross Section of 243Am

The existing evaluations of the 243Am neutron-induced fission cross section have been questioned by recent studies performed at the GNEISS facility. In the neutron energy range from 1 to 6 MeV the GNEISS data present deviations of more than 15% with respect to the evaluations. In order to solve this problem, we have performed a first quasi-absolute measurement of this fission cross section from the fission threshold up to the onset of secondchance fission. To achieve this goal we have used the neutron-proton scattering cross section as reference reaction to determine the incident neutron flux. This cross section is known with a precision better than 1% for a wide range of neutron energies (1meV to 20 MeV).JRC.D.5-Neutron physic

243Am neutron-induced fission cross section in the fast neutron energy range

The existing evaluations of the 243Am neutron-induced fission cross section have been questioned by recent measurements performed at the GNEISS facility. In the neutron energy range from 1 to 6 MeV, the GNEISS data present deviations of more than 15% with respect to the evaluations. In order to solve this problem, we have measured this cross section in reference to three different standard cross sections. The first standard reaction used corresponds to the neutron on proton elastic scattering cross section, which is known with a precision better than 0.5% over a wide neutron-energy range of 1 meV to 20 MeV. The other two experiments were conducted in reference to the 235U(n, f) and 238U(n, f) reactions. The comparison between these three standard reactions ensures that systematic parameters have been correctly evaluated. Moreover, a sensitivity analysis of parameters and correlations of parameters is described and a complete variance-covariance matrix of the measurements is presented and discussed.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Quasi-absolute neutron-induced fission cross section of 243Am

International audienc