High resolution Magic Angle Spinning Solid State Nuclear Magnetic Resonance Facility for Actinides-bearing compounds

Solid-state Nuclear Magnetic Resonance (NMR) using Magic Angle Spinning (MAS) is a very powerful analytical method as it is sensitive to short-range and atomic scale structure. Moreover, this technique allows the study of amorphous samples, and minor crystalline phases, sometimes beyond detection limits of X-ray diffraction (XRD). In 2007, Ian Farnan, Herman Cho and William J. Weber, at Pacific Northwest National Laboratory (PNNL), caused a stir in the actinide community with their MAS-NMR investigation of a-irradiation damage in natural and 238/239Pu-doped zircons (ZrSiO4). At the Joint Research Centre's (JRC) Institute for Transuranium Elements (ITU), we were immediately enthusiastic about this breakthrough and sought to establish a similar facility in Europe. In this publication, we will give an overview about the new and unique NMR spectrometer with an active glovebox allowing to perform MAS experiments at very high-spinning speed on highly radioactive compounds. Some of the first and very promising results will also be presented.JRC.E.4-Nuclear fuel

Ferromagnetic ordering in NpAl2: Magnetic susceptibility and 27Al nuclear magnetic resonance

We report on the magnetic properties of the neptunium based ferromagnetic compound NpAl2. We used magnetization measurements and 27Al NMR spectroscopy to access magnetic features related in the paramagnetic and in the ordered state below TC (56 K). While very precise DC SQUID magnetization measurements confirm the FM state, they show as a reduced reverse field (HC~3000 Oe) and a small hysteresis loop at 5 K, well below the ordered state. The variable offset cumulative spectra (VOCS) acquired in the paramagnetic state shows a high sensitivity of the 27Al nuclei to the ferromagnetic ordering (Knight shifts and line broadening) even at room temperature. The oversimplified picture of NpAl2 as a well localised 5f system used as a reference compound for Mössbauer spectroscopy should be slightly reconsidered with some partly delocalised 5f states interacting at high temperature.JRC.E.4-Nuclear Fuel Safet

A nuclear magnetic resonance spectrometer concept for hermetically sealed magic angle spinning investigations on highly toxic, radiotoxic, or air sensitive materials

A concept to integrate a commercial high-resolution, magic angle spinning nuclear magnetic resonance (MAS-NMR) probe capable of very rapid rotation rates (70 kHz) in a hermetically sealed enclosure for the study of highly radiotoxic materials has been developed and successfully demonstrated. The concept centres on a conventional wide bore (89 mm) solid-state NMR magnet operating with industry standard 54 mm diameter probes designed for narrow bore magnets. Rotor insertion and probe tuning take place within a hermetically enclosed glovebox, which extends into the bore of the magnet, in the space between the probe and the magnet shim system. Oxygen-17 MAS-NMR measurements demonstrate the possibility of obtaining high quality spectra from small sample masses(10 mg) of highly radiotoxic material and the need for high spinning speeds to improve the spectral resolution when working with actinides. The large paramagnetic susceptibility arising from actinide paramagnetism in (Th1−xUx)O2 solid solutions gives rise to extensive spinning sidebands and poor resolution at 15 kHz, which is dramatically improved at 55 kHz. The first 17OMAS-NMR measurements on NpO2+x samples spinning at 55 kHz are also reported. The glovebox approach developed here for radiotoxic materials can be easily adapted to work with other hazardous or even air sensitive materials.JRC.E.4-Nuclear fuel

A 27Al NMR study of Actinides compounds at low Temperatures: AnPd5Al2 and AnAl2 systems

The recent increase of studies of actinides and specifically transuranium elements and compounds using microscopic probe techniques (EELS, RIX, XMCD, NQR-NMR) has shed a new light on our understanding of the basic properties of nuclear materials. These advances have been motivated also by the interest raised by the discovery of new superconductors based on transuranium compounds such as PuCoGa5 and NpPd5Al2 which stand for archetypes of 5f transuranium superconductors displaying exotic features. For instance, the unconventional nature of superconductivity in PuCoGa5 and NpPd5Al2 has been revealed by NQR experiments. Here we report a NMR study at low temperature of single crystals of CePd5Al2, the cerium counterpart of NpPd5Al2, presenting Kondo lattice features with two antiferromagnetic transitions at TN1 = 3.9 K and TN2 = 2.7 K, respectively. This compound becomes superconductor under pressure and displays a lot of similarities with PuPd5Al2, which is an antiferromagnet below TN = 5.1 K. We will report also a low temperature basic properties study of a ferromagnetic system presenting localised features, namely NpAl2.JRC.E.6-Actinide researc

Insight into the crystal structures and physical properties of the uranium borides UB1.78±0.02,_{1.78±0.02,} UB3.61±0.041_{3.61±0.041} and UB11.19±0.13_{11.19±0.13}

International audienceIn this study we reported the synthesis of three polycrystalline uranium borides UB$_{1.78±0.02,}$ UB$_{3.61±0.041}$ and UB$_{11.19±0.13}$ and their analyses using chemical analysis, X-ray diffraction, SQUID magnetometry, solid-state NMR, and Fourier transformed infrared spectroscopy. We discuss the effects of stoichiometry deviations on the lattice parameters and magnetic properties. We also provide their static and MAS-NMR spectra showing the effects of the 5f-electrons on the $^{11}$B shifts. Finally, the FTIR measurements showed the presence of a local disorder

High-Resolution Solid-State Oxygen-17 NMR of Actinide-Bearing Compounds: An Insight into the 5f Chemistry

A massive interest has been generated lately by the improvement of solid-state magic-angle spinning (MAS) NMR methods for the study of a broad range of paramagnetic organic and inorganic materials. The open-shell cations at the origin of this paramagnetism can be metals, transition metals, or rare-earth elements. Actinide-bearing compounds and their 5f unpaired electrons remain elusive in this intensive research area due to their well-known high radiotoxicity. A dedicated effort enabling the handling of these highly radioactive materials now allows their analysis using high-resolution MAS NMR (\textgreater55 kHz). Here, the study of the local structure of a series of actinide dioxides, namely, ThO2, UO2, NpO2, PuO2, and AmO2, using solid-state 17O MAS NMR is reported. An important increase of the spectral resolution is found due to the removal of the dipolar broadening proving the efficiency of this technique for structural analysis. The NMR parameters in these systems with numerous and unpaired 5f electrons were interpreted using an empirical approach. Single-ion model calculations were performed for the first time to determine the z component of electron spin on each of the actinide atoms, which is proportional to the shifts. A similar variation thereof was observed only for the heavier actinides of this study

High-Resolution Solid-State Oxygen-17 NMR of Actinide-Bearing Compounds: An Insight into the 5f Chemistry

A massive interest has been generated lately by the improvement of solid-state magic-angle spinning (MAS) NMR methods for the study of a broad range of paramagnetic organic and inorganic materials. The open-shell cations at the origin of this paramagnetism can be metals, transition metals, or rare-earth elements. Actinide-bearing compounds and their 5f unpaired electrons remain elusive in this intensive research area due to their well-known high radiotoxicity. A dedicated effort enabling the handling of these highly radioactive materials now allows their analysis using high-resolution MAS NMR (>55 kHz). Here, the study of the local structure of a series of actinide dioxides, namely, ThO₂, UO₂, NpO₂, PuO₂, and AmO₂, using solid-state ¹⁷O MAS NMR is reported. An important increase of the spectral resolution is found due to the removal of the dipolar broadening proving the efficiency of this technique for structural analysis. The NMR parameters in these systems with numerous and unpaired 5f electrons were interpreted using an empirical approach. Single-ion model calculations were performed for the first time to determine the <i>z</i> component of electron spin on each of the actinide atoms, which is proportional to the shifts. A similar variation thereof was observed only for the heavier actinides of this study