Preparation of monodisperse cerium oxide particle suspensions from a tetravalent precursor

Cerium oxide particles are a unique material that enables studying the intersection of metal oxides, f-elements, and nanomaterials. Distinct from diverse applications in catalysis, energy, and medicine, cerium possesses additional influence as a non-radioactive actinide surrogate. Herein, we present a synthesis for sub-micron cerium particles using hexamethylenetetramine and ammonium hydroxide as precipitating agents with a CeIV precursor. The combinatorial homogeneous precipitation approach yields monodisperse and moderately-stable CeO2 particle suspensions in ethanol, as determined by powder X-ray diffraction, scanning electron microscopy, dynamic light scattering, and zeta potential measurements. Various additives may be used to moderate and manipulate the surface charge of the particles. Proof-of-concept electrophoretic deposition of the particles produces a uniform layer of CeO2 on graphite. The synthesis and suspension properties are developed as a methodology towards future controlled actinide hydrolysis and film deposition.

Harvesting 88Zr from heavy-ion beam irradiated tungsten at the National Superconducting Cyclotron Laboratory

Tungsten is a commonly used material at many heavy-ion beam facilities, and it often becomes activated due to interactions with a beam. Many of the activation products are useful in basic and applied sciences if they can be recovered efficiently. In order to develop the radiochemistry for harvesting group (IV) elements from irradiated tungsten, a heavy-ion beam containing ⁸⁸Zr was embedded into a stack of tungsten foils at the National Superconducting Cyclotron Laboratory and a separation methodology was devised to recover the ⁸⁸Zr. The foils were dissolved in 30% hydrogen peroxide, and the ⁸⁸Zr was chemically purified from the tungsten matrix and from other co-implanted radionuclides (such as ⁸⁵Sr and ⁸⁸Y) using strong cation-exchange (AG MP-50) chromatographic resin in sulfuric acid media. The procedure provided ⁸⁸Zr in approximately 60 mL 0.5 M sulfuric acid with no detectable radio-impurities. The overall recovery yield for ⁸⁸Zr was (92.3 ± 1.2)%. This proof-of-concept experiment has facilitated the development of methodologies to harvest from tungsten and tungsten-alloy parts that are regularly irradiated at heavy-ion beam facilities.

3D printed field-deployable microfluidic systems for the separation and assay of Pu in nuclear forensics

A compact field-deployable microfluidic system has been developed to improve timelines for the rapid analysis of debris in post-detonation nuclear forensics. We used a high-resolution 3D printer to miniaturize typical laboratory-based procedures into a fieldable platform. Microfluidic half-modules were produced for the purification of Pu from excess U, along with a portable alpha chamber for the following isotopic analysis of the Pu stream. A porous PTFE membrane is soaked with a hydrophobic tributyl phosphate (TBP) solution and is placed between two half-modules; separation is performed as a liquid-liquid extraction in an extraction channel across this membrane, where the forward and back-extractions occur within one complete module. Following separation, a 100 μL sampling of the Pu-bearing stream is injected into a small-footprint 3D printed alpha chamber for isotopic assay via alpha spectrometry as part of an online process. In this first demonstration of microfluidic separation coupled with online alpha spectrometry, high extraction yields have been obtained for Pu (98.9 ± 4.0)% and U (97.5 ± 2.5)%. The process uses less than 800 μL of solution with separation chemistry complete within 45 minutes and subsequent alpha spectrometry initiating 25 minutes after separation.

Production, Collection, and Purification of 47Ca for the Generation of 47Sc through Isotope Harvesting at the National Superconducting Cyclotron Laboratory

An experiment was performed at the National Superconducting Cyclotron Laboratory using a 140 MeV/nucleon ⁴⁸Ca beam and a flowing-water target to produce ⁴⁷Ca for the first time with this production route. A production rate of 0.020 ± 0.004 ⁴⁷Ca nuclei per incoming beam particle was measured. An isotope harvesting system attached to the target was used to collect radioactive cationic products, including ⁴⁷Ca, from the water on a cation-exchange resin. The ⁴⁷Ca collected was purified using three separation methods optimized for this work: (1) DGA extraction chromatography resin with HNO₃ and HCl, (2) AG MP-50 cation-exchange resin with an increasing concentration gradient of HCl, and (3) AG MP-50 cation-exchange resin with a methanolic HCl gradient. These methods resulted in ≥99 ± 2% separation yield of ⁴⁷Ca with 100% radionuclidic purity within the limits of detection for HPGe measurements. Inductively coupled plasma-optical emission spectrometry (ICP-OES) was used to identify low levels of stable ions in the water of the isotope harvesting system during the irradiation and in the final purified solution of ⁴⁷Ca. For the first time, this experiment demonstrated the feasibility of the production, collection, and purification of ⁴⁷Ca through isotope harvesting for the generation of ⁴⁷Sc for nuclear medicine applications.

Harvesting 48V at the National Superconducting Cyclotron Laboratory

As part of an effort to develop aqueous isotope harvesting techniques at radioactive beam facilities, ⁴⁸V and a cocktail of primary- and secondary-beam ions created by the fragmentation reaction of a 160 MeV/nucleon ⁵⁸Ni beam were stopped in an aqueous target cell. After collection, ⁴⁸V was separated from the mixture of beam ions using cation-exchange chromatography. The extraction efficiency from the aqueous solution was (47.0 ± 2.5)%, and the isolated ⁴⁸V had a radiochemical purity of 95.8%. This proof-of-concept work shows that aqueous isotope harvesting could provide significant quantities of rare isotopes which are currently unavailable at conventional facilities.

Rapid acquisition of data dense solid-state CPMG NMR spectral sets using multi-dimensional statistical analysis

The development of multi-dimensional statistical methods has been demonstrated on variable contact time (VCT) 29Si{1H} cross-polarization magic angle spinning (CP/MAS) data sets collected using Carr-Purcell-Meiboom-Gill (CPMG) type acquisition. These methods utilize the transformation of the collected 2D VCT data set into a 3D data set and use tensor-rank decomposition to extract the spectral components that vary as a function of transverse relaxation time (T2) and CP contact time. The result is a data dense spectral set that can be used to reconstruct CP/MAS spectra at any contact time with a high signal to noise ratio and with an excellent agreement to 29Si{1H} CP/MAS spectra collected using conventional acquisition. These CPMG data can be collected in a fraction of time that would be required to collect a conventional VCT data set. We demonstrate the method on samples of functionalized mesoporous silica materials and show that the method can provide valuable surface specific information about their functional chemistry.

Organic layer formation and sorption of U(vi) on acetamide diethylphosphonate-functionalized mesoporous silica

Solid-state NMR is used to connect the molecular structure of acetamide phosphonate-functionalized mesoporous silica with its macroscopic U(vi) extraction properties.

Probing the interaction of U(vi) with phosphonate-functionalized mesoporous silica using solid-state NMR spectroscopy

Solid-state NMR techniques combined with batch contact experiments elucidate how U(vi) binds to phosphonate-functionalized mesoporous silica.

Development and Testing of Diglycolamide Functionalized Mesoporous Silica for Sorption of Trivalent Actinides and Lanthanides

Sequestration of trivalent actinides and lanthanides present in used nuclear fuel and legacy wastes is necessary for appropriate long-term stewardship of these metals, particularly to prevent their release into the environment. Organically modified mesoporous silica is an efficient material for recovery and potential subsequent separation of actinides and lanthanides because of its high surface area, tunable ligand selection, and chemically robust substrate. We have synthesized the first novel hybrid material composed of SBA-15 type mesoporous silica functionalized with diglycolamide ligands (DGA-SBA). Because of the high surface area substrate, the DGA-SBA was found to have the highest Eu capacity reported so far in the literature of all DGA solid-phase extractants. The sorption behavior of europium and americium on DGA-SBA in nitric and hydrochloric acid media was tested in batch contact experiments. DGA-SBA was found to have high sorption of Am and Eu in pH 1, 1 M, and 3 M nitric and hydrochloric acid concentrations, which makes it promising for sequestration of these metals from used nuclear fuel or legacy waste. The kinetics of Eu sorption were found to be two times slower than that for Am in 1 M HNO3. Additionally, the short-term susceptibility of DGA-SBA to degradation in the presence of acid was probed using (29)Si and (13)C solid-state NMR spectroscopy. The material was found to be relatively stable under these conditions, with the ligand remaining intact after 24 h of contact with 1 M HNO3, an important consideration in use of the DGA-SBA as an extractant from acidic media.