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DOE OSTI2020

Materials Data on Cs3CoI4NO3 by Materials Project

Cs3CoNO3I4 crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. there are two inequivalent Cs1+ sites. In the first Cs1+ site, Cs1+ is bonded in a 1-coordinate geometry to three O2- and six I1- atoms. There are one shorter (3.13 Å) and two longer (3.27 Å) Cs–O bond lengths. There are a spread of Cs–I bond distances ranging from 3.91–4.01 Å. In the second Cs1+ site, Cs1+ is bonded in a 9-coordinate geometry to three O2- and six I1- atoms. There are a spread of Cs–O bond distances ranging from 3.19–3.44 Å. There are a spread of Cs–I bond distances ranging from 4.04–4.24 Å. Co2+ is bonded in a tetrahedral geometry to four I1- atoms. There are a spread of Co–I bond distances ranging from 2.63–2.65 Å. N5+ is bonded in a trigonal planar geometry to three O2- atoms. All N–O bond lengths are 1.27 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to three Cs1+ and one N5+ atom. In the second O2- site, O2- is bonded in a distorted single-bond geometry to three Cs1+ and one N5+ atom. There are three inequivalent I1- sites. In the first I1- site, I1- is bonded in a 1-coordinate geometry to four Cs1+ and one Co2+ atom. In the second I1- site, I1- is bonded in a distorted single-bond geometry to five Cs1+ and one Co2+ atom. In the third I1- site, I1- is bonded in a 1-coordinate geometry to five Cs1+ and one Co2+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs3GeSe3 by Materials Project

Cs3GeSe3 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are four inequivalent Cs1+ sites. In the first Cs1+ site, Cs1+ is bonded in a 6-coordinate geometry to six Se2- atoms. There are a spread of Cs–Se bond distances ranging from 3.53–4.04 Å. In the second Cs1+ site, Cs1+ is bonded in a 6-coordinate geometry to six Se2- atoms. There are a spread of Cs–Se bond distances ranging from 3.69–3.96 Å. In the third Cs1+ site, Cs1+ is bonded in a 6-coordinate geometry to six Se2- atoms. There are a spread of Cs–Se bond distances ranging from 3.56–3.84 Å. In the fourth Cs1+ site, Cs1+ is bonded in a 6-coordinate geometry to six Se2- atoms. There are a spread of Cs–Se bond distances ranging from 3.68–3.73 Å. Ge3+ is bonded in a trigonal non-coplanar geometry to three Se2- atoms. There are one shorter (2.40 Å) and two longer (2.42 Å) Ge–Se bond lengths. There are three inequivalent Se2- sites. In the first Se2- site, Se2- is bonded in a 7-coordinate geometry to six Cs1+ and one Ge3+ atom. In the second Se2- site, Se2- is bonded in a 1-coordinate geometry to six Cs1+ and one Ge3+ atom. In the third Se2- site, Se2- is bonded in a 7-coordinate geometry to six Cs1+ and one Ge3+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CsSe4 by Materials Project

CsSe4 crystallizes in the orthorhombic Pbcm space group. The structure is three-dimensional. there are four inequivalent Cs1+ sites. In the first Cs1+ site, Cs1+ is bonded in a 10-coordinate geometry to ten Se+0.25- atoms. There are a spread of Cs–Se bond distances ranging from 3.67–4.21 Å. In the second Cs1+ site, Cs1+ is bonded in a 10-coordinate geometry to ten Se+0.25- atoms. There are a spread of Cs–Se bond distances ranging from 3.73–4.23 Å. In the third Cs1+ site, Cs1+ is bonded in a 10-coordinate geometry to ten Se+0.25- atoms. There are a spread of Cs–Se bond distances ranging from 3.70–4.25 Å. In the fourth Cs1+ site, Cs1+ is bonded in a 12-coordinate geometry to twelve Se+0.25- atoms. There are a spread of Cs–Se bond distances ranging from 3.65–4.35 Å. There are nine inequivalent Se+0.25- sites. In the first Se+0.25- site, Se+0.25- is bonded in a 5-coordinate geometry to three Cs1+ and two Se+0.25- atoms. There are one shorter (2.38 Å) and one longer (2.39 Å) Se–Se bond lengths. In the second Se+0.25- site, Se+0.25- is bonded to two equivalent Cs1+ and four Se+0.25- atoms to form corner-sharing SeCs2Se4 octahedra. The corner-sharing octahedral tilt angles are 48°. There are two shorter (2.52 Å) and two longer (2.92 Å) Se–Se bond lengths. In the third Se+0.25- site, Se+0.25- is bonded in a 6-coordinate geometry to three Cs1+ and three Se+0.25- atoms. There are one shorter (2.37 Å) and one longer (3.38 Å) Se–Se bond lengths. In the fourth Se+0.25- site, Se+0.25- is bonded in a 6-coordinate geometry to four Cs1+ and two Se+0.25- atoms. The Se–Se bond length is 3.07 Å. In the fifth Se+0.25- site, Se+0.25- is bonded in a 3-coordinate geometry to two equivalent Cs1+ and two equivalent Se+0.25- atoms. Both Se–Se bond lengths are 2.39 Å. In the sixth Se+0.25- site, Se+0.25- is bonded in a 3-coordinate geometry to three Cs1+ and two Se+0.25- atoms. The Se–Se bond length is 2.41 Å. In the seventh Se+0.25- site, Se+0.25- is bonded in a 5-coordinate geometry to two Cs1+ and three Se+0.25- atoms. The Se–Se bond length is 2.42 Å. In the eighth Se+0.25- site, Se+0.25- is bonded in a 4-coordinate geometry to two Cs1+ and two Se+0.25- atoms. In the ninth Se+0.25- site, Se+0.25- is bonded in a 2-coordinate geometry to two Cs1+ and three Se+0.25- atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Characterization of Tank 11H Samples from Tank Closure Cesium Removal (TCCR) Batch 3 - Intermediate and Final Samples

Savannah River Remediation (SRR) is currently operating the Tank Closure Cesium Removal (TCCR) process to remove 137 Cs from tank waste supernate using an ion exchange process. The TCCR unit processes dissolved salt from Tank 10H through a series of ion exchange columns containing crystalline silicotitanate (CST) and the effluent is then discharged to Tank 11H. Four interim samples pulled from Tank 11H during and just after the completion of processing of Batch 3 through the TCCR process have been analyzed for 137 Cs activity and density. The 137 Cs activity was found to decrease with each subsequent sample, which is consistent with the addition of decontaminated solution to Tank 11H. When compared to the expected composition from mixing the Tank 10H Batch 3 feed with the material already present in Tank 11H, the bulk chemical composition was as expected. A corrosion control sample collected from Tank 11H in June 2020 showed changes in the chemical composition and 137 Cs activity when compared to the composition measured at the end of Batch 2 processing. As there were no additions made to the tank during this period, these changes were attributed to leaching of the solids present in Tank 11H. Additional analyses of the 4 th interim sample are pending and will be documented in a revision to this report.

11H↗
DOE OSTI2022

Characterization of Tank 11H Samples from Tank Closure Cesium Removal 1A (TCCR 1A) Batch 1

Savannah River Mission Completion (SRMC) is currently operating the Tank Closure Cesium Removal 1A (TCCR 1A) process to remove 137 Cs from tank waste supernate using an ion exchange process. The TCCR 1A unit processes dissolved salt fed from Tank 10H through a series of ion exchange columns containing crystalline silicotitanate (CST, IONSIV TM R9120-B, 30x60) and the effluent is then discharged to Tank 11H. In support of the TCCR 1A program, SRNL analyzed samples taken from Tank 11H (without tank mixing) before, during, and at the completion of TCCR 1A Batch 1 processing. Tank 11H serves as the receipt tank for the filtered and cesium removed product from the TCCR 1A system. Processing of Batch 1 commenced on January 13, 2022 and completed on February 17, 2022, after processing approximately 70,100 gallons. A pre-production sample was collected from the heel remaining in Tank 11H just before Batch 1 processing began. In addition, five interim surface samples were collected from Tank 11H during processing, and both a surface and a variable depth sample (VDS, ~7” from tank bottom) were collected just after processing completed. Analysis of all samples included density and gamma spectroscopy, in addition to a more comprehensive suite of analytes for the pre- and post-production samples. The density of the pre-production sample was the highest of all samples measured and was then observed to decrease for the first two interim samples, followed by becoming fairly consistent for the remainder of the samples (~1.3 g/mL). The density of 1.3 g/mL is similar to the density measured for one of the three Tank 10H qualification samples (HTF-10-21-126). The 137 Cs activity was found to decrease as additional decontaminated effluent from the TCCR columns was added to Tank 11H during processing; however, an increase in activity was observed during periods of no processing which can be attributed to leaching of 137 Cs from the known solids in Tank 11H. The Cs isotope concentrations in the Tank 11H postproduction surface sample were determined to be 99.7-99.8% lower than the concentrations measured in the Tank 10H feed as measured by mass spectrometry.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Understanding the Instability of the Halide Perovskite CsPbI 3 through Temperature-Dependent Structural Analysis

Despite the tremendous interest in halide perovskite solar cells, the structural reasons that cause the all-inorganic perovskite CsPbI 3 to be unstable at room temperature remain mysterious, especially since many tolerance-factor-based approaches predict CsPbI 3 should be stable as a perovskite. Here single-crystal X-ray diffraction and X-ray pair distribution function (PDF) measurements characterize bulk perovskite CsPbI3 from 100 to 295 K to elucidate its thermodynamic instability. While Cs occupies a single site from 100 to 150 K, it splits between two sites from 175 to 295 K with the second site having a lower effective coordination number, which, along with other structural parameters, suggests that Cs rattles in its coordination polyhedron. PDF measurements reveal that on the length scale of the unit cell, the Pb-I octahedra concurrently become greatly distorted, with one of the I-Pb-I angles approaching 82° compared to the ideal 90°. The rattling of Cs, low number of Cs-I contacts, and high degree of octahedral distortion cause the instability of perovskite-phase CsPbI 3 . These results reveal the limitations of tolerance factors in predicting perovskite stability and provide detailed structural information that suggests methods to engineer stable CsPbI 3 -based solar cells.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Endothermic Charge Separation Occurs Spontaneously in Non–Fullerene Acceptor/Polymer Bulk Heterojunction

Organic photovoltaics (OPVs) based on non-fullerene acceptors (NFAs) have achieved a power conversion efficiency close to 20%. These NFA OPVs can generate free carriers efficiently despite a very small energy level offset at the donor/acceptor interface. Why these NFAs can enable efficient charge separation (CS) with low energy losses remains an open question. Here, the CS process in the PM6:Y6 bulk heterojunction is probed by time-resolved two-photon photoemission spectroscopy. It is found that the CS, the conversion from bound charge transfer (CT) excitons to free carriers, is an endothermic process with an enthalpy barrier of 0.15 eV. The CS can occur spontaneously despite being an endothermic process, which implies that it is driven by entropy. It is further argued that the morphology of the PM6:Y6 film and the anisotropic electron delocalization restrict the electron and hole wavefunctions within the CT exciton such that they can primarily contact each other through point-like junctions. Furthermore, this configuration can maximize the entropic driving force.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Bioaccumulation of Mercury and Radiocesium in Waterfowl Introduced to a Site with Legacy Contamination

Despite the propensity of waterfowl species to readily accumulate anthropogenic contaminants within polluted environments, few studies have examined bioaccumulation rates over time when entering such a contaminated site. We examined mercury (Hg) and radiocesium ( 137 Cs) bioaccumulation over time in two waterfowl species released into a wetland system containing legacy contamination on the US Department of Energy's Savannah River Site in South Carolina. Released birds were collected at select time intervals over an exposure period of 94 days. We quantified total Hg concentrations in blood, muscle, and liver tissues, and 137 Cs activity in whole-body and muscle tissues. The relationship between the contaminant burdens of different body tissue types was examined over time. Likely a result of microhabitat selection, mallards in our study readily accumulated both Hg and 137 Cs at consistent rates over time within our study system, while ring-neck ducks did not. The findings demonstrated that whole blood can be used as a robust, nondestructive sampling alternative to estimate Hg burdens within muscle and liver, and whole-body 137 Cs activity is a good predictor of muscle burdens. Understanding such bioaccumulation information in waterfowl is useful for the assessment of the potential health risk in wildlife, as well as being important for human risk assessment toward the consumption of popular game species. Environ Toxicol Chem 2022;41:2479–2487. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2022

Nondestructive and destructive assay for forensics characterization of weapons-grade plutonium produced in LEU irradiated in a thermal neutron spectrum

A post-irradiation examination (PIE) of an enriched uranium sample was performed to advance a nuclear forensics methodology, based on intra-elemental nuclide ratios. The PIE was carried out on a few milligrams of low enriched uranium dioxide (LEUO 2 ) sample, irradiated to a burnup of 1 GWd/MTU. The PIE of the LEUO 2 sample provided the concentration of selected plutonium and fission product nuclides ( 239 Pu, 240 Pu, 241 Pu, 91 Y, 95 Zr, 95 Nb, 103 Ru, 133 Cs, 134 Cs, 135 Cs, 137 Cs, 136 Ba, 138 Ba, 140 Ba, 140 La, 141 Ce, 144 Ce, 149 Sm, 150 Sm, 152 Sm, 153 Eu, and 154 Eu). The PIE supported validation of the MCNP (Monte Carlo N-Particle neutronics simulation code) predicted concentration of these nuclides in the irradiated LEUO 2 sample. This study showed that most of the MCNP predicted nuclide concentrations were within 15% and several within 10% compared to the PIE results. Furthermore, gamma and mass spectrometry of nuclides in irradiated LEUO 2 enabled the determination of uranium burnup and time since irradiation.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Analytical Determination of Radioactive Strontium and Cesium by Thermal Ionization Mass Spectrometry

Thermal ionization mass spectrometry (TIMS) has been evaluated for the detection of the radioactive isotopes of strontium and cesium. The instrument was investigated for the analysis of isotopic ratios of 89Sr to 90Sr and 135Cs to 137Cs in the presence of atomic isobars (Y and Zr for Sr analysis and Ba for Cs analysis). Signicant discrimination using TIMS was found for both Sr and Cs through evaluation using stable isotopes. Fusion procedures with different flux were evaluated for preparation of sample matrices. Chemical separations were developed and used after fusion to isolate the Sr and Cs from a prepared background matrix (i.e., Montana Soil). A graded approach, increasing in stable background isotopes, was performed to monitor the chemistry and instrument response. A thermal neutron irradiation was performed to produce a sample that contained the radioisotopes of Sr and Cs. Even though the irradiated sample was not a certified standard it does provide accurate expectation values via published, well understood cumulative fission yield data. The results presented in this work correlate extremely well with the published data. Furthermore, a significant decrease in uncertainty (by a factor of 5 { 10) was found for the isotopic ratios measured with TIMS compared to the published values.

TIMS, environmental contamination, radiostrontium,↗
DOE OSTI2020

In-situ to ex-situ in-plane structure evolution of stern layers on Pt(111) surface: Surface X-ray scattering studies

Here, in-situ to ex-situ evolution of the Cs + in-plane structure in electrochemical Stern layers are investigated on Pt(111) surface with surface X-ray scattering studies. The Cs + single-sublattice (2 x 2) structure of the Stern layer formed in situ in 0.1 M CsF electrolyte evolves eventually to the two-sublattice (2 x 2) structure upon emersion from the electrolyte. While the Cs+ layers maintain the (2 x 2) symmetry, the ex situ layer increases the density progressively over several minutes by incorporating Cs + ions of the electrolyte during the emersion process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Calorimetry can detect the early onset of hydrolysis in hybrid supercapacitors with aqueous electrolytes

This study investigates the effect of cation species on the onset of electrolyte hydrolysis in hybrid supercapacitors with aqueous electrolytes using isothermal operando calorimetry. The cells consisted of a positive α-MnO 2 cryptomelane electrode and a negative activated carbon (AC) electrode with either 0.5 M K 2 SO 4 or 0.5 M Cs 2 SO 4 aqueous electrolytes. They were characterized using cyclic voltammetry and galvanostatic cycling. In addition, the instantaneous heat generation rate at each electrode was measured using a custom isothermal operando calorimeter. Heat generation associated with resistive losses (Joule heating) and reversible ion adsorption/desorption was clearly identified. For larger potential windows, an endothermic dip, attributed to the onset of hydrolysis, was observed at the positive α-MnO 2 electrode where K + and Cs + ions engaged in fast surface redox reactions. Interestingly, this endothermic dip appeared at 1.8 V and 2.0 V for K 2 SO 4 and Cs 2 SO 4 aqueous electrolytes, respectively. The difference in the stable operating potential window was attributed to thinner solvation shell around Cs + cation than for K + thus reducing the amount of water present near the electrodes as ions partially shed their solvation shells during adsorption. The early onset of hydrolysis could be observed by isothermal operando calorimetry before it could be observed with conventional electrochemical methods.

42 ENGINEERING↗
DOE OSTI2024

Strong interlayer coupling and long-lived interlayer excitons in two-dimensional perovskite derivatives and transition metal dichalcogenides van der Waals heterostructures

Two-dimensional (2D) van der Waals (vdW) heterostructures offer new platforms for exploring novel physics and diverse applications ranging from electronics and photonics to optoelectronics at the nanoscale. The studies to date have largely focused on transition-metal dichalcogenides (TMDCs) based samples prepared by mechanical exfoliation method, therefore it is of signi ficant interests to study high-quality vdW heterostructures using novel materials prepared by a versatile method. Here, we report a two-step vapor phase growth process for the creation of high-quality vdW heterostructures based on perovskites and TMDCs, such as 2D Cs 3 Bi 2 I 9 /MoSe 2 , with a large lattice mismatch. Supported by experimental and theoretical investigations, we discover that the Cs 3 Bi 2 I 9 /MoSe 2 vdW heterostructure possesses hybrid band alignments consisting of type -I and type-II heterojunctions because of the existence of defect energy levels in Cs 3 Bi 2 I 9 . More importantly, we demonstrate that the type-II heterojunction in the Cs 3 Bi 2 I 9 /MoSe 2 vdW heterostructure not only shows a higher interlayer exciton density, but also exhibits a longer interlayer exciton lifetime than traditional 2D TMDCs based type-II heterostructures. We attribute this phenomenon to the reduced overlap of electron and hole wavefunctions caused by the large lattice mismatch. Finally, our work demonstrates that it is possible to directly grow high-quality vdW heterostructures based on entirely different materials which provide promising platforms for exploring novel physics and cutting-edge applications, such as optoelectronics, valleytronics, and high-temperature super fluidity.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Additive manufacturing of a metastable high entropy alloy: Metastability engineered microstructural control via process variable driven elemental segregation

Compositional paradigm shift in high entropy alloys (HEAs) provided new opportunities for microstructural engineering, whereas process control during laser powder bed fusion (LPBF) additive manufacturing (AM) enable fine microstructure tailoring. Metastability engineering in transformation induced plasticity (TRIP) HEAs by addition of minor alloying elements is an attractive strategy for fine microstructural tuning. This study explored in detail the microstructural evolution during LPBF AM of a metastable Fe 40 Mn 20 Co 20 Cr 15 Si 5 (at.%) dual phase HEA (CS-HEA). LPBF processing window for CS-HEA was established based on quantitative analysis and experiments. Based on melt pool overlap lack of fusion pores were observed at lower energy densities (J) of $\textit{J}$ ≤ 31.25 J/mm 3 and key-hole formation by melt pool destabilization in case of $\textit{J}$ ≥ 75 J/mm 3 . The microstructure of CS-HEA consists of metastable FCC-γ and HCP-ε phases; LPBF process parameters governed the final phase fraction in the alloy which has been correlated to metastability alteration of the high temperature γ phase. Final microstructural engineering was devised by LPBF process control which enabled cooling rate manipulation to guide Mn and Si segregation at the cell boundaries, thereby controlling the matrix metastability and final phase fraction. Additionally, high resolution transmission electron microscopy (TEM) revealed disparity in stacking fault morphology in CS-HEA with LPBF process variable alterations associated with local variations in chemical composition and stacking fault energy. Further, the phase evolution with process parameters also affected the nanomechanical behavior of the alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Impurity-enhanced core valence luminescence via Zn-doping in cesium magnesium chlorides

Scintillators with faster timing capabilities are currently in high demand for use in radiation detection systems in the fields of nuclear and medical physics. The limited number of suitable materials that meet the performance criteria of next generation detection systems presents an opportunity for discovery of new fast scintillator materials. In this work, the effects of doping several ultrafast core-valence luminescent (CVL) scintillators with divalent Zn is explored. Three compounds are investigated – CsMgCl 3 , Cs 2 MgCl 4 , and Cs 3 MgCl 5 – and single crystals of each doped with 5 mol% Zn are grown via the Bridgman method. Additionally, mixing across the full range of concentrations (from 0 % to 100 % Zn) is explored in the Cs 2 Mg 1-x Zn x Cl 4 and Cs 3 Mg 1-x Zn x Cl 5 systems. For low concentrations of Zn, light yields of all three compounds are enhanced (by up to ~60 %) compared to the pure crystals, achieving what we believe to be the brightest known CVL, CsMgCl 3 :Zn 5 % (3400 ± 170 ph/MeV light yield). More importantly, Zn doping does not affect the ultrafast timing properties, with each composition maintaining a single-component decay time around 1–3 ns. A sub-100 ps coincidence time resolution (CTR) is also achieved with CsMgCl 3 :Zn 5 %. The results of this work reveal a new avenue towards obtaining brighter CVL materials, which could open up possibilities for more advanced ultrafast scintillators to be discovered moving forward.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Elemental fractionation in aerosol laser-induced breakdown spectroscopy with nanosecond and femtosecond laser ablation

For the purpose of realizing atmospheric radiation plume tracking, laser-induced breakdown spectroscopy (LIBS) was performed to characterize Cs atomic emissions from airborne nanoparticles in a binary particle matrix using nanosecond and femtosecond laser ablation. As a surrogate to multi-element nuclear fallout particulates, both Cs and Na solutions were mixed with Cu at a 1:1.45 M concentration ratio and aerosolized to study elemental fractionation in atomic emissions, revealing Na I resonance emissions are enhanced whereas Cs I resonance emissions are reduced with Cu present despite sharing similar electronic and chemical properties. Femtosecond laser ablation reduced elemental fractionation effects by more than 50% while retaining the same temporal fractionation trends for Cs and Na. The origin of elemental fractionation in aerosol LIBS was further investigated using Al and Ti aerosols which revealed that the particle matrix induces changes to the local plasma temperature, population of atomic states, and subsequent molecular association and emission.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Identification and Quantification of Technetium Species in Hanford Waste Tank AN-102

Technetium-99 (Tc) generated from the fission of 235U and 239Pu in high yields is one of the most difficult contaminants to be addressed at the U.S. Department of Energy Hanford Site. In strongly alkaline solutions typifying Hanford tank waste, Tc exists as pertechnetate (TcO4-) (oxidation state VII) as well as in reduced forms (oxidation state < VII) collectively known as non-pertechnetate species. Designing strategies for effective Tc management, including separation and immobilization, necessitates understanding the molecular structure of the non- pertechnetate species and their identification in the actual tank waste samples, which would facilitate development of new treatment technologies effective for dissimilar Tc species. Toward this objective, a spectroscopic library of the Tc(I) [fac-Tc(CO)3]+ and Tc(IV, VII) compounds was generated using a range of techniques and applied to the characterization of the actual tank waste supernatant collected from the tank 241-AN-102 at Hanford, WA. A sample of the 241-AN-102 tank waste supernatant was processed to adjust Na concentration to about 5.6 M and remove 137Cs by spherical resorcinol-formaldehyde (sRF) ion exchange resin. Cesium-loaded sRF column was eluted with 0.5 M HNO3. As received AN-102, Cs-depleted AN-102 effluent, and sRF eluate fractions were comprehensively characterized for chemical composition and speciation of Tc using 99Tc nuclear magnetic resonance spectroscopy and X-ray absorption spectroscopy. It was demonstrated for the first time that non-pertechnetate Tc present in the 241-AN-102 tank waste is composed of several low-valent Tc species, including the Tc(I) [fac-Tc(CO)3]+ and Tc(IV) compounds. This is the second experimental observation of the [fac-Tc(CO)3]+ species in the Hanford tank waste and the first demonstration of multiple forms of non-pertechnetate species existing simultaneously in the waste, cumulatively highlighting their importance for the waste processing.

Low Activity Waste (LAW), High Level Waste, nuclea↗
DOE OSTI2024

The NanoSIMS-HR: The Next Generation of High Spatial Resolution Dynamic SIMS

The high lateral resolution and sensitivity of the NanoSIMS 50 and 50L series of dynamic SIMS instruments have enabled numerous scientific advances over the past 25 years. Here, in this study, we report on the NanoSIMS-HR, the first major upgrade to the series, and analytical tests in a suite of sample types, including an aluminum sample containing silicon crystals, microalgae, and plant roots colonized with a symbiotic fungus. Significant improvements have been made in the Cs + ion source, high voltage (HV) control, stage reproducibility, and other aspects of the instrument that affect performance. The modified design of the NanoSIMS-HR thermal-ionization Cs + source enables a 5 pA primary ion beam to be focused into a 100 nm spot, a ~2.5-fold increase compared to Cs + sources on previous instruments (~2 pA at 100 nm). The brightness of the new Cs + source enables an ultimate lateral resolution as high as 30 nm and improved detection limits for a given analysis area. Sample stage movement accuracy is higher than 500 nm, enabling many-fold higher throughput automated analyses. With the new HV control, the primary ion beam impact energy can be reduced from 16 to 2 keV, which enables higher depth resolution during depth profiling (a 2-fold improvement), albeit with a 5-fold decrease in lateral resolution. In the NanoSIMS-HR, the secondary ion column and detection system are identical to those used in the previous series, and the isotopic analysis performance is as precise as in previous NanoSIMS instruments.

54 ENVIRONMENTAL SCIENCES↗