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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Cs by Materials Project

Cs is alpha structured and crystallizes in the cubic I-43m space group. The structure is three-dimensional and consists of two cesium molecules and one Cs framework. In the Cs framework, there are three inequivalent Cs sites. In the first Cs site, Cs is bonded in a trigonal non-coplanar geometry to three equivalent Cs atoms. All Cs–Cs bond lengths are 5.32 Å. In the second Cs site, Cs is bonded in a 8-coordinate geometry to eight Cs atoms. There are a spread of Cs–Cs bond distances ranging from 4.90–5.56 Å. In the third Cs site, Cs is bonded in a 8-coordinate geometry to eight Cs atoms. Both Cs–Cs bond lengths are 5.52 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs(SO2)2 by Materials Project

Cs(SO2)2 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Cs sites. In the first Cs site, Cs is bonded in a 10-coordinate geometry to two equivalent S and eight O atoms. Both Cs–S bond lengths are 3.84 Å. There are a spread of Cs–O bond distances ranging from 3.13–3.56 Å. In the second Cs site, Cs is bonded in a 10-coordinate geometry to ten O atoms. There are a spread of Cs–O bond distances ranging from 3.13–3.67 Å. There are four inequivalent S sites. In the first S site, S is bonded in a bent 120 degrees geometry to two O atoms. Both S–O bond lengths are 1.46 Å. In the second S site, S is bonded in a trigonal non-coplanar geometry to one S and three O atoms. The S–S bond length is 2.14 Å. There are a spread of S–O bond distances ranging from 1.46–1.48 Å. In the third S site, S is bonded in a 4-coordinate geometry to two equivalent Cs and two S atoms. The S–S bond length is 2.16 Å. In the fourth S site, S is bonded in a trigonal non-coplanar geometry to one S and three O atoms. There is one shorter (1.46 Å) and two longer (1.47 Å) S–O bond length. There are eight inequivalent O sites. In the first O site, O is bonded in a single-bond geometry to two Cs and one S atom. In the second O site, O is bonded in a single-bond geometry to one Cs and one S atom. In the third O site, O is bonded in a distorted single-bond geometry to three Cs and one S atom. In the fourth O site, O is bonded in a distorted single-bond geometry to two equivalent Cs and one S atom. In the fifth O site, O is bonded in a distorted single-bond geometry to three Cs and one S atom. In the sixth O site, O is bonded in a distorted single-bond geometry to two equivalent Cs and one S atom. In the seventh O site, O is bonded in a single-bond geometry to three Cs and one S atom. In the eighth O site, O is bonded in a single-bond geometry to two Cs and one S atom.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Dynamically tunable multicolor emissions from zero-dimensional Cs 3 LnCl 6 (Ln: europium and terbium) nanocrystals with wide color gamut

This study demonstrates dynamically tunable multicolor emissions from a single component, zero-dimensional (0-D) cesium europium chloride (Cs 3 EuCl 6 ) and cesium terbium chloride (Cs 3 TbCl 6 ) nanocrystals (NCs). Highly uniform colloidal Cs 3 EuCl 6 and Cs 3 TbCl 6 NCs are synthesized via the heating-up method. Excitation-wavelength-dependent multicolor emissions from Cs 3 EuCl 6 and Cs 3 TbCl 6 NCs are observed. Under excitation of 330–400 nm, both NCs exhibit blue photoluminescence (PL). Under wavelengths shorter than 330 nm, characteristic red and green emissions are observed from Cs 3 EuCl 6 and Cs 3 TbCl 6 , respectively, owing to the atomic emissions from the f-orbitals in trivalent europium (Eu 3+ ) and terbium (Tb 3+ ) ions. Cs 3 EuCl 6 and Cs 3 TbCl 6 NCs exhibit broadband excitation spectra and enhanced absorption properties. Particularly, Cs 3 EuCl 6 NCs exhibit a very narrow full-width at half-maximum in both blue and red PL and no overlap between the two spectra. Further, the photophysical properties of these NCs are further investigated to understand the multicolor PL origins by time-resolved and temperature-dependent PL measurements. Finally, the potential applications of Cs 3 EuCl 6 and Cs 3 TbCl 6 NCs as anti-counterfeiting inks for high-level security are demonstrated. Given their broadband excitation with enhanced absorption properties and dynamically tunable colors with a wide color gamut, Cs 3 EuCl 6 and Cs 3 TbCl 6 NCs have great potential as novel multicolor NC emitters for many emerging applications.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Materials Data on Cs(BBr)6 by Materials Project

Cs(BBr)6 crystallizes in the trigonal R-3 space group. The structure is two-dimensional and consists of three Cs(BBr)6 sheets oriented in the (0, 0, 1) direction. there are two inequivalent Cs sites. In the first Cs site, Cs is bonded to twelve Br atoms to form distorted edge-sharing CsBr12 cuboctahedra. There are a spread of Cs–Br bond distances ranging from 3.86–4.05 Å. In the second Cs site, Cs is bonded in a 9-coordinate geometry to six Br atoms. There are three shorter (3.80 Å) and three longer (3.86 Å) Cs–Br bond lengths. There are four inequivalent B sites. In the first B site, B is bonded in a distorted single-bond geometry to one Br atom. The B–Br bond length is 1.96 Å. In the second B site, B is bonded in a distorted single-bond geometry to one Br atom. The B–Br bond length is 1.97 Å. In the third B site, B is bonded in a distorted single-bond geometry to one Br atom. The B–Br bond length is 1.96 Å. In the fourth B site, B is bonded in a distorted single-bond geometry to one Br atom. The B–Br bond length is 1.97 Å. There are four inequivalent Br sites. In the first Br site, Br is bonded in a distorted single-bond geometry to two Cs and one B atom. In the second Br site, Br is bonded in a single-bond geometry to two equivalent Cs and one B atom. In the third Br site, Br is bonded in a single-bond geometry to one Cs and one B atom. In the fourth Br site, Br is bonded in a single-bond geometry to one Cs and one B atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs(BCl)6 by Materials Project

Cs(BCl)6 crystallizes in the trigonal R-3 space group. The structure is three-dimensional. there are two inequivalent Cs sites. In the first Cs site, Cs is bonded in a 9-coordinate geometry to nine Cl atoms. There are a spread of Cs–Cl bond distances ranging from 3.66–4.09 Å. In the second Cs site, Cs is bonded to twelve Cl atoms to form distorted edge-sharing CsCl12 cuboctahedra. There are a spread of Cs–Cl bond distances ranging from 3.72–3.84 Å. There are four inequivalent B sites. In the first B site, B is bonded in a single-bond geometry to one Cl atom. The B–Cl bond length is 1.80 Å. In the second B site, B is bonded in a single-bond geometry to one Cl atom. The B–Cl bond length is 1.79 Å. In the third B site, B is bonded in a single-bond geometry to one Cl atom. The B–Cl bond length is 1.80 Å. In the fourth B site, B is bonded in a single-bond geometry to one Cl atom. The B–Cl bond length is 1.80 Å. There are four inequivalent Cl sites. In the first Cl site, Cl is bonded in a single-bond geometry to two equivalent Cs and one B atom. In the second Cl site, Cl is bonded in a single-bond geometry to two equivalent Cs and one B atom. In the third Cl site, Cl is bonded in a single-bond geometry to one Cs and one B atom. In the fourth Cl site, Cl is bonded in a single-bond geometry to two Cs and one B atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs(BI)6 by Materials Project

Cs(BI)6 crystallizes in the trigonal R-3 space group. The structure is three-dimensional. there are two inequivalent Cs sites. In the first Cs site, Cs is bonded in a 6-coordinate geometry to six I atoms. There are three shorter (4.03 Å) and three longer (4.06 Å) Cs–I bond lengths. In the second Cs site, Cs is bonded to twelve I atoms to form distorted edge-sharing CsI12 cuboctahedra. There are a spread of Cs–I bond distances ranging from 4.09–4.30 Å. There are four inequivalent B sites. In the first B site, B is bonded in a distorted single-bond geometry to five B and one I atom. There is two shorter (1.79 Å) and three longer (1.80 Å) B–B bond length. The B–I bond length is 2.19 Å. In the second B site, B is bonded in a distorted single-bond geometry to five B and one I atom. There is four shorter (1.79 Å) and one longer (1.80 Å) B–B bond length. The B–I bond length is 2.18 Å. In the third B site, B is bonded in a distorted single-bond geometry to five B and one I atom. Both B–B bond lengths are 1.80 Å. The B–I bond length is 2.18 Å. In the fourth B site, B is bonded in a distorted single-bond geometry to five B and one I atom. Both B–B bond lengths are 1.80 Å. The B–I bond length is 2.19 Å. There are four inequivalent I sites. In the first I site, I is bonded in a single-bond geometry to one Cs and one B atom. In the second I site, I is bonded in a distorted single-bond geometry to two Cs and one B atom. In the third I site, I is bonded in a distorted single-bond geometry to two equivalent Cs and one B atom. In the fourth I site, I is bonded in a distorted single-bond geometry to one Cs and one B atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs by Materials Project

Cs crystallizes in the orthorhombic Cmce space group. The structure is three-dimensional. there are two inequivalent Cs sites. In the first Cs site, Cs is bonded in a 11-coordinate geometry to eleven Cs atoms. There are a spread of Cs–Cs bond distances ranging from 5.20–5.57 Å. In the second Cs site, Cs is bonded in a 10-coordinate geometry to ten Cs atoms. All Cs–Cs bond lengths are 5.35 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs by Materials Project

Cs is alpha La structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. there are two inequivalent Cs sites. In the first Cs site, Cs is bonded to twelve Cs atoms to form a mixture of face, edge, and corner-sharing CsCs12 cuboctahedra. There are six shorter (5.45 Å) and six longer (5.47 Å) Cs–Cs bond lengths. In the second Cs site, Cs is bonded to twelve Cs atoms to form a mixture of face, edge, and corner-sharing CsCs12 cuboctahedra. All Cs–Cs bond lengths are 5.47 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs by Materials Project

Cs is beta structured and crystallizes in the cubic P4_132 space group. The structure is three-dimensional. there are two inequivalent Cs sites. In the first Cs site, Cs is bonded in a distorted water-like geometry to two equivalent Cs atoms. Both Cs–Cs bond lengths are 5.42 Å. In the second Cs site, Cs is bonded in a 12-coordinate geometry to six Cs atoms. All Cs–Cs bond lengths are 5.02 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Cs 3 Bi 2 I 9 -hydroxyapatite composite waste forms for cesium and iodine immobilization

Perovskite-based ceramic composites were developed as potential waste form materials for immobilizing cesium (Cs) and iodine (I) with high waste loadings and chemical durability. The perovskite Cs 3 Bi 2 I 9 has high Cs (22 wt%) and I (58 wt%) content, and thus can be used as a potential host phase to immobilize these critical radionuclides. In this work, the perovskite Cs 3 Bi 2 I 9 phase was synthesized by a cost effective solution-based approach, and was embedded into a highly durable hydroxyapatite matrix by spark plasma sintering to form dense ceramic composite waste forms. The chemical durabilities of the monolithic Cs 3 Bi 2 I 9 and Cs 3 Bi 2 I 9 -hydroxyapatite composite pellets were investigated by static and semi-dynamic leaching tests, respectively. Cs and I are incongruently released from the matrix for both pure Cs 3 Bi 2 I 9 and composite structures. The normalized Cs release rate is faster than that of I, which can be explained by the difference in the strengths between Cs-I and Bi-I bonds as well as the formation of insoluble micrometer-sized BiOI precipitates. The activation energies of elemental releases based on dissolution and diffusion-controlled mechanisms are determined with significantly higher energy barriers for dissolution from the composite versus that of the monolithic Cs 3 Bi 2 I 9 . The ceramic-based composite waste forms exhibit excellent chemical durabilities and waste loadings, commensurate with the state-of-the-art glass-bonded perovskite composites for I and Cs immobilization.

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

Materials Data on Cs by Materials Project

Cs crystallizes in the cubic Pm-3n space group. The structure is three-dimensional. there are two inequivalent Cs sites. In the first Cs site, Cs is bonded in a 6-coordinate geometry to six Cs atoms. There are two shorter (4.91 Å) and four longer (5.49 Å) Cs–Cs bond lengths. In the second Cs site, Cs is bonded to twelve equivalent Cs atoms to form a mixture of edge and face-sharing CsCs12 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Modified Isotherm Modeling to Predict Cs Exchange with Crystalline Silicotitanate in Tank Waste Simulants

The U.S. Department of Energy is working to expedite processing of Hanford tank waste supernate at the Hanford Waste Treatment and Immobilization Plant. To support this goal, Washington River Protection Solutions is designing a Tank Side Cesium Removal (TSCR) system for suspended solids and cesium (Cs/ 137 Cs) removal from Hanford tank waste supernate. The ion exchange media selected for Cs removal at TSCR is crystalline silicotitanate (CST) that is manufactured in a nearly spherical form by Honeywell UOP LLC (UOP; Des Plaines, IL) as product IONSIV® R9140-B (Na form). The Zheng Anthony Miller (ZAM) isotherm model (Zheng et al. 1997) is a multicomponent ion exchange model used to predict the exchange of Group I metals onto CST. The ZAM isotherm has historically been used to predict Cs distribution values from Hanford and Savannah River Site (SRS) tank waste simulants. Figure S.1 summarizes model predictions from the ZAM isotherm that indicate poor prediction of Cs distribution values for simple and complex simulants with the engineered form of CST, IONSIV® R9140-B, and IONSIV® R9120-B where the solid line indicates a perfect fit by the model. The dotted lines indicate ±20% error. Batch contact testing with Hanford tank waste complex and simple simulants was used in conjunction with SRS simulants to experimentally determine Cs distribution values using a modification to the original isotherm model. The experimentally determined maximum Cs capacity for IONSIV® R9140-B CST in both the simple and complex matrices was found to be 0.53±0.3 mmoles Cs/g of CST. This value is not drastically different from the maximum Cs capacity of 0.58 mmoles Cs/g TAM-5 reported by Zheng et al. (1997). However, it is important to note that TAM-5 (commercially IONSIV® IE-910) is a powder. Hamm et al. (2002) determined that a dilution factor was needed to account for the Zr(OH)2 binder in the engineered form of CST. Hamm et al. determined that a dilution factor of 0.68 was appropriate to account for binder contribution and correct overprediction of Cs exchange on the engineered form of CST in ZAM calculations. This reduced the total capacity from 0.58 mmol/g with TAM-5 to 0.39 mmol/g for the engineered form of CST (Hamm et al. 2002). Despite substituting the experimentally determined maximum Cs capacity of 0.55 mmoles Cs/g for the literature-reported capacity of 0.39 mmoles Cs/g, it was determined that additional modifications to the model’s equilibrium rate constants were necessary in refining the isotherm model. The modified model overpredicted K+ uptake by the CST when compared to digested CST results described by Campbell et al. (2019). The modified model was further revised to omit three of the five K+ exchange equilibrium reactions described by ZAM to reduce the additional K+ loading seen by the model. Figure S.2 summarizes the revised model isotherm predictions plotted against measured Kd values.

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

Determining Cs-137 Background body burdens for Wild Pigs At Savannah River Site

Savannah River Site (SRS) is a unique U.S. Department of Energy facility in that most of the 310-square miles of land has not be industrialized since operations began in 1953. This has allowed abundant, undisturbed vegetation structure to exists as well as an increase in herd sizes among wildlife populations onsite. Cs-137 is widespread across SRS due to the production of nuclear materials, but is mostly from global atmospheric fallout from nuclear weapons testing. Due to most of SRS being undisturbed land, the concentrations of Cs-137 are higher on site than off site. The SRS began conducting annual deer harvests that were open to the public beginning in 1965. All animals harvested during these hunts are monitored for Cs-137, which is measured using a Sodium Iodide detector. There has been an effective method for calculating the background Cs-137 body burden for the deer population at the SRS, developed by Gaines and Novak using data collected during hunts and gamma overflight data to determine the areas contaminated by site activities. For animals that have a Cs-137 concentration above the established background level, a dose is assigned to the hunter. By applying the same method for wild pigs using data collected from hunts, gamma overflight, and developing a site-specific home range of wild pigs, we were able to calculate the Cs-137 background body burden concentrations of wild pigs on site. Objectives: Develop site-specific home range for wild pigs at SRS; Determine the average concentrations of Cs-137 in wild pigs from background; Use Gaines and Novak method for determining background Cs-137 body burdens wild pigs on SRS. Methods and Materials: Development of site-specific home range of wild pigs was determined to be 2.5 miles using: Four studies conducted between 1969 and 1992 for the SRS wild pig population. (Mayer and Brisbin) The background compartments were determined using: Gamma overflight data showing contaminated areas; Site-specific home range of the wild pigs. Results and Conclusion: All data were generated through the JMP software to provide a histogram and summary statistics. The estimate of an upper tolerance limit for the background contamination with 95% confidence is 1.965 pCi/g for the wild pigs. This means that for wild pigs on SRS from the background compartments are expected to have Cs-137 concentrations of less than 1.965 pCi/g. The current background for the deer is 2.59 pCi/g. For the background compartments Cs-137 concentrations from 2012-2018: Mean: 0.815 pCi/g, Maximum: 2.341 pCi/g, Minimum: -0.704 pCi/g.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2021

Cs absorption capacity and selectivity of crystalline and amorphous Hf and Zr phosphates

Removal of radioactive Cs from sodium-rich solutions is a technical challenge that goes back to post World War II nuclear waste storage and treatment; and interest in this topic was reinvigorated by the Fukushima-Daiichi nuclear power plant disaster, 10 years ago. Since the 1960's there has been considerable focus on layered Zr phosphates as robust inorganic sorbents for separation of radionuclides such as Cs. Here we present synthesis and characterization, and direct comparison of Cs sorption capacity and selectivity of four related materials: 1) crystalline α-Zr phosphate and α-Hf phosphate, and 2) amorphous analogues of these. Powder X-ray diffraction, thermogravimetry, solid-state 31P magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy, and compositional analysis (inductively coupled plasma optical emission spectroscopy and mass spectroscopy, ICP OES and ICP MS) provided formulae; respectively M(HPO4)2∙1H2O and M(HPO4)2∙4H2O (M = Hf, Zr) for crystalline and amorphous analogues. Maximum Cs loading, competitive Cs-Na selectivity and maximum Cs-Na loading followed by the above characterizations plus 133Cs MAS-NMR spectroscopy revealed that amorphous analogues are considerably better Cs-sorbents (based on maximum Cs-loading and selectivity over Na) than the well-studied crystalline Zr-analogue. Additionally, crystalline α-Hf phosphate is better Cs-sorbent than crystalline α-Zr phosphate. All these studies consistently show that Hf phosphate is less crystallize than Zr phosphate, when obtained under similar or identical synthesis conditions. We attribute this to lower solubility of Hf phosphate compared to Zr phosphate, preventing ‘defect healing’ during the synthesis process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Influence of Cs Loading on Pt/m-ZrO 2 Water–Gas Shift Catalysts

Certain alkali metals (Na, K) at targeted loadings have been shown in recent decades to significantly promote the LT-WGS reaction. This occurs at alkali doping levels where a redshift in the C-H band of formate occurs, indicating electronic weakening of the bond. The C-H bond breaking of formate is the proposed rate-limiting step of the formate associative mechanism, lending support to the occurrence of this mechanism in H2-rich environments of the LT-WGS stage of fuel processors. Continuing in this vein of research, 2%Pt/m-ZrO 2 was promoted with various levels of Cs in order to explore its influence on the rate of formate intermediate decomposition, as well as that of LT-WGS in a fixed bed reactor. In situ DRIFTS experiments revealed that Cs promoter loadings of 3.87% to 7.22% resulted in significant acceleration of the forward formate decomposition in steam at 130 °C. Of all of the alkali metals tested to date, the redshift in the formate ν(CH) band with the incorporation of Cs was the greatest. XANES difference experiments at the Pt L 2 and L 3 edges indicated that the electronic effect was not likely due to an enrichment of electronic density on Pt. CO 2 TPD experiments revealed that, unlike Na and K promoters, Cs behaves more like Rb in that the decomposition of the second intermediate in LT-WGS, carbonate species, is hindered due to (1) increased basicity of Cs, (2) the tendency of Cs to cover Pt sites that facilitate CO 2 decomposition, and (3) the tendency of Cs to increase Pt particle size as shown by EXAFS results, resulting in fewer Pt sites that facilitate CO2 decomposition. As such, the LT-WGS rate was hindered overall and the rate-limiting step shifted to carbonate decomposition (CO 2 removal). Like its Rb counterpart, low levels of added Cs (e.g., 0.72%Cs) were found to improve the stability of the catalyst relative to the unpromoted catalyst; the stability comparison was made at similar CO conversion level as well as similar space velocity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

A newly proposed isotherm model to predict Cs exchange with crystalline silicotitanate in tank waste simulants

The Zheng Anthony Miller (ZAM) computer model, a multicomponent ion exchange model used to predict the exchange of Group I metals onto crystalline silicotitanate (CST), has historically been used to predict Cs distribution coefficients from Hanford and Savannah River Site (SRS) tank waste simulants. Comparison of experimentally determined Cs distribution coefficients from tank waste simulants with ZAM isotherm model predictions indicate overprediction of Cs and K distribution coefficients for simple and complex simulants with the engineered form of CST. Additionally, recent changes in chemical composition/manufacturing of IONSIV TM R9140-B have resulted in increased Cs capacity from high-salt, highly alkaline solutions. Here, this work served to assess different isotherm models and refine equilibrium parameters to develop a model that can be applied to Hanford and SRS tank waste Cs removal efforts. Toward this goal, the Campbell Westesen Peterson (CWP) model was developed. This model utilized the experimentally determined Cs capacity, and simplified ZAM equilibria expressions to include only the binary substitution of Cs + or K + on the Na + sites. Equilibrium constants for these equations were refined using experimentally determined distribution coefficients. Overall, the CWP model significantly improved our ability to predict both Cs and K loading capacity from complex matrices.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2022

Temporal evolution of Pu and Cs sediment contamination in a seasonally stratified pond

There remains a lack of knowledge regarding ecosystem transfer, transport processes, and mechanisms, which influence the long-term mobility of Pu-239 and Cs-137 in natural environments. Monitoring the distribution and migration of trace radioisotopes as ecosystem tracers has the potential to provide insight into the underlying mechanisms of geochemical cycles. This study investigated the distribution of anthropogenic radionuclides Pu-239 and Cs-137 along with total organic carbon, iron, and trace element in contaminated sediments of Pond B at the Savannah River Site (SRS). Pond B received reactor cooling water from 1961 to 1964, and trace amounts of Pu-239 and Cs-137 during operations. Our study collected sediment cores to determine concentrations of Pu-239, Cs-137, and major and minor elements in solid phase, pore water and an electrochemical method was used on wet cores to determine dissolved elemental concentrations. More than 50 years after deposition, Pu-239 and Cs-137 in sediments are primarily located in the upper 5 cm in area where deposition of particulate-bound contaminants was prevalent and located between 5 and 10 cm in areas of high sedimentation, showing a limited migration of Pu-239 and Cs-137. A Factor analysis demonstrated different sediment facies across the pond resulting in a range of geochemical processes controlling accumulation of Pu and Cs. Highest concentrations appear to be controlled by particulate input from the influent canal, dominated by clay, silt, and sand minerals bearing Fe. Elevated Pu-239 in the sediments were observed in areas with high organic matter and higher deposition rate relative to the Pond B system near the outlet indicating strong association of Pu with OM and particulates. Therefore, organic matter cycling likely plays a role in Pu redistribution between sediment and overlying pond water, and deposition in organic rich sediments accumulating near the outlet. Though Pu appears to have been distributed throughout the pond, Cs-137 concentrations remained the highest near the influent canal.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2025

First-principles study of structural, elastic, electronic, transport properties, and dielectric breakdown of Cs 2 Te photocathode

The pursuit to operate photocathodes at high accelerating gradients to increase brightness of electron beams is gaining interests within the accelerator community, particularly for applications such as free electron lasers (FEL) and compact accelerators. Cesium telluride (Cs 2 Te) is a widely used photocathode material and it is presumed to offer resilience to higher gradients because of its wider band gap compared to other semiconductors. Despite its advantages, crucial material properties of Cs 2 Te remain largely unknown both in theory and experiments. In this study, we employ first-principles calculations to provide detailed structural, elastic, electronic and transport properties of Cs 2 Te. It is found that Cs 2 Te has an intrinsic mobility of 20 cm 2 /Vs for electrons and 2.0 cm 2 /Vs for holes at room temperature. The low mobility is primarily limited by the strong polar optical phonon scattering. Cs 2 Te also exhibits ultralow lattice thermal conductivity of 0.2 W/(m*K) at room temperature. Based on the energy gain/loss balance under external field and electron–phonon scattering, we predict that Cs 2 Te has a dielectric breakdown field in the range from ~ 60 to ~ 132 MV/m at room temperature dependent on the doping level of Cs 2 Te. Our results are crucial to advance the understanding of applicability of Cs 2 Te photocathodes for high-gradient operation.

36 MATERIALS SCIENCE↗