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Mechanisms and Consequences of Intra-Crystalline Enrichment of Ancient Radiogenic Pb in Detrital Hadean Zircons from the Jack Hills, Western Australia

The recent discovery of Pb* (radiogenic lead) -enriched domains (PEDs) in zircon using high-resolution scanning ion imaging, atom probe tomography and transmission electron microscopy indicates that the U-Pb isotopic system in zircon can be affected not only by Pb* loss but also by intra-crystalline Pb* enrichment. However, the formation mechanism of PEDs and the consequences for in-situ U-Pb dating remain elusive. To further understand these issues, scanning ion imaging and U-Pb dating were carried out on 51 Hadean detrital zircon grains from the Jack Hills, Western Australia. Of these, 8 grains were found to contain micrometer-scale PEDs with elevated Pb-207 and Pb-206 in the ion images. Isotope profiles across these PEDs confirm that they represent unsupported Pb* resulting from intra-grain mobilization and local enrichment of Pb* during ancient overprinting events. The PEDs are rare in most grains, with only 1 – 3 Pb* hotspots present in any ~70 μm × 70 μm imaged area, and are located either in dark-CL, high-U growth zones, or associated with bright-CL, low-Th recrystallized domains, suggesting that they were likely formed by local-scale processes. The PEDs located in dark-CL, high-U growth zones likely resulted from Pb* trapped in local, interconnected pathways produced by radiation damage during thermal overprinting events. Those associated with bright-CL, low-Th domains are interpreted as Pb* concentrated in nanoscale pores formed during fluid-present recrystallization of non-metamict zircon. Our interpretations therefore imply that intra-crystalline enrichment of Pb* in zircon can occur at various scales and through diverse mechanisms. Age calculations based on the ion images demonstrate that incorporation of PEDs in conventional in-situ SIMS spots produces spuriously old ages that are either reversely discordant or concordant, depending on the time of Pb* mobilization and the analytical precision. The implication is that careful investigation of intra-grain distribution of U-Th-Pb isotopes is required in order to better understand the U-Pb isotopic system and to obtain reliable crystallization ages for ancient zircons affected by complex Pb* mobilization and redistribution.

Unsupported radiogenic lead↗

An Analysis of Exploration Capability Gaps for Future Habitation Systems to Inform Risk Assessment and Development Priorities

Within NASA, exploration capability gaps are defined as the difference between the current state-of-the-art in capabilities and the anticipated needs of future human spaceflight architectures. As NASA and its partners’ capabilities for human exploration of deep space continue to mature, it is necessary to understand the capability gaps that require closure to support future habitation systems, such as the Lunar Surface Habitat (SH) and Mars Transit Habitat (TH) currently in concept development. This paper will identify high-priority capability gaps for exploration habitation and show potential options for gap closure through investment in technology, development, and testing. High-priority capability gaps are divided into the following general taxonomy areas: human health/life support/habitation systems, flight computing and avionics, power and energy storage, communications and navigation, thermal management systems, human exploration destination systems, autonomous systems, sensors and instruments, GNC (guidance, navigation, and control), robotic systems, ground and uncrewed surface systems, and materials/structures/mechanical systems/manufacturing. In the gap identification process, teams of discipline experts from across NASA reviewed the latest habitation architecture needs against current capabilities to understand where gaps may exist. The results of the assessment established a basis for the current state-of-the-art within each gap and identified the capability needs of the proposed exploration missions the gap links to. An assessment of how each test platform (e.g., Ground, International Space Station (ISS), Commercial Low Earth Orbit (LEO) Destinations, Gateway) may be leveraged to mature capabilities and potentially provide a route to gap closure will be discussed. The notional timeline for gap closure to support reference missions and impacts to overall schedule are also assessed where appropriate. Based on the capability gap analysis described above, the paper summarizes important technology maturation considerations for human exploration architectures, with a focus on the Mars TH. The previously published NASA habitation ground rules and assumptions document is used as the basis to classify gaps as enabling, enhancing, or “push” opportunities for a particular architecture. Stepwise technology maturation plans/considerations are presented for some selected critical gaps. Overall, the analysis in this paper is intended to help influence development priorities for habitation systems, where high-priority, critical gaps are those currently assessed as having a low probability of closure by the anticipated need date. Capability gap analysis also informs the risk register for exploration habitation systems and mitigation strategies to ensure readiness of key technologies to support future mission timelines. Linkage between capability gaps for Moon and Mars is noted, as closure of a gap at a Lunar destination may subsequently enable or enhance Mars TH architectures.

technology development↗

An Analysis of Exploration Capability Gaps for Future Habitation Systems to Inform Risk Assessment and Development Priorities

Within NASA, exploration capability gaps are defined as the difference between the current state-of-the-art in capabilities and the anticipated needs of future human spaceflight architectures. As NASA and its partners’ capabilities for human exploration of deep space continue to mature, it is necessary to understand the capability gaps that require closure to support future habitation systems, such as the Lunar Surface Habitat (SH) and Mars Transit Habitat (TH) currently in concept development. This paper will identify high-priority capability gaps for exploration habitation and show potential options for gap closure through investment in technology, development, and testing. High-priority capability gaps are divided into the following general taxonomy areas: human health/life support/habitation systems, flight computing and avionics, power and energy storage, communications and navigation, thermal management systems, human exploration destination systems, autonomous systems, sensors and instruments, GNC (guidance, navigation, and control), robotic systems, ground and uncrewed surface systems, and materials/structures/mechanical systems/manufacturing. In the gap identification process, teams of discipline experts from across NASA reviewed the latest habitation architecture needs against current capabilities to understand where gaps may exist. The results of the assessment established a basis for the current state-of-the-art within each gap and identified the capability needs of the proposed exploration missions the gap links to. An assessment of how each test platform (e.g., Ground, International Space Station (ISS), Commercial Low Earth Orbit (LEO) Destinations, Gateway) may be leveraged to mature capabilities and potentially provide a route to gap closure will be discussed. The notional timeline for gap closure to support reference missions and impacts to overall schedule are also assessed where appropriate. Based on the capability gap analysis described above, the paper summarizes important technology maturation considerations for human exploration architectures, with a focus on the Mars TH. The previously published NASA habitation ground rules and assumptions document is used as the basis to classify gaps as enabling, enhancing, or “push” opportunities for a particular architecture. Stepwise technology maturation plans/considerations are presented for some selected critical gaps. Overall, the analysis in this paper is intended to help influence development priorities for habitation systems, where high-priority, critical gaps are those currently assessed as having a low probability of closure by the anticipated need date. Capability gap analysis also informs the risk register for exploration habitation systems and mitigation strategies to ensure readiness of key technologies to support future mission timelines. Linkage between capability gaps for Moon and Mars is noted, as closure of a gap at a Lunar destination may subsequently enable or enhance Mars TH architectures.

technology development↗

Future Homes in Space: Development of Concepts for Exploration Space Habitats

NASA’s Artemis campaign seeks to return humans to the moon and establish a sustained presence on the lunar surface. This session will emphasize how habitation capabilities on the moon and in cislunar space can potentially contribute to the sustainability objectives of Artemis. Habitable elements represent opportunities to enable longer duration stays, increase the number of crew members present, enhance science and utilization activities, drive technology development for future Mars exploration, perform analog missions, and fuel economic opportunities for US industry. Panelists include Paul Kessler (NASA Marshall Space Flight Center, deputy lead for lunar surface habitation); Andrew Choate (NASA Marshall Space Flight Center, Mars habitation lead); Krystofer Dudzinski (NASA Marshall Space Flight Center, a space architect within the MSFC Advanced Concepts Office); and Larry Toups (retired from NASA Johnson Space Center, currently an adjunct professor at University of Houston in space architecture). The panel is moderated by Tracie Prater (NASA Marshall Space Flight Center, Habitation Systems Development Office). The panel will begin with an overview of the history of habitation concepts and an academic perspective on general considerations in space habitat design (Larry Toups). Paul Kessler and Andrew Choate will introduce NASA’s principle of “architecting from the right” to help define objectives for Artemis missions, needs/characteristics, use cases, and functions (as published in the agency’s Architecture Definition Document) and provide perspective on how this principle informs habitation concept development work. NASA panelists will discuss key engineering challenges identified for developing, deploying, and operating habitable assets on the lunar surface and/or in deep space. These may include dust mitigation, outfitting of inflatable softgoods (for concepts which may use softgoods as a primary structural material), survival in lunar darkness, human health and performance considerations, maintenance/repair/sparing, and autonomy. These identified challenges represent risks for habitation systems development and relate closely to capability gaps identified by the agency. While the work of NASA Marshall Space Flight Center’s habitation development office is primarily focused on habitats which are launched from earth pre-integrated (referred to as Class I in the framework previously developed by NASA space architects Kennedy/Cohen) or launched from earth and deployed at the point of use (Class II), there is also extensive work in NASA, academia, and companies on constructed habitats, which would be built on a planetary surface using indigenous resources (Class III habitats). Panelist Krystopher Dudzinski will discuss potential evolutionary pathways from Class I and Class II habitats to Class III habitats, unique and common architectural challenges within each habitat class, and key gaps in implementing Class III habitats from an architectural perspective. NASA panelists and the moderator will also provide an overview of partnership opportunities and avenues for further engagement to advance habitation systems for the SpaceCom audience. NASA is currently developing notional concepts for a lunar surface habitat and Mars transit habitat, which will be discussed during this panel session and used as examples. These concepts represent options for habitation system design and are a point of departure. They do not represent a final plan or formal recommendation on the part of the agency. Based on the most recent analysis cycle, NASA’s lunar surface habitat (SH) concept nominally supports two crew members for 30 days, with the capacity to support four crew during a surge period where crew will swap between the SH and another surface asset, such as a pressurized rover. This example design has a metallic airlock for ingress/egress and the upper portion is an inflatable material system which serves as the habitation module. The notional interior of the habitat is a three-deck layout/configuration which supports all crew mission functions, including exercise, stowage, extravehicular activity (EVA), sleep, hygiene waste collection, maintenance and repair, and meal preparation. Under analysis assumptions for habitation, the Mars Transit Habitat (TH) concept would support four crew on an up to 1,200 day Mars mission. One option for the concept is to initially dock Transit Habitat at Gateway, where it can be used to increase the duration of crew stays in cislunar space and perform shakedown and analog missions prior to a Mars departure. One challenge in longer duration missions which involve both surface exploration and transit is understanding crew adaptation when transitioning between partial gravity and microgravity environments. TH at Gateway offers an opportunity to study this transition and in doing so reduce risks associated with future Mars exploration. Like lunar SH, the most recent analysis cycle concept of a Mars TH is a hybrid structure design, with a metallic section supporting EVAs, axial/radial docking, and Safe Haven capabilities, and an inflatable softgoods structure for the primary habitation function. Interior layouts to optimize crew usability and livability are currently under trade. The panel will include presentation material, but also seeks to engage the audience in a highly interactive conversation regarding the potential role for habitation in future exploration initiatives. Potential topics for discussion include the influence of the crew experience on habitation systems design and livability/usability considerations, the benefits of space habitation development in terrestrial applications, and challenges and opportunities in “feeding forward” lunar surface habitation systems development to Mars exploration.

space habitats↗

Accelerated Coupled Monte Carlo-Thermal Hydraulic Calculations using a Hybrid GTF-Diffusion-based Prediction Block: First Results

Accurate predictions of spatial power and temperature distributions require the coupling of a neutron transport solver with a thermal-hydraulic (TH) feedback. Nowadays, Monte Carlo (MC) codes are widely coupled to TH solvers, typically via a Picard iteration (PI) method, due to the higher fidelity that such frameworks can produce. To speed up a PI, a prediction step can produce an improved initial guess for a source distribution and feed it to the MC code. Recent work [1, 2] investigated a prediction step that uses generalized transfer functions (GTFs) to predict the macroscopic cross sections’ variations following a perturbation in TH properties, such as coolant density. The previous method also relied on first order perturbation (FOP) theory to predict perturbed power profiles, rather than using an expensive MC iterate. The implemented FOP method relied on generating a fission matrix from which the forward and adjoint eigenmodes were extracted and later used to for power calculations. The generation of the fission matrix can introduce a significant computational overhead, therefore undermining the performance of the proposed hybrid technique when applied to high-dimensional problems, e.g., full core calculations. This work attempts to improve the GTF-FOP prediction step by replacing the FOP solver with a nodal diffusion solver, thus eliminating the need to calculate a fission matrix. The GTF-diffusion step was tested for various moderator density perturbations. In each case, the predicted power distribution showed good agreement with the reference case. The latter is attributed to the generally good prediction of most spatially distributed macroscopic cross sections, except the transport cross section, which will become the focus of future work.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

Comprehensive Baseline Environmental Monitoring of an Interim Legacy Waste Store in Arid Zone Australia - 20062

Radionuclide containing soil and rubble from the clean-up of a former uranium, thorium and rare earth minerals processing research facility carried out in the early 50's and 60's is currently stored at the Woomera Test Range in South Australia awaiting final disposal. Prior to developing a final disposal pathway commensurate with waste acceptance criteria, a comprehensive baseline environmental monitoring has been carried out to establish the background radiation levels. The survey included in situ gamma scanning of the surface soil ({sup 238}U, {sup 232}Th, {sup 40}K), a laboratory analysis of 86 soil samples (from 0-20 cm depth), which involved XRF measurements (U, Th, and rare earth metals) and spectroscopic analysis ({sup 238}U, {sup 232}Th, {sup 226}Ra and daughter nuclides). A time series of radon concentration measurements in air was established, while soil radon ({sup 222}Rn) and thoron ({sup 220}Rn) flux measurements were undertaken at 18 different locations. The 2018 comprehensive baseline survey demonstrated radiation levels in the immediate vicinity of the Woomera interim waste store are typical background values of soil and rock. No contamination was detected. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

Systems and methods for separating radium from lead, bismuth, and thorium

Methods for separating Ra from Pb, Bi, and Th are provided, the methods can include: providing a first mixture comprising Ra, Pb, Bi, and/or Th; providing a system that can include: a first vessel housing a first media; a second vessel in fluid communication with the first vessel, the second vessel housing a second media; and a third vessel in fluid communication with the second vessel, the third vessel housing a third media; and exposing the first mixture to the first media within the first vessel then, through the fluid communication, exposing the first remainder to the second media in the second vessel, then, through fluid communication, exposing the next remainder to the third media in the third vessel, the exposing separating the Th and Bi from the Ra and Pb, and the Ra from the Pb. Methods for separating Ra from being associated with a media are also provided. The methods can include: exposing the Ra and media to a chelating agent to form a mixture comprising the Ra complexed with the chelating agent.

O'Hara, Matthew J.↗

Materials Data on ThPS by Materials Project

ThPS is Matlockite structured and crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. Th4+ is bonded in a 9-coordinate geometry to four equivalent P2- and five equivalent S2- atoms. All Th–P bond lengths are 2.96 Å. There are four shorter (2.92 Å) and one longer (3.00 Å) Th–S bond lengths. P2- is bonded in a 8-coordinate geometry to four equivalent Th4+ atoms. S2- is bonded to five equivalent Th4+ atoms to form a mixture of distorted edge and corner-sharing STh5 trigonal bipyramids.

36 MATERIALS SCIENCE↗

Materials Data on SrTh2Se5 by Materials Project

SrTh2Se5 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. Sr2+ is bonded in a 8-coordinate geometry to eight Se2- atoms. There are a spread of Sr–Se bond distances ranging from 3.11–3.47 Å. There are two inequivalent Th4+ sites. In the first Th4+ site, Th4+ is bonded to seven Se2- atoms to form distorted edge-sharing ThSe7 pentagonal bipyramids. There are a spread of Th–Se bond distances ranging from 2.86–3.06 Å. In the second Th4+ site, Th4+ is bonded in a 8-coordinate geometry to eight Se2- atoms. There are a spread of Th–Se bond distances ranging from 3.01–3.17 Å. There are five inequivalent Se2- sites. In the first Se2- site, Se2- is bonded to four Th4+ atoms to form distorted SeTh4 trigonal pyramids that share corners with six SeSr2Th3 square pyramids, corners with six SeTh4 trigonal pyramids, edges with three SeSr2Th3 square pyramids, and an edgeedge with one SeTh4 trigonal pyramid. In the second Se2- site, Se2- is bonded in a 5-coordinate geometry to two equivalent Sr2+ and three Th4+ atoms. In the third Se2- site, Se2- is bonded to two equivalent Sr2+ and three Th4+ atoms to form distorted SeSr2Th3 square pyramids that share corners with four equivalent SeSr2Th3 square pyramids, corners with eight SeSr2Th2 trigonal pyramids, edges with three SeSr2Th3 square pyramids, edges with two SeTh4 trigonal pyramids, and a faceface with one SeSr2Th3 square pyramid. In the fourth Se2- site, Se2- is bonded to two equivalent Sr2+ and three Th4+ atoms to form distorted SeSr2Th3 square pyramids that share corners with eight SeSr2Th3 square pyramids, corners with four SeTh4 trigonal pyramids, an edgeedge with one SeSr2Th3 square pyramid, edges with four SeSr2Th2 trigonal pyramids, and a faceface with one SeSr2Th3 square pyramid. In the fifth Se2- site, Se2- is bonded to two equivalent Sr2+ and two equivalent Th4+ atoms to form distorted SeSr2Th2 trigonal pyramids that share corners with six SeSr2Th3 square pyramids, corners with six SeTh4 trigonal pyramids, edges with three SeSr2Th3 square pyramids, and an edgeedge with one SeSr2Th2 trigonal pyramid.

36 MATERIALS SCIENCE↗

Materials Data on K3NaTh2O6 by Materials Project

K3NaTh2O6 is High Pressure (4-7GPa) Tellurium-derived structured and crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are two inequivalent K1+ sites. In the first K1+ site, K1+ is bonded to six O2- atoms to form distorted KO6 octahedra that share corners with two equivalent NaO6 octahedra, corners with four ThO6 octahedra, edges with two equivalent NaO6 octahedra, edges with four ThO6 octahedra, and edges with six equivalent KO6 octahedra. The corner-sharing octahedra tilt angles range from 13–18°. There are two shorter (2.70 Å) and four longer (2.95 Å) K–O bond lengths. In the second K1+ site, K1+ is bonded to six O2- atoms to form distorted KO6 octahedra that share corners with two equivalent NaO6 octahedra, corners with four ThO6 octahedra, edges with two equivalent NaO6 octahedra, edges with four ThO6 octahedra, and edges with six KO6 octahedra. The corner-sharing octahedra tilt angles range from 14–17°. There are a spread of K–O bond distances ranging from 2.76–2.97 Å. Na1+ is bonded to six O2- atoms to form NaO6 octahedra that share corners with six KO6 octahedra, edges with six KO6 octahedra, and edges with six ThO6 octahedra. The corner-sharing octahedra tilt angles range from 17–18°. There are four shorter (2.64 Å) and two longer (2.65 Å) Na–O bond lengths. There are two inequivalent Th4+ sites. In the first Th4+ site, Th4+ is bonded to six O2- atoms to form ThO6 octahedra that share corners with six KO6 octahedra, edges with three equivalent NaO6 octahedra, edges with three equivalent ThO6 octahedra, and edges with six KO6 octahedra. The corner-sharing octahedra tilt angles range from 13–14°. There are four shorter (2.35 Å) and two longer (2.36 Å) Th–O bond lengths. In the second Th4+ site, Th4+ is bonded to six O2- atoms to form ThO6 octahedra that share corners with six KO6 octahedra, edges with three equivalent NaO6 octahedra, edges with three equivalent ThO6 octahedra, and edges with six KO6 octahedra. The corner-sharing octahedra tilt angles range from 13–14°. All Th–O bond lengths are 2.35 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded to three K1+, one Na1+, and two Th4+ atoms to form a mixture of distorted edge and corner-sharing OK3NaTh2 octahedra. The corner-sharing octahedra tilt angles range from 0–12°. In the second O2- site, O2- is bonded to three K1+, one Na1+, and two Th4+ atoms to form a mixture of distorted edge and corner-sharing OK3NaTh2 octahedra. The corner-sharing octahedra tilt angles range from 0–12°. In the third O2- site, O2- is bonded to three K1+, one Na1+, and two Th4+ atoms to form a mixture of distorted edge and corner-sharing OK3NaTh2 octahedra. The corner-sharing octahedra tilt angles range from 0–10°.

36 MATERIALS SCIENCE↗

Materials Data on Li2ThN2 by Materials Project

Li2ThN2 crystallizes in the trigonal P-3 space group. The structure is three-dimensional. Li1+ is bonded to four equivalent N3- atoms to form distorted LiN4 tetrahedra that share corners with six ThN6 octahedra, corners with six equivalent LiN4 tetrahedra, edges with three ThN6 octahedra, and edges with three equivalent LiN4 tetrahedra. The corner-sharing octahedra tilt angles range from 5–62°. There are a spread of Li–N bond distances ranging from 2.05–2.40 Å. There are two inequivalent Th4+ sites. In the first Th4+ site, Th4+ is bonded to six equivalent N3- atoms to form ThN6 octahedra that share corners with twelve equivalent LiN4 tetrahedra, edges with six equivalent ThN6 octahedra, and edges with six equivalent LiN4 tetrahedra. All Th–N bond lengths are 2.48 Å. In the second Th4+ site, Th4+ is bonded to six equivalent N3- atoms to form ThN6 octahedra that share corners with twelve equivalent LiN4 tetrahedra, edges with six ThN6 octahedra, and edges with six equivalent LiN4 tetrahedra. There are three shorter (2.47 Å) and three longer (2.49 Å) Th–N bond lengths. N3- is bonded in a 7-coordinate geometry to four equivalent Li1+ and three Th4+ atoms.

36 MATERIALS SCIENCE↗

Materials Data on ThNCl by Materials Project

ThNCl is Matlockite structured and crystallizes in the tetragonal P4/nmm space group. The structure is three-dimensional. Th4+ is bonded in a 9-coordinate geometry to four equivalent N3- and five equivalent Cl1- atoms. All Th–N bond lengths are 2.35 Å. There are one shorter (3.24 Å) and four longer (3.26 Å) Th–Cl bond lengths. N3- is bonded to four equivalent Th4+ atoms to form a mixture of edge and corner-sharing NTh4 tetrahedra. Cl1- is bonded in a 5-coordinate geometry to five equivalent Th4+ atoms.

36 MATERIALS SCIENCE↗

Materials Data on ThBrN by Materials Project

ThNBr is Matlockite structured and crystallizes in the tetragonal P4/nmm space group. The structure is two-dimensional and consists of one ThNBr sheet oriented in the (0, 0, 1) direction. Th4+ is bonded in a 4-coordinate geometry to four equivalent N3- and four equivalent Br1- atoms. All Th–N bond lengths are 2.34 Å. All Th–Br bond lengths are 3.36 Å. N3- is bonded to four equivalent Th4+ atoms to form a mixture of edge and corner-sharing NTh4 tetrahedra. Br1- is bonded in a 4-coordinate geometry to four equivalent Th4+ atoms.

36 MATERIALS SCIENCE↗

Materials Data on ThIN by Materials Project

ThNI crystallizes in the tetragonal P4/nmm space group. The structure is two-dimensional and consists of one ThNI sheet oriented in the (0, 0, 1) direction. Th4+ is bonded in a 4-coordinate geometry to four equivalent N3- and four equivalent I1- atoms. All Th–N bond lengths are 2.35 Å. All Th–I bond lengths are 3.54 Å. N3- is bonded to four equivalent Th4+ atoms to form a mixture of corner and edge-sharing NTh4 tetrahedra. I1- is bonded in a 4-coordinate geometry to four equivalent Th4+ atoms.

36 MATERIALS SCIENCE↗

Materials Data on Th11(Ru2C3)6 by Materials Project

Th11Ru12C18 crystallizes in the cubic I-43m space group. The structure is three-dimensional and consists of two thorium molecules and one Th5(Ru2C3)3 framework. In the Th5(Ru2C3)3 framework, there are two inequivalent Th4+ sites. In the first Th4+ site, Th4+ is bonded to six equivalent C4- atoms to form distorted corner-sharing ThC6 pentagonal pyramids. There are three shorter (2.74 Å) and three longer (2.88 Å) Th–C bond lengths. In the second Th4+ site, Th4+ is bonded in a 8-coordinate geometry to eight C4- atoms. There are four shorter (2.63 Å) and four longer (2.80 Å) Th–C bond lengths. Ru+2.33+ is bonded in a trigonal non-coplanar geometry to three C4- atoms. There are two shorter (1.98 Å) and one longer (2.10 Å) Ru–C bond lengths. There are two inequivalent C4- sites. In the first C4- site, C4- is bonded in a 7-coordinate geometry to four equivalent Th4+, two equivalent Ru+2.33+, and one C4- atom. The C–C bond length is 1.41 Å. In the second C4- site, C4- is bonded to four Th4+ and two equivalent Ru+2.33+ atoms to form a mixture of edge and corner-sharing CTh4Ru2 octahedra. The corner-sharing octahedra tilt angles range from 6–68°.

36 MATERIALS SCIENCE↗

Materials Data on ThZrF8 by Materials Project

ThZrF8 crystallizes in the monoclinic P2_1/c space group. The structure is three-dimensional. there are two inequivalent Th4+ sites. In the first Th4+ site, Th4+ is bonded in a 9-coordinate geometry to nine F1- atoms. There are a spread of Th–F bond distances ranging from 2.30–2.44 Å. In the second Th4+ site, Th4+ is bonded in a 9-coordinate geometry to nine F1- atoms. There are a spread of Th–F bond distances ranging from 2.30–2.50 Å. There are two inequivalent Zr4+ sites. In the first Zr4+ site, Zr4+ is bonded to seven F1- atoms to form distorted corner-sharing ZrF7 pentagonal bipyramids. There are a spread of Zr–F bond distances ranging from 2.07–2.16 Å. In the second Zr4+ site, Zr4+ is bonded to seven F1- atoms to form corner-sharing ZrF7 pentagonal bipyramids. There are a spread of Zr–F bond distances ranging from 2.05–2.15 Å. There are sixteen inequivalent F1- sites. In the first F1- site, F1- is bonded in a distorted bent 150 degrees geometry to one Th4+ and one Zr4+ atom. In the second F1- site, F1- is bonded in a linear geometry to two Th4+ atoms. In the third F1- site, F1- is bonded in a distorted bent 150 degrees geometry to one Th4+ and one Zr4+ atom. In the fourth F1- site, F1- is bonded in a bent 150 degrees geometry to two Th4+ atoms. In the fifth F1- site, F1- is bonded in a distorted bent 150 degrees geometry to one Th4+ and one Zr4+ atom. In the sixth F1- site, F1- is bonded in a distorted linear geometry to one Th4+ and one Zr4+ atom. In the seventh F1- site, F1- is bonded in a distorted bent 150 degrees geometry to one Th4+ and one Zr4+ atom. In the eighth F1- site, F1- is bonded in a distorted bent 150 degrees geometry to two Zr4+ atoms. In the ninth F1- site, F1- is bonded in a distorted bent 150 degrees geometry to two Th4+ atoms. In the tenth F1- site, F1- is bonded in a distorted bent 150 degrees geometry to one Th4+ and one Zr4+ atom. In the eleventh F1- site, F1- is bonded in a distorted bent 150 degrees geometry to one Th4+ and one Zr4+ atom. In the twelfth F1- site, F1- is bonded in a distorted bent 150 degrees geometry to one Th4+ and one Zr4+ atom. In the thirteenth F1- site, F1- is bonded in a bent 150 degrees geometry to one Th4+ and one Zr4+ atom. In the fourteenth F1- site, F1- is bonded in a bent 150 degrees geometry to one Th4+ and one Zr4+ atom. In the fifteenth F1- site, F1- is bonded in a linear geometry to one Th4+ and one Zr4+ atom. In the sixteenth F1- site, F1- is bonded in a bent 150 degrees geometry to one Th4+ and one Zr4+ atom.

36 MATERIALS SCIENCE↗

Materials Data on ThCN by Materials Project

NCTh crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Th4+ is bonded in a 7-coordinate geometry to three equivalent C2- and four equivalent N2- atoms. There are two shorter (2.82 Å) and one longer (2.85 Å) Th–C bond lengths. There are a spread of Th–N bond distances ranging from 2.36–2.39 Å. C2- is bonded in a rectangular see-saw-like geometry to three equivalent Th4+ and one C2- atom. The C–C bond length is 1.26 Å. N2- is bonded to four equivalent Th4+ atoms to form a mixture of edge and corner-sharing NTh4 tetrahedra.

36 MATERIALS SCIENCE↗

Materials Data on ThF4 by Materials Project

ThF4 crystallizes in the monoclinic C2/c space group. The structure is three-dimensional. there are two inequivalent Th4+ sites. In the first Th4+ site, Th4+ is bonded in a 8-coordinate geometry to eight F1- atoms. There are a spread of Th–F bond distances ranging from 2.33–2.40 Å. In the second Th4+ site, Th4+ is bonded in a 8-coordinate geometry to eight F1- atoms. There are a spread of Th–F bond distances ranging from 2.30–2.38 Å. There are seven inequivalent F1- sites. In the first F1- site, F1- is bonded in a distorted bent 150 degrees geometry to two equivalent Th4+ atoms. In the second F1- site, F1- is bonded in a distorted linear geometry to two Th4+ atoms. In the third F1- site, F1- is bonded in a distorted linear geometry to two equivalent Th4+ atoms. In the fourth F1- site, F1- is bonded in a linear geometry to two Th4+ atoms. In the fifth F1- site, F1- is bonded in a bent 150 degrees geometry to two Th4+ atoms. In the sixth F1- site, F1- is bonded in a linear geometry to two equivalent Th4+ atoms. In the seventh F1- site, F1- is bonded in a distorted bent 150 degrees geometry to two Th4+ atoms.

36 MATERIALS SCIENCE↗