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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Polyvinyl acetate-based polymer host for optical and far-infrared spectroscopy of individualized nanoparticles

Preparation techniques for producing films of individualized solution-dispersed nanoparticles (NPs) for optical spectroscopy are frequently technically challenging and tailored for a specific NP system. In this work, we present a rapid, easy, and economical technique for producing polyvinyl acetate (PVAc)-based NP-polymer films on the order of 100’s of micrometers thick that exhibit high uniformity, low aggregation, excellent optical transparency, and low terahertz absorption. In addition, we find that these films are robust at cryogenic temperatures and have a high laser damage threshold of 0.3 TW cm –2 , which make them suitable for pulsed laser measurements. We show that free-standing, flexible, PVAc films can incorporate both one-dimensional single-wall carbon nanotubes (SWCNTs) and zero-dimensional Au NPs. Using absorbance, Raman scattering, and photoluminescence excitation spectroscopy, we observe that SWCNT individualization is maintained, and minimized polymer strain imposed, when the nanotubes are transitioned from the solution to the polymer host. This PVAc-based polymer host presents researchers with a straightforward method for producing free-standing and flexible NP films with low aggregation.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Use of vibrational spectroscopy to identify the formation of neptunyl–neptunyl interactions: a paired density functional theory and Raman spectroscopy study

Actinyl–Actinyl interactions (AAIs) occur in pentavalent actinide systems, particularly for neptunium (Np), and lead to complex vibrational signals that are challenging to analyze and interpret. Previous studies have focused on neptunyl–neptunyl dimeric species, but trimers and tetramers have been identified as the primary motif for extended topologies observed in solid-state materials. Our hypothesis is that trimeric and tetrameric AAIs lead to the additional signals in the vibrational spectra, but this has yet to be explored systematically. Herein, we investigate three different neptunyl–neptunyl subunits (dimeric, trimeric, tetrameric) and determine the vibrational frequencies of the O=Np=O stretches using both computational and experimental approaches. Density Functional Theory (DFT) was used to identify distinct vibrational motions related to specific neptunyl oligomers and compared to previous literature precedent from Np(V) in HClO 4 and HCl systems. The vibrational behavior of Np(V) in HNO 3 was then evaluated via Raman spectroscopy. As the solution evaporated signals were linked to trimeric and tetrameric models. Solid phases produced in the evaporation include (NpO 2 ) 2 (NO 3 ) 2 (H 2 O) 5 and newly identified crystalline phase, Na(NpO 2 )(NO 3 ) 2 ·4H 2 O (NpNa). Furthermore, the combined computational studies and vibrational analysis provide evidence for unique observable vibrational bands for each polymerized subunit, allowing us to assign spectral features to trimeric and tetrameric models within three different simple anionic systems.

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

Materials Data on Np2CoH8F10 by Materials Project

(NpF5)2CoH6H2 crystallizes in the monoclinic P2_1/c space group. The structure is two-dimensional and consists of four hydrogen molecules; two CoH6 clusters; and one NpF5 sheet oriented in the (0, 0, 1) direction. In each CoH6 cluster, Co2+ is bonded in an octahedral geometry to six H+0.25+ atoms. There is two shorter (1.53 Å) and four longer (1.57 Å) Co–H bond length. There are three inequivalent H+0.25+ sites. In the first H+0.25+ site, H+0.25+ is bonded in a 2-coordinate geometry to one Co2+ and one H+0.25+ atom. The H–H bond length is 0.90 Å. In the second H+0.25+ site, H+0.25+ is bonded in a single-bond geometry to one Co2+ atom. In the third H+0.25+ site, H+0.25+ is bonded in a 2-coordinate geometry to one Co2+ and one H+0.25+ atom. In the NpF5 sheet, Np3+ is bonded in a 9-coordinate geometry to nine F1- atoms. There are a spread of Np–F bond distances ranging from 2.05–2.56 Å. There are five inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one Np3+ atom. In the second F1- site, F1- is bonded in a 1-coordinate geometry to two equivalent Np3+ atoms. In the third F1- site, F1- is bonded in a distorted bent 120 degrees geometry to two equivalent Np3+ atoms. In the fourth F1- site, F1- is bonded in a bent 120 degrees geometry to two equivalent Np3+ atoms. In the fifth F1- site, F1- is bonded in a bent 120 degrees geometry to two equivalent Np3+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on K3NpO2F5 by Materials Project

K3NpO2F5 crystallizes in the tetragonal I4_1/a space group. The structure is three-dimensional. there are three inequivalent K1+ sites. In the first K1+ site, K1+ is bonded in a 9-coordinate geometry to two equivalent O2- and seven F1- atoms. There are one shorter (3.07 Å) and one longer (3.16 Å) K–O bond lengths. There are a spread of K–F bond distances ranging from 2.65–3.23 Å. In the second K1+ site, K1+ is bonded to four equivalent O2- and four equivalent F1- atoms to form distorted KO4F4 hexagonal bipyramids that share corners with four equivalent NpO2F5 pentagonal bipyramids and edges with two equivalent NpO2F5 pentagonal bipyramids. All K–O bond lengths are 2.90 Å. All K–F bond lengths are 2.75 Å. In the third K1+ site, K1+ is bonded to six F1- atoms to form KF6 octahedra that share corners with six equivalent NpO2F5 pentagonal bipyramids. There are four shorter (2.59 Å) and two longer (2.67 Å) K–F bond lengths. Np6+ is bonded to two equivalent O2- and five F1- atoms to form NpO2F5 pentagonal bipyramids that share corners with two equivalent KO4F4 hexagonal bipyramids, corners with three equivalent KF6 octahedra, and an edgeedge with one KO4F4 hexagonal bipyramid. The corner-sharing octahedra tilt angles range from 0–35°. Both Np–O bond lengths are 1.83 Å. There are a spread of Np–F bond distances ranging from 2.25–2.31 Å. O2- is bonded in a distorted single-bond geometry to three K1+ and one Np6+ atom. There are three inequivalent F1- sites. In the first F1- site, F1- is bonded in a 4-coordinate geometry to four K1+ and one Np6+ atom. In the second F1- site, F1- is bonded in a 2-coordinate geometry to five K1+ and one Np6+ atom. In the third F1- site, F1- is bonded to three K1+ and one Np6+ atom to form a mixture of distorted edge and corner-sharing FK3Np tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Second Report of the Nuclear Data Subcommittee of the Nuclear Science Advisory Committee

The central importance of the nuclear data curated by the US Nuclear Data Program (USNDP) for clean energy generation, national security, nonproliferation, medical applications, and space exploration as well as basic science was described in a prior report issued by the DOE/NSF Nuclear Science Advisory Committee subcommittee on Nuclear Data (NSAC-ND) in September 2022. In this report, we present a set of fourteen (14) recommendations that will enhance and advance DOE-NP's stewardship of nuclear data. The first three recommendations focus on the existing core USNDP capabilities, namely: 1) Support the nuclear structure evaluation workforce to improve the currency, consistency, and accessibility of the Evaluated Nuclear Structure Data File (ENSDF); 2) Enhance nuclear reaction evaluation within the USNDP in support of the Evaluated Nuclear Data File (ENDF) through expansion of the workforce and integration of high-performance computing, automation, and machine learning and; 3) Continue atomic mass evaluation in support AME and NUBASE databases. This is followed by eight (8) recommendations representing new cross-cutting initiatives involving both measurement and evaluation to address outstanding nuclear data needs. These new initiatives require a highly trained, diverse workforce that includes personnel with expertise from both inside and outside the nuclear physics community from which evaluators have traditionally been recruited. As such, many of these initiatives are accomplished via a Topical Nuclear Data Collaborations (TNDC). A TNDC is made up of domestic and international stakeholders, subject matter and nuclear data experts, and nuclear data evaluators and features a workforce development plan to ensure that nuclear data evaluators maintain currency in the relevant applications and are seen as equity partners in the endeavor. These include: 1) Establish a coordinated effort to improve evaluation and modeling in nuclear astrophysics for stellar dynamics, multi-messenger astronomy and nucleosynthesis; 2) Initiate a TNDC to develop and maintain nuclear structure evaluation beyond discrete states, including nuclear level densities, photon strength functions and photonuclear data for improved reaction modeling, and exploring nuclear structure at finite temperature; 3) Create a TNDC to perform correlated fission data evaluation, including cross sections, fragment yields, v(A), v(E n ) for nuclear energy, national security, nonproliferation and basic science; 4) From a panel of subject matter experts to establish and annually update a roster of key decay data to nurture its accelerated dissemination including both measurement and evaluation for targeted high-value nuclides for national security, nonproliferation and medical applications; 5) Comprehensive, consistent neutron-induced structure and reaction data for nuclear energy, national security, nonproliferation and planetary nuclear spectroscopy; 6) Charged-particle stopping powers for detector design, space effects and ion beam therapy; 7) High-energy reactions for space exploration and medical nuclide production, and; 8) The creation of an infrastructure for open data and data preservation for use by the entire nuclear physics community. All told, these initiatives require approximately $6.5M increase in NP support of the USNDP in fiscal year 2023 dollars and would require at least 3-5 years to carry out due to the length of time needed to recruit and train new nuclear data researchers. This relatively modest investment would help ensure that the fruits of the nuclear data research carried out by DOE-NP and its collaborators would be brought to bear to address some of the most important needs of our nation and the world. To ensure effective execution of this plan, we present an overview of recruitment, training, and retention goals for the USNDP, the centerpiece of which is a mutually agreed upon code of conduct. Finally, we identify the facility and instrumentation needed to perform the recommended experimental activities. This includes a short review of target fabrication capabilities, reactors, neutron beam, light- and heavy-stable ion, gamma-ray, high-energy and radioactive ion beam facilities. Lastly, a more complete appendix of experimental facilities previously compiled is included with new input provided for 6 facilities.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

O 2 -Oxidation of Individual Graphite and Graphene Nanoparticles in the 1200 – 2200 K Range: Particle-to-Particle Variations and the Evolution of the Reaction Rates and Optical Properties

The kinetics for O 2 oxidation of individual graphite and graphene platelet nanoparticles (NPs) were studied as a function of temperature (1200 to 2200 K) at varying oxygen partial pressures, using a single nanoparticle mass spectrometry method. NP temperature (TNP) was measured by measuring the NP thermal emission spectra during the kinetics studies. The initial oxidation efficiency is found to peak in the 1200 to 1500 K range, dropping by an order of magnitude as TNP was increased above 2000 K. There were large NP-to-NP variations in the oxidation rates, attributed to variations in the NP surface structure. In addition, the oxidation efficiencies evolved, non-monotonically, as the NPs reacted, decreasing by factors of between 10 and 300. This evolution of reactivity is attributed to changes in the NP surface structure due to the combination of oxidation and annealing. In conclusion, the optical properties, including wavelength dependence of the emissivity and the absorption cross section for the 532 nm heating laser, also tended to evolve as the NPs oxidized, but differently for each individual NP, presumably reflecting differences in the initial structures and their evolution.

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

Efficient Topology Design Algorithms for Power Grid Stability

The dynamic response of power grids to small disturbances influences their overall stability. This letter examines the effect of network topology on the linearized time-invariant dynamics of electric power systems. The proposed framework utilizes H 2 -norm based stability metrics to study the optimal placement of lines on existing networks as well as the topology design of new networks. The design task is first posed as an NP-hard mixed-integer nonlinear program (MINLP) that is exactly reformulated as a mixed-integer linear program (MILP) using McCormick linearization. To improve computation time, graph-theoretic properties are exploited to derive valid inequalities (cuts) and tighten bounds on the continuous optimization variables. Moreover, a cutting plane generation procedure is put forth that is able to interject the MILP solver and augment additional constraints to the problem on-the-fly. Finally, the efficacy of our approach in designing optimal grid topologies is demonstrated through numerical tests on the IEEE 39-bus network.

24 POWER TRANSMISSION AND DISTRIBUTION↗
DOE OSTI2020

Materials Data on NpTl2F6 by Materials Project

NpTl2F6 crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Np4+ is bonded in a 8-coordinate geometry to eight F1- atoms. There are a spread of Np–F bond distances ranging from 2.20–2.47 Å. Tl1+ is bonded in a 9-coordinate geometry to nine F1- atoms. There are a spread of Tl–F bond distances ranging from 2.91–3.15 Å. There are three inequivalent F1- sites. In the first F1- site, F1- is bonded in a 1-coordinate geometry to one Np4+ and four equivalent Tl1+ atoms. In the second F1- site, F1- is bonded in a 2-coordinate geometry to two equivalent Np4+ and one Tl1+ atom. In the third F1- site, F1- is bonded in a distorted single-bond geometry to one Np4+ and four equivalent Tl1+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Assessment of Impurities in Neptunium Metal Using Double-Focusing SF-ICP-MS

In the transmutation process, minor actinides such as neptunium, americium and curium obtained from spent nuclear fuel are incorporated into new fuel that can be placed into a fast reactor, where these elements fission into products with shorter half-lives which reduces the health and safety hazards. In order to better understand the all the involved processes, fundamental physical properties of actinides should be investigated, and for that reason, high-purity materials need to be produced. One of the main challenges in characterizing these materials is the lack of pure metal available for study, and lack of analytical methods to determine the purity. Trans-uranic elements are challenging to study because of the need to be handled in specialized facilities, safeguards concerns and they are not easily purchased and/or produced. High-purity Np metal is being produced at the Materials and Fuels Complex (MFC) of Idaho National Laboratory (INL), in a process of direct oxide reduction developed by Squires and Lessing, with a target purity of 99.999%. The goal of this research is to develop methods to determine the impurities in the Np metal, with detection limits low enough to achieve this purity level. In this work, we have used several ICP-MS and ICP OES techniques, but the focus was the method development using a recently acquired Double-Focusing Sector Field Inductively Coupled Plasma Mass Spectrometer (SF-ICP-MS). To produce the Np metal, approximately 20 g of the neptunium oxide powder was calcined at 800 oC for 6 h in a magnesium oxide crucible, which is placed inside a stainless steel crucible, that goes into the Hot Uniaxial Press (HUP) furnace insert. After the calcining step, the Np oxide was mixed with approximately 9 g of calcium metal and 100 g of ultra-dry calcium chloride. The HUP furnace was heated in a ramp rate of 50 oC min -1 up to 1000 oC. When the reaction mixture reached 850 oC, a tantalum stirrer was activated at 100 rpm. After the tantalum stirrer was removed and the mixture cooled overnight, the MgO crucible was opened with a hammer and chisel to retrieve the Np metal button at the bottom of the reaction mixture. Prior to the dissolution process, the surface contaminants of the sample were removed. The Np button was washed in 10 mL of ultra-pure water for 1 min, with a faint reaction observed on the surface, indicating the presence of Ca metal. The water-washed sample was placed in a tube with 2 M HCl for only 3 s, as a vigorous reaction in the button surface was observed. The leachates were saved for further analysis. The sample was then rinsed with ultra-pure water and air-dried prior to dissolution. The cleaned sample was placed in a PTFE beaker and 25 mL of 6 M HCl and 150 µL of 24 M HF were added. After 10 minutes of reaction, the beaker was placed on a hot plate for 1 h and 30 min, followed by the addition of 1 mL of 16 M HNO3 and allowed to react for a further 1 h and 20 min. The sample was removed from heat and 10 mL of HNO3 16 M was added to react with the HCl. The beaker was covered and left for overnight reaction, producing a solution with approximately 20 mL of final volume. A Quadrupole Inductively Coupled Plasma Mass Spectrometer (Q-ICP-MS, Perkin Elmer ELAN DRC II Q-ICP-MS) was used to obtain qualitative mass spectra for the dissolution blank, each of the leachates and the dissolved sample. In the water leachate spectrum mainly Ca and Mg were observed, while the acid wash had a similar peak pattern to the one observed for the Np metal sample, indicating that the process not only removed surface contamination, but also reacted with the sample itself. In the Np material spectrum, Ta and actinides were identified as candidates for major contaminants, as the most intense peaks corresponded to the mass-to-charge ratios of these elements. Minor contaminants included Al, Au, Ca, Cr, Fe, I, Na, Nb, Pb, Sn, Ti, Tl, V, Y. The presence of impurities in the material could have originated from several sources, such as the materials used for the casting process, the use of impure NpO2 or contamination of reagents and materials used for the analysis. Some of the isotopes listed as potential contaminants are susceptible to spectral interferences, so Double-Focusing SF-ICP-MS (Nu Instruments Attom ES HR-ICP-MS) was used for the quantitative analysis. For each isotope determined, several items were evaluated: raw signal of a blank solution, sensitivity and determination coefficient of calibration curves, possibility of interferences and comparison of results obtained for at least two resolving powers (RP): 300 and 4000. The evaluation of the signal in a blank solution can indicate if a spectral interference from the plasma gas and/or the solvent was successfully resolved (commonly observed for 52Cr+/40Ar12C+, for example). It is important to highlight that a signal reduction is expected when a higher RP is used, as the ion beam transmission is decreased by the use of narrower slits

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

Materials Data on ReNCl4O3 by Materials Project

ReNO3Cl4 is alpha Np structured and crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of eight ReNO3Cl4 clusters. In four of the ReNO3Cl4 clusters, Re5+ is bonded in a 2-coordinate geometry to two O2- and four Cl1- atoms. There is one shorter (1.71 Å) and one longer (1.73 Å) Re–O bond length. There are a spread of Re–Cl bond distances ranging from 2.29–2.93 Å. N5+ is bonded in a distorted single-bond geometry to one O2- and one Cl1- atom. The N–O bond length is 1.13 Å. The N–Cl bond length is 2.34 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one Re5+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to one N5+ atom. In the third O2- site, O2- is bonded in a single-bond geometry to one Re5+ atom. There are four inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a 2-coordinate geometry to one Re5+ and one N5+ atom. In the second Cl1- site, Cl1- is bonded in a distorted single-bond geometry to one Re5+ atom. In the third Cl1- site, Cl1- is bonded in a single-bond geometry to one Re5+ atom. In the fourth Cl1- site, Cl1- is bonded in a single-bond geometry to one Re5+ atom. In four of the ReNO3Cl4 clusters, Re5+ is bonded in a 2-coordinate geometry to two O2- and four Cl1- atoms. Both Re–O bond lengths are 1.72 Å. There are a spread of Re–Cl bond distances ranging from 2.30–2.61 Å. N5+ is bonded in a single-bond geometry to one O2- and one Cl1- atom. The N–O bond length is 1.13 Å. The N–Cl bond length is 2.49 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one Re5+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to one N5+ atom. In the third O2- site, O2- is bonded in a single-bond geometry to one Re5+ atom. There are four inequivalent Cl1- sites. In the first Cl1- site, Cl1- is bonded in a single-bond geometry to one Re5+ atom. In the second Cl1- site, Cl1- is bonded in a single-bond geometry to one Re5+ atom. In the third Cl1- site, Cl1- is bonded in a single-bond geometry to one Re5+ atom. In the fourth Cl1- site, Cl1- is bonded in a 2-coordinate geometry to one Re5+ and one N5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Cs2Np2PO4F7 by Materials Project

Cs2Np2PO4F7 crystallizes in the monoclinic P2_1/c 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 two O2- and six F1- atoms. There are one shorter (3.05 Å) and one longer (3.20 Å) Cs–O bond lengths. There are a spread of Cs–F bond distances ranging from 2.87–3.39 Å. In the second Cs1+ site, Cs1+ is bonded in a 2-coordinate geometry to two O2- and six F1- atoms. There are one shorter (3.10 Å) and one longer (3.12 Å) Cs–O bond lengths. There are a spread of Cs–F bond distances ranging from 2.88–3.50 Å. There are two inequivalent Np4+ sites. In the first Np4+ site, Np4+ is bonded in a 9-coordinate geometry to two O2- and seven F1- atoms. There are one shorter (2.28 Å) and one longer (2.33 Å) Np–O bond lengths. There are a spread of Np–F bond distances ranging from 2.25–2.49 Å. In the second Np4+ site, Np4+ is bonded in a 8-coordinate geometry to two O2- and six F1- atoms. There are one shorter (2.31 Å) and one longer (2.33 Å) Np–O bond lengths. There are a spread of Np–F bond distances ranging from 2.17–2.42 Å. P5+ is bonded in a tetrahedral geometry to four O2- atoms. There is two shorter (1.55 Å) and two longer (1.56 Å) P–O bond length. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a 1-coordinate geometry to one Cs1+, one Np4+, and one P5+ atom. In the second O2- site, O2- is bonded in a 1-coordinate geometry to one Cs1+, one Np4+, and one P5+ atom. In the third O2- site, O2- is bonded in a 1-coordinate geometry to one Cs1+, one Np4+, and one P5+ atom. In the fourth O2- site, O2- is bonded in a 1-coordinate geometry to one Cs1+, one Np4+, and one P5+ atom. There are seven inequivalent F1- sites. In the first F1- site, F1- is bonded in a 2-coordinate geometry to two equivalent Cs1+ and two Np4+ atoms. In the second F1- site, F1- is bonded in a distorted bent 150 degrees geometry to two Np4+ atoms. In the third F1- site, F1- is bonded in a 2-coordinate geometry to two Cs1+ and two equivalent Np4+ atoms. In the fourth F1- site, F1- is bonded in a 3-coordinate geometry to two equivalent Cs1+ and two Np4+ atoms. In the fifth F1- site, F1- is bonded in a 2-coordinate geometry to two Cs1+ and two equivalent Np4+ atoms. In the sixth F1- site, F1- is bonded in a 3-coordinate geometry to two Cs1+ and one Np4+ atom. In the seventh F1- site, F1- is bonded in a 2-coordinate geometry to two Cs1+ and two equivalent Np4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on KNpN3O11 by Materials Project

KNpN3O11 crystallizes in the trigonal R-3c space group. The structure is three-dimensional. K1+ is bonded in a 2-coordinate geometry to fourteen O2- atoms. There are a spread of K–O bond distances ranging from 2.96–3.37 Å. Np6+ is bonded in a distorted linear geometry to two equivalent O2- atoms. Both Np–O bond lengths are 1.79 Å. N5+ is bonded in a trigonal planar geometry to three O2- atoms. There is one shorter (1.23 Å) and two longer (1.29 Å) N–O bond length. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted single-bond geometry to one K1+ and one N5+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to two equivalent K1+ and one N5+ atom. In the third O2- site, O2- is bonded in a distorted single-bond geometry to one K1+ and one Np6+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on RbNpN3O11 by Materials Project

RbNpN3O11 crystallizes in the trigonal R-3c space group. The structure is three-dimensional. Rb1+ is bonded in a 2-coordinate geometry to fourteen O2- atoms. There are a spread of Rb–O bond distances ranging from 3.07–3.46 Å. Np6+ is bonded in a distorted linear geometry to two equivalent O2- atoms. Both Np–O bond lengths are 1.79 Å. N5+ is bonded in a trigonal planar geometry to three O2- atoms. There is one shorter (1.23 Å) and two longer (1.29 Å) N–O bond length. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one Rb1+ and one Np6+ atom. In the second O2- site, O2- is bonded in a 1-coordinate geometry to one Rb1+ and one N5+ atom. In the third O2- site, O2- is bonded in a single-bond geometry to two equivalent Rb1+ and one N5+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

New Physics from the Neutrino Portal: Early Universe Implications and Detection Prospects

Despite their ubiquity, the nature of Dark Matter (DM) and neutrinos remains mysterious. Both are examples of particles which are neutral, stable, and require physics beyond the Standard Model (SM) of particle physics. It is therefore natural to investigate theories which relate them. If DM has more than gravitational interactions, it must not couple very sizably to the Standard Mode (SM) in order to have escaped detection so far. The nature of this coupling (or “portal”) is of paramount importance in determining the optimal experimental search strategies. This proposal aims to focus on the implications of “Hidden Sector” models of new physics where the dominant interaction is from the neutrino-mixing portal. Such scenarios give rise to new neutrino self-interactions and DM-neutrino interactions with a variety of consequences. By undertaking the thorough study of neutrino portal (NP) theories of DM this proposal seeks to achieve the following specific objectives: (1) Expand and deepen the theoretical foundations of self-interacting neutrinos in the early universe with application to sterile neutrino DM, (2) establish theoretical and phenomenological bases for DM-modified neutrino oscillations, (3) establish sensitivity projections for neutrino self-interactions from future IceCube data. The proposed research will intellectually contribute to the physics literature by thoroughly characterizing the consequences of “hidden sector” models incorporating DM and neutrinos. Theoretical consistency and a complete description of their impact on the early universe will constitute one component of this work. As a result of the additional structure in the neutrino sector the detectability of various aspects of neutrino physics will be impacted. This includes modifications to oscillation experiments, ultra-high-energy neutrino telescopes (e.g. IceCube, KM3NET), and Cosmic Microwave Background data. The success of this research proposal will depend on the successful integration of these complementary probes of new physics in the proper context of theoretically motivated scenarios determined from their impact on the early universe.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

Characterization of Aluminum Metal Powders for Plutonium-238 Program

As part of radioisotope thermoelectric generator (RTG) production for power sources in deep space exploration, Oak Ridge National Laboratory (ORNL) produces plutonium-238 ( 238 Pu). To produce 238 Pu, neptunium-237 ( 237 Np) targets are fabricated at ORNL and subsequently irradiated at the High Flux Isotope Reactor (HFIR) at ORNL and the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL). Specifically, current flowsheets utilize neptunium dioxide ( 237 NpO 2 ) targets. Aluminum (Al) powder is blended with 237 NpO 2 target material to improve thermal conductivity during irradiation. The current composition of 237 NpO 2 /Al pellets (i.e., cermets, or ceramic–metallics) is 20% 237 NpO 2 , 70% Al, and 10% void space. Al powders utilized by the 238 Pu program are high-fired under vacuum before blending into targets. The primary objective of this work is to measure the physical, chemical, and thermal properties of Al before and after the high-firing process. Properties of interest include the morphology, surface texture, particle size, crystal phase(s), and thermal conductivity of the material. These properties are measured with existing materials characterization equipment at ORNL, including powder x-ray diffraction (pXRD), scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS), laser flash analysis (LFA), and thermogravimetric analysis (TGA). A secondary objective of this work is to compare the Al powders before and after the high-firing procedure to determine the effects of high-firing on chemical, physical, and thermal properties and to determine the efficacy of the high-firing process.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Light-Controlled Nanoparticle Collision Experiments

Electrochemical monitoring of catalytically amplified collisions of individual metal nanoparticles (NP) with ultramicroelectrodes (UME) has been extensively used to study electrocatalysis, mass-transport, and charge-transfer processes at the single NP level. More recently, photoelectrochemical collision experiments were carried out with semiconductive NPs. Here we introduce two new types of light-controlled nano-impact experiments. The first experiment involves localized photodeposition of catalyst (Pt) on TiO 2 NPs with a glass-sheathed carbon fiber simultaneously serving as the light guide and collector UME. The collisions of in situ prepared Pt@TiO 2 NPs with the carbon surface produced blips of water oxidation current, while the activity of pristine TiO 2 NPs was too low to yield measurable signal. In another experiment, collisions of catalytic (Ir oxide) NPs with the semiconductor (Nb doped n-type TiO 2 rutile single crystal) electrode are monitored by measuring the photocurrent of water oxidation.

14 SOLAR ENERGY↗
DOE OSTI2024

Fundamentals of Scalable Nanoparticle Assembly in Engineering Polymres

Systematically improving the properties of polymer nanocomposites is contingent on effectively controlling nanoparticle (NP) dispersion; further, it is necessary to attain this at scale if these methods are to impact practical applications. While most past work has focused on amorphous polymers, ≈ 70% of all polymers sold annually are semicrystalline. Inspired by this apparent disconnect, our work in the current DOE funded grant and this renewal proposal employs a novel handle, polymer crystallization, to organize NPs into the various amorphous zones of the lamellar semicrystalline morphology (interlamellar, interfibrillar and interspherulitic domains) of stereoregular polymers. We hypothesize that the isothermal crystallization rate of a polymer host, G, and NP diffusivity, are the two relevant control parameters in this context. In the case where the NPs are miscible in the melt, they remain spatially well-dispersed when the polymer is crystallized at a rate that is fast relative to NP diffusion. In contrast, monolayer-thick NP sheets with intersheet spacing of ~10-100nm form in slowly crystallized samples. This sheet stacking is remarkably similar to that seen in natural materials, e.g., Nacre. There is also ordering of the NPs at the larger interfibrillar scale. Importantly, the relative fraction of engulfed, interlamellar and interfibrillar NPs is determined by G. Further, the modulus of these materials can increase by a factor of 2-3 due to the organization state of the NPs, while leaving fracture toughness unaffected. We have established the broad applicability of this approach in two polymers, polyethylene (PE) and polyethyleneoxide (PEO). To achieve this goal we developed a method for grafting long PE chains from NPs with controlled graft density and molecular weight, giving us the ability to tailor their dispersion in the PE melt prior to crystallization. In this renewal proposal, we will develop the fundamental, quantitative understanding that will allow us to independently tailor polymer crystallization rate, NP diffusivity and NP agglomeration state in semicrystalline polymers so as to facilely control NP ordering and hence properties. A program that tightly integrates experiment and theory is proposed, and a key outcome of this research will be a three-dimensional design map for different regimes of NP organization (and hence properties) that can be achieved by polymer crystallization. A second independent outcome is the role of directional solidification and how it competes with the rates of polymer crystallization and NP mobility to affect the organization of the NP.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NpPO4F by Materials Project

NpPO4F crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Np4+ is bonded in a 6-coordinate geometry to six O2- and two equivalent F1- atoms. There are a spread of Np–O bond distances ranging from 2.23–2.65 Å. Both Np–F bond lengths are 2.29 Å. P5+ is bonded in a tetrahedral geometry to four O2- atoms. There is two shorter (1.53 Å) and two longer (1.57 Å) P–O bond length. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Np4+ and one P5+ atom. In the second O2- site, O2- is bonded in a 2-coordinate geometry to two equivalent Np4+ and one P5+ atom. In the third O2- site, O2- is bonded in a distorted bent 150 degrees geometry to one Np4+ and one P5+ atom. F1- is bonded in a distorted bent 150 degrees geometry to two equivalent Np4+ atoms.

36 MATERIALS SCIENCE↗