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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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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Isotope effect in formaldehyde steam reforming on Pt/m-ZrO 2 : Insight into chemical promotion by alkalis

Infrared spectroscopy, temperature programmed reaction mass spectrometry (TP-reaction/MS), and catalyst testing were used to investigate alkali promotion of dehydrogenation selectivity during formaldehyde steam reforming (FSR) on Pt/m-ZrO 2 . In a preferred pathway, formaldehyde reacts with water forming hydrogen and formate, followed by forward formate decomposition to CO 2 and H 2 . Alkali-doping of 2 wt% Pt/m-ZrO 2 increases catalyst basicity, which weakens the formate C-H bond promoting formate dehydrogenation / decarboxylation. Promotion by alkali in FSR was observed through a formate nu(CH) band shift to lower wavenumbers in infrared spectroscopy, and through a decrease in the normal isotope effect in switching from H-to D-labeled formalde-hyde in TP-reaction/MS.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Automated reactor physics analysis framework of High Flux Isotope Reactor low-enriched uranium silicide dispersion fuel designs

The High Flux Isotope Reactor (HFIR) is a versatile research reactor that provides one of the highest steady-state neutron fluxes of any reactor in the world. The HFIR reactor physics team investigated the conversion of the current 93 wt% highly enriched uranium U 3 O 8 -Al dispersion fuel to a 19.75% low-enriched uranium (LEU) U 3 Si 2 -Al dispersion fuel. The team continuously develops a Python module to streamline the analysis steps required for an LEU core design to ensure reproducible and agile design iteration. The Python module automates the data processing between analysis steps and automates the input perturbation for branch calculations and design changes. The automated framework has proven to significantly increase the efficiency and reproducibility of the reactor physics team to design High Flux Isotope Reactor (HFIR) LEU cores and thoroughly analyze performance metrics, safety metrics, and thermal safety margins. Consequently, the team can now respond rapidly to fuel fabrication engineer and thermal-hydraulic-structural analyst requests. Numerous combinations of LEU fuel designs are explored, of which two LEU fuel designs are presented here in this paper: a low density silicide design, and a high-density silicide design. Results show that both designs meet or exceed safety and performance metrics with exception for minor differences caused by the hardened spectrum from LEU.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2026

Absolute efficiency response of the γ-ray spectrometer GRETINA for high-energy γ rays up to 6 MeV

GRETINA (Gamma-Ray Energy Tracking In-beam Nuclear Array), a state-of-the-art γ-ray tracking spectrometer, has been instrumental in advancing nuclear structure studies, particularly in experiments using fast beams of rare isotopes where the γ rays emitted in flight are subject to large Doppler shifts. This work presents an experimental determination of the γ-ray detection efficiency of GRETINA at energies up to 6 MeV. The high-energy γ rays originated from states that were populated in nucleon-removal reactions from a projectile beam at an intermediate beam energy of about 85 MeV/nucleon. Utilizing γ-γ coincidences, efficiency values were extracted in-beam and translated into a source efficiency at rest employing GEANT4 Monte Carlo simulations. A systematic discrepancy in the efficiency of the forward-positioned detectors was identified which is attributed to specific dead-time effects caused by high-energy light-particle events prevalent at forward angles, generating signals in the Ge crystals that saturate the preamplifier’s first stage. Furthermore, this study provides refined efficiency benchmarks for in-beam experiments, improving the accuracy of quantitative γ-ray spectroscopy analyses with GRETINA and GRETA (Gamma Ray Energy Tracking Array) in the future.

GRETINA↗
DOE OSTI2022

High-Temperature Superconductivity in Hydrides: Experimental Evidence and Details

Abstract Since the discovery of superconductivity at ~ 200 K in H 3 S [1], similar or higher transition temperatures, T c s, have been reported for various hydrogen-rich compounds under ultra-high pressures [2]. Superconductivity was experimentally proved by different methods, including electrical resistance, magnetic susceptibility, optical infrared, and nuclear resonant scattering measurements. The crystal structures of superconducting phases were determined by X-ray diffraction. Numerous electrical transport measurements demonstrate the typical behavior of a conventional phonon-mediated superconductor: zero resistance below T c , shift of T c to lower temperatures under external magnetic fields, and pronounced isotope effect. Remarkably, the results are in good agreement with the theoretical predictions, which describe superconductivity in hydrides within the framework of the conventional BCS theory. However, despite this acknowledgement, experimental evidences for the superconducting state in these compounds have recently been treated with criticism [3–7], which apparently stems from misunderstanding and misinterpretation of complicated experiments performed under very high pressures. Here, we describe in greater detail the experiments revealing high-temperature superconductivity in hydrides under high pressures. We show that the arguments against superconductivity [3–7] can be either refuted or explained. The experiments on the high-temperature superconductivity in hydrides clearly contradict the theory of hole superconductivity [8] and eliminate it [3].

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Unraveling metabolism underpinning biomass composition shift in Scenedesmus obliquus under simulated outdoor conditions using 13 C-fluxomics

To render the resulting biomass more attractive and amenable for utilization as the basis for low-carbon intensity bioproducts, single-celled algae need to be biochemically and metabolically poised to assimilate and store the delivered carbon in the fastest and most efficient manner. Accelerating biochemical carbon storage, as primarily carbohydrates or lipids, is critical to achieve the high carbon capture potential that is assigned to algae. To guide strain optimization and engineering for maximizing carbon capture and storage, it is essential to elucidate the link between carbon metabolism and biomass composition. Most published metabolomics work in algae remains largely restricted to ideal and simplified environmental conditions in model organisms, thereby limiting their translation to outdoor implementation. In this work, we utilize 13 C isotopic labeling to characterize distinct intracellular metabolic fluxes before, during, and after nitrogen depletion-induced compositional shifts in Scenedesmus obliquus UTEX 393. The results indicate that a transition to carbohydrates is characterized by diverting flux to starch instead of replenishing the Calvin cycle for CO 2 fixation whereas the subsequent transition to lipids is fueled by NADPH produced by upregulating the phosphoenolpyruvate carboxylase (PEPC)–malic enzyme (ME) cycle flux. Our work highlights bottlenecks to carbohydrate- and lipid-rich biomass and can guide implementable strategies to control the fate of fixed carbon in S. obliquus.

09 BIOMASS FUELS↗
DOE OSTI2021

Proton decays in 16 Ne and 18 Mg and isospin-symmetry breaking in carbon isotopes and isotones

We report that proton-rich nuclei possess unique properties in the nuclear chart. Due to the presence of both continuum coupling and Coulomb interaction, phenomena such as halos, Thomas-Ehrman shift, and proton emissions can occur. Relevant experimental data are difficult to obtain, so that theoretical calculations are needed to understand nuclei at drip lines and to guide experimentalists. In particular, the 16 Ne and 18 Mg isotopes are supposed to be one-proton and/or two-proton emitting nuclei, but associated experimental data are either incomplete or even unavailable. Consequently, we performed Gamow shell model calculations of carbon isotones bearing A = 15 - 18 . Isospin-symmetry breaking occurring in carbon isotones and isotopes is also discussed. It is hereby shown that the mixed effects of continuum coupling and Coulomb interaction at drip lines generate complex patterns in isospin multiplets. Added to that, it is possible to determine the one-proton and two-proton widths of 16 Ne and 18 Mg . Obtained decay patterns are in agreement with those obtained in previous experimental and theoretical works. Moreover, to our knowledge, this is the first theoretical calculation of binding energy and partial decay widths of 18 Mg in a configuration interaction picture.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Phonon engineering of boron nitride via isotopic enrichment

Phonon polaritons (PhPs) enable a variety of applications, yet it requires PhPs supported in the desired frequency range. The two BN allotropes (cubic and hexagonal, cBN and hBN) are of particular interest, as their optic phonons fall within the so-called molecular-fingerprint region (~ 1000–1610 cm -1 ). However, there remains a spectral gap between PhPs covered by these two, limiting applications. Thus, we isotopically engineered hBN and cBN and examined the optic phonons. Furthermore, for hBN, enhancement of the optic phonon lifetimes and shifted frequencies are observed. However, lifetimes are observed to decrease with the enrichment of cBN by 10 B, 11 B, and 15 N. We propose that the reduced lifetimes are not due to intrinsic loss, but rather increased defect concentrations resulting from the modified growth, supported by first-principles calculations. Thus, reducing the extrinsic defects in isotopically engineered cBN may present a path toward overcoming these restrictions for applications in the molecular-fingerprint region.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Measurement and Theory of Gas-Phase Ion Mobility Shifts Resulting from Isotopomer Mass Distribution Changes

The unanticipated discovery of recent ultra-high-resolution ion mobility spectrometry (IMS) measurements revealing that isotopomers-compounds that differ only in the isotopic substitution sites-can be separated has raised questions as to the physical basis for their separation. A study comparing IMS separations for two isotopomer sets in conjunction with theory and simulations accounting for ion rotational effects provides the first-ever prediction of rotation-mediated shifts. The simulations produce observable mobility shifts due to differences in gas–ion collision frequency and translational-to-rotational energy transfer. These differences can be attributed to distinct changes in the moment of inertia and center of mass between isotopomers. The simulations are in broad agreement with the observed experiments and consistent with relative mobility differences between isotopomers. These results provide a basis for refining IMS theory and a new foundation to obtain additional structural insights through IMS.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Origin of 182 W Anomalies in Ocean Island Basalts

Ocean island basalts (OIB) show variable 182 W deficits that have been attributed to either early differentiation of the mantle or core-mantle interaction. However, 182 W variations may also reflect nucleosynthetic isotope heterogeneity inherited from Earth's building material, which would be evident from correlated 182 W and 183 W anomalies. Some datasets for OIB indeed show hints for such correlated variations, meaning that a nucleosynthetic origin of W isotope anomalies in OIB cannot be excluded. We report high-precision W isotope data for OIB from Samoa and Hawaii, which confirm previously reported 182 W deficits for these samples, but also demonstrate that none of these samples have resolvable 183 W anomalies. These data therefore rule out a nucleosynthetic origin of the 182 W deficits in OIB, which most likely reflect the entrainment of either core material or an overabundance of late-accreted materials within OIB mantle sources. If these processes occurred over Earth's history, they may have also been responsible for shifting the 182 W composition of the bulk mantle to its modern-day value. We also report Mo isotope data for some Hawaiian OIB, which reveal no resolved nucleosynthetic Mo isotopic anomalies. This is consistent with inheritance of 182 W deficits in OIB from the addition of either core or late-accreted material, but only if these materials have a non-carbonaceous (NC) meteorite-like heritage. As such, these data rule out significant contributions of carbonaceous chondrite (CC)-like materials to either Earth's core or late accretion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Grain Boundary-Limited Thermal Transport in Suspended Thin Graphite across an Unexplored Thickness Regime

Here, we present systematic thermal conductivity (κ) measurements of suspended thin graphite ribbons, 234–527 nm thick, using a four-probe 3ω method. Unlike recent reports of phonon hydrodynamics and exceptionally high κ in micrometer-thick graphite ( Science, 2020), we observe significantly lower κ and no signatures of collective phonon flow in this intermediate thickness regime. Instead, our measured κ lies between few-layer graphene and bulk graphite. These results agree with a first-principles-informed Peierls–Boltzmann transport model with spatially resolved Monte Carlo sampling. Additionally, the temperature for the peak κ shifts lower with increasing thickness, due to the interplay of phonon-boundary and phonon-isotope scattering. Incorporating grain boundary scattering into simulations is necessary to replicate the experimental trends. These findings delineate the boundary between ballistic, hydrodynamic, and diffusive transport regimes in graphite and underscore the dominant role of disorder and geometry in phonon transport in quasi-two-dimensional materials, offering insights for nanoscale thermal management.

Boltzmann transport model↗
DOE OSTI2020

The Brachiopod δ 11 B Record Across the Carboniferous-Permian Climate Transition

In this work, we present the δ 11 B of well-preserved brachiopod fossils coupled with geochemical modeling to examine how seawater boron responded to abrupt and dynamic climate changes in the Late Paleozoic. The Late Carboniferous, a time of major coal formation and glacioeustatic sea level changes, is characterized by relatively stable brachiopod δ11B of 15–17‰, similar to values seen in modern brachiopods. Brachiopod δ 11 B dropped by ~5‰ in the early Permian and then restabilized at a new value of 10‰ within a few million years. Mass balance models of seawater δ 11 B reproduced the overall trends in our brachiopod data but failed to capture the large drop in δ11B in the early Permian. Published seawater 87 Sr/ 86 Sr and δ 44 / 40 Ca data based on brachiopod shells also shift to lower values in the early Permian, suggesting a common control on all three seawater isotope systems. The Permian terrestrial record of evaporites and eolian deposits suggests a prolonged reduced delivery of dissolved weathering products to the ocean, accounting for the change in seawater 87 Sr/ 86 Sr. This reduced weathering, in turn, led to increased atmospheric CO 2 and lowered seawater pH, which may have significantly decreased major removal mechanisms for seawater calcium and boron leading to declines in both isotope systems. We propose that boron removal via coprecipitation in carbonates and adsorption onto clay minerals was significantly diminished due to a reduction in the availability of the borate aqueous species caused by lowered seawater pH.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2021

Technological aspects in blanket design: Effects of micro-alloying and thermo-mechanical treatments of EUROFER97 type steels after neutron irradiation

Presently available data on neutron irradiation damage raise doubts on the feasibility of using EUROFER97 steel for a water-cooled starter blanket in a DEMO reactor, since the ductile-to-brittle transition temperature (DBTT) increases significantly for irradiation temperatures below 350°C. The additional DBTT shift caused by H and He transmutation can only be estimated based on very few results with isotopically tailored EUROFER97 steel. Conservative calculations show that the DBTT of EUROFER97 steel could exceed the operating temperature in water-cooled starter blankets within a relatively short time period. This paper presents results from a EUROfusion funded irradiation campaign that was performed in the High Flux Isotope Reactor at Oak Ridge National Laboratory. The paper compares ten newly developed reduced activation ferritic-martensitic (RAFM) steels irradiated to a nominal dose of 2.5 dpa at 300°C. The post-irradiation experiments using Small Specimen Test Technology included hardness, tensile, and fracture mechanics tests combined with fractography and microstructure analysis are presented. Results show that micro-alloying EUROFER97-type steels influenced the mechanical properties but a dominating impact on irradiation damage resistance could not be identified. In contrast, specific thermo-mechanical treatments lead to better DBTT behavior. Discussion about irradiation response to heat treatment conditions is also given. Here, despite requiring data also at high dpa values, the results indicate that with these modified materials an increased lifetime and potentially also an increased operating temperature window can be achieved compared to EUROFER97.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Triaxiality of neutron-rich ruthenium nuclei studied by lifetime measurements

The breaking of axial symmetry in nuclei enables otherwise precluded behaviours, making it an interesting phenomenon to study. Experimental fingerprints such as very low-lying $2^+_2$ states suggest pronounced triaxial deformation for the neutron-rich ruthenium isotopes. Nevertheless, theoretical calculations differ in the description of the triaxial deformation and its evolution with neutron number, making experimental data crucial to understanding it. We investigated the evolution of the degree of triaxiality and $γ$ rigidity in neutron-rich ruthenium isotopes by measuring lifetimes of excited states in 108-112 Ru with the recoil distance Doppler-shift method. The experiment was carried out at the Grand Accélérateur National d’Ions Lourds using the Advanced Gamma Tracking Array coupled to the Variable Mode Spectrometer. We obtained B(E2) values for 29 transitions in the studied nuclei and compared them with fully microscopic symmetry conserving configuration mixing calculations, and phenomenological generalized triaxial rotor and triaxial particle-rotor models. The models generally reproduce the measured transition strengths, and show an increase in triaxiality with neutron number, reaching near maximum triaxiality in 112 Ru. The results are consistent with a transition from soft to rigid motion as the neutron number increases.

Heines, Johannes Sorby [Univ. of Oslo (Norway); No↗
DOE OSTI2026

Composition and persistence of soil organic matter along eroding and depositional transects in buried vs. modern soil layers: A case of the Brady paleosol at Wauneta, Nebraska

Paleosols form when soils are buried through deposition by aeolian, colluvial, alluvial or other processes. Burial of former topsoil isolates soil organic matter (SOM) from surface conditions, allowing carbon to accumulate and potentially remain stable for millennia. In this study, SOM composition, distribution, and persistence were analyzed in the Brady Soil of Nebraska, USA to compare SOM spatial variability in modern and buried soils, as well as the impact of erosional exposure on SOM stability. The Brady Soil, formed as a surface soil during the Pleistocene-Holocene transition and now a paleosol buried up to 6 m deep (or more) by loess deposition during the Holocene, was sampled along burial (up to 5.8 m depth) and erosional (up to 1.8 m depth) transects to compare SOM dynamics in different geomorphic settings. Fourier Transform Infrared Spectroscopy (FTIR) and Fourier Transform ion cyclotron resonance mass spectrometry (FTICR-MS) were used to analyze SOM composition, while δ 13 C isotope analyses identified SOM sources and radiocarbon values were used to estimate turnover rates. Results confirmed a vegetation shift from C3 to C4 plants after Brady Soil formation, reflecting warming climatic conditions. Increasing SOM age and decreasing δ 13 C and δ 15 N values with depth indicated slowing of decomposition rate in buried soils. Higher pH in the Brady Soil suggested greater base cation content, supporting SOM stabilization through organo-mineral associations and aggregate formation. However, exposure of the Brady Soil due to surface erosion caused faster SOM turnover. This result suggested susceptibility of buried SOM to losses via decomposition upon erosional exposure, possibly accelerated by priming in response to modern SOM inputs. These findings highlight the potential loss of carbon stocks in buried soils under future climate change, as shifts in soil physicochemical properties may destabilize long-preserved SOM.

Environmental sciences↗
DOE OSTI2023

New thermal decomposition pathway for TATB

Abstract Understanding the thermal decomposition behavior of TATB (1,3,5-triamino-2,4,6-trinitrobenzene) is a major focus in energetic materials research because of safety issues. Previous research and modelling efforts have suggested benzo-monofurazan condensation producing H 2 O is the initiating decomposition step. However, early evolving CO 2 (m/z 44) along with H 2 O (m/z 18) evolution have been observed by mass spectrometric monitoring of head-space gases in both constant heating rate and isothermal decomposition studies. The source of the CO 2 has not been explained, until now. With the recent successful synthesis of 13 C 6 -TATB ( 13 C incorporated into the benzene ring), the same experiments have been used to show the source of the CO 2 is the early breakdown of the TATB ring, not adventitious C from impurities and/or adsorbed CO 2 . A shift in mass m/z 44 (CO 2 ) to m/z 45 is observed throughout the decomposition process indicating the isotopically labeled 13 C ring breakdown occurs at the onset of thermal decomposition along with furazan formation. Partially labeled (N 18 O 2 ) 3 -TATB confirms at least some of the oxygen comes from the nitro-groups. This finding has a significant bearing on decomposition computational models for prediction of energy release and deflagration to detonation transitions, with respect to conditions which currently do not recognize this oxidation step.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Lifetime measurements in the even-even Cd 102 – 108 isotopes

The heaviest T z = 0 doubly-magic nucleus, Sn 100 , and the neighboring nuclei offer unique opportunities to investigate the properties of nuclear interaction. For instance, the structure of light-Sn nuclei has been shown to be affected by the delicate balance between nuclear-interaction components, such as pairing and quadrupole correlations. From Cd to Te, many common features and phenomena have been observed experimentally along the isotopic chains, leading to theoretical studies devoted to a more general and comprehensive study of the region. In this context, having only two proton holes in the Z = 50 shell, the Cd isotopes are expected to present properties similar to those found in the Sn isotopic chain. The aim of this work was to measure lifetimes of excited states in neutron-deficient nuclei in the vicinity of Sn 100 . Here, the neutron-deficient nuclei in the N ≈ Z ≈ 50 region were populated using a multinucleon transfer reaction with a Cd 106 beam and a Mo 92 target. The beamlike products were identified by the VAMOS + + spectrometer, while the γ rays were detected using the AGATA array. Lifetimes of excited states were determined using the recoil distance Doppler-shift method, employing the Cologne differential plunger. Lifetimes of low-lying states were measured in the even-mass Cd 102 – 108 isotopes. In particular, multiple states with excitation energy up to ≈ 3 MeV, belonging to various bands, were populated in Cd 106 via inelastic scattering. The transition strengths corresponding to the measured lifetimes were compared with those resulting from state-of-the-art beyond-mean-field calculations using the symmetry-conserving configuration-mixing approach. Conclusions: Despite the similarities in the electromagnetic properties of the low-lying states, there is a fundamental structural difference between the ground-state bands in the Z = 48 and Z = 50 isotopes. The comparison between experimental and theoretical results revealed a rotational character of the Cd nuclei, which have prolate-deformed ground states with β 2 ≈ 0.2 . At this deformation Z = 48 becomes a closed-shell configuration, which is favored with respect to the spherical one.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Investigating trends in actinide covalency and magnetism with 35/37 Cl SSNMR spectroscopy and first-principles calculations

Solid-state NMR (SSNMR) spectroscopy is a powerful technique for studying actinide chemistry but has been significantly limited due to the complex paramagnetism, and radiological hazards presented by these materials. Lanthanide and actinide salts often feature magnetic ordering and can be paramagnetic, ferromagnetic, or antiferromagnetic depending on temperature and electronic structure. Paramagnetic interactions can manifest in SSNMR both as secular spectral shifts and/or couplings as well as contributions from non-secular relaxation. Both effects can be directly measured with NMR and used to extrapolate rich chemical information such as coordination environments, bonding characteristics, local molecular dynamics, and correlation times. Typically, these studies are carried out on high-γ and highly abundant NMR-active isotopes (e.g., 1 H, 6/7 Li, 19 F, 23 Na, etc.) or on enriched rare isotopes (e.g., 2 H and 17 O), which can be expensive. Herein, we present a facile methodology to measure the 35/37 Cl electric-field gradient (EFG) and paramagnetic shift anisotropy (SA) tensor components using static wideline SSNMR measurements of LaCl 3 , NdCl 3 , UCl 3 , and UCl 4 . The static powder spectra were measured with both 35 Cl and 37 Cl SSNMR to increase the fidelity of the extracted tensor parameters. Variable temperature NMR of a select case confirms the Curie–Weiss paramagnetism. Relaxation measurements of both nuclei further corroborate observations owing to the paramagnetic relaxation enhancement and reveal simultaneous quadrupolar relaxation mechanisms. Density functional theory (DFT) calculations using Hubbard U corrections to the uranium valence orbitals show excellent agreement with experimental EFG tensor parameters and help describe the bonding characteristics in these lanthanide and actinide systems.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Fundamental 235 Uranium Nuclear Resonance Spectroscopy (End of Year Report)

Uranium-235 is ubiquitous in the nuclear industry however, detailed characterization by magnetic resonance spectroscopy has remained largely elusive to-date. Conventional nuclear magnetic resonance techniques are ill-suited for characterizing 235 U due to the small gyromagnetic ratio and extremely large quadrupole moment of this spin$^{7}$ /2 isotope. Thus, we have designed and built a high-frequency nuclear quadrupole resonance spectrometer for measuring the quadrupole resonance of this important isotope. A successful nuclear quadrupole resonance measurement of 235 U would be a significant accomplishment and could yield valuable physical parameters such as chemical shifts, local electric field gradients, and through-bond and through-space internuclear couplings, all of which are directly related to local structure. These terms can be used to understand structural details of poorly characterized uranium materials and can improve computational models of uranium for which accurate reference data is lacking

07 ISOTOPE AND RADIATION SOURCES↗