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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 OSTI2026

Unveiling the electronic structure and chemical bonding of the deprotonated cisplatin anion [(NH 3 )(NH 2 )PtCl 2 ] − via low-temperature photoelectron spectroscopy and theoretical calculations

The dehydrogenated cisplatin anion, [(NH 3 )(NH 2 )PtCl 2 ] − , was investigated via low-temperature photoelectron spectroscopy and theoretical calculations. Seven and four spectral peaks are respectively resolved at 193 and 266 nm, yielding rich electronic structure information for both the anion and neutral. From the threshold and maximum of the lowest electron binding energy band, the experimental adiabatic (ADE) and vertical detachment energies (VDE) are determined to be 3.3 ± 0.1 and 3.525 ± 0.025 eV, respectively. Theoretical calculations indicate the dominant isomer adopting a cis-geometry, in which the platinum center is coplanar with two chlorine and two nitrogen ligands. The calculated VDE of 3.54 eV based on this structure agrees well with the experimental value. Charge analyses reveal that the excess electron in the anion is primarily localized on the Pt and Cl atoms. A suite of theoretical analysis tools was employed to elucidate the bonding characteristics and interaction strength between Pt and its ligands.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Theoretical Calculation Study of Nanomaterials

In recent years, theoretical simulations using computational physics and chemistry models have been used widely to predict the physical, chemical, and structural properties of nanomaterials. To reflect such rapid progress, two Special Issues on the theoretical study of nanomaterials were published. The 36 articles collected cover broad re-search fields and applications. In this Editorial, we provide an overview of these pub-lications and summarize the main findings. Based on these research outcomes, we lay out some future research directions.

First-principles calculations↗
DOE OSTI2025

Experimental determination of the magnetic anisotropy in five-coordinated Co( II ) field-induced single molecule magnets

Magnetic anisotropy of the central metal atom is a crucial property of single molecule magnets (SMMs). Small structural changes can alter the magnetic properties, and accurate experimental methods to investigate magnetic anisotropy are therefore critical. Here, we investigate two five-coordinated Co( II ) SMMs, [CoCl 2 Cltpy] (1) and [CoBr 2 Cltpy] (2) (Cltpy = 4′-chloro-2,2′:6′,2′′-terpyridine), through multiple techniques. Ab initio theoretical calculations performed on the two compounds show that both possess axial magnetic anisotropy with the magnetic easy axis pointing towards one of the terminal halogen atoms. Theoretical calculations on SMMs are typically done on isolated molecular species, and to validate this approximation the magnetic anisotropy was further studied through experimental techniques. EPR measurements confirm an axial anisotropy of 1, and magnetic measurements provide experimental Zero-Field Splitting (ZFS) parameters, showing that the values from theoretical calculations are slightly overestimated. The X-ray electron density determined from 20 K single-crystal synchrotron X-ray diffraction data provides estimated d-orbital populations also suggesting axial magnetic anisotropy in both systems, and furthermore suggesting a more pronounced axiality in 1 compared to 2. This is in good agreement with the results obtained from both magnetic measurements and theoretical calculations. The magnetic anisotropy of 1 is quantified experimentally through polarized powder neutron diffraction via the site susceptibility method, confirming an axial magnetic anisotropy of the compound. A slight deviation in the easy axis direction is observed between experimental and theoretical results. This, together with the overestimation of the ZFS parameters from theoretical calculations, shows that experimental investigation of the magnetic anisotropy of SMMs is of high relevance. Magnetic anisotropy of the central metal atom is a crucial property of single molecule magnets (SMMs).

Slavensky, Hannah H. [Aarhus Univ. (Denmark)] (ORC↗
DOE OSTI2026

Collapse of Nuclear Collectivity along the 𝑁 = 𝑍 Line

The lifetime of the 𝐽 𝜋 = 2 + state in the self-conjugate 88 Ru nucleus has been determined in an experiment performed using rare-isotope beams provided by the new Facility for Rare Isotope Beams. This is the heaviest 𝑁 = 𝑍 nucleus for which such a measurement has been achieved. 88 Ru was populated by both one-neutron knockout and charge-exchange reactions, and the lifetime of 14.3$^{+2.5}_{−3.4}$ ps was determined using the triple-foil plunger technique. The extracted electromagnetic transition strength shows that the quadrupole collectivity has dropped significantly compared with the highly deformed 𝑁 = 𝑍 region around 𝐴 ∼ 80. These results are compared with state-of-the-art large-scale shell-model and discrete nonorthogonal shell-model calculations. The theoretical calculations indicate a moderate triaxial deformation and suggest that low-lying states in this nucleus are no longer dominated by strong many-particle many-hole excitations, unlike the lighter, highly deformed 𝑁 = 𝑍 nuclei nearby.

59 ≤ A ≤ 89↗
DOE OSTI2025

Measurements of Gamow-Teller transitions from 59 Co via the 59 Co ⁢(𝑡, 3 He +𝛾) charge-exchange reaction and its application to the stellar electron-capture rates

Electron-capture reactions on iron-group nuclei play a crucial role in the late stages of massive star evolution. Since stellar evolution simulations depend on accurate electron-capture rates—which are highly sensitive to the detailed Gamow-Teller (GT) strength distributions—reliable theoretical models are essential. However, experimental data on GT strength distributions are scarce. High-resolution measurements are therefore vital for benchmarking and improving these theoretical calculations. To provide high-resolution data on Gamow-Teller strength distributions of iron-group nuclei and to compare these results with theoretical calculations within this mass region. Differential cross sections for the 59 Co ⁢(𝑡, 3 He)⁢ 59 Fe charge-exchange reaction at 115 MeV/u were measured using the S800 spectrometer. Furthermore, to resolve individual levels that are not distinguishable in the S800 particle singles data, coincident 𝛾 rays from the 59 Fe residual nucleus were detected by using the Gamma-Ray Energy Tracking In-beam Nuclear Array 𝛾-ray tracking array. Here, the Gamow-Teller transition strength distribution from the ground state of 59 Co to 59 Fe was extracted up to an excitation energy of 10 MeV. Additionally, transition strengths for several low-lying states were determined from coincident 𝛾-ray measurements. Electron-capture rates calculated using the present data indicate that these low-lying states contribute significantly to the overall rates in relevant stellar environments. The experimental results show reasonable agreement with theoretical predictions based on both shell-model and projected shell-model calculations. High-resolution data on Gamow-Teller strength distributions—particularly for individual low-lying states—are essential for accurately determining electron-capture rates in iron-group nuclei. Coincident 𝛾-ray measurements provide a powerful tool for obtaining such detailed information. While the present work demonstrates that shell-model calculations successfully reproduce the experimental results, such comparisons are scarce and more experimental data are desirable.

59 ≤ A ≤ 89↗
DOE OSTI2025

Measurement of ω meson production in pp collisions at $\sqrt{s}$ = 13 TeV

The p T -differential cross section of ω meson production in pp collisions at $\sqrt{s}$ =13 TeV at midrapidity (|y| < 0.5) was measured with the ALICE detector at the LHC, covering an unprecedented transverse-momentum range of 1.6 < p T < 50 GeV/c. The meson is reconstructed via the ω → π + π − π 0 decay channel. The results are compared with various theoretical calculations: PYTHIA8.2 with the Monash 2013 tune overestimates the data by up to 50%, whereas good agreement is observed with Next-to-Leading Order (NLO) calculations incorporating ω fragmentation using a broken SU(3) model. The ω/π 0 ratio is presented and compared with theoretical calculations and the available measurements at lower collision energies. The presented data triples the p T ranges of previously available measurements. A constant ratio of C ω/π0 = 0.578 ± 0.006 (stat.) ± 0.013 (syst.) is found above a transverse momentum of 4 GeV/c, which is in agreement with previous findings at lower collision energies within the systematic and statistical uncertainties.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2025

Electronic structure of a nodal line semimetal candidate TbSbTe

The 𝐿⁢𝑛⁢SbTe (𝐿⁢𝑛 = Lanthanides) family, like isostructural ZrSiS-type compounds, has emerged as a fertile playground for exploring the interaction of electronic correlations and magnetic ordering with the nodal line band topology. Here, we report on a detailed electronic band structure investigation of TbSbTe, corroborated by electrical transport, thermodynamic, and magnetic studies. Temperature-dependent magnetic susceptibility and thermodynamic transport studies indicate the onset of antiferromagnetic ordering below 𝑇 𝑁 ∼ 5.8K. The electronic band structure study, carried out with high-resolution angle-resolved photoemission spectroscopy measurements aided with density functional theory–based first-principles calculations reveal presence of a nonsymmorphic symmetry-protected Dirac crossing in the Γ-X high-symmetry (HS) direction, which is part of a nodal line along the X-R HS direction. Another Dirac crossing occurs along the Γ-X direction at a relatively higher binding energy, which occurs from $\tilde{𝒞}$ 2⁢𝜈⁢ 𝒫 symmetry which is gapped in the theoretical calculations with the effect of spin-orbit coupling considered. Parallel to this direction, our theoretical calculations and experimental results exhibit strongly momentum-dependent surface bands. In this study, we open an avenue to further uncover the intricate interplay among symmetry-protected topological band structure, spin-orbit coupling, and magnetism in this material and the 𝐿⁢𝑛⁢SbTe family, in general.

Angle-resolved photoemission spectroscopy↗
DOE OSTI2025

Spectroscopic Investigation into P(NDI2OD-T2) Charge Localization

P(NDI2OD-T2), commonly referred to as N2200, stands out as a promising electron-transporting (n-type) polymer for low-cost, flexible (photo)electrochemical applications due to its reversible two-electron reduction and high electron mobility. UV–vis spectroelectrochemistry in the tetrabutyl ammonium hexafluorophosphate/acetonitrile electrolyte shows two sets of chemically reversible redox signals in the cyclic voltammetry corresponding to the reduction of the neutral polymer film to polaronic and bipolaronic species. These electrochemical signatures suggest a distinct electronic reorganization upon reduction (polaron/bipolaron formation), highlighting the need for molecular-level insights into how charges are accommodated within the polymer backbone. While it has been previously hypothesized that charge predominantly localizes on the naphthalene diimide (NDI) unit during reductive charging, specific changes in atomic environments that confirm this localization have not been characterized in n-type polymers. Herein, we use near-edge X-ray absorption fine structure (NEXAFS) spectroscopy to probe electronic transitions in an electrochemically charged polymer to deduce charge localization. The O K-edge (1s) spectra exhibit two distinct π* peaks; the intensity of the lower-energy π* a peak that corresponds to an excitation to a largely localized carbonyl state decreases with reductive potentials relative to the higher-energy π* b peak. We corroborate this with Raman spectroscopy at different potentials, which shows a decrease in intensity on the C–C/C═C and C═O stretching bands of NDI as well as a red shift of the carbonyl band due to the formation of a polaron on the NDI. Additionally, new Raman active NDI signals associated with elongated C═O and C═C bonds are observed at lower energy during the formation of charged states. Together with theoretical calculations, these findings show that the injected charge spatially localizes on the NDI units and is dominantly distributed on the carbonyl groups. In conclusion, the combination of NEXAFS, optical and vibrational spectroscopies, and theoretical calculations is generalizable to other pi-conjugated polymers and can identify charge localization for the further development of organic semiconductors.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Using data-science approaches to unravel insights for enhanced transport of lithium ions in single-ion conducting polymer electrolyte

Solid polymer electrolytes have yet to achieve the an ionic conductivity > 1 mS/cm at room temperature for realistic applications. This target implies the need to reduce the effective energy barriers of ion transport in polymer electrolytes to around 20 kJ/mol. In this work, we combine information extracted from existing experimental results with theoretical calculations to provide insights into ion transport in single-ion conductors (SICs) with a focus on lithium ion SICs. Through the analysis of temperature-dependent ionic conductivity data obtained from the literature, we evaluate different methods of extracting energy barriers for lithium transport. The traditional Arrhenius fit to the temperature-dependent ionic conductivity data indicates that the Meyer-Neldel rule holds for SICs. However, the values of the fitting parameters remain unphysical. Our modified approach based on recent work (Macromolecules, 56, 15, 6051(2023)), which incorporates a fixed pre-exponential factor, reveals that the energy barriers exhibit temperature dependence over a wide range of temperatures. Using this approach, we identify a series of anions leading to the energy barriers less than 30 kJ/mol, which include trifluoromethane sulfonimide (TFSI), fluoromethane sulfonimide (FSI), and boron-based organic anions. In our efforts to design the next generation of anions, which can exhibit the energy barriers less than 20 kJ/mol, we focused on boron-containing SICs, and performed density functional theory (DFT) based calculations to connect the chemical structures via the binding energy of cation (lithium)-anion pairs with the experimentally derived effective energy barriers for ion transport. Not only have we identified a correlation between the binding energy and the energy barriers, but we also propose a strategy to design new boron-based anions by using the correlation. This combined approach involving experiments and theoretical calculations is capable of facilitating the identification of promising new anions, which can exhibit ionic conductivity $> 1$ mS/cm near room temperature, thereby expediting the development of novel superionic single-ion conducting polymer electrolytes. The published datasets include all the temperature-dependent ionic conductivity collected from the literature with literature DOIs, DFT calculated binding energies, and python scripts to analyze data, construct statistical models, and generate plots.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Total absorption spectroscopy for the 𝛽 + decay strength distribution of 60 Ga

𝛽-decay properties play an important role in most astrophysical processes. In the absence of experimental data, astrophysical models rely on global theoretical calculations to provide the relevant properties. It is therefore important to provide strong experimental constraints when possible. In the case of 𝛽-decay, the most sensitive probe is the 𝛽-decay strength distribution. We report here on the first measurement of the latter quantity for the 𝛽 + decay of 60 Ga using the total absorption spectroscopy technique. The experimental results are compared to theoretical calculations often used in astrophysical models, namely the shell model and the quasiparticle random phase approximation (QRPA), as well as an extension of QRPA that includes higher-order nucleonic calculations. Both models are in reasonable agreement with the experimental results.

59 ≤ A ≤ 89↗
DOE OSTI2024

Using Data-Science Approaches to Unravel Insights for Enhanced Transport of Lithium Ions in Single-Ion Conducting Polymer Electrolytes

Solid polymer electrolytes have yet to achieve the desired ionic conductivity (>1 mS/cm) near room temperature required for many applications. This target implies the need to reduce the effective energy barriers for ion transport in polymer electrolytes to around 20 kJ/mol. In this work, we combine information extracted from existing experimental results with theoretical calculations to provide insights into ion transport in single-ion conductors (SICs) with a focus on lithium ion SICs. Through the analysis of temperature-dependent ionic conductivity data obtained from the literature, we evaluate different methods of extracting energy barriers for lithium transport. The traditional Arrhenius fit to the temperature-dependent ionic conductivity data indicates that the Meyer–Neldel rule holds for SICs. However, the values of the fitting parameters remain unphysical. Our modified approach based on recent work (Macromolecules 2023, 56, 15, 6051), which incorporates a fixed pre-exponential factor, reveals that the energy barriers exhibit temperature dependence over a wide range of temperatures. Using this approach, we identify anions leading to the energy barriers <30 kJ/mol, which include trifluoromethane sulfonimide (TFSI), fluoromethane sulfonimide (FSI), and boron-based organic anions. In our efforts to design the next generation of anions, which can exhibit the energy barriers <20 kJ/mol, we have performed density functional theory (DFT) based calculations to connect the chemical structures of boron-based anions via the binding energy of cation (lithium)-anion pairs with the experimentally derived effective energy barriers for ion hopping. Not only have we identified a correlation between the binding energy and the energy barriers, but we also propose a strategy to design new boron-based anions by using the correlation. This combined approach involving experiments and theoretical calculations is capable of facilitating the identification of promising new anions, which can exhibit ionic conductivity >1 mS/cm near room temperature, thereby expediting the development of novel superionic single-ion conducting polymer electrolytes.

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

Biomass-Derived Carbon and Their Composites for Supercapacitor Applications: Sources, Functions, and Mechanisms

Biomass-derived carbons are eco-friendly and sustainable materials, making them ideal for supercapacitors due to their high surface area, excellent conductivity, cost-effectiveness, and environmental benefits. This review provides valuable insights into biomass-derived carbon and modified carbon for supercapacitors, integrating both experimental results and theoretical calculations. This review begins by discussing the origins of biomass-derived carbon in supercapacitors, including plant-based, food waste-derived, animal-origin, and microorganism-generated sources. Then, this review presents strategies to improve the performance of biomass-derived carbon in supercapacitors, including heteroatom doping, surface functionalization, and hybrid composite construction. Furthermore, this review analyzes the functions of biomass-derived carbon in supercapacitors both in its pure form and as modified materials. The review also explores composites derived from biomass-based carbon, including carbon/MXenes, carbon/MOFs, carbon/graphene, carbon/conductive polymers, carbon/transition metal oxides, and carbon/hydroxides, providing a thorough investigation. Most importantly, this review offers an innovative summary and analysis of the role of biomass-derived carbon in supercapacitors through theoretical calculations, concentrating on four key aspects: energy band structure, density of states, electron cloud density, and adsorption energy. Finally, the review concludes the future research directions for biomass carbon-based supercapacitors, including the discovery of novel biomass materials, tailoring surface functional groups, fabricating high-performance composite materials, exploring ion transfer mechanisms, and enhancing practical applications. In summary, this review offers a thorough exploration of the sources, functions, and mechanisms of biomass-derived carbon in supercapacitors, providing valuable insights for future research.

biomass-derived carbon↗
DOE OSTI2025

Nitrate-To-Ammonia Electroconversion at Neutral pH on Polycrystalline Vanadium Sulfide Derived from Vanadium Disulfide

The electrochemical nitrate reduction reaction (NO3RR) offers a pathway to produce NH3 for fuel and fertilizer from waste NO3-. In this work, a polycrystalline vanadium sulfide (VSx), which is derived from solvothermally grown and annealed VS2, is shown to exhibit excellent NO3RR activity (2.3 +- 0.6 mg.cm-2 geo..h-1 @ -0.92 VRHE) and Faradaic efficiency to NH4+ (69 +- 6% at -0.69 VRHE) in buffered neutral pH electrolyte containing 0.1 M NO3-. A variety of characterization techniques are leveraged to support the VSx assignment, including X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, selected area electron diffraction, and X-ray diffraction measurements. The VS2 annealing step reduces the oxide character and generates VSx, which, based on the improved NO3RR activity, results in the creation of active sites for NO3- binding. To help shed light on NO3RR on VSx, VS2 is used as a model system, and a grand-canonical density functional theory (GC-DFT) investigation of VS2 shows strong evidence that S vacancies are active sites for NO3RR, where NO3- outcompetes H+ for adsorption at the S-vacancy sites. Moreover, GC-DFT results highlight a thermodynamically favorable reaction to generate NH4+ in an aqueous electrolyte at relevant cathodic potentials. As an annealed material, VSx may contain undersaturated V sites, which show an electronic structure similar to the theoretically calculated S-vacancy site of VS2, and these sites may contribute to the observed increase in NO3RR activity and selectivity for NH4+ on VSx versus unannealed VS2. Finally, kinetic isotope effect measurements suggest that the kinetic rate-limiting step of the NO3RR on VSx is not proton-coupled, indicating it may be the first electron transfer to adsorbed NO3*.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Resonance plasmonic coupling: selective enhancement of band edge emission over trap state emission of CdSe quantum dots

The photoluminescence properties of quantum dots (QDs) are often enhanced by eliminating surface trap states through chemical methods. Alternatively, a physical approach is presented here for improving photoluminescence purity in QDs by employing frequency-specific plasmon resonance coupling. Emitter-bound plasmonic hybrids are designed by electrostatically binding negatively charged QDs in water to positively charged gold nanoparticles having a thin polymer coating. Herein, two types of QDs are used: (i) bare CdSe, which exhibits both band edge and trap state emission, and (ii) CdSe overcoated with a ZnS shell (CdSe/ZnS) devoid of trap state emission. Tuning the extinction spectrum of the plasmonic system to match the band edge emission of CdSe enables the selective enhancement of band edge emission over trap state emission. Excellent match in the extinction spectrum of the gold nanoparticle with both, experimentally calculated photoluminescence enhancement factor and theoretically calculated radiative rate enhancement signifies the role of frequency-specific plasmon resonance coupling. Plasmon-coupled photoluminescence of CdSe/ZnS is further investigated by varying the number density of emitter on the surface of plasmonic nanoparticle. An enhancement in the photoluminescence is observed at a lower emitter density of CdSe/ZnS and the photoluminescence enhancement factor closely follows the plasmon resonance. However, photoluminescence quenching occurs with an increase in CdSe/ZnS due to plasmon-assisted nonradiative energy transfer between nearby QDs, as indicated by a red shift in the PL maximum. These studies establish that resonance plasmonic coupling is a convenient physical strategy for tuning the intrinsic photoluminescence properties of QDs for various optoelectronic applications.

Paul, Livin↗
DOE OSTI2026

Comparison of theory with the experimental characterization of the spatial frequency response of interferometers using a binary pseudo-random array sample

Experimental evaluations of the surface height response of an interference microscope using a binary pseudo-random array test sample are compared with a theory based on a Fourier optics model. Measurements of key instrument characteristics, including the illumination, imaging, and obscuring apertures of three different Mirau objectives, support the theoretical calculations. Agreement between experimental and theoretical modeling confirms the predictability of the spatial frequency response for the purpose of specification and optimization of instrument configuration for specific metrology tasks. The results also provide confidence in methods of compensating for the decrease in instrument response with spatial frequency.

Calibration↗
DOE OSTI2024

A RELAP5-3D Model of the Lobo Lead Loop

The goal of our research is to build upon the capability of RELAP5-3D to model molten lead systems. Molten lead has several potential uses in future advanced reactors like the lead fast reactor or fusion reactors that utilize dual-coolant lead lithium blankets. This potential for use in future generations of reactors highlights the necessity to develop molten lead models to ensure that they can accurately predict the thermohydraulic behavior. We have developed a RELAP5-3D model of the Lobo Lead Loop facility, located at the University of New Mexico, to verify the accuracy of RELAP5-3D via comparison to existing computational fluid dynamics results and analytical calculations. It was found that RELAP5-3D accurately calculated radiative heat transfer (within < 1%) when compared to theoretical calculations. In addition, pressure drop calculations done in RELAP5-3D demonstrated reasonable agreement within 20 kPa, mostly within ~7-15%, when compared to the computational fluid dynamics model of the facility developed by the University of New Mexico, and captured the dependence of pressure drop on flow velocity accurately. Finally, a hypothetical loss of flow transient was imposed on the RELAP5-3D model to determine the feasibility of performing a similar experiment with the Lobo Lead Loop. It was found that such an experiment could be possible as the RELAP5-3D model indicated that the temperatures of the fluid would not exceed limiting temperatures of the structure (1658 K) nor the maximum temperature of the electromagnetic pump inlet (823 K). Although there is not experimental data to begin validation, the model will be readily available for future validation studies when the experimental data is generated, especially as the model continues to evolve over time. Furthermore, the results so far demonstrate a promising first step in the verification/validation of the RELAP5-3D model of the Lobo Lead Loop.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2025

Exploring Nontrivial Topological Superconductivity in 2M-WS2 for Topological Quantum Computation

This project has two main research goals: (1) growing the high-quality two-dimensional (2D) 2M-pahse WS 2 (2M-WS 2 ) single crystals and identifying clear signatures of the unconventional superconductivity in the 2M-WS 2 ; and (2) establishing the layer-dependence of the Majorana zero mode in the 2M-WS 2 down to the monoatomic layer limit. These goals were planned to be achieved by growing high-quality and large-scale 2M-WS 2 single crystals and transferring their thin layers onto different substrates for the proposed measurements. The layer-dependent unconventional superconductivity in 2M-WS 2 were systematically studied by different techniques, including transport measurements (charge, thermal and spin), scanning tunneling microscopy and spectroscopy (STM/S), angle-resolved photoemission spectroscopy (ARPES), and theoretical calculations. The research team is comprised of researchers from University of Wyoming (UW) and three DOE National Laboratories (DOE NLs), including Argonne National Laboratory (ANL), Lawrence Berkeley National Laboratory (LBNL) and Sandia National Laboratories (SNL), with complete and complementary expertise: PI Tian: Handling 2D materials, nanofabrication, nanodevices, and quantum transport; Co-Is: Ackerman and Leonard: van der Waals material crystal growth and handling; Chien: Nanoimaging with STM/S; and Tang: Magnetic measurements and charge and thermal transport; National lab collaborators (NLs): Guisinger (ANL): STM/S and nanoimaging; Mo and Rotenberg (LBNL): ARPES and nano ARPES (nARPES); Lu (SNL): Quantum information science, quantum transport, and nanofabrication; and Baczewski (SNL): Theoretical modeling and calculations.

36 MATERIALS SCIENCE↗
DOE OSTI2025

First experimental determination of the ⁴⁰Ar(𝑛, 2𝑛)³⁹Ar reaction cross section and ³⁹Ar production in Earth’s atmosphere

The cosmogenic ³⁹Ar(t1∕2 = 268 years) isotope of argon is used for geophysical dating and tracing of underground and ocean water, as well as ice owing to its appropriate half-life and chemical inertness as a noble gas; ³⁹Ar serves also in nuclear weapon test monitoring. We measured for the first time the total cross section of the main ³⁹Ar cosmogenic production reaction in the atmosphere, namely ⁴⁰Ar(𝑛, 2𝑛)39 Ar, using 14.8 ± 0.3 MeV neutrons. The neutrons, produced by a deuterium-tritium generator, impinged on a stainless steel sphere filled with Ar gas highly enriched in the ⁴⁰Ar isotope and were monitored by a stack of fast-neutron activation foils. The reaction yield was measured by atom counting of long-lived ³⁹Ar with noble gas accelerator mass spectrometry and, independently, by decay counting relative to atmospheric argon (³⁹Ar/Ar= 8.12 × 10−16 ). A total ⁴⁰Ar(𝑛, 2𝑛)39 Ar cross section of 610 ± 100 mb was determined at 14.8 ± 0.3 MeV incident neutron energy. This result serves as a benchmark for recent theoretical calculations and evaluations, found to reproduce well the experimental total cross section. We use these energy-dependent theoretical cross sections together with experimental spectra of cosmogenic neutrons at different altitudes to calculate the global average rate of neutron-induced ³⁹Ar atmospheric production, resulting in 770 ± 240 39 Ar atoms/cm²/day. The secular equilibrium between the ³⁹Ar calculated production rate and radioactive decay rate leads to a partial isotopic abundance ³⁹Ar/Ar = (5.9 ± 1.8) × 10−16 , showing that ≈73% of atmospheric ³⁹Ar is produced by cosmogenic neutrons, the remaining part believed to be induced by muons and high-energy 𝛾 rays. The ⁴⁰Ar(𝑛, 2𝑛)³⁹Ar cross section at 14 MeV is also a key parameter for quantifying the anthropogenic contribution to atmospheric 39 Ar produced during the thermonuclear tests of the 1960s. We estimate that anthropogenic ³⁹Ar accounts for roughly 20% of the present atmospheric inventory.

39 Ar atmospheric production↗