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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Indirect measurement of the 90 Sr ⁢(𝑛, 𝛾)⁢ 91 Sr reaction cross section and the implications for astrophysical Zr production

Here, the intermediate neutron-capture process (𝑖 process) has gained notable traction within the past decade as a way to describe stellar abundance observations which cannot be explained by the slow and rapid neutron-capture processes. Despite the general success of 𝑖-process models, many open questions remain. Among the observations, Zr stands out, as its elemental abundance is difficult to replicate with available 𝑖-process models, while the reactions that affect its production through the 𝑖 process are close enough to stability to study experimentally. Here, we present the experimental constraint of the nuclear level density and 𝛾-strength function (𝛾 SF) of 91 Sr using the 𝛽-Oslo method, which were then input into the TALYS Hauser-Feshbach code to produce the first experimental constraint of the 90 Sr ⁢(𝑛, 𝛾)⁢ 91 Sr capture reaction. This constraint was used alongside that of 92 Sr ⁢(𝑛, 𝛾)⁢ 93 Sr for a reduction in the uncertainty of [Y/Zr] production in the 𝑖-process relevant environmental neutron density of 10 13.5 and 10 14.5 neutrons/cm 3 .

Physics - Nuclear physics and radiation physics↗
NASA NTRS2013

Oxygen Isotope Measurements of a Rare Murchison Type A CAI and Its Rim

Ca-, Al-rich inclusions (CAIs) from CV chondrites commonly show oxygen isotope heterogeneity among different mineral phases within individual inclusions reflecting the complex history of CAIs in both the solar nebula and/or parent bodies. The degree of isotopic exchange is typically mineral-specific, yielding O-16-rich spinel, hibonite and pyroxene and O-16-depleted melilite and anorthite. Recent work demonstrated large and systematic variations in oxygen isotope composition within the margin and Wark-Lovering rim of an Allende Type A CAI. These variations suggest that some CV CAIs formed from several oxygen reservoirs and may reflect transport between distinct regions of the solar nebula or varying gas composition near the proto-Sun. Oxygen isotope compositions of CAIs from other, less-altered chondrites show less intra-CAI variability and 16O-rich compositions. The record of intra-CAI oxygen isotope variability in CM chondrites, which commonly show evidence for low-temperature aqueous alteration, is less clear, in part because the most common CAIs found in CM chondrites are mineralogically simple (hibonite +/- spinel or spinel +/- pyroxene) and are composed of minerals less susceptible to O-isotopic exchange. No measurements of the oxygen isotope compositions of rims on CAIs in CM chondrites have been reported. Here, we present oxygen isotope data from a rare, Type A CAI from the Murchison meteorite, MUM-1. The data were collected from melilite, hibonite, perovskite and spinel in a traverse into the interior of the CAI and from pyroxene, melilite, anorthite, and spinel in the Wark-Lovering rim. Our objectives were to (1) document any evidence for intra-CAI oxygen isotope variability; (2) determine the isotopic composition of the rim minerals and compare their composition(s) to the CAI interior; and (3) compare the MUM-1 data to oxygen isotope zoning profiles measured from CAIs in other chondrites.

Matzel, J. E. P.↗
DOE OSTI2025

Highly charged ion approach to measure nuclear charge radii of Fr, Ra, and Rn isotopes for precision measurements

Conventional electron scattering and muonic atom spectroscopy techniques are challenging to apply to heavy ions unless the element has at least one stable or extremely long-lived isotope. To overcome this limitation, a recently introduced method for determining nuclear charge radii relies on extreme-ultraviolet (EUV) spectroscopy of the D 1 line in highly charged Na-like ions. In this work, we present an experimental approach to measure the nuclear charge radii of isotopes of radioactive elements such as Fr, Ra, and Rn using this method at TRIUMF’s Ion Trap for Atomic and Nuclear Science (TITAN) instrument, located at the ISAC radioactive beam facility. We also explore the potential of using Na-like D 2 lines in the soft x-ray region for future measurements.

Electron beam ion trap↗
DOE OSTI2025

Spectral line-shape in collinear laser spectroscopy after atomic charge exchange

Collinear laser spectroscopy experiments on fast, neutral beams have been extensively used for studies on short-lived radioactive nuclei, taking advantage of its high sensitivity. The resulting resonance line-shape is known to show significant distortion, due to the energy exchange during the charge-exchange neutralization process, which can cause large systematic uncertainty in the determined centroid. A model for the line shape was constructed and simulated to be compared to measured Al, Si, and Ni hyperfine spectra. It is shown that the distortion is caused mainly by the transfer of electron into many different energy levels in the projectile atom and subsequent decays, rather than secondary inelastic collisions, which were often assumed in the line shape analysis before. Furthermore, the model can also be applied to other projectile–alkali pairs, providing a reliable line-shape with less fitting parameters than conventional phenomenological models.

Atom↗
DOE OSTI2026

The nucleardatapy toolkit for simple access to experimental nuclear data, astrophysical observations, and theoretical predictions

Systematic comparisons across theoretical predictions for the properties of dense matter, nuclear physics data, and astrophysical observations (also called meta-analyses) are performed. Existing predictions for symmetric nuclear and neutron matter properties are considered, and they are shown in this paper as an illustration of the present knowledge. Asymmetric matter is constructed assuming the isospin asymmetry quadratic approximation. It is employed to predict the pressure at twice saturation energy-density based only on nuclear-physics constraints, and we find it compatible with the one from the gravitational-wave community. To make our meta-analysis transparent, updated in the future, and to publicly share our results, the Python toolkit nucleardatapy is described and released here. Hence, this paper accompanies nucleardatapy, which simplifies access to nuclear-physics data, including theoretical calculations, experimental measurements, and astrophysical observations. This Python toolkit is designed to easily provide data for: (i) predictions for uniform matter (from microscopic or phenomenological approaches); (ii) correlation among nuclear properties induced by experimental and theoretical constraints; (iii) measurements for finite nuclei (nuclear chart, charge radii, neutron skins or nuclear incompressibilities, etc.) and hypernuclei (single particle energies); and (iv) astrophysical observations. This toolkit provides data in a unified format for easy comparison and provides new meta-analysis tools. It will be continuously developed, and we expect contributions from the community in our endeavor.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Probing the limits of statistical neutron capture for the r process: Experimental constraints on 141 Cs nuclear level densities

The r-process abundance peaks, particularly near mass number A ∼ 130, reflect underlying nuclear structure effects such as closed neutron shells, yet modeling the nucleosynthesis in this region remains hindered by uncertain neutron-capture rates. These rates are especially sensitive to nuclear level densities (NLDs) and γ-ray strength functions of neutron-rich nuclei, where experimental data are scarce. We present the first experimental constraint on the NLD of 141 Cs using the β-Oslo method, extending sensitivity to the neutron-rich regime near the N = 82 closed shell. Our data allow for critical calibration of microscopic NLD models and reveal that 141 Cs lies near the limit of statistical model applicability. Using this experimental input, we evaluate radiative neutron-capture rates across neighboring isotones using both Hauser–Feshbach (HF) and High Fidelity Resonance (HFR) models. Our results show order-of-magnitude rate increases for nuclei along the N = 86 line, signaling a transition to resonance-dominated capture in this region. These findings underscore the importance of constraining NLDs to improve r-process reaction network predictions, particularly in environments where the validity of statistical models breaks down.

Nuclear level density↗
NASA NTRS1977

Exposure histories of lunar rocks 71135 and 71569

Rare-gas isotopic analyses have been performed on lunar rocks 71135 and 71569. The conventional (Kr-81)-Kr cosmic-ray exposure ages are 103 + or - 3 m.y. for 71135 and 134 + or - 7 m.y. for 71569. An approach is outlined to deducing complex exposure histories from rare-gas data using depth profiles of the production rates of the cosmogenic rare-gas isotopes. Examination of the Xe isotopes by means of a 'concordia' plot suggests that 71569 may have a simple one-stage exposure history whereas 71135 has a more complex history. An attempt is made to construct exposure models for these two rocks which account for the abundances of all the cosmogenic rare gases, the Xe isotopic compositions, and the apparent (Kr-81)-Kr exposure ages. This study demonstrates the depreciation of (Kr-81)-Kr ages for rocks exposed at shallow depths, caused by the relatively rapid variation of the Kr-81 production as the rock is eroded. Possible implications of the tentative results for the formation age of the Central Cluster unit are discussed.

Niemeyer, S.↗
DOE OSTI2024

Role of the likelihood for elastic scattering uncertainty quantification

In the last decade, uncertainty quantification (UQ) for optical model potentials (OMPs) has become a focal point for nuclear reaction theory, and several competing approaches for OMP UQ have recently been developed. Here, we clarify recent efforts to compare frequentist and Bayesian approaches in the context of OMP UQ [G. B. King et al., Phys. Rev. Lett. 122, 232502 (2019)]. We replicate a portion of that OMP UQ study but use independent statistical tools. Specifically, we compare two methods for OMP parameter inference from elastic scattering data: the Levenberg-Marquardt algorithm for χ 2 minimization on one hand and Markov chain Monte Carlo (MCMC) sampling on the other. Separately, we assess the common practice of using a renormalized likelihood (χ 2 /N), N being the number of data points, instead of the canonical weighted-least-squares likelihood (χ 2 ), as a way of accounting for unknown data correlations. Here, we show that for a generic linear model and for a five-parameter OMP analysis, frequentist and uniform-prior Bayesian approaches recover the same optimum and uncertainty estimates—not systematically larger uncertainties for the Bayesian approach, as was concluded in G. B. King et al., Phys. Rev. Lett. 122, 232502 (2019). Further, we show that if an additional, near-degenerate parameter is introduced into the same OMP analysis such that the parameter posterior becomes non-Gaussian, then covariance-based estimates of uncertainty become unreliable. Finally, we show that regardless of optimization approach, if χ 2 /N is used for the likelihood, the resulting parametric uncertainties increase by $\sqrt{N}$, and that this is responsible for the conclusions drawn in the revisited study. Based on our replication results, we find that a fortuitous cancellation of unreported errors and the renormalization factor can lead to improvement in empirical coverages, as was the case in the original comparative study. We emphasize that developing and applying a realistic likelihood function is an essential task in a UQ analysis, and that several recent UQ studies that employed a renormalized likelihood (i.e., including a 1/N factor) may have yielded unrealistically large uncertainties for elastic-scattering observables. If the parameter posterior deviates from multivariate-normal, a sampling-based approach like MCMC has a clear advantage over methods that assume the Laplace approximation holds. We note that empirical coverage can serve as an important internal check for the analyst whose model or data may have additional, unaccounted-for uncertainties.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Determination of nuclear charge radius by extreme-ultraviolet spectroscopy of Na-like ions

We report on a method for determining the absolute nuclear charge radius of high-𝑍 elements using extreme-ultraviolet spectroscopy of highly charged Na-like ions in tandem with highly accurate atomic structure calculations of transition energy differences. The application of this method has reduced the nuclear charge radius uncertainty of 191 Ir by a factor of 8 from the currently accepted literature value, with a recently reported charge radius of 5.435(12) fm. The result reduces the charge radius uncertainty along the full Ir isotopic chain when combined with prior optical isotope shift measurements. The technique utilizes only a few million ions stored in an ion trap, which should apply to measurements with small quantities of radioactive nuclei.

Atom & ion trapping & guiding↗
DOE OSTI2025

High-precision Penning trap mass measurements of neutron-rich chlorine isotopes at the 𝑁 = 28 shell closure

Although it is known that the N = 28 spherical shell closure erodes, the strength of the closure with decreasing proton number Z < 20 is an open question in nuclear structure. Here, in this region of interest, high-precision mass measurements of neutron-rich 43-45 Cl isotopes were performed at the Low Energy Beam and Ion Trap (LEBIT) when coupled to the National Superconducting Cyclotron Lab. The resulting mass excesses (MEs) are ME(⁴³Cl) = -24114.4(1.7) keV, ME(⁴⁴Cl) = -20450.8(10.6) keV, and ME(⁴⁵Cl) = -18240.1(3.7) keV, and improve the uncertainty of these masses by up to a factor of ∼40 compared to the previous values reported in the 2020 Atomic Mass Evaluation. Comparison to ab initio calculations using the Valence-Space In-Medium Similarity Renormalization Group (VS-IMSRG) shows good agreement up to and including the closure.

Erington, H. [Michigan State Univ., East Lansing, ↗
DOE OSTI2022

RAPID UNSEPARATED RARE EARTH ELEMENT ANALYSES BY ISOTOPE DILUTION MULTICOLLECTOR INDUCTIVELY COUPLED MASS SPECTROMETRY (ID-MC-ICP-MS)

We present a method for analyzing rare earth elements (REEs) by isotope dilution without separation of individual elements. Utilizing a Nu Plasma 2 multicollector inductively coupled plasma mass spectrometer (MC-ICP-MS) equipped with an Aridus II desolvation nebulizer, sample introduction tuning parameters (torch position, gas flows) were investigated and used to minimize oxide formation (e.g., NdO/Nd <0.05%) and remove the need to analyze the REEs as separated “cuts.” Ratios for spike/sample isotopes in mixed synthetic standards containing varying amounts of Ce, Nd, Sm, Eu, Gd, Dy, Er, and Yb were measured accurately within 1% of IUPAC values. La and Lu in the standards were more than 2% off from expected values due to more demanding interference corrections. A USGS BCR-2 rock standard was also processed with flux fusion, iron coprecipitation and a single column pass bulk separation followed by analysis. The concentrations for Ce, Nd, Sm, Eu, Dy, Er, and Yb fell within 2% of consensus values. A United States Geological Survey (USGS) BIR-1A rock standard was also processed in triplicate by hydrofluoric and nitric acid digestion, yielding rare earth concentrations within 3% of consensus values with 0.3% relative standard deviation (n=3). This demonstrates the ability to produce high quality REE patterns of comparable quality to traditional methods involving labor and time intensive REE separation, with sample preparation and analytical times that are comparable to analyses against isotope dilution by single-collector ICP-MS.

Shen, Steve D.↗
DOE OSTI2025

Deformation and Collectivity in Doubly Magic 208 Pb

Lead-208 is the heaviest known doubly magic nucleus and its structure is therefore of special interest. Despite this magicity, which acts to provide a strong restorative force toward sphericity, it is known to exhibit both strong octupole correlations and some of the strongest quadrupole collectivity observed in doubly magic systems. In this Letter, we employ state-of-the-art experimental equipment to conclusively demonstrate, through four Coulomb-excitation measurements, the presence of a large, negative, spectroscopic quadrupole moment for both the vibrational octupole 3$^{−}_{1}$ and quadrupole 2$^{+}_{1}$ state, indicative of a preference for prolate deformation of the states. The observed quadrupole moment is discussed in the context of the expected splitting of the 3 − ⊗3 − two-phonon states, due to the coupling of the quadrupole and octupole motion. These results are compared with theoretical values from three different methods, which are unable to reproduce both the sign and magnitude of this deformation. Thus, in spite of its well-studied nature, 208 Pb remains a puzzle for our understanding of nuclear structure.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Dipole Strength Distribution of 8 He and Decay Characteristics

The weak binding and spatially extended neutron densities characteristic of drip-line nuclei give rise to a distinctive low-energy dipole response. The drip-line nucleus 8 He is the most neutron-rich bound nucleus with a mass-to-charge ratio of 𝐴/𝑍 = 4. We measure the dipole response of 8 He, including for the first time the four-neutron decay channel. A total dipole strength of ∑𝐵⁡(𝐸⁢1)(𝐸*< 15 MeV) = 0.95⁢(16)⁢𝑒 2 fm 2 and a dipole polarizability of 𝛼 𝐷 = 0.61⁢(1) fm 3 are extracted from the differential Coulomb-excitation cross section and compared to state-of-the-art theoretical calculations employing coupled cluster and three-body approaches. We find that the dipole continuum is dominated, even at high excitation energies well above the 4⁢𝑛 decay threshold, by two-neutron emission, pointing to a 6 He + 2⁢𝑛 structure of the excited dipole mode. No indication was found for a 4⁢𝑛 final-state correlation, while pronounced 𝑛⁢𝑛 and 6 He−𝑛 final-state correlations are apparent.

Lehr, C. [Technical University of Darmstadt (Germa↗
DOE OSTI2024

Evolution of shell gaps in the neutron-poor calcium region from invariant-mass spectroscopy of 37,38 Sc, 35 Ca, 34 K

A fast secondary beam of 37 Ca impinged on a 9 Be target resulting in a set of reactions populating proton-rich nuclei including 35 Ca and the first observations of 37,38 Sc and 34 K. Invariant-mass spectroscopy, used to reconstruct proton decays for these nuclei, yielded three new ground-state masses and information on their low-lying structures. The newly measured mass excesses are: ΔM( 37 Sc) = 3500(410) keV, ΔM( 38 Sc) = –4656(14) keV, and ΔM( 34 K) = –1487(17) keV. These nuclei straddle the well-known Z = 20 shell closure as well as the N = 16 subshell closure. Furthermore, trends in separation energies help elucidate how nuclear structure evolves showing a fading of the Z = 20 shell gap for N ≥ 18 and indications of a N = 16 subshell gap.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1971

Isotopic studies in returned lunar samples

Analysis of lunar soil samples returned by Apollo 11 and 12 flights are discussed. Isotopic studies of the rare gases from Apollo 11 flight lunar samples are presented. The lunar soil analyses indicated the following: (1) high concentrations of solar wind rare gases, (2) isotopic match between solar wind gases and gas components in gas-rich meteorites, and (3) rare gases attributable to spallation reactions induced in heavier nuclides by cosmic ray particles.

Alexander, E. C., Jr.↗