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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Beta-Delayed Neutron Emission of 𝑁=84 132Cd

Using the time-of-flight technique, we measured the beta-delayed neutron emission of 132 Cd . From our large-scale shell model (LSSM) calculation using the N3⁢LO interaction [, Phys. Rev. Lett. 131, 022501 (2023)], we suggest the decay is dominated by the transformation of a neutron in the 𝑔7/2 orbital, deep below the Fermi surface, into a proton in the 𝑔9/2 orbital. We compare the beta-decay half-lives and neutron branching ratios of nuclei with 𝑍<50 and 𝑁 ≥82 obtained with our LSSM with those of leading “global” models such as finite-range droplet model (FRDM). Our calculations match known half-lives and neutron branching ratios well and suggest that current leading models overestimate the yet-to-be-measured half-lives. Our model, backed by the 132 Cd decay data presented here, offers robust predictive power for nuclei of astrophysical interest such as 𝑟-process waiting points.

Madurga, M [Department of Physics and Astronomy, U↗
DOE OSTI2025

Deviations from the Isobaric Multiplet Mass Equation due to Threshold States

Recent studies have completed the A=16 isospin quintets for states with J π =0 + and 2 + . The dependence of their masses as a function of isospin projection shows evidence for deviations from quadratic behavior indicating isospin violation beyond the expectation from two-body forces. The deviation is most pronounced for the 2 + states. Predictions from the shell model embedded in the continuum (SMEC) allow us to explain that this isospin violation is associated with a modification of the nuclear structure due to the open-quantum-system nature of the proton-rich members of the quintet. In particular, the 0 + and 2 + states in 16 Ne and the 2 + state in 16 F are threshold resonances located just above a proton-decay threshold where s-wave coupling to the continuum is expected. The measured deviations of these threshold states from the quadratic behavior of the remaining members of the multiplets makes it possible to obtain information on the magnitude and the energy dependence of the continuum-coupling energy correction. Finally, continuum coupling is also indicated for the ground state of 8 C, but this time through p-wave coupling

coulomb energies & analogue states↗
DOE OSTI2024

Lifetimes of excited states in $^{16}$C as a benchmark for ab initio developments

Lifetimes of higher-lying states ($2_2^+$ and $4_1^+$) in 16 C have been measured, employing the Gammasphere and Microball detector arrays, as key observables to test and refine ab initio calculations based on interactions developed within chiral Effective Field Theory. The presented experimental constraints to these lifetimes of $\tau ({2_2^+}) = [244, 446]\,~\textrm{fs}$ and $\tau ({4_1^+}) = [1.8, 4]\,~\textrm{ps}$, combined with previous results on the lifetime of the $2_1^+$ state of 16 C, provide a rather complete set of key observables to benchmark the theoretical developments. We present No-Core Shell-Model calculations using state-of-the-art chiral 2- (NN) and 3-nucleon (3N) interactions at next-to-next-to-next-to-leading order for both the NN and the 3N contributions and a generalized natural-orbital basis (instead of the conventional harmonic-oscillator single-particle basis) which reproduce, for the first time, the experimental findings remarkably well. The level of agreement of the new calculations as compared to the CD-Bonn meson-exchange NN interaction is notable and presents a critical benchmark for theory.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Short-range correlations in nuclei

Atomic nuclei are held together by the strong nuclear force acting between protons and neutrons (nucleons). While the long range, averaged part of this force is well described by the nuclear shell model, the short-range and tensor components create a fascinating substructure: pairs of nucleons that momentarily approach each other very closely, acquiring large relative momenta. These short-range correlated (SRC) pairs account for roughly 20% of all nucleons in any nucleus and almost all of the high momentum nucleons. This chapter provides an introduction to SRC pairs: their origin in the nucleon-nucleon tensor force, the experimental methods used to study them, principally deep inelastic and quasielastic electron and proton scattering, and the comprehensive picture that has emerged over the past three decades.

FOS: Physical sciences↗
DOE OSTI2026

Structural and physicochemical insights into pH-responsive poly(DEAEMA- co -HEMA)-grafted mesoporous silica nanoparticles

Mesoporous silica nanoparticles (SiO 2 ) grafted with responsive polymer shells are versatile hybrid systems. Understanding their three-dimensional organization in the hydrated state remains a significant challenge. Here, in this study, SiO 2 nanoparticles were functionalized with a poly(DEAEMA-co-HEMA) shell via a “grafting-from” polymerization strategy in aqueous media. Successful surface modification was confirmed by FTIR, thermogravimetric analysis, transmission electron microscopy, X-ray photoelectron spectroscopy, N 2 sorption, and ζ-potential, yielding grafting contents of 22% (p1 DEAEMA-co-HEMA ) and 49% (p2 DEAEMA-co-HEMA ). Small-angle neutron scattering (SANS) with solvent contrast variation was employed to elucidate the solution-state core–shell architecture of p1 and p2 hybrids at pH 2, where the grafted polymer shell is protonated and highly hydrated. Near contrast matching of the silica core, theoretically estimated at 58% D 2 O, suppressed the scattering intensity, enhancing sensitivity to the polymer shell. Constrained core–shell ellipsoid modeling across solvent contrasts revealed a systematic increase in shell thickness, overall particle dimensions, and shell anisotropy with increasing grafting content. In solution, the hydrated polymer shells were markedly more extended and structurally anisotropic than suggested by dry-state techniques structural characterization, highlighting the importance of solution-state structural analysis for accurately describing grafted polymer architectures.

Core-shell biomaterials↗
DOE OSTI2026

Production of Heavy α -Elements and 44 Ti in Cas A: Comparison to Abundances from 1D Core-collapse Supernova Models and Evidence for Carbon–Oxygen Shell Mergers

The merger between the carbon (C) and oxygen (O) shells hours to days before the collapse of a massive star significantly changes its nucleosynthesis, which is reflected in the elemental ratios observed in supernova remnants (SNRs). We present a nucleosynthesis study of 44 Ti production in core-collapse supernovae (CCSNe), highlighting large silicon (Si), sulfur (S), calcium (Ca), and, most importantly, argon (Ar) to neon (Ne) ratios as diagnostics for carbon–oxygen (C–O) shell mergers. We compare yields from eight different sets of CCSNe models to observations of Cassiopeia A (Cas A), and show that C–O shell mergers are consistently the models that best match X-ray and infrared observations. These models produce high Ar/Ne ratios (≳0.1), due to 20 Ne depletion and production of 36 Ar and 38 Ar, while lower ratios are obtained from nonmerger cases. Based on the Ar/Ne diagnostic, we compare the range of expected 44 Ti produced by C–O shell mergers, which is up to ∼20%–30% of the overall 44 Ti, but expected to be located outside the reverse shock. Based on the sets of models considered, the photon flux expected from the 44 Ti synthesized in the C–O shell merger in Cas A is below the NuSTAR and COSI detection limits, compatible with current limits locating most of the 44 Ti interior to the reverse shock, but might be detectable from proposed missions like ASCENT. Finally, for the SNR of 1987A, a dominant C–O merger origin of the observed 44 Ti is unlikely based on the observed redshift in its 44 Ti line.

79 ASTRONOMY AND ASTROPHYSICS↗
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↗
DOE OSTI2024

Simplified projection on total spin zero for state preparation on quantum computers

Here, we introduce a simple algorithm for projecting on J = 0 states of a many-body system by performing a series of rotations to remove states with angular momentum projections greater than zero. Existing methods rely on unitary evolution with the two-body operator J 2 , which when expressed in the computational basis contains many complicated Pauli strings requiring Trotterization and leading to very deep quantum circuits. Our approach performs the necessary projections using the one-body operators J x and J z . By leveraging the method of Cartan decomposition, the unitary transformations that perform the projection can be parametrized as a product of a small number of two-qubit rotations, with angles determined by an efficient classical optimization. Given the reduced complexity in terms of gates, this approach can be used to prepare approximate ground states of even-even nuclei by projecting onto the J = 0 component of deformed Hartree-Fock states. We estimate the resource requirements in terms of the universal gate set {H,S, CNOT ,T} and briefly discuss a variant of the algorithm that projects onto J = 1/2 states of a system with an odd number of fermions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Extraction of the non-spin- and spin-transfer isovector responses via the 12 C ⁡( 10 Be, 10 B + 𝛾)⁢ 12 B reaction

The isovector response in 12 B was investigated via the 12 C ⁡( 10 Be, 10 B + 𝛾)⁢ 12 B* reaction at 100⁢𝐴MeV. By utilizing the 𝛾-decay properties of the 1.74 MeV 0 + and 0.718 MeV 1 + states in 10 B, the separate extraction of the non-spin-transfer (Δ⁢𝑆 = 0) and spin-transfer (Δ⁢𝑆 = 1) isovector responses up to an excitation energy of 50 MeV in 12 B in a single measurement is demonstrated. The experimental setup employed the S800 spectrometer to detect and analyze the 10 B ejectiles and the Gamma-Ray Energy Tracking In-beam Nuclear Array (GRETINA) for obtaining the Doppler-reconstructed spectrum for 𝛾 rays emitted in flight by 10 B. A 12 C foil was placed at the pivot point of the spectrograph. Here, the 12 B reaction product was not detected. Contributions from transitions associated with the transfer of different units of angular momentum in the non-spin- and spin-transfer responses were analyzed using a multipole decomposition analysis. The extracted non-spin-dipole (Δ⁢𝑆 = 0, Δ⁢𝐿 = 1) and spin-dipole (Δ⁢𝑆 = 1, Δ⁢𝐿 = 1) responses were found to be consistent with available data from other charge-exchange probes, validating the non-spin- and spin-transfer filters used. While statistical uncertainties and experimental resolutions were relatively large due to the modest intensity of the 10 Be secondary beam, the results show that, with the much higher intensities that will be available at new rare-isotope beam facilities, the ( 10 Be, 10 B + 𝛾) reaction and its Δ⁢𝑇 𝑧 = −1 partner, the ( 10 C, 10 B + 𝛾) reaction, are powerful tools for elucidating the isovector non-spin- and spin-transfer responses in nuclei.

Charge-exchange reactions↗
DOE OSTI2026

Robust Automatic EXAFS First-Shell Fits

Extended X-ray absorption fine structure (EXAFS) is a widely used technique for atomic structure determination. Fourier transformation connects EXAFS in k space and R space. However, determining the appropriate k-range for the transformation can be challenging, but critical for the first-shell fit. In this study, we present an automatic method to determine the k-range using the Larch package and a Python program. The first step is to estimate spectral noise across a series of k-ranges with a fixed minimum value and identify the optimal maximum value in the k-range (k max ). The k max is determined by an empirical noise threshold that marks the point where the noise level in the Fourier transformed spectrum changes dramatically. Using the obtained k max value, the first shell is modeled to determine the minimum k value (k min ) by optimizing the background function through alignment of the spectrum with theory. The optimal k min corresponds to the point of the minimum R-factor, which quantifies the difference between the experimental and fitted spectrum. Our method was tested on various typical datasets and yielded suitable k-ranges for Fourier transformation and accurate first-shell fits. This approach helps avoid unreliable, irreproducible data analysis, especially for noisy data from diluted samples, and enables robust automatic first-shell EXAFS fitting.

EXAFS analysis↗
DOE OSTI2024

Distilling the Essential Elements of Nuclear Binding via Neural-Network Quantum States

To distill the essential elements of nuclear binding, we seek the simplest Hamiltonian capable of modeling atomic nuclei with percent-level accuracy. A critical aspect of this endeavor consists of accurately solving the quantum many-body problem without incurring an exponential computing cost with the number of nucleons. Furthermore, we address this challenge by leveraging a variational Monte Carlo method based on a highly expressive neural-network quantum state ansatz. In addition to computing binding energies and charge radii of nuclei with up to 𝐴 = 20 nucleons, by evaluating their magnetic moments, we demonstrate that neural-network quantum states are able to correctly capture the self-emerging nuclear shell structure. To this end, we introduce a novel computational protocol based on adding an external magnetic field to the nuclear Hamiltonian, which allows the neural network to learn the preferred polarization of the nucleus within the given magnetic field.

Binding energy & masses↗
DOE OSTI2024

In-medium similarity renormalization group with flowing 3-body operators, and approximations thereof

Here, we explore the impact of retaining three-body operators within the in-medium similarity renormalization group (IMSRG), as well as various approximations schemes. After studying two toy problems, identical fermions with a contact interaction and the Lipkin-Meshkov-Glick model, we employ the valence-space formulation of the IMSRG to investigate the even- A carbon isotopes with a chiral two-body potential. We find that retaining only those commutators expressions that scale as N 7 provides an excellent approximation of the full three-body treatment.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Quenching of single-particle strength inferred from nucleon-removal transfer reactions on 15 C

The difference in the proton and neutron separation energies (ΔS) of the weakly bound 15 C ground state is -19.86 MeV, an extreme value. Data from intermediate-energy heavy-ion induced (HI-induced) knockout reactions on nuclei spanning -20 ≲ ΔS ≲ +20 MeV, suggest that the degree to which single-particle strength is quenched, R s , has a negative correlation with ΔS, decreasing from unity around -20 MeV to around 0.2 at +20 MeV. For the 15 C ground state (R s = 0.96 (4) in HI-induced knockout), contrasting results have recently been obtained via the neutron-adding transfer reaction, which reveal a value of R s = 0.64 (15), similar to the value observed at modest and more extreme values of ΔS with reaction probes other than HI knockout. In order to explore the any potential differences between adding and removing processes in transfer reactions at extreme ΔS, single-neutron removal transfer reactions on 15 C were performed at 7.1 MeV/u in inverse kinematics. The removal of a valence neutron in 2s 1/2 orbit using both (p, d) and (d, t) reactions shows consistent quenching factors and agrees with those from the neutron-adding reaction. The present results, which can be compared with neutron knockout reaction, suggest that correlations, represented by the quenching factor, show limited dependence on neutron-proton asymmetry under the most extreme asymmetry conditions so far achieved in transfer reactions.

quenching factor↗
DOE OSTI2026

In-beam 𝛾-ray spectroscopy of 29 S populated in direct knockout, dissipative reactions, and fragmentation

Excited states in the neutron-deficient nucleus 29 S were populated in one-neutron knockout and several-nucleon removal reactions and studied using in-beam 𝛾-ray spectroscopy. New excited states and 𝛾-ray transitions were established using the Segmented Germanium Array SeGA and the 𝛾-ray tracking array GRETINA. The new transitions observed in the highly dissipative tail of the parallel momentum distribution from one-nucleon knockout and in five- and nine-nucleon removal reactions were utilized to calculate mirror energy differences with 29 Al . Highly dissipative reactions further prove to be a valuable tool in populating excited states typically inaccessible in direct reactions. The relative populations of the states in 29 S from the several-nucleon removal reactions were found to be consistent, suggesting for the first time that five-nucleon removal behaves predominately like statistical fragmentation.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Robust ab initio predictions for dimensionless ratios of 𝐸⁢2 and radius observables. I. Electric quadrupole moments and deformation

We report that converged results for 𝐸⁢2 observables are notoriously challenging to obtain in ab initio no-core configuration interaction approaches. Matrix elements of the 𝐸⁢2 operator are sensitive to the large-distance tails of the nuclear wave function, which converge slowly in an oscillator basis expansion. Similar convergence challenges beset ab initio prediction of the nuclear charge radius. However, we exploit systematic correlations between the calculated 𝐸⁢2 and radius observables to yield meaningful predictions for relations among these observables. In particular, we examine ab initio predictions for dimensionless ratios of the form 𝑄/𝑟 2 for nuclei throughout the 𝑝 shell. Meaningful predictions for electric quadrupole moments may then be made by calibrating to the ground-state charge radius, if experimentally known, or vice versa. Moreover, these dimensionless ratios provide ab initio insight into the nuclear quadrupole deformation.

ab initio calculations↗
DOE OSTI2026

𝑙-forbidden 𝑀⁢1 strengths near 100 Sn from knockout reactions in Cd and Sn

Neutron knockout reactions on beams of 104,102 Cd and 104 Sn are presented. States in the residual 103,101 Cd and 103 Sn nuclei are populated, including low-lying 7/2 + states of 𝜈⁢𝑔 7/2 character. These states have half-lives ≈ 400 ps due to their low energy and hindered 𝐵⁡(𝑀⁢1;7/2 + →5/2 + ) strengths. The excited-state half-lives were measured using their Doppler-shifted line shapes, and the resulting 𝐵⁡(𝑀⁢1) strengths are compared to valence space in medium similarity renormalization group (VS-IMSRG) calculations. Lastly, the VS-IMSRG calculations underpredict the 𝑙-forbidden 𝑀⁢1 strengths in the 100 Sn region, as well as in other regions of the nuclear chart near 40 Ca and 208 Pb.

90 ≤ A ≤ 149↗
DOE OSTI2025

Robust ab initio predictions for dimensionless ratios of 𝐸⁢2 and radius observables. II. Estimation of 𝐸⁢2 transition strengths by calibration to the charge radius

Converged results for 𝐸⁢2 observables are notoriously challenging to obtain in ab initio no-core configuration interaction approaches. Matrix elements of the 𝐸⁢2 operator are sensitive to the large-distance tails of the nuclear wave function, which converge slowly in an oscillator basis expansion. Similar convergence challenges beset ab initio prediction of the nuclear charge radius. However, we exploit systematic correlations between the calculated 𝐸⁢2 and radius observables to yield meaningful predictions for relations among these observables. In particular, we examine ab initio predictions for dimensionless ratios of the form 𝐵⁡(𝐸⁢2)/(𝑒 2 ⁢𝑟 4 ) for nuclei throughout the 𝑝 shell. Finally, meaningful predictions for 𝐸⁢2 transition strengths may then be made by calibrating to the ground-state charge radius if experimentally known.

ab initio calculations↗