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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Remeasurement of the 239 Pu(n,f)/ 235 U(n,f) Cross-Section Ratio with the NIFFTE fission Time Projection Chamber Using Vapor-deposited Targets

The NIFFTE fission Time Projection Chamber (fissionTPC) has been used to measure the 239 Pu(n,f)/ 235 U(n,f) cross-section ratio for neutron-induced fission in the range of 0.1–100 MeV, with high precision. A white neutron source was provided by the Los Alamos Neutron Science Center, where the experiment was conducted as a remeasurement to evaluate a roughly 2% discrepancy of the previous fissionTPC results with ENDF/B-VIII.0. Further, a detailed accounting of measurement uncertainties was performed, based on the fissionTPC's novel ability to provide three-dimensional reconstruction of fission-fragment ionization profiles. Current results obtained using a vapor-deposited, highly uniform 239 Pu target, in comparison to the measurement published in 2021, where a 239 Pu electroplated target was used, are presented and discussed. The remeasurement presented here is in agreement with the previous fissionTPC result within measurement uncertainties.

235U↗
DOE OSTI2020

Mass-asymmetric fission of 205,207,209 Bi at energies close to the fission barrier using proton bombardment of 204,206,208 Pb

Background: Recent observation of mass-asymmetric fission in neutron-deficient Hg and Pt nuclei has reignited interest in fission fragment mass distributions close to Pb. Investigations at energies close to the fission barrier, where mass-asymmetric fission is expected to be most obvious and the sensitivity to shell effects is maximized, are limited in this mass region. Purpose: To measure fission mass distributions for 205,207,209 Bi nuclei at the lowest possible excitation energies to determine how the mass distributions change with excitation energy and the neutron number of the compound nucleus. Method: Proton beams bombarding targets of 204,206,208 Pb were used to study the fission of 205,207,209 Bi at energies from just above to 10 MeV above their fission barriers. Fission fragments were measured using the CUBE fission spectrometer. Fission fragment mass distributions were determined using a newly developed time difference analysis method. Mass distributions were characterized by triple-Gaussian fits to determine the systematic trends across each isotope with excitation energy. Results: Measured mass distributions of all three Bi isotopes exhibit a component of mass-asymmetric fission at all energies studied. The probability of mass-asymmetric fission decreases significantly with increasing excitation energy, from ≈70 to ≈40% over a 10-MeV range. Comparisons between the three Bi isotopes hint at an increase in the mass-symmetric fission yield with increasing neutron number, which could be due to a decrease in the difference between the symmetric and asymmetric fission barriers. The centroids of the mass-asymmetric peaks suggest that several deformed shell gaps in the fission fragments could be contributing to the presence of the mass-asymmetric fission mode with Z light ≃ 38, Z heavy ≃ 45, and N light ≃ 56 all present in the fission fragments. Conclusions: Measurements of fission mass distributions at the lowest possible excitation energies above the fission barrier provide an excellent platform to investigate the origins of the mass-asymmetric fission mode. Finally, further systematic measurements at these energies offer an opportunity to rigorously test new models of fission in this mass region.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Spin inhibition in γ -decay probabilities for states above S n in Sm and Dy nuclei

When a compound nucleus is formed at an excitation energy above the neutron-separation threshold, it is assumed that its de-excitation will proceed via neutron emission. However, if the excited nucleus is in a high-spin state, but does not have enough excitation energy to conserve angular momentum by either photon emission after neutron emission or relative angular momentum carried off by the neutron, the nucleus will de-excite via γ -emission instead. This effect, the spin inhibition, provides an insight into the structure of the compound nuclei and can aid the understanding of the distribution of the populated spin states in a compound nuclear reaction. In this work, the effects of spin inhibition on the γ-decay probabilities from states in 146,147Sm and 160Dy are presented. For high-spin states above the Sn, spin inhibition is able to suppress neutron emission, and de-excitation via γ -ray emission is observed for states up to 3 MeV above the Sn .

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Quantum simulations of nuclear resonances with variational methods

Background: The many-body nature of nuclear physics problems poses significant computational challenges. These challenges become even more pronounced when studying the resonance states of nuclear systems, which are governed by the non-Hermitian Hamiltonian. Quantum computing, particularly for quantum many-body systems, offers a promising alternative, especially within the constraints of current noisy intermediate-scale quantum (NISQ) devices. Purpose: This work aims to simulate nuclear resonances using quantum algorithms by developing a variational framework compatible with non-Hermitian Hamiltonians and implementing it fully on a quantum simulator. Methods: We employ the complex scaling technique to extract resonance positions classically and adapt it for quantum simulations using a two-step algorithm. First, we transform the non-Hermitian Hamiltonian into a Hermitian form by using the energy variance as a cost function within a variational framework. Second, we perform 𝜃-trajectory calculations to determine optimal resonance positions in the complex energy plane. To address resource constraints on NISQ devices, we utilize Gray code (GC) encoding to reduce qubit requirements. Results: We first validate our approach using a schematic potential model that mimics a nuclear potential, successfully reproducing known resonance energies with high fidelity. We then extend the method to a more realistic 𝛼−𝛼 nuclear potential and compute the 𝐷- and 𝐺-wave resonance energies with a basis size of 𝑁=16, using only four qubits. The quantum simulation results closely match the classical values, demonstrating the feasibility of our approach. Conclusions: This study demonstrates, for the first time, that the complete 𝜃-trajectory method can be implemented on a quantum computer without relying on any classical input beyond the Hamiltonian. The results establish a scalable and efficient quantum framework for simulating resonance phenomena in nuclear systems. This work represents a significant step toward quantum simulations of open quantum systems and lays the foundation for future investigations into resonance structures in nuclear, atomic, and molecular physics.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Improving Fission Products at CARIBU: Near Field Detection (Q2/FY20 Quarterly Progress Report)

In the past quarter, we have produced a sample of ¹⁵⁶Eu at Argonne National Laboratory and performed a subsequent measurement of the ¹⁵⁶Eu ß-decay at Texas A&M University. This experiment required a significant amount of travel to ANL and TAMU and effort by several LLNL team members. Additionally, in preparation for the next measurements, we have submitted a proposal for the beamtime required to collect and measure samples of ¹⁶¹Tb and ¹¹¹Ag. This proposal was received very positively, and we have been granted our full request of 6 days of beamtime at CARIBU.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Energy Dependent Fission Product Yields

This project utilized a 10-meter Fast Transfer System (called RABITTS) and Decay Station. FPYs are measured using neutron activation of U-235 and Pu-239 followed by gamma ray spectroscopy. We irradiated targets with mono-energetic neutrons produced at the TUNL tandem accelerator laboratory. The gamma spectra collected in these target irradiations are being analyzed to determine FPY values.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Doppler Broadening and Other Temperature Effects

In this paper I attempt to document what I have learned and still remember about temperature effects, particularly Doppler broadening, on nuclear data, as it applies to ENDF formatted data. My focus is on the SIGMA1 method of Doppler broadening that I developed over 50 years ago. However, I do realize that there are currently many different methods used in computer codes, and I have tried to keep my discussion general as it applies to ALL of these methods. In particular, ALL of the MYTHS I describe below apply to all Doppler broadening methods: they all solve the parabolic diffusion equation in spherical geometry in (speed, reaction rate) versus temperature. These methods differ only in how the cross section is represented. So, at 85 years old here is what I still remember.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Alpha Decay Chains as Thermal Power Sources: Analysis and Applications for RTGs

Radioactive sources can provide power in remote and environmentally harsh locations such as the arctic or space. The generators powered by such sources are rugged and can withstand extreme temperatures, lack of sunlight, and require no human intervention for multiple years. Radioisotopes are used in thermoelectric generators to provide power at remote sites and deep in space. Isotopes like Pu-238, Cm-244, and Am-241 are used in these generators by NASA for power in space probes and spacecrafts. These power sources deliver a steady supply of energy over extended periods of time. Alpha particles created during decay do not travel far in a material. Their kinetic energy is transferred to heat that we can then convert into energy. Unlike beta and gamma decay, the slower-moving alpha particles stop in the material, making their energy available for use. Energy from these natural decay processes provides a reliable source of power. Spontaneous fission is rare and unreliable, and unlike induced fission processes, alpha decay occurs naturally and does not require external management or ignition. The ideal properties of an isotope for use as a power source depend upon the intended use. For use in an Arctic research base over a period of several years, but less than a decade, an isotope that provides high power output over a shorter lifespan may be the most suitable option. Whereas, for deep space missions where a consistent power source for decades or perhaps more than 100 years is needed that would require a very different isotope. One with a much longer half-life that would provide consistent power throughout that time and survive in that state in for these extended periods of time. These examples represent two extreme sides in terms of time frames. By analyzing the power produced by different radioactive decay processes over time, we can evaluate the suitability of various isotope decay chains for specific uses. Some unstable isotopes undergo a series of radioactive decays, transforming into different isotopes at each step and resulting in a stable isotope. The lists of isotopes in these decay processes are known as decay chains. Some of these chains, illustrated in the figures below, are currently being investigated for use in radioisotope thermoelectric generators (RTGs) designed for a range of operational durations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Fission Evaluation Tools and Analytics (FETA)

This living document presents the Python package FETA. FETA computes observables resulting from the fission process. This document provides the definition of these observables as well as the physics models that are implemented to compute them. Some of these models are used to determine the initial conditions of fission fragments, e.g., the excitation energy E* and spin distribution p(J, π) at scission for prompt decay, while others are related to the nuclear structure and decay properties of the fragments, e.g. the ground-state properties, level density and low-lying excitation spectrum, γ-strength functions and electromagnetic transitions, and neutron transmission coefficients. The end goal for FETA is to enable users to substitute every one of these models by their own files providing these quantities.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Measurements of the 238 U/ 235 U and 239 Pu/ 235 U Fission Cross-Section Ratios Using Monoenergetic Neutron Beams

A quasi-monoenergetic neutron beam was used to measure the neutron-induced fission cross-section ratios for 238 U(n,f)/ 235 U(n,f) (Table 1) and 239 Pu(n,f)/ 235 U(n,f) (Table 2). These results are plotted in comparison with data from the fissionTPC and ENDF/B-VIII.0 in Figs.1-3. For each cross section ratio, the total, systematic, and statistical uncertainties are listed, along with the total beamtime required.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Measurements of the 239 Pu(n,f)/ 235 U(n,f) and 238 U(n,f)/ 235 U(n,f) Cross-Section Ratios Using Quasi-Monoenergetic Neutron Beams

Neutron-induced fission cross-section ratio measurements were carried out at Triangle Universities Nuclear Laboratory (TUNL) over multiple experiment campaigns from 2021-2023. The total beam time for these measurements across all the experimental campaigns was approximately three weeks. This work was intended to serve as an independent validation of the fissionTPC cross-section ratio measurements. In contrast to the white spectrum neutron source and time-projection chamber utilized in the fissionTPC, these measurements utilized pulsed, quasi-monoenergetic neutron beams and fission ionization chambers. Therefore, this work has different sources of systematic error and can be used as a complementary measurement. In this report we describe our fission cross-section ratio measurements, analysis, results and provide a detailed uncertainty budget.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Experimental Unevaluated Nuclear Data List (XUNDL)

Contains nuclear structure and decay data from published articles. Data include nuclear level properties, such as energy, half-life, decay modes, spin and parity, as well as energy and intensity for radiation types such as gammas, alphas, betas and neutrons. For articles published in Physical Review C and the European Physical Journal, compilation takes place during the article submission process. Data from approximately 250 articles are added per year. All the compilation effort is supported by the US Nuclear Data Program and coordinated by the National Nuclear Data Center at Brookhaven National Laboratory, which is also responsible for its web dissemination.

Basic Nuclear Research, nuclear structure and deca↗
DOE OSTI2023

Measurement of the 25 Al(𝑑,𝑛)⁢ 26 Si reaction and impact on the 25 Al⁢(𝑝,𝛾)⁢ 26 Si reaction rate

The 25 Al(p,γ) 26 Si reaction plays a key role in nucleosynthesis pathways that influence the galactic abundance of 26 Al. A more precise determination of the proton strength of the lowest ℓ = 0 proton resonance in 26 Si is needed to improve reaction-rate calculations. This work measures the 25 Al(d,n) 26 Si proton-transfer reaction in inverse kinematics using a radioactive ion beam at RESOLUT, determining excitation energies and cross sections for the lowest ℓ = 0 resonance associated with the 3 + 3 state at 5.92(2) MeV. Coupled-reaction-channels calculations (FRESCO) are used to extract the ℓ = 0 spectroscopic factor and the corresponding proton width, yielding Γₚ = 2.19(45) eV and a (p,γ) resonance strength of 26(10) meV. This resonance is found to dominate the 25 Al(p,γ) 26 Si reaction rate above 0.2 GK.

20 ≤ A ≤ 38↗
DOE OSTI2022

Thermonuclear reaction rate of 29 Si(p,γ) 30 P

The thermonuclear rate of the 29 Si(p,γ) 30 P reaction impacts the 29 Si abundance in classical novae. A reliable reaction rate is essential for testing the nova paternity of presolar stardust grains. At present, the fact that no classical nova grains have been unambiguously identified in primitive meteorites among thousands of grains studied is puzzling, considering that classical novae are expected to be prolific producers of dust grains. We investigated the 29 Si + p reaction at center-of-mass energies of 200–420 keV, and present improved values for resonance energies, level excitation energies, resonance strengths, and branching ratios. One new resonance was found at a center-of-mass energy of 303 keV. For an expected resonance at 215 keV, an experimental upper limit could be determined for the strength. We evaluated the level structure near the proton threshold, and present new reaction rates based on all the available experimental information. Our new reaction rates have much reduced uncertainties compared with previous results at temperatures of T ≥ 140 MK, which are most important for classical nova nucleosynthesis. Furthermore, future experiments to improve the reaction rates at lower temperatures are discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Cross sections of the 83 Rb⁢(p,γ)⁢ 84 Sr and 84 Kr⁢(p,γ)⁢ 85 Rb reactions at energies characteristic of the astrophysical γ process

We have measured the cross section of the Rb 83 ( p , γ ) Sr 84 radiative capture reaction in inverse kinematics using a radioactive beam of Rb 83 at incident energies of 2.4 and 2.7 A MeV. Prior to the radioactive beam measurement, the Kr 84 ( p , γ ) Rb 85 radiative capture reaction was measured in inverse kinematics using a stable beam of Kr 84 at an incident energy of 2.7 A MeV. The effective relative kinetic energies of these measurements lie within the relevant energy window for the γ process in supernovae. The central values of the measured partial cross sections of both reactions were found to be 0.17 – 0.42 times the predictions of statistical model calculations. Assuming the predicted cross section at other energies is reduced by the same factor leads to a slightly higher calculated abundance of the p nucleus Sr 84 , caused by the reduced rate of the Sr 84 ( γ , p ) Rb 83 reaction derived from the present measurement.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Superallowed decays within and beyond the standard model

This note reviews the role of superallowed transitions in determining the strength of the weak interaction among the lightest quarks and in searching for new physics beyond the standard electroweak model. The two sets of superallowed decays in nuclei considered here are pure Fermi and mirror transitions. The first have been scrutinized for more than 50 years. Here, the most relevant results are presented and the role of the nucleus-dependent radiative correction and nucleus-independent inner radiative correction are reviewed. In this context, the systematic study of mirror transitions started about 15 years ago. Despite the significant progress made since then, the data is still limited by experimental uncertainties. Combining the results from all superallowed transitions, which are fully consistent, provides a test of unitarity of the first row of the Cabibbo-Kobayashi-Maskawa matrix, which displays a 2σ tension with the standard model.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗