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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Consistent Nuclear Data Evaluations for Criticality Safety

Evaluations of nuclear data are based on statistical analysis of available experimental data and their uncertainties plus model calculations and their uncertainties. As the models are currently rather limited, the evaluations are heavily biassed toward experimental data, with the caveat that a thorough analysis is also required to understand possible discrepancies between data sets. Hence, as new experimental data become available, they are incorporated into the evaluation procedure. Recent measurements of the 233 U capture to fission cross section ratio at the Los Alamos Neutron Science Center have prompted a re-evaluation of the capture cross section in the resonance and fast regions up to 250 keV. We will discuss the challenges of including the new fast neutron experimental data in an evaluation that is consistent with the resonance region. We will also discuss our consistent evaluation procedure based on the Hauser-Feshbach statistical model for nuclear reactions and its application to the evaluations of 239 Pu and 139 La neutron-induced reactions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

NACS 2022 FRIB Investment Strategy

The Facility for Rare Isotope Beams (FRIB) that will begin operations later this year will vastly increase the number of unstable isotopes available for experiments that, together with new theoretical developments will expand our understanding of nuclear structure and nuclear reactions that produce the elements of the periodic table and power the cosmos. The knowledge and understanding gained from FRIB will benefit a variety of applications including stockpile science, nuclear forensics, nonproliferation, nuclear energy, and nuclear medicine. LLNL is actively involved in a variety of basic and applied science activities related to FRIB. These activities are listed below and documented in the following sections: 1. FRIB Decay Station, 2. Isotope Harvesting, 3. Direct Reactions, 4. Surrogate Reactions, 5. Nuclear Structure and Collectivity, 6. Nuclear Fission, and 7. Nuclear Theory.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2021

Investigation of secondary γ -ray angular distributions using the N 15 ( p , α 1 γ ) C * 12 reaction

The observation of secondary γ-rays provides an alternative method of measuring cross sections that populate excited final states in nuclear reactions. The angular distributions of these γ-rays also provide information on the underlying reaction mechanism. Despite a large amount of data of this type in the literature, publicly available R-matrix codes do not have the ability to calculate these types of angular distributions. In this report, the mathematical formalism derived in Brune and deBoer is implemented in the R-matrix code AZURE2 and calculations are compared with previous data from the literature for the 15 N( p, α1γ ) 12 C* reaction. In addition, new measurements, made at the University of Notre Dame Nuclear Science Laboratory using the Hybrid Array of Gamma Ray Detectors (HAGRiD), are reported that span an energy range from E p = 0.88 to 4.0 MeV. Excellent agreement between data and the phenomenological fit is obtained up to the limit of the previous fit at E p = 2.0 MeV and the R-matrix fit is extended from E x ≈ 13.5 up to E x ≈ 15.3 MeV, where 15 N+p and 12 C+α reactions are fit simultaneously for the first time. An excellent reproduction of the 15 N( p, α1γ ) 12 C* and 12 C(α, α) 12 C data is achieved, but inconsistencies and difficulty in fitting other data is encountered and discussed.

6 ≤ A ≤ 19↗
DOE OSTI2021

Reaction losses of charged particles in CsI(Tl) crystals

To efficiently detect energetic light charged particles, it is common to use arrays of energy-loss telescopes involving two or more layers of detection media. As the energy of the particles increases, thicker layers are usually needed. However, carrying out measurements with thick-telescopes may require corrections for the losses due to nuclear reactions induced by the incident particles on nuclei within the detector and for the scattering of incident particles out of the detector, without depositing their full energy in the active material. In this paper, we develop a method for measuring such corrections and determine the reaction and out-scattering losses for data measured with the silicon-CsI(Tl) telescopes of the newly developed HiRA10 array. Here, the extracted efficiencies are in good agreement with model predictions using the GEANT4 reaction loss algorithm for Z = 1 and Z = 2 isotopes. After correcting for the HiRA10 geometry, we obtain a general function that describes the loss of efficiency due to reaction losses in CsI(Tl) crystals as a function of range.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

Toward the Discovery of New Elements: Production of Livermorium (𝑍 = 116) with 50 Ti

The 244 Pu ⁢(50 Ti ,𝑥⁢𝑛)⁢ 294−𝑥 Lv reaction was investigated at Lawrence Berkeley National Laboratory’s 88-Inch Cyclotron. The experiment was aimed at the production of a superheavy element with 𝑍 ≥114 by irradiating an actinide target with a beam heavier than 48 Ca. Produced Lv ions were separated from the unwanted beam and nuclear reaction products using the Berkeley Gas-filled Separator and implanted into a newly commissioned focal-plane detector system. Two decay chains were observed and assigned to the decay of 290 Lv . The production cross section was measured to be 𝜎 prod = 0.44($^{+0.58}_{−0.28}$) pb at a center-of-target center-of-mass energy of 220(3) MeV. Furthermore, this represents the first published measurement of the production of a superheavy element near the “island of stability,” with a beam of 50 Ti and is an essential precursor in the pursuit of searching for new elements beyond 𝑍 =118.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Applied nonrelativistic conformal field theory: Scattering-length and effective-range corrections to rate of production of three neutrons at low relative momenta

Due to an accidentally large s-wave scattering length, in a relatively wide range of energy, neutrons are approximately described by the nonrelativistic conformal field theory of unitarity fermions, perturbed by one relevant and an infinite number of irrelevant operators. We develop a formalism which provides a nonperturbative definition of local operators in that nonrelativistic conformal field theory. We compute the scattering-length and effective-range corrections to the two-point functions of primary charge-three operators using the technique of conformal perturbation theory. These calculations allow us to find the first corrections to the scale-invariant behavior of the rate of nuclear reactions with three neutrons in the final state in the regime when the neutrons have small relative momenta.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Learning from knockout reactions using a dispersive optical model

We present the empirical dispersive optical model (DOM) as applied to direct nuclear reactions. The DOM links both scattering and bound-state experimental data through a dispersion relation, which allows for fully consistent, data-informed predictions for nuclei where such data exist. In particular, we review investigations of the electron-induced proton knockout reaction from both 40 Ca and 48 Ca in a distorted-wave impulse approximation (DWIA) utilizing the DOM for a fully consistent description. Viewing these reactions through the lens of the DOM allows us to connect the documented quenching of spectroscopic factors with the increased high-momentum proton content in neutron-rich nuclei. A similar DOM-DWIA description of the proton-induced knockout from 40 Ca, however, does not currently fit in the consistent story of its electron-induced counterpart. With the main difference in the proton-induced case being the use of an effective proton–proton interaction, we suggest that a more sophisticated in-medium interaction would produce consistent results.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

The São Paulo Potential and the 3 He Breakup Reaction at 130 MeV on 93 Nb and 197 Au

Nuclear reactions induced by weakly bound nuclei often result in the emission of light particles as products of the projectile breakup. The incident particle is expected to fragment before reaching the interior of the target nuclei, a characteristic that tends to favor forward angular emission. Although the first models developed for such reactions were proposed many decades ago by Udagawa and Tamura, Ichimura, Austern, Vincent, and Kasano, and Hussein and McVoy, to this date most of the attention has been dedicated to the breakup of the deuteron and other very weakly bound systems, while more strongly bound projectiles have not been fully explored. Here, we describe the production of protons and deuterons from the breakup of 3He. The breakup of 3 He on two heavy targets, 93 Nb and 197 Au, is analyzed in this study. However, the incoming energy involved is much larger than that of the standard phenomenological optical potentials available in the literature for the 3He entrance channel. We have overcome this difficulty by using the São Paulo potential and adjusting the nuclear diffusivity. The deuteron inclusive spectra were calculated at several angles and compared well with the experimental data. Theoretical proton emission predictions are also given for future reference, since no inclusive measurements were performed for the targets under study. Finally, one of our goals is to verify the description of deuteron emission from fast projectiles, for which many partial waves contribute to the scattering process.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Thermonuclear Reaction Rates and Primordial Nucleosynthesis

Assuming the best numerical value for the cosmic baryonic density and the existence of three neutrino flavors, standard Big Bang nucleosynthesis is a parameter-free model. It is important to assess if the observed primordial abundances can be reproduced by simulations. Numerous studies have shown that the simulations overpredict the primordial 7 Li abundance by a factor of ≈3 compared to the observations. The discrepancy may be caused by unknown systematics in 7 Li observations, poorly understood depletion of lithium in stars, errors in thermonuclear rates that take part in the lithium and beryllium synthesis, or physics beyond the standard model. Here, we focus on the likelihood of a nuclear physics solution. The status of the key nuclear reaction rates is summarized. Big Bang nucleosynthesis simulations are performed with the most recent reaction rates, and the uncertainties of the predicted abundances are established using a Monte Carlo technique. Correlations between abundances and reaction rates are investigated based on the metric of mutual information. The rates of four reactions impact the primordial 7 Li abundance: 3 He(α,γ) 7 Be, d(p,γ) 3 He, 7 Be(d,p)2α, and 7 Be(n,p) 7 Li. We employ a genetic algorithm to search for simultaneous rate changes in these four reactions that may account for all observed primordial abundances. Furthermore, when the search is performed for reaction rate ranges that are much wider than recently reported uncertainties, no acceptable solutions are found. Based on the currently available evidence, we conclude that it is highly unlikely for the cosmological lithium problem to have a nuclear physics solution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Quasi-differential neutron induced neutron emissions from 235 U, and 239 Pu

Uncertainty in nuclear reaction cross sections, angular distributions, and other nuclear data directly impact how well simulations of nuclear systems represent physical observations. Here, to determine how well the nuclear data in ENDF/B-VIII.0, JEFF-3.3, and JENDL-4.0 evaluations describe the physical behaviour of 235 U, and 239 Pu when subjected to a neutron flux, the neutron emission spectrum was measured for carbon, 93.0% 235 U, and 93.9% 239 Pu samples, and compared against detailed MCNP6 simulations. The measurements were performed at the Los Alamos Neutron Science Center using a quasi-differential method previously developed at Rensselaer Polytechnic Institute. The measurement spanned 0.82–20 MeV and 30–150 degrees. The measurements show there are a significant number of discrepancies between library predictions of the neutron yield and physical observation. A few of the main discrepancies found are described in this paper. Based on these results a new evaluation utilizing these results for carbon, 235 U, and 239 Pu is recommended.

235U↗
DOE OSTI2023

Structure studies of 13 Be from the 12 Be ⁢(𝑑,𝑝) reaction in inverse kinematics on a solid deuteron target

The low-lying structure of 13 Be has remained an enigma for decades. Despite numerous experimental and theoretical studies, large inconsistencies remain. Being both unbound and one neutron away from 14 Be, the heaviest bound beryllium nucleus, 13 Be is difficult to study through simple reactions with weak radioactive-ion beams or more complex reactions with stable-ion beams. Here, we present the results of a study using the 12 Be (𝑑,𝑝)⁢ 13 Be reaction in inverse kinematics using a 9.5 MeV per nucleon 12 Be beam from the ISAC-II facility. The solid deuteron target of IRIS was used to achieve an increased areal thickness compared to conventional deuterated polyethylene targets. The 𝑄-value spectrum below −4.4 MeV was analyzed using a Bayesian method with geant4 simulations. A three-point angular distribution with the same 𝑄-value gate was fit with a mixture of 𝑠- and 𝑝-wave, 𝑠- and 𝑑-wave, or pure 𝑝-wave transfer. The 𝑄-value spectrum was also compared with geant simulations obtained using the energies and widths of states reported in four previous works. As a result, it was found that our results are incompatible with works that revealed a wide 5/2 + resonance but shows better agreement with ones that reported a narrower width.

6 ≤ A ≤ 19↗
DOE OSTI2025

Molecular 9 Be + $p$ fusion reaction

Here, we study (nuclear) fusion reactions in beryllium. We argue that some are nuclear long-distance molecular processes of interest for low-energy nuclear reactions. For these, we develop a novel reaction model. We note a chain of reactions that can naturally arise in beryllium target created by nonequilibrium proton reactions.

Rafelski, Johann [Univ. of Arizona, Tucson, AZ (Un↗
DOE OSTI2024

Tunable-fidelity wave functions for the ab initio description of scattering and reactions

Here, the no-core shell model (NCSM) is an ab initio method that solves the nuclear many-body problem by expanding the many-particle wave function into a (typically) harmonic oscillator basis and minimizing the energy to obtain the expansion coefficients. Extensions of the NCSM, such as its coupling with microscopic-cluster basis states, further allow for an ab initio treatment of light-ion nuclear reactions of interest for both astrophysics and nuclear technology applications. A downside of the method is the exponential scaling of the basis size with increasing number of nucleons and excitation quanta, which limits its applicability to mass A ≲ 16 nuclei, except for variants where the basis is further down-selected via some truncation scheme. We consider a basis selection method for the NCSM that was first introduced in the context of the large-scale shell model and captures the essential degrees of freedom of the nuclear wave function leading to a favorable complexity scaling for calculations and enabling ab initio reaction calculations in sd-shell nuclei. The particle configurations within the NCSM basis are ordered based on their contribution to the first moment of the Hamiltonian matrix that results from the projection onto the many-body basis. The truncation scheme then consists in retaining only the lowest-first-moment configurations, which typically contain only few many-body basis states (Slater determinants). As the energy threshold above which configurations are disregarded is increased, the size of the basis becomes an almost-continuous variable, allowing for tunable fidelity in the obtained wave functions. The resulting wave functions can then be used directly in ab initio reaction calculations. We present calculations for 7 Li and n + 12 C scattering using nucleon-nucleon interactions derived from chiral effective field theory and softened using the similarity renormalization group method. The obtained energy levels invariably demonstrate exponential convergence with the size of the basis, and we find improved convergence in scattering calculations. To demonstrate the possibilities enabled by the approach, we also present a first calculation for the scattering of neutrons from 24 Mg. The method presented in this work appears promising for future studies of nuclei with mass A > 16, opening multiple future research directions impacting both nuclear astrophysics and nuclear technology applications.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Indirect reactions and connection with R-matrix theory

It is often the case that nuclear reactions that are important for societal applications or basic science are difficult to measure directly in existing facilities for accelerated beams. The difficulty might be associated with an exceedingly small cross section, as the ones obtained at beam energies well below the Coulomb barrier, or with the impossibility of devising a short-lived target, as is the case for neutron-induced reactions on unstable isotopes. The fruitful line of experimental research addressing this issue with alternative (indirect) reactions has been developed in parallel to the theory needed to make the connection between the observed data and the desired cross sections of the (direct) reaction under study. Within this context, we present here an explicit connection between the indirect cross section and the R-matrix parameters which describe the energy-dependent cross section of the desired direct reaction.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Nuclear structure opportunities with GeV radioactive beams at FAIR

The Facility for Antiproton and Ion Research (FAIR) is in its final construction stage next to the campus of the Gesellschaft für Schwerionenforschung Helmholtzzentrum for heavy-ion research in Darmstadt, Germany. Once it starts its operation, it will be the main nuclear physics research facility in many basic sciences and their applications in Europe for the coming decades. Owing to the ability of the new fragment separator, Super-FRagment Separator, to produce high-intensity radioactive ion beams in the energy range up to about 2 GeV/nucleon, these can be used in various nuclear reactions. This opens a unique opportunity for various nuclear structure studies across a range of fields and scales: from low-energy physics via the investigation of multi-neutron systems and halos to high-density nuclear matter and the equation of state, following heavy-ion collisions, fission and study of short-range correlations in nuclei and hypernuclei. Here, the newly developed reactions with relativistic radioactive beams (R3B) set up at FAIR would be the most suitable and versatile for such studies. An overview of highlighted physics cases foreseen at R3B is given, along with possible future opportunities, at FAIR.

FAIR↗
DOE OSTI2025

Constraining explosive nucleosynthesis by indirect reaction methods at storage rings using unstable beams in batch mode

Nuclear reaction studies on unstable isotopes can strongly help in improving our understanding of nucleosynthesis in stars. Indirect approaches to determining astrophysical reaction rates are increasingly common-place and undergoing continuous refinement. Of particular interest is the use of such indirect techniques at storage rings, which, among other aspects, allow to recycle rare unstable beams. Here, we propose to investigate the reaction rates of astrophysical interest using indirect methods (surrogate, Trojan horse, etc.) in reverse kinematics at the IMP-CAS storage ring. Long lived radioactive ion beams, produced remotely, can be accelerated, and made to interact with light targets. The proposed reactions are 85 Kr(p, p’γ), 85 Kr(d, pγ), constraining the neutron flux in an s-process branching point, 79 Se(p, p’γ), 79 Se(d, pγ), constraining the temperature in s-process nucleosyntheses, and 59 Fe(d, pγ), constraining core collapse supernovae.

Angelis, G. de [National Inst. of Nuclear Physics ↗
DOE OSTI2020

First Direct Measurement of Mg (α,p) 25 Al and Implications for X-Ray Burst Model-Observation Comparisons

Type-I x-ray bursts can reveal the properties of an accreting neutron star system when compared with astrophysics model calculations. However, model results are sensitive to a handful of uncertain nuclear reaction rates, such as 22 Mg(α , p). We report the first direct measurement of 22 Mg(α , p), performed with the Active Target Time Projection Chamber. The corresponding astrophysical reaction rate is orders of magnitude larger than determined from a previous indirect measurement in a broad temperature range. Overall, our new measurement suggests a less-compact neutron star in the source GS1826-24.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2026

Correlated fission fragment spin dynamics

Here, this study explores the role of nucleon exchange for the generation of the fission fragment angular momenta. For a number of typical fission cases, samples of 10 4 shape evolutions are generated by Langevin simulation and, subsequently, for each such evolution, the nucleon exchange transport theory previously developed for damped nuclear reactions is used to obtain the development of the fragment spin-spin distribution within the Fokker-Planck transport framework. The characteristic evolution of both parallel and perpendicular spin components is discussed. A common feature is that the rotational modes fall out of equilibrium before scission when the temperature rises rapidly while the concurrent shrinking of the neck suppresses further exchange. A number of fission observables are extracted from the event ensembles: the distribution of the magnitude of the fragment spin and its orientation relative to the fission axis, as well as the correlation between the two spins and the distribution of their opening angle. The dependence of these observables on the mass asymmetry is also examined.

fission↗