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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 OSTI2026

Baryon–antibaryon photoproduction cross sections off the proton

The GlueX experiment at Jefferson Lab has observed 𝑝⁢$\overline{p}$ and, for the first time, Λ$\overlineΛ$ and 𝑝$\overlineΛ$ photoproduction from a proton target at photon energies up to 11.6 GeV. The angular distributions are forward peaked for all produced pairs, consistent with Regge-like 𝑡-channel exchange. Asymmetric wide-angle antibaryon distributions show the presence of additional processes. In a phenomenological model, we find consistency with a double-𝑡-channel exchange process where antibaryons are created only at the middle vertex. The model matches all observed distributions with a small number of free parameters. In the hyperon channels, we observe a clear distinction between photoproduction of the Λ$\overlineΛ$ and 𝑝$\overlineΛ$ systems but general similarity to the 𝑝$\overline{p}$ system. We report both total cross sections and cross sections differential with respect to momentum transfer and the invariant masses of the created particle pairs. No narrow resonant structures were found in these reaction channels. The suppression of 𝑠$\overline{s}$ quark pairs relative to 𝑑$\overline{d}$ quark pairs is similar to what has been seen in other reactions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

J/Psi Photoproduction Near Threshold With CLAS12

The structure of the proton is comprised of quarks and a sea of gluons. A mechanism that can extract the characteristics of the hidden-color correlations of the nuclear wavefunction is the production of charm near threshold. Due to the fact that momentum transfer is large near threshold in the production of J/ψ , all three valence quarks must act coherently to ex- change energy for the reaction to occur. Models have been developed to predict the nature of J/ψ photoproduction at these specific energies. These include production mechanisms with the two-gluon and three-gluon exchanges. The transferred momentum dependence of the differential cross sections are sensitive to the gluonic form factors, which describe the distribution of color charge in the proton. The CLAS12 detector is capable of measuring J/ψ photoproduction at the energy range close to the threshold. Work showcased in this dissertation encompasses the preparation of the CLAS12 experiments, including the optimization of tracking reconstruction through the study of the Torus magnetic field. In terms of software, contributions were made to the CLAS12 Event Builder, a key stage of reconstruction where event-by-event information is summarized for efficient data analysis. After the run periods were successfully completed, analysis of the RG-A data commenced and an analysis framework was developed to measure the differential and total cross sections of J/ψ photoproduction in Hall B.

Newton, Joseph↗
DOE OSTI2024

Direct cross-section measurement of the weak r -process Sr 88 ( α , n ) Zr 91 reaction in ν -driven winds of core-collapse supernovae

About half of the heavy elements beyond iron are known to be produced by the rapid neutron capture process, known as the r process. However, the astrophysical site producing the r process is still uncertain. Chemical abundances observed in several cosmic sites indicate that different mechanisms should be at play. For instance, the abundances around silver measured in a subset of metal-poor stars indicate the presence of a weak r process. This process may be active in neutrino-driven winds of core collapse supernovae where (α,n) reactions dominate the synthesis of Ζ ≈ 40 elements in the expelled materials. Scarcely measured, the rates of (α,n) reactions are determined from statistical Hauser-Feshbach calculations with α-optical-model potentials, which are still poorly constrained. Further, the uncertainties of the (α,n) reaction rates therefore make a significant contribution to the uncertainties of the abundances determined from stellar modeling. In this work, the 88 Sr (α,n)⁢ 91 Zr reaction which impacts the weak r-process abundances has been probed at astrophysics energy for the first time; directly measuring the total cross sections at astrophysical energies of 8.37–13.09 MeV in the center of mass (3.8–7.5 GK). Two measurements were performed at ATLAS with the electrically segmented ionization chamber MUSIC, in inverse kinematics, while following the active target technique. The cross sections of this α-induced reaction on 88 Sr, located at the shell closure N = 50, have been found to be lower than expected, by a factor of 3, despite recent statistical calculations validated by measurements on neighboring nuclei. This result encourages more experimental investigations of (α,n) reactions, at Ν = 50 and towards the neutron-rich side, to further test the predictive power and reliability of such calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS1981

Interpretation of cosmic ray composition - The path length distribution

The chemical composition of cosmic ray nuclei, the value of Z varying between 3 and 28, and being between a few hundred MeV/nucleon and a few hundred GeV/nucleon, is compared with a consistent set of propagation calculations. These include the effects of spallation (energy-dependent cross sections are used), escape, ionization loss in the interstellar medium, and deceleration in the solar cavity. The amount of matter traversed by cosmic rays is found to be approximately 7 g/sq cm, independent of energy between 100 MeV/nucleon and 2 GeV/nucleon. Above 2 GeV/nucleon, the escape length varies as the -0.4 + or 0.1 power of the energy. In addition, a procedure has been developed to measure the shape of the cosmic ray path length distribution. Utilizing the ratio of Fe secondaries to Fe in the cosmic rays, presently available data are found to be consistent with an exponential distribution and they eliminate models in which the path length distribution is severely truncated. To tie down the shape of the distribution more precisely, new measurements of the cosmic ray composition, presently becoming available from experiments on the HEAO 3 satellite, will have to be coupled with improved measurements of the energy dependence of partial and total cross sections.

Protheroe, R. J.↗
NASA NTRS1993

Near-Threshold Rovibrational Excitation of HF by Electron Impact

The pronounced threshold peaks found in cross sections for electron-impact excitation of the vibrational levels of HF have been studied using an R-matrix method, in which electron exchange, correlation effects and polarization are included. Vibration is modelled inside the R-matrix sphere using the energy-modified adiabatic phase matrix method (EMAP). Rotation of the target molecule is treated outside the R-matrix sphere, using the frame transformation method. The external rovibronic close-coupling equations are solved by analytic methods. Analysis of the multichannel threshold structures indicates that the peaks found for rovibrational excitation of nu = 1 can be interpreted as virtual states while those for nu = 2 correspond to nuclear-excited Feshbach resonances. These two different results correspond simply to a change of sign of a small parameter that is determined by the threshold analysis. Whereas the overall shapes of the excitation peaks agree with earlier theoretical results, we have found detailed rotational fine structures for scattering energies on the order of the rotational constant above and below the opening of the vibrational channels. The partial and total cross sections for rovibrational state-to-state transitions in the energy region of the peaks are analysed. Characteristic cusp structures and excitation peaks are found at the rovibrational thresholds for transitions with small angular momentum transfer (Delta)j =0, 1 and 2. Differential cross sections are similar to recent measurements. These experimental data do not show the relatively sharp rise at the vibrational thresholds indicated by theory. Theory and experiment are in good agreement for the shape and magnitude of the angular dependence of cross sections for rovibrational state-to-state transitions, especially at larger energies.

Thummel, Helmar T.↗
NASA NTRS2011

Dynamical Model for the Zodiacal Cloud and Sporadic Meteors

The solar system is dusty, and would become dustier over time as asteroids collide and comets disintegrate, except that small debris particles in interplanetary space do not last long. They can be ejected from the solar system by Jupiter, thermally destroyed near the Sun, or physically disrupted by collisions. Also, some are swept by the Earth (and other planets), producing meteors. Here we develop a dynamical model for the solar system meteoroids and use it to explain meteor radar observations. We find that the Jupiter Family Comets (JFCs) are the main source of the prominent concentrations of meteors arriving to the Earth from the helion and antihelion directions. To match the radiant and orbit distributions, as measured by the Canadian Meteor Orbit Radar (CMOR) and Advanced Meteor Orbit Radar (AMOR), our model implies that comets, and JFCs in particular, must frequently disintegrate when reaching orbits with low perihelion distance. Also, the collisional lifetimes of millimeter particles may be longer (approx. > 10(exp 5) yr at 1 AU) than postulated in the standard collisional models (approx 10(exp 4) yr at 1 AU), perhaps because these chondrule-sized meteoroids are stronger than thought before. Using observations of the Infrared Astronomical Satellite (IRAS) to calibrate the model, we find that the total cross section and mass of small meteoroids in the inner solar system are (1.7-3.5) 10(exp 11) sq km and approx. 4 10(exp 19) g, respectively, in a good agreement with previous studies. The mass input required to keep the Zodiacal Cloud (ZC) in a steady state is estimated to be approx. 10(exp 4)-10(exp 5) kg/s. The input is up to approx 10 times larger than found previously, mainly because particles released closer to the Sun have shorter collisional lifetimes, and need to be supplied at a faster rate. The total mass accreted by the Earth in particles between diameters D = 5 micron and 1 cm is found to be approx 15,000 tons/yr (factor of 2 uncertainty), which is a large share of the accretion flux measured by the Long Term Duration Facility (LDEF). Majority of JFC particles plunge into the upper atmosphere at <15 km/s speeds, should survive the atmospheric entry, and can produce micrometeorite falls. This could explain the compositional similarity of samples collected in the Antarctic ice and stratosphere, and those brought from comet Wild 2 by the Stardust spacecraft. Meteor radars such as CMOR and AMOR see only a fraction of the accretion flux (approx 1- 10% and approx 10-50%, respectively), because small particles impacting at low speeds produce ionization levels that are below these radars detection capabilities.

Nesvorny, David↗
NASA NTRS1973

Calculation of total electron excitation cross-sections and partial electron ionization cross-sections for the elements

Computer programs were used to calculate the total electron excitation cross-section for atoms and the partial ionization cross-section. The approximations to the scattering amplitude used are as follows: (1) Born, Bethe, and Modified Bethe for non-exchange excitation; (2) Ochkur for exchange excitation; and (3) Coulomb-Born of non-exchange ionization. The amplitudes are related to the differential cross-sections which are integrated to give the total excitation (or partial ionization) cross-section for the collision. The atomic wave functions used are Hartree-Fock-Slater functions for bound states and the coulomb wave function for the continuum. The programs are presented and the results are examined.

Green, T. J.↗
NASA NTRS2001

Complex Correlation Kohn-T Method of Calculating Total and Elastic Cross Sections: Electron-Hydrogen Elastic Scattering - Part 1

We report on the first part of a study of electron-hydrogen scattering, using a method which allows for the ab initio calculation of total and elastic cross sections at higher energies. In its general form the method uses complex 'radial' correlation functions, in a (Kohn) T-matrix formalism. The titled method, abbreviated Complex Correlation Kohn T (CCKT) method, is reviewed, in the context of electron-hydrogen scattering, including the derivation of the equation for the (complex) scattering function, and the extraction of the scattering information from the latter. The calculation reported here is restricted to S-waves in the elastic region, where the correlation functions can be taken, without loss of generality, to be real. Phase shifts are calculated using Hylleraas-type correlation functions with up to 95 terms. Results are rigorous lower bounds; they are in general agreement with those of Schwartz, but they are more accurate and outside his error bounds at a couple of energies,

Bhatia, A. K.↗
DOE OSTI2023

Total neutron cross-section measurement on CH with a novel 3D-projection scintillator detector

In order to extract neutrino oscillation parameters, long-baseline neutrino oscillation experiments rely on detailed models of neutrino interactions with nuclei. These models constitute an important source of systematic uncertainty, partially because detectors to date have been blind to final state neutrons. Three-dimensional projection scintillator trackers comprise components of the near detectors of the next generation long-baseline neutrino experiments. Due to the good timing resolution and fine granularity, this technology is capable of measuring neutron kinetic energy in neutrino interactions on an event-by-event basis and will provide valuable data for refining neutrino interaction models and ways to reconstruct neutrino energy. Two prototypes have been exposed to the neutron beamline at Los Alamos National Laboratory (LANL) in both 2019 and 2020, with neutron energies between 0 and 800 MeV. In order to demonstrate the capability of neutron detection, the total neutron-scintillator cross section as a function of neutron energy is measured and compared to external measurements. The measured total neutron cross section in scintillator between 98 and 688 MeV is 0.36 ± 0.05 barn.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Suppression of diffraction in deep-inelastic scattering on nuclei and dynamical mechanism of leading twist nuclear shadowing

Abstract Using the leading twist approach (LTA) to nuclear shadowing, we calculate the ratios of diffractive and usual parton distributions for a heavy nucleus (Pb) and the proton,$$ {R}_{A/p}=\left({f}_{i/A}^{D(3)}/{f}_{i/A}\right)/\left({f}_{i/p}^{D(3)}/{f}_{i/p}\right) $$ R A / p = f i / A D 3 / f i / A / f i / p D 3 / f i / p , for coherent and summed (coherent plus quasi-elastic) nuclear deep-inelastic scattering. We find thatR A/p ≈ 0.5 − 1 for quarks as well as for the ratio of the diffractive and total cross sections$$ {\left[\left({d\sigma}_{\textrm{diff}}/{d M}_X^2\right)/{\sigma}_{\textrm{tot}}\right]}_{eA}/{\left[\left({d\sigma}_{\textrm{diff}}/{d M}_X^2\right)/{\sigma}_{\textrm{tot}}\right]}_{ep} $$ dσ diff / dM X 2 / σ tot eA / dσ diff / dM X 2 / σ tot ep andR A/p ≈ 0.5 − 1.3 for gluons in a broad range ofx, including the kinematics of the Electron-Ion Collider, which reaffirms the difference from the nuclear enhancement ofR A/p predicted in the gluon saturation framework. We demonstrate that the magnitude ofR A/p is controlled by the cross section of the interaction of hadronic fluctuations of the virtual photon with target nucleons, which explains an enhancement ofR A/p in the color dipole model and its suppression in LTA. We argue that the black disk limit corresponds toR A/p = 1 and$$ {R}_{A/p}^{\textrm{coh}} $$ R A / p coh = 0.86 for the summed and coherent scattering, respectively. Relying on an intuitive definition of the saturation scale, we show that the ratio of the saturation scales of a heavy nucleus and proton$$ {Q}_{sA}^2(b)/{Q}_{sp}^2(b)\approx 1 $$ Q sA 2 b / Q sp 2 b ≈ 1 at small impact parametersbdue to the strong leading twist nuclear shadowing and diluteness of the nuclear density.

Physics↗
DOE OSTI2023

Simulation of dark bremsstrahlung in Geant4

A technique for the simulation of dark bremsstrahlung for electrons and muons in GEANT4 is presented. The total cross section is calculated using the Weizsäcker-Williams approximation and the outgoing kinematics are produced by scaling events produced in MadGraph/MadEvent to lower incident lepton energies, allowing the simulation to account for thick targets and lepton sources without fixed energies. In conclusion, compared with dedicated samples produced at an arbitrary particle energy, typical precision of better than 5% is achieved.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

J/ψ photoproduction at the threshold with GlueX

High-statistics total cross sections for the vector meson photoproduction at the threshold: γp → ωp (from A2 at MAMI, ELPH, and CBELSA), γp → ϕp (from CLAS6 at JLab and LEPS at SPring-8), and γp → J/ψp (from GlueX at JLab) allow one to extract the absolute value of vector meson nucleon scattering length using Vector Meson Dominance (VMD) model. The “young” vector meson hypothesis may explain the fact that the obtained scattering length values for the nucleon. ϕ-meson compared to the typical hadron size of approximately ∼ 1 fm indicates that the proton is more transparent for the ϕ-meson compared to the ω-meson and is much less transparent than the J/ψ-meson. The extended analysis of Υ-meson photoproduction using quasi-data from the QCD approach is in perfect agreement with the light-meson findings using experimental data. Finally, the ability of J-PARC to measure $π^{–}p → ϕn$ and $π^{–}p → J/ψn$ at the threshold, which are free from the VMD model, is presented. It enables one to understand the dynamics of $s\bar{s}$ and $c\bar{c}$ production at threshold and to search for the effects of LHCb’s heavy quark exotic states.

Vector meson nucleon scattering length↗
DOE OSTI2023

Comparative assessment of different aluminum alloys for neutron beam window applications

The choice of an aluminum alloy window along a neutron beam requires careful consideration depending on the requirements of the instrument end station. The windows should generally be thin to minimize loss of neutrons from the beam due to scattering and absorption but still thick enough to be structurally sound for safety requirements. Further, the microstructure of the material is dependent on the alloy and the preparation method and may introduce scattering artifacts or smearing of the instrument resolution that are not desirable. In this manuscript, SANS and total cross section measurements of several different aluminum alloys will be presented and compared in order to provide some useful insight to engineers working on future neutron instrument design.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2020

Higgs boson pair production via gluon fusion at N 3 LO in QCD

We present next-to-next-to-next-to-leading order ( N 3 LO ) QCD predictions for the Higgs boson pair production via gluon fusion at hadron colliders in the infinite top-quark mass limit. Besides the inclusive total cross sections at various collision energies, we also provide the invariant mass distribution of the Higgs boson pair. Our results show that the N 3 LO QCD corrections enhance the next-to-next-to-leading order cross section by 3.0% (2.7%) at s = 13 ( 100 ) TeV , while the scale uncertainty is reduced substantially below 3% (2%). We also find that a judicious scale choice can significantly improve the perturbative convergence. For the invariant mass distribution, our calculation demonstrates that the N 3 LO corrections improve the scale dependence but almost do not change the shape.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Searching for solitons in heavy-ion reactions near the fermi energy

Solitons are special shape-conserving hydrodynamical solutions that appear in many areas of physics. Here, we explore the existence of such solutions in microscopic descriptions of the heavy ion reaction 12 C + 28 Si → 12 C*+ 7α in the range E/A = 10 – 65 MeV/u. After recognizing the centrality of the collision and time-reversibility as fundamental requirements for the presence of solitonic 12 C, we utilize the Hybrid α-Cluster model for our analysis with a novel methodology. Our results suggest soliton production for E/A = 25 – 45 MeV/u in the forward direction, with a total cross section being at least in the order of a few μb. This, apart from being encouraging for possible experimental studies, maybe connected to possible toroid states of 28 Si at low angular momenta.

Heavy ion reactions↗
DOE OSTI2024

Insights from multinucleon transfer reactions in 206 Pb+ 118 Sn

Multinucleon transfer reactions for the 206 Pb + 118 Sn system were measured at E lab = 1200 MeV using the PRISMA large solid-angle magnetic spectrometer. The experiment was conducted at laboratory angles around the grazing angle, covering an angular range of approximately 20°. The resulting differential and total cross sections, along with Q-value distributions for various neutron and proton pick-up and stripping channels, are presented. The Q-value distributions suggest a transition from quasi-elastic to deep inelastic collision processes, particularly in channels involving nucleon transfers. The experimental results have been compared with GRAZING code calculations, showing good agreement for few-nucleon transfer channels, while channels with large nucleon transfers are underestimated, indicating the involvement of more complex processes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2026

Selection of a Pair of Experiments to Optimally Reduce Uncertainty in Targeted Nuclear Data

We propose a novel process to select a pair of differential and integral experiments that best reduce uncertainties in targeted 239 ⁢Pu nuclear data while compressing the current nuclear data pipeline from 20 to 3 years. 239⁢ Pu nuclear data are poorly understood for neutrons in the intermediate energy range due to sparsity and uncertainty in historical experiments. New experiments targeting this range will enable better understanding of these nuclear data, but choosing the ideal experiments to conduct is challenging. Beginning with a prior distribution represented by samples of nuclear data generated from theory, generalized least squares adjustments are made to incorporate data from historical experiments. To quantify potential uncertainty reduction obtainable from a pair of candidate experiments, we compute the D-optimality criterion of the posterior covariance of intermediate energy range nuclear data compared to the equivalent covariance after additional adjustment to the pair of candidate experiments. Repeating the process for each of many candidate pairs facilitates the final selection. Results support 63⁢ Cu total cross section measurements for differential experiments and alumina and alumina/graphite configurations for integral experiments. This analysis enables choosing differential and integral experiments to be executed concurrently while shortening decision times relative to the current nuclear data pipeline.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Convergent close-coupling calculations of electrons scattering on electronically excited molecular hydrogen

We use the adiabatic-nuclei molecular convergent close-coupling method to perform calculations of 0.01–1000 eV electrons scattering on the c 3 Π u , a 3 $Σ$$^{+}_{g}$, B 1 $Σ$$^{+}_{u}$, C 1 Π u , and EF 1 $Σ$$^{+}_{g}$ states of H 2 in the v=0 vibrational level. Elastic, superelastic, ionization, and grand-total cross sections are presented, as well as cross sections for excitation of the n=2–3 singlet and triplet states of H 2 (where n is the atomic-limit principle quantum number). Comparison with available theoretical results is made. Good agreement is found with the recent R-matrix results [J. Phys. B 53, 245203 (2020)] for most of the exchange and dipole-forbidden transitions, but not for the dipole-allowed transitions. Here, the sources of disagreement were found to be an unconverged partial-wave expansion and the utilization of the fixed-nuclei approximation (as opposed to adiabatic-nuclei) in the R-matrix calculations.

74 ATOMIC AND MOLECULAR PHYSICS↗