Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Cross Reactions”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Ion dipole capture cross sections at low ion and rotational energies - Comparison of integrated capture cross sections with reaction cross sections for NH3 and H2O parent-ion collisions.

The numerical capture cross section is calculated from the capture ratio, defined as the fraction of trajectories reaching a prescribed minimum separation of 3 A. The calculated capture cross sections for a rotational temperature of 77 K suggest large reaction cross sections in 80 K experiments for the large dipole-moment target, methyl cyanide.

Dugan, J. V., Jr.↗
DOE OSTI2017

Measurement of the Am 242 m neutron-induced reaction cross sections

The neutron-induced reaction cross sections of 242m Am were measured at the Los Alamos Neutron Science Center using the Detector for Advanced Neutron-Capture Experiments array along with a compact parallel-plate avalanche counter for fission-fragment detection. A new neutron-capture cross section was determined, and the absolute scale was set according to a concurrent measurement of the well-known 242m Am(n,f) cross section. The (n,γ) cross section was measured from thermal energy to an incident energy of 1 eV at which point the data quality was limited by the reaction yield in the laboratory. Our new 242m Am fission cross section was normalized to ENDF/B-VII.1 to set the absolute scale, and it agreed well with the (n,f) cross section from thermal energy to 1 keV. Lastly, the average absolute capture-to-fission ratio was determined from thermal energy to E n = 0.1 eV, and it was found to be 26(4)% as opposed to the ratio of 19% from the ENDF/B-VII.1 evaluation.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Development of a Method for Measurement of Photonuclear-Reaction Cross Sections with the Aid of Simulated Quasimonoenergetic-Photon Spectra

A procedure for measuring photonuclear-reaction cross sections by employing the method of quasimonochromatization of the bremsstrahlung photon spectrum is developed. This procedure permits determining reaction cross sections via measuring the reaction yield at three fixed values of the electron energy. The procedure is equivalent to measuring the cross section in question for quasimonochromatic photons. Bremsstrahlung-photon spectra are obtained using state-of-the-art simulation means involving the GEANT4 code as applied to a specific experiment with allowance for its geometry, target thicknesses, electron-beam parameters, etc. The results obtained by simulating quasimonochromatic distributions of bremsstrahlung photons are presented for experiments at the LUE-8-5 linear electron accelerator of Institute for Nuclear Research (Moscow, Russian Academy of Sciences). These results are found to be in good agreement with the experimental energy distribution of the cross section for the reaction {sup 111}Cd(γ, γ') in the energy range between 5 and 8 MeV.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Modeled Neutron and Charged-Particle Induced Nuclear Reaction Cross Sections and their Uncertainties in the Region 37 < A < 47 (Rb-Ag)

A modeling effort to calculate nuclear reaction cross sections for use in radiochemical di-agnostics is presented. Systematics for the input parameters required by the Hauser-Feshbachstatistical model were developed and used to calculate neutron, proton, and deuteron inducednuclear reaction cross sections for targets ranging from Rubidium (Z= 37) to Silver (Z= 47).This is an expansion of the previous modeling effort described in Hoffman et. al. 2006(UCRL-TR-222275) that allows us to now calculate all new cross sections for radiochemical detector sets Rb, Rh, and Ag. We have also developed new systematics affecting our treatments of the nuclear level density and the gamma-ray strength function. Coupled with a range of the main parameter that affects pre-equilibrium, we develop upper and lower bounds to our recommended cross sections

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Neutron Induced Nuclear Reaction Cross Sections for Radiochemistry in the Region of Thallium, Lead, and Bismuth

We have developed a set of modeled nuclear reaction cross sections for use in radiochemical detector diagnostics. Systematics for the input parameters required by the Hauser-Feshbach statistical model developed in the TALYS code system are used to calculate neutron induced nuclear reaction cross sections for targets ranging from Thallium (Z = 81) to Bismuth (Z = 83).

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
NASA NTRS1982

On the geometric nature of high energy nucleus-nucleus reaction cross sections

Within the context of a high energy double-folding optical potential approximation to the exact nucleus-nucleus multiple-scattering series, eikonal scattering theory is used to investigate the validity of geometric reaction cross sections in relativistic heavy ion collisions. The potential used includes a finite range interaction and nuclear single-particle densities extracted from nuclear charge distributions by unfolding the finite proton charge distribution. Pauli correlation effects are also included in an approximate way. The sensitivity of the predictions to the assumed interaction, Pauli correlation approximation, and nuclear density distributions is investigated. These results are in agreement with early predictions concerning the geometric nature of relativistic heavy ion collisions and in disagreement with a recent analysis, utilizing the zero range approximation, which suggested otherwise. Reasons for the lack of agreement between the analyses are also presented. Finally, approximate applicability limits for geometric reaction cross sections are determined.

Townsend, L. W.↗
DOE OSTI2017

Proton capture reaction cross section measurements on Er 162 as a probe of statistical model calculations

It is crucial to measure reaction cross sections relevant to the astrophysical γ process so that theoretical reaction rates can be tested and validated with experimental data. Here, the total cross sections for the 162 Er(p,γ) 163 Tm and the 162 Er(p,n) 162 Tm reactions have been measured by the activation method in center-of-mass energies from 3.973 to 8.944 MeV and from 5.962 to 8.944 MeV, respectively. The nucleus 162 Er is the heaviest p nuclide to be measured by the activation method using γ -ray spectroscopy, so far. It is important to note that the energy range for the (p,γ) reaction measurement covers a large fraction of the astrophysically relevant energy region between 2.71 and 5.34 MeV. The targets were prepared by evaporating 28.2 % isotopically enriched 162 Er 2 O 3 powder onto carbon backing foils, and bombarded with proton beams provided by the FN Tandem Accelerator at the University of Notre Dame. The reaction yields have been determined by the observed activity of produced radioactive isotopes, which was detected offline by a high-purity germanium detector. The results are presented and compared with calculations from two statistical model codes: NON-SMOKER and TALYS.

150 ≤ A ≤ 189↗
DOE OSTI2021

Statistical Hauser-Feshbach model calculation for (α, n) reaction cross section and discrete level population

We calculate the α-particle induced reactions on 17,18 O, 19 F, and 23 Na, in the energy range 0 ≤ E α ≤ 10 MeV, with a particular attention to the branching ratios of populated discrete levels in the (α,n) channels. Since there are too many open channels to employ the R-matrix theory, we apply the statistical Hauser-Feshbach model to calculate these reaction cross sections and branching ratios. The branching ratio is defined as b n = $\frac{σ_n}{Σ_iσ_i + σ_c}$ , where σ n is the n-th level production cross section after the neutron emission, and σ c is the production of the continuum state. In the cases of our target nuclei and the energy range of interest, the residual nuclei of the neutron emission channel are always in their discrete states, so that σ c can be negligible.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Photoneutron reaction cross section measurements on Mo 94 and Zr 90 relevant to the p -process nucleosynthesis

The photodisintegration cross sections for the 94 Mo(γ,n) and 90 Zr(γ,n) reactions have been experimentally investigated with quasi-monochromatic photon beams at the High Intensity γ-ray Source (HIγS) facility of the Triangle Universities Nuclear Laboratory (TUNL). The energy dependence of the photoneutron reaction cross sections was measured with high precision from the respective neutron emission thresholds up to 13.5 MeV. Here, these measurements contribute to a broader investigation of nuclear reactions relevant to the understanding of the p-process nucleosynthesis. The results are compared with the predictions of Hauser-Feshbach statistical model calculations using two different models for the dipole γ-ray strength function. Lastly, the resulting 94 Mo(γ,n) and 90 Zr(γ,n) photoneutron stellar reaction rates as a function of temperature in the typical range of interest for the p-process nucleosynthesis show how sensitive the photoneutron stellar reaction rate can be to the experimental data in the vicinity of the neutron threshold.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

First Direct Measurement Constraining the Ar 34 ( α , p ) K 37 Reaction Cross Section for Mixed Hydrogen and Helium Burning in Accreting Neutron Stars

The rate of the final step in the astrophysical αp process, the 34 Ar(α,p) 37 K reaction, suffers from large uncertainties due to a lack of experimental data, despite having a considerable impact on the observable light curves of x-ray bursts and the composition of the ashes of hydrogen and helium burning on accreting neutron stars. Here, we present the first direct measurement constraining the 34Ar(α,p)37K reaction cross section, using the Jet Experiments in Nuclear Structure and Astrophysics gas jet target. The combined cross section for the 34 Ar,Cl(α,p) 37 K,Ar reaction is found to agree well with Hauser-Feshbach predictions. The 34 Ar(α,2p) 36 Ar cross section, which can be exclusively attributed to the 34 Ar beam component, also agrees to within the typical uncertainties quoted for statistical models. This indicates the applicability of the statistical model for predicting astrophysical (α,p) reaction rates in this part of the αp process, in contrast to earlier findings from indirect reaction studies indicating orders-of-magnitude discrepancies. This removes a significant uncertainty in models of hydrogen and helium burning on accreting neutron stars.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Importance of cross reaction covariance data for user applications

The characterization of the uncertainty in radiation damage metrics presents many challenges. This paper examines the current approaches to characterizing radiation damage metrics such as hydrogen and helium gas production, material heating, trapped charge in microelectronics, and lattice displacement damage. Critical uncertainty aspects go beyond just the material cross sections and involve the consideration of energy-dependent cross reaction correlations, the recoil ion energy spectrum, and models used for the partitioning of the recoil ion energy into various forms of energy deposition. This paper starts with a review of terminology and then examines the current approaches in the characterization of uncertainty in radiation damage metrics for several applications. The major deficiencies in the uncertainty of the damage metric characterization are also identified.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Forward modeling approach to nuclear reaction cross sections: Applications in neutron inelastic scattering

The development of nuclear reaction models for the production of evaluated nuclear data has traditionally been performed by comparing measured cross sections with predictions from reaction model codes whose physical input parameters are adjusted to obtain the best agreement between measured and modeled results. To more directly probe reaction model inputs, this work introduces a forward modeling approach to experimental reaction cross-section determination, where the most important physical input parameters to reaction model calculations are obtained via 𝜒 2 minimization between measured and calculated observables. This was demonstrated using data collected by the Gamma Energy Neutron Energy Spectrometer for Inelastic Scattering (GENESIS) at the 88-inch cyclotron at Lawrence Berkeley National Laboratory, a detection array consisting of organic liquid scintillators and high-purity germanium (HPGe) detectors. Using a broad-spectrum neutron beam and a 99.98%-enriched 56 Fe target, GENESIS was used to perform a simultaneous measurement of 56 Fe 𝛾-ray production cross sections and secondary neutron energy and angle distributions. The results of the forward modeling approach to the determination of energy-differential 𝛾-ray production cross sections for the yrast 4 + → 2 + and 6 + → 4 + transitions, as well as eight other off-yrast transitions, were compared against those obtained using conventional techniques, and the results are in good agreement. In addition to discrete 𝛾-ray yield total scattered neutron energy-angular distributions as a function of incident neutron energy were also obtained using forward modeling and found to agree with evaluated data, with the exception of elastic scattering at small angles. The fitted reaction model parameters obtained through forward modeling were also used to calculate the cross section for the unobserved (𝑛, 2⁢𝑛) reaction; excellent agreement with the current evaluation was obtained, providing a validation of the predictive capabilities of the forward model approach. This work bridges the gap between nuclear data experiment and evaluation by providing a new means for extracting inelastic neutron-scattering cross sections and neutron-induced 𝛾-ray production data while directly probing reaction model physics.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗