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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 OSTI2026

Mapping Rydberg States of H 2 with the Halfium R-Matrix Method

In this article, we use the Halfium R-matrix method to investigate the Rydberg states of the H 2 molecule up to n = 20, filling the gap above the low-lying bound states already calculated with configuration interaction packages. Moreover, we show that the use of Quantum Defect Theory scaling laws, allows for a comprehensive analysis of the regular patterns resulting from the coupling between Rydberg series and doubly excited states. The results should open the door for more efficient quasi-diabatization of the potential energy curves which is required for calculating cross sections and rate coefficients of the (e + H 2 + ) collisional processes, involved in the plasma modeling for fusion devices.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

EDA R-Matrix Evaluations Report on n+ 9 Be, n+ 16 O [Slides]

This presentation discusses new developments in light-element R-matrix evaluation and recent light-element work. The presentation also reviewed R-matrix theory, EDAf90 code implementation, including interface EDAf90 with NJOY, ENDFtk, EXFOR/CSISRS, and a new evaluation for n+ 9 Be. The presentation concludes by stating that further development is needed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

R-matrix description of particle energy spectra produced by low-energy 3 H + 3 H reactions

An R-matrix model for three-body final states is presented and applied to a recent measurement of the neutron energy spectrum from the 3 H + 3 H→ 2n + α reaction. The calculation includes the n alpha and n n interactions in the final state, angular momentum conservation, antisymmetrization, and the interference between different channels. A good fit to the measured spectrum is obtained, where clear evidence for the 5 He ground state is observed. The model is also used to predict the alpha-particle spectrum from 3 H + 3 H as well as particle spectra from 3 He + 3 He. The R-matrix approach presented here is very general, and can be adapted to a wide variety of problems with three-body final states.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2023

R-Matrix Analysis of the Neutron-Induced Cross Sections on 143 Nd Measured at LANSC [Slides]

An established use of R-Matrix codes is being implemented at LANSCE. There are unique features accessible with detectors at LANSCE that can be used to perform more complete R-Matrix analysis. Further, Spin separation is a powerful technique that can be applied in DANCE measurements. Additionally, a unique method to measure transmission with DICER is being undertaken. Transmission and capture data were analyzed in this work. The study can be extended to other channels. The results of the 143 Nd data are presented in this work. New resonances found in this work: 21 compared to ENDF/B-VIII.0 and JEFF-3.3, and 24 compared to JENDL-5. Wrong spin assignment in 23 resonances in ENDF/B-VIII.0, 25 in JEFF-3.3 and 26 in JENDL-5. The 143 Nd and 147,149 Sm have been analyzed. Exciting future for new measurements and analysis!

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2010

Electron collisions with the BH{sub 2} radical using the R-matrix method

Differential, integral, and momentum-transfer cross sections for the rotationally elastic and inelastic scattering of electron by the BH{sub 2} radical at low collision energies (0-8 eV) are reported in a 22-state molecular R-matrix method. The excitation cross sections from the ground X {sup 2}A{sub 1} state to the first two excited states {sup 2}B{sub 1} and {sup 4}A{sub 2} are calculated as well, for incident electron energies from the respective thresholds up to 8 eV. Configuration-interaction wave functions are used to represent the target states which account for the correlation effects. Four shape and three Feshbach resonances are detected. The Born-closure approximation is applied for the elastic and dipole-allowed transitions to account for the l>4 partial waves excluded from the R-matrix calculations.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1996

FEM R-Matrix Calculations of Electron-H2 Collisions

Electron-H2 Collisions have been studied using the finite-element R-matrix method. Our approach uses a mixed finite-element and Gaussian basis to describe the continuum electron. In the inner region, the multi-centered nature of the Gaussian basis provides an efficient representation in the regions of space near the nuclei, whereas the piecemeal and energy-independent nature of the FEM basis is particular well suited for R-matrix calculations. Fixed nuclei calculations have been carried out at 1.4 a(sub 0), the equilibrium internuclear distance of the ground state. Up to six target states are included: the X(sup 1)E+(sub g), b(sup 3)E+(sub u), a(sup 3)E+(sub g), B(sup 1)E+(sub u), c(sup 3)II(sub u), and C(sup 1)II(sub u) states, and configuration-interaction functions are used to describe the target states. The results will be compared with available theoretical and experimental data.

Huo, Winifred M.↗
DOE OSTI2018

Electron impact excitation of N-like ions from the ICFT R-matrix calculation

We carried out intermediate coupling frame transformation (ICFT) R-matrix calculations on N-like ions (11≤Z≤20), which included a total of 272 fine structure levels in both the configuration interaction (CI) and close-coupling (CC) collision expansions. Comparisons with previous theoretical values were made in terms of energy levels, radiative transition rates, and oscillator strengths. The effective collision strengths (ϒ) were estimated in the temperature range of 10{sup 4}–10{sup 7} K. An excellent agreement with available computations was reached for dipole-allowed transitions, while differences in ϒ were found for non-dipole allowed and forbidden transitions. This discrepancy is mainly attributed to the difference in CC expansions. Our calculations provide a good supplement to the electron impact excitation data on N-like ions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

$\mathcal{R}$ -matrix analysis of η + nat Cl reactions relevant to molten-salt reactor designs [Abstract]

Performed with support from the U.S. Nuclear Criticality Safety Program in an effort to provide improved chlorine cross section and corresponding covariance data, the R-matrix analysis of neutron induced reactions for two stable chlorine isotopes, 35,37 Cl, was performed in the energy range of thermal up to 1.2 MeV. Starting from the repository of the ENDF/B-VIII.0 library and following recent measurement campaigns, this work represents a significant improvement in the evaluation of the ( η , p ) reaction channel. The evaluation methodology uses the $\mathcal{R}$ -matrix code SAMMY to generate a set of Reich-Moore resonance parameters. As predicted by recently measured 35 Cl( η , p ) data, the presented evaluation features a dramatic increase in the magnitude of the ( η , p ) reaction channel over the ENDF/B-VIII.0 and previous nuclear data ENDF/B released libraries. Together with details of the evaluation procedure, the impact of the updates in the outgoing proton emissions on reactivity coefficients for different molten-salt reactor designs is presented and discussed.

charged-particle↗
DOE OSTI2023

Light Elements $R$-matrix Analyses with the SAMMY code towards the Foundation of Charged-particle Nuclear Data Libraries [Slides]

This presentation covers newly developed SAMMY module for inverse channel transformation. Additionally covered is the R-matrix analysis of 7 Be compound nucleus and the R-­matrix analysis of 17 O compound nucleus. Further touched on is the evaluated Nuclear Data File generation and processing with the AMPX code. The presentation concludes with talks on future evaluation work and tests on light nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Electron-impact excitation of Fe{sup 2+}: A comparison of intermediate coupling frame transformation, Breit-Pauli and Dirac R-matrix calculations

Modeling the spectral emission of low-charge iron group ions enables the diagnostic determination of the local physical conditions of many cool plasma environments such as those found in H II regions, planetary nebulae, active galactic nuclei, etc. Electron-impact excitation drives the population of the emitting levels and, hence, their emissivities. By carrying-out Breit-Pauli and intermediate coupling frame transformation (ICFT) R-matrix calculations for the electron-impact excitation of Fe{sup 2+}, which both use the exact same atomic structure and the same close-coupling expansion, we demonstrate the validity of the application of the powerful ICFT method to low-charge iron group ions. This is in contradiction to the finding of Bautista et al., who carried-out ICFT and Dirac R-matrix calculations for the same ion. We discuss possible reasons.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

R-Matrix Codes for Charged-particle Induced Reactionsin the Resolved Resonance Region

A Consultant’s Meeting was held at the IAEA Headquarters, from 5 to 7 December 2016, to discuss the status of R-matrix codes currently used in calculations of charged-particle induced reaction cross sections at low energies. The meeting was a follow-up to the R-matrix Codes meeting held in December 2015, and served the purpose of monitoring progress in: the development of a translation code to enable exchange of input/output parameters between the various codes in different formats, fitting procedures and treatment of uncertainties, the evaluation methodology, and finally dissemination. The details of the presentations and technical discussions, as well as additional actions that were proposed to achieve all the goals of the meeting are summarized in this report.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

R-matrix Resolved Resonance Region Evaluation of 140,142 Ce

Oak Ridge National Laboratory completed the resolved resonance region (RRR) evaluation of the two most abundant cerium isotopes, 140 Ce (88.45%) and 142 Ce (11.11%), as requested by the US Nuclear Criticality Safety Program. These evaluations are based on recent high-resolution transmission and capture measurements performed on nat Ce and highly enriched 142 Ce samples at the JRC-Geel Linear Accelerator facility, as well as measured thermal constants available from the EXFOR database. Starting from the resonance parameters of the ENDF/B-VIII.0 library followed by a preliminary R-matrix analysis, an updated set of resonance parameters and corresponding covariance information were derived by fitting these measured data using the Reich–Moore approximation of the R -matrix theory, as implemented in the SAMMY code system. The 140 Ce RRR upper energy limit was kept at 200 keV, whereas the 142 Ce resonance region was extended from 13 to 26 keV. Updated statistical properties were obtained for the new evaluations and compared to those derived from the ENDF/B-VIII.0 nuclear data library. The new evaluation work improved some of the discrepancies found in previous work, such as the capture resonance integral and stellar Maxwellian-averaged cross sections. These integral quantities were mainly derived from the fit of the latest measured data, especially the neutron capture yield data for 142 Ce isotope.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Progress on the R-matrix Analysis for the n+ 181 Ta Evaluation [Slides]

This presentation discusses how nuclear data evaluations can influence the accuracy of computational nuclear design calculations. It also discusses the motivation for a new evaluation of 181 Ta. The goals of the evaluations are to generate a set of resonance parameters in the Resolved Resonance Region (RRR) that extends up to 2.6 keV, to generate a set of average resonance parameters in the Unresolved Resonance Region (URR) up to 100 keV (derived from the RRR parameters), and to generate covariance information for both RRR and URR. The presentation discusses how several different experimental data sets will be fit simultaneously in the evaluation of 181 Ta. It states that the level density of 181 Ta can make R-matrix fitting a challenge as the width of the levels increase with energy (as well as decreasing experimental resolution) and the measured resonances can overlap. The presentation concludes by discussing R-matrix analysis and covariance information as the latter is important when propagated to quantify the uncertainty on output responses of nuclear design calculations such as the multiplication factor k .

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2016

R-matrix and inverse Shapovalov form

We construct the inverse Shapovalov form of a simple complex quantum group from its universal R-matrix based on a generalized Nagel-Moshinsky approach to lowering operators. We establish a connection between this algorithm and the ABRR equation for dynamical twist.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Electron-impact study of SOS using the R-matrix method

We have carried out a comprehensive study of electron impact on open SOS isomer by using the R-matrix method. Elastic (integrated and differential), momentum-transfer, excitation, and ionization cross sections along with efffective collision frequency over a wide electron temperature range (100-30 000 K) have been presented. The target states are represented by including correlations via a configuration interaction technique. The results of the static-exchange, correlated one-state, and 31-state close-coupling approximation are presented. Our study has detected a shape resonance, five core-excited shape resonances, and two Feshbach resonances in the 31-state model. We detect a stable bound state of SOS{sup -} having configuration 1a{sub 1}{sup 2}2a{sub 1}{sup 2}...9a{sub 1}{sup 2},1b{sub 1}{sup 2}2b{sub 1}{sup 2}3b{sub 1},1b{sub 2}{sup 2}2b{sub 2}{sup 2}...7b{sub 2}{sup 2},1a{sub 2}{sup 2}2a{sub 2}{sup 2} with a vertical electronic affinity value of 1.999 eV. The ionization cross sections are calculated in the binary-encounter Bethe model in which Hartree-Fock molecular orbitals at self-consistent level are used to calculate kinetic and binding energies of the occupied molecular orbitals.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2022

Modernization efforts for the R-Matrix code SAMMY [Slides]

This presentation details modernization efforts for the R-Matrix code SAMMY. It provides an overview of SAMMY, modernization and maintenance goals, modernization accomplishments, covariance data, SAMMY API development, as well as future plans.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Recent Developments in the R-Matrix Code SAMMY [Slides]

This presentation covers recent developments in the R-Matrix Code SAMMY. The presentation starts with a discussion around SAMMY releases. Secondly it provides updates in the program flow. The presentation concludes with goals and achievements in the modernization efforts.

97 MATHEMATICS AND COMPUTING↗