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Phenomenology of light systems using R-matrix theory.

Description: Over the last 30 years, a program of R-matrix analyses has been carried out at Los Alamos in the mass range 2 {le} A {le} 18 that gives useful information about the light systems. These analyses provide data for astrophysics, as well as for neutronic and thermonuclear applications, and can yield important constraints from the experimental measurements on the nature of few-body interactions. Following a brief introduction to R-matrix theory, I will describe recent work on reactions in the A=2 (NN) and A=4 systems. Finally, some comments will be made about extending the theory to complex energies in order to obtain information about resonances and other types of S-matrix singularities.
Date: January 1, 2001
Creator: Hale, G. M. (Gerald M.)
Partner: UNT Libraries Government Documents Department

The Structure of 12N using 11C + p resonance scattering

Description: The level structure of {sup 12}N has been investigated from 2.2 to 11.0 MeV in excitation energy using a {sup 11}C + p resonance interaction with thick targets and inverse kinematics. Excitation functions were fitted using an R-matrix approach. Sixteen levels in {sup 12}N were included in the analysis, several of them are new. Spin-parity assignments, excitation energies and widths are proposed for these levels. To fit the high energy part of the excitation function, imaginary phase shifts had to be added to the phase shifts generated by the hard sphere scattering.
Date: March 2, 2006
Creator: Perajarvi, K.; Chang, Bo Fu; Rogachev, G.V.; Chubarian, G.; Goldberg, V.Z.; Guo, Q. et al.
Partner: UNT Libraries Government Documents Department

Study of low-lying resonant states in 16F using an 15O radioactiveion beam

Description: A 120 MeV {sup 15}O radioactive ion beam with an intensity on target of 4.5 x 10{sup 4} pps has been developed at the 88-inch cyclotron at the Lawrence Berkeley National Laboratory. This beam has been used to study the level structure of {sup 16}F at low energies via the p({sup 15}O,p) reaction using the thick target inverse kinematics method on a polyethylene target. The experimental excitation function was analyzed using R-matrix calculations. Significantly improved values for the level widths of the four low-lying states in 16F are reported. Good agreement with the theoretical spectroscopic factors is also obtained.
Date: January 22, 2007
Creator: Lee, D.W.; Perajarvi, K.; Powell, J.; O'Neil, J.P.; Moltz, D.M.; Goldberg, V.Z. et al.
Partner: UNT Libraries Government Documents Department

Uncoupled achromatic tilted S-bend

Description: A particular section of the electron beam transport line, to be used in the e-cooling project [l] of the Relativistic Heavy Ion Collider (RHIC), is constrained to displace the trajectory with both horizontal and vertical offsets so that the outgoing beamline is parallel to the incoming beamline. We also require that section be achromatic in both planes. This mixed horizontal and vertical achromatic Sbend is accomplished by rotating the two dipoles and the quadrupoles of the line, about the longitudinal axis of the incoming beam. However such a rotation of the magnetic elements may couple the transported beam through the first order beam transfer matrix (linear coupling). In this paper we study a sufficient condition, that the first order transport matrix (R-matrix) can satisfy, so that this section of beam transfer line is both achromatic and linearly uncoupled. We provide a complete solution for the beam optics which satisfies both conditions.
Date: June 23, 2008
Creator: Tsoupas,N.; Kayran, D.; Litvinenko, V. & MacKay, W.W.
Partner: UNT Libraries Government Documents Department

R-matrix for a geodesic flow associated with a new integrable peakon equation

Description: We use the r-matrix formulation to show the integrability of geodesic flow on an N-dimensional space with coordinates q k, with k = 1, ..., N, equipped with the co-metric g i j = e-141--431(2 - e-Iq1-q3l). This flow is generated by a symmetry of the integrable partial differential equation (pde) mt + um, + 3mux = 0, m = u - a2uZx( ai s a constant), which was recently proven to be completely integrable and possess peakon solutions by Degasperis, Holm and Hone. The isospectral eigenvalue problem associated with this integrable pde is used to find a new Lax representation for its N-peakon solution dynamics. By employing this Lax matrix we obtain the r-matrix for the integrable geodesic flow.
Date: January 1, 2001
Creator: Holm, Darryl D. & Qiao, Z. (Zhijun)
Partner: UNT Libraries Government Documents Department

On the Geometry of the Quantum Poincare Group

Description: We review the construction of the multiparametric inhomogeneousorthogonal quantum group ISO{sub q,r}(N) as a projection from SO{sub q,r}(N+2), and recall the conjugation that for N=4 leads to the quantum Poincare group. We study the properties of the universal enveloping algebra U{sub q,r}(iso(N)), and give an R-matrix formlation. A quantum Lie algebra and a bicovariant differential calculus on twisted ISO(N) are found.
Date: May 1, 1997
Creator: Aschieri, P.
Partner: UNT Libraries Government Documents Department

Informal Progress Report Contract Number: DE-FG03-02NA00074/A000

Description: OAK B127 We report on work performed under contract DE-FG03-03NA00074 since January 1,2003. The research is in the area of low energy nuclear reactions and nuclear structure. The progress on research on level densities and improvement to R-Matrix calculations are presented. The preparations to begin high resolution experiments on p-shell nuclei are reviewed.
Date: October 10, 2003
Creator: Brune, Carl R. & Grimes, Steven M.
Partner: UNT Libraries Government Documents Department

SAMDIST: A Computer Code for Calculating Statistical Distributions for R-Matrix Resonance Parameters

Description: The: SAMDIST computer code has been developed to calculate distribution of resonance parameters of the Reich-Moore R-matrix type. The program assumes the parameters are in the format compatible with that of the multilevel R-matrix code SAMMY. SAMDIST calculates the energy-level spacing distribution, the resonance width distribution, and the long-range correlation of the energy levels. Results of these calculations are presented in both graphic and tabular forms.
Date: January 1, 1995
Creator: Leal, L.C.
Partner: UNT Libraries Government Documents Department

Updated User's Guide for Sammy: Multilevel R-Matrix Fits to Neutron Data Using Bayes' Equations

Description: In 1980 the multilevel multichannel R-matrix code SAMMY was released for use in analysis of neutron-induced cross section data at the Oak Ridge Electron Linear Accelerator. Since that time, SAMMY has evolved to the point where it is now in use around the world for analysis of many different types of data. SAMMY is not limited to incident neutrons but can also be used for incident protons, alpha particles, or other charged particles; likewise, Coulomb exit hannels can be included. Corrections for a wide variety of experimental conditions are available in the code: Doppler and resolution broadening, multiple-scattering corrections for capture or reaction yields, normalizations and backgrounds, to name but a few. The fitting procedure is Bayes' method, and data and parameter covariance matrices are properly treated within the code. Pre- and post-processing capabilities are also available, including (but not limited to) connections with the Evaluated Nuclear Data Files. Though originally designed for use in the resolved resonance region, SAMMY also includes a treatment for data analysis in the unresolved resonance region.
Date: October 1, 2008
Creator: Larson, Nancy M.
Partner: UNT Libraries Government Documents Department

Updated Users' Guide for RSAP -- A Code for Display and Manipulation of Neutron Cross Section Data and SAMMY Fit Results

Description: RSAP [1] is a computer code for display and manipulation of neutron cross section data and selected SAMMY output. SAMMY [2] is a multilevel R-matrix code for fitting neutron time-of-flight cross-section data using Bayes' method. This users' guide provides documentation for the recently updated RSAP code (version 6). The code has been ported to the Linux platform, and several new features have been added, including the capability to read cross section data from ASCII pointwise ENDF files as well as double-precision PLT output from SAMMY. A number of bugs have been found and corrected, and the input formats have been improved. Input items are parsed so that items may be separated by spaces or commas.
Date: July 29, 2003
Creator: Sayer, R.O.
Partner: UNT Libraries Government Documents Department

Laboratory Measurements of 3 --> 2 X-ray Line Ratios of F-like Fe XVIII and Ni XX

Description: The intensity ratios of 3 {yields} 2 emission lines of Fe XVIII and Ni XX were measured on the Livermore electron beam ion trap (EBIT-I) with a flat-field grating spectrometer. The results were compared with distorted-wave (DW) calculations obtained with the Flexible Atomic Code and recent close-coupling calculations using the R-matrix code. The measured 3s {yields} 2p/3d {yields} 2p ratios are about 20-40% higher than the theoretical values. When more extended configuration interaction is included in the DW theory, the agreement with the measurements improved slightly. At the beam energies of these measurements, no significant resonance contribution is expected to be present, and the discrepancies represent the uncertainties in the direct excitation cross sections.
Date: March 8, 2007
Creator: Gu, M F; Chen, H; Brown, G V; Beiersdorfer, P & Kahn, S M
Partner: UNT Libraries Government Documents Department

Nuclear structure studies via neutron interactions. Progress report, 1 July 1994--30 June 1995

Description: Neutron total cross section measurements of {sup 122}Sn has been analyzed over the energy range 0.013 to 0.310 MeV. The R - matrix analysis has resulted in resonance and average parameters which provide for a complete representation of the neutron entrance the s{sub 1/2}, p{sub 1/2}, and p{sub 3/2} contributions. The s - and p - neutron strength functions have been determined to be 0.123 {plus_minus} 0.023 and 2.0 {plus_minus} 0.200, respectively (in units of 10{sup {minus}4}). Limits are placed on level spacings and strength functions for the individual partial wave components. The s - wave potential scattering radius has been determined to be 6.3 {plus_minus} 0.1 fm. Average scattering functions, deduced from the average parameters, have been used to determine the real well depth of an optical model potential which reproduces these functions. We find, as have others, that the real well depth is parity dependent. Two computer codes were developed: (1) a minimization program for finding parameters of a dispersive optical model which reproduce the high resolution data of the ORELA facility, and (2) an X-windows graphical user interface has been developed to permit interactive resonance analysis of the neutron total cross section data using analysis-and-minimization codes developed previously. These will contribute to the more routine analysis of ORELA data.
Date: January 1, 1995
Creator: Carlton, R.F.
Partner: UNT Libraries Government Documents Department

R-Matrix Evaluation of 160 Neutron Cross Sections up to 6.3 MeV

Description: We have evaluated {sup 16}O neutron cross sections in the resolved resonance region with the multilevel Reich-Moore code SAMMY. Resonance parameters were determined by a consistent analysis, including both Doppler and resolution broadening effects. To properly treat the {alpha} particle exit channel, an algorithm to calculate charged particle penetrabilities and shifts was incorporated into SAMMY.
Date: October 25, 2001
Creator: Sayer, R.O.
Partner: UNT Libraries Government Documents Department

R-Matrix Evaluation of {sup 16}O neutron cross sections up to 6.3 MeV

Description: In this paper the authors describe an evaluation of {sup 16}O neutron cross sections in the resolved resonance region with the multilevel Reich-Moore R-matrix formalism. Resonance analyses were performed with the computer code SAMMY [LA98] which utilizes Bayes' method, a generalized least squares technique.
Date: August 1, 2000
Creator: Sayer, R.O.; Leal, L.C.; Larson, N.M.; Spencer, R.R. & and Wright, R.Q.
Partner: UNT Libraries Government Documents Department

Data analysis and evaluation with SAMMY

Description: Various steps are required prior to the use of SAMMY to search for resonance parameters that best represent the experimental data. This lecture will focus on the common practice utilized to perform data evaluation, in particular, the evaluation procedure used for data analysis in the resolved-energy region using the reduced R-matrix formalism i.e., the Reich-Moore approximation. A similar approach can be used for data analysis and evaluation in other energy regions. The first step in the evaluation process consists of defining the energy range for which the evaluation will be carried out and making sure that all possible open reaction channels (i.e., inelastic channel, charged particle channels, etc.,) are identified.
Date: March 16, 2000
Creator: Leal, L.
Partner: UNT Libraries Government Documents Department

Recent experiments on near-threshold electron-impact excitation of multiply charged ions

Description: Some recent measurements of excitation of multiply charged ions by electrons studied in beam-beam experiments are highlighted. The emphasis is on absolute total cross sections measured with the merged electron-ion beams energy-loss (MEIBEL) technique, although some results obtained with the crossed-beams fluorescence method are also presented. The MEIBEL technique allows the investigation of optically-allowed and forbidden transitions with sufficient energy resolution, typically about 0.2 eV, to resolve resonance structures in the cross sections. Results from the JILA/ORNL MEIBEL experiment on dipole-allowed transitions in several ions demonstrate the success of various theoretical methods in predicting cross sections in the absence of resonances. Comparisons of R-matrix calculations and measured cross sections for spin-forbidden transitions in Mg-like Si{sup 2+} and Ar{sup 6+}, however, show that further refinements to the theory are needed in order to more accurately predict cross sections involving significant contributions from dielectric resonance`s and interactions between neighboring resonances.
Date: April 1, 1998
Creator: Bannister, M.E.; Djuric, N.; Woitke, O.; Dunn, G.H.; Chung, Y.S.; Smith, A.C.H. et al.
Partner: UNT Libraries Government Documents Department

SAMDIST: A computer code for calculating statistical distributions for R-matrix resonance parameters

Description: The SAMDIST computer code has been developed to calculate distribution of resonance parameters of the Reich-Moore R-matrix type. The program assumes the parameters are in the format compatible with that of the multilevel R-matrix code SAMMY. SAMDIST calculates the energy-level spacing distribution, the resonance width distribution, and the long-range correlation of the energy levels. Results of these calculations are presented in both graphic and tabular forms.
Date: September 1, 1995
Creator: Leal, L.C. & Larson, N.M.
Partner: UNT Libraries Government Documents Department

L/sup 2/ approach to R-matrix propagation: followup report. [Close-coupling methods, hybrid approach]

Description: A hybridized R-matrix propagation program was used to solve the four test problems presented by the NRCC workshop on close coupling methods. The hybrid method used both the L/sup 2/ approach reported earlier and the analytic (constant reference potential) method. Observations on the utility of the hybrid approach are presented. 2 references.
Date: January 1, 1979
Creator: Walker, R.B.
Partner: UNT Libraries Government Documents Department

Studies in Low-Energy Nuclear Science

Description: This report presents a summary of research projects in the area of low energy nuclear reactions and structure, carried out between 1 January 2003 and 31 December 2005 and supported by U.S. DOE grant number DE-FG03-03NA00074. Cross sections measured with high resolution have been subjected to an Ericson theory analysis to infer information about the nuclear level density. Other measurements were made of the spectral shape of particles produced in evaporation processes; these also yield level density information. A major project was the development of a new Hauser-Feshbach code for analyzing such spectra. Other measurements produced information on the spectra of gamma rays emitted in reactions on heavy nuclei and gave a means of refining our understanding of gamma-ray strength functions. Finally,reactions on light nuclei were studied and subjected to an R-matrix analysis. Cross sections fora network of nuclear reactions proceedingthrough a given compound nucleus shouldgreatly constrain the family of allowed parameters. Modifications to the formalism andcomputer code are also discussed.
Date: March 30, 2006
Creator: Brune, Carl R. & Grimes, Steven M.
Partner: UNT Libraries Government Documents Department