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Analysis of neutron data in the resonance region via the computer code SAMMY

Description: Procedures for analysis of resonance neutron cross-section data have been implemented in a state-of-the-art computer code SAMMY, developed at the Oak Ridge Electron Linear Accelerator (ORELA) at Oak Ridge National Laboratory. A unique feature of SAMMY is the use of Bayes' equations to determine ''best'' values of parameters, which permits sequential analysis of data sets (or subsets) while giving the same results as would be given by a simultaneous analysis. Another important feature is the inclusion of data-reduction parameters in the fitting procedure. Other features of SAMMY are also described.
Date: January 1, 1985
Creator: Larson, N.M.
Partner: UNT Libraries Government Documents Department

Uncertainty propagation from raw data to final results. [ALEX]

Description: Reduction of data from raw numbers (counts per channel) to physically meaningful quantities (such as cross sections) is in itself a complicated procedure. Propagation of experimental uncertainties through that reduction process has sometimes been perceived as even more difficult, if not impossible. At the Oak Ridge Electron Linear Accelerator, a computer code ALEX has been developed to assist in the propagation process. The purpose of ALEX is to carefully and correctly propagate all experimental uncertainties through the entire reduction procedure, yielding the complete covariance matrix for the reduced data, while requiring little additional input from the experimentalist beyond that which is needed for the data reduction itself. The theoretical method used in ALEX is described, with emphasis on transmission measurements. Application to the natural iron and natural nickel measurements of D.C. Larson is shown.
Date: January 1, 1985
Creator: Larson, N.M.
Partner: UNT Libraries Government Documents Department

Preliminary study of pseudorandom binary sequence pulsing of ORELA

Description: It has been suggested that pseudorandom binary sequence (PRBS) pulsing might enhance the performance of the Oak Ridge Electron Linear Accelerator (ORELA) for neutron-induced, time-of-flight (TOF) cross-section measurements. In this technical memorandum, equations are developed for expected count rates, statistical variances, and backgrounds for a pulsing scheme in which a PRBS is superimposed on the periodic equalintensity ORELA bursts. Introduction of the PRBS modification permits neutrons of different energies originating from different bursts to reach the detector simultaneously, and the signal corresponding to a unique flight time to be extracted mathematically. Relative advantages and disadvantages of measurements from conventional and PRBS pulsing modes are discussed in terms of counting statistics and backgrounds. Computer models of TOF spectra are generated for both pulsing modes, using as examples a 20-meter /sup 233/U fission-chamber measurement and a 155-meter /sup 238/U sample-in transmission measurement. Detailed comparisons of PRBS vs conventional results are presented. This study indicates that although PRBS pulsing could enhance ORELA performance for selected measurements, for general ORELA operation the disadvantages from PRBS pulsing probably outweigh the advantages.
Date: March 1, 1980
Creator: Larson, N. M. & Olsen, D. K.
Partner: UNT Libraries Government Documents Department

Introduction to the theory and analysis of resolved (and unresolved) neutron resonances via SAMMY

Description: Neutron cross-section data are important for two distinct purposes: First, they provide insight into the nature of matter, thus assisting in the understanding of fundamental physics. Second, they are needed for practical applications (e.g., for calculating when and how a reactor will become critical, or how much shielding is needed for storage of nuclear materials, and for medical applications). Neutron cross section data in the resolved-resonance region are generally obtained by time-of-flight experiments, which must be carefully analyzed if they are to be properly understood and utilized. In this paper, important features of the analysis process are discussed, with emphasis on the particular techniques used in the analysis code SAMMY. Other features of the code are also described; these include such topics as calculation of group cross sections (including covariance matrices), generation and fitting of integral quantities, and extensions into the unresolved-resonance region and higher energy regions.
Date: February 1, 1998
Creator: Larson, N. M.
Partner: UNT Libraries Government Documents Department

Resonance parameter analysis with SAMMY

Description: The multilevel R-matrix computer code SAMMY has evolved over the past decade to become an important analysis tool for neutron data. SAMMY uses the Reich-Moore approximation to the multilevel R-matrix and includes an optional logarithmic parameterization of the external R-function. Doppler broadening is simulated either by numerical integration using the Gaussian approximation to the free gas model or by a more rigorous solution of the partial differential equation equivalent to the exact free gas model. Resolution broadening of cross sections and derivatives also has new options that more accurately represent the experimental situation. SAMMY treats constant normalization and some types of backgrounds directly and treats other normalizations and/or backgrounds with the introduction of user-generated partial derivatives. The code uses Bayes' method as an efficient alternative to least squares for fitting experimental data. SAMMY allows virtually any parameter to be varied and outputs values, uncertainties, and covariance matrix for all varied parameters. Versions of SAMMY exist for VAX, FPS, and IBM computers.
Date: January 1, 1988
Creator: Larson, N.M. & Perey, F.G.
Partner: UNT Libraries Government Documents Department

Introduction to the Theory and Analysis of Resolved (and Unresolved) Neutron Resonances via SAMMY

Description: Neutron cross-section data are important for two purposes: First, they provide insight into the nature of matter, increasing our understanding of fundamental physics. Second, they are needed for practical applications (e.g., for calculating when and how a reactor will become critical, or how much shielding is needed for storage of nuclear materials, or for medical applications). Neutron cross section data in the resolved-resonance region are generally obtained by time-of-flight experiments, which must be carefully analyzed if they are to be properly understood and utilized. In this report, important features of the analysis process are discussed, with emphasis on the particular techniques used in the analysis code SAMMY. Other features of the code are also described; these include such topics as calculation of group cross sections (including covariance matrices), generation and fitting of integral quantities, and extensions into the unresolved-resonance region and higher-energy regions.
Date: March 13, 2000
Creator: Larson, N.
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

Multilevel resonance analysis of sup 59 Co neutron transmission measurements

Description: Large discrepancies exist between the high-resolution {sup 59}Co neutron transmission data to Harvey et al. and the resolved resonance parameters of ENDF/B-VI. In order to provide new resonance parameters consistent with these data, the high-resolution transmission measurements have been analyzed with the computer code SAMMY. Results of that analysis are reported here.
Date: January 1, 1991
Creator: de Saussure, G. & Larson, N.M.
Partner: UNT Libraries Government Documents Department

User's guide for SAMMY: a computer model for multilevel r-matrix fits to neutron data using Bayes' equations

Description: A method is described for determining the parameters of a model from experimental data based upon the utilization of Bayes' theorem. This method has several advantages over the least-squares method as it is commonly used; one important advantage is that the assumptions under which the parameter values have been determined are more clearly evident than in many results based upon least squares. Bayes' method has been used to develop a computer code which can be utilized to analyze neutron cross-section data by means of the R-matrix theory. The required formulae from the R-matrix theory are presented, and the computer implementation of both Bayes' equations and R-matrix theory is described. Details about the computer code and compelte input/output information are given.
Date: November 1, 1980
Creator: Larson, N. M. & Perey, F. G.
Partner: UNT Libraries Government Documents Department

Statistical properties of the S-wave resonances of {sup 235}U

Description: The resonance parameters of {sup 235}U in the energy range 0 eV to 2.25 keV were obtained from a generalized least squares analysis of a large set of experimental data using the Reich-Moore formalism in the fitting code SAMMY. The aim of the present paper is to present the statistical properties of the s-wave resonance parameters generated from this study.
Date: June 1, 1997
Creator: Leal, L.C.; Derrien, H. & Larson, N.M.
Partner: UNT Libraries Government Documents Department

Covariance matrices for use in criticality safety predictability studies

Description: Criticality predictability applications require as input the best available information on fissile and other nuclides. In recent years important work has been performed in the analysis of neutron transmission and cross-section data for fissile nuclei in the resonance region by using the computer code SAMMY. The code uses Bayes method (a form of generalized least squares) for sequential analyses of several sets of experimental data. Values for Reich-Moore resonance parameters, their covariances, and the derivatives with respect to the adjusted parameters (data sensitivities) are obtained. In general, the parameter file contains several thousand values and the dimension of the covariance matrices is correspondingly large. These matrices are not reported in the current evaluated data files due to their large dimensions and to the inadequacy of the file formats. The present work has two goals: the first is to calculate the covariances of group-averaged cross sections from the covariance files generated by SAMMY, because these can be more readily utilized in criticality predictability calculations. The second goal is to propose a more practical interface between SAMMY and the evaluated files. Examples are given for {sup 235}U in the popular 199- and 238-group structures, using the latest ORNL evaluation of the {sup 235}U resonance parameters.
Date: September 1, 1997
Creator: Derrien, H.; Larson, N.M. & Leal, L.C.
Partner: UNT Libraries Government Documents Department

Merger of Nuclear Data with Criticality Safety Calculations

Description: In this paper we report on current activities related to the merger of differential/integral data (especially in the resolved-resonance region) with nuclear criticality safety computations. Techniques are outlined for closer coupling of many processes � measurement, data reduction, differential-data analysis, integral-data analysis, generating multigroup cross sections, data-testing, criticality computations � which in the past have been treated independently.
Date: September 20, 1999
Creator: Derrien, H.; Larson, N. M. & Leal, L. C.
Partner: UNT Libraries Government Documents Department

Introduction to theory and analysis of resolved (and unresolved) neutron resonances via SAMMY

Description: Neutron cross-section data are important for two distinct purposes: first, they provide insight into the nature of matter, thus assisting in the understanding of fundamental physics; second, they are needed for practical applications (e.g., for calculating when and how a reactor will become critical, or how much shielding is needed for storage of nuclear materials, and for medical applications). Neutron cross section data in the resolved-resonance region are generally obtained by time-of-flight experiments, which must be carefully analyzed if they are to be properly understood and utilized. In this paper, important features of the analysis process are discussed, with emphasis on the particular technique used in the analysis code SAMMY. Other features of the code are also described; these include such topics as calculation of group cross sections (including covariance matrices), generation and fitting of integral quantities, and extensions into the unresolved-resonance region and higher-energy regions.
Date: July 1, 1998
Creator: Larson, N.M.
Partner: UNT Libraries Government Documents Department

Resonance structure in the fission of (/sup 235/U + n)

Description: A new multilevel reduced R-matrix analysis of the neutron-induced resonance cross sections of /sup 235/U has been carried out. We used as a constraint in the analysis the angular anisotropy measurements of Pattenden and Postma, obtaining a Bohr-channel (or J, K channel) representation of the resonances in a two-fission vector space for each spin state. Hambsch et al., have reported definitive measurements of the mass- and kinetic-energy distributions of fission fragments of (/sup 235/U + n) in the resonance region and analyzed their results according to the fission-channel representation of Brosa et al., extracting relative contributions of the two asymmetric and one symmetric Brosa fission channels. We have explored the connection between Bohr-channel and asymmetric Brosa-channel representations. The results suggest that a simple rotation of coordinates in channel space may be the only transformation required: the multilevel fit to the total and partial cross sections is invariant to such a transformation. 32 refs., 4 figs.
Date: January 1, 1989
Creator: Moore, M.S.; de Saussure, G.; Leal, L.C.; Perez, R.B. & Larson, N.M.
Partner: UNT Libraries Government Documents Department

Aerosol optical depth derived from solar radiometry observations at northern mid-latitude sites

Description: Routine, automated solar radiometry observations began with the development of the Mobile Automated Scanning Photometer (MASP) and its installation at the Rattlesnake Mountain Observatory (RMO). We have introduced a microprocessor controlled rotating shadowband radiometer (RSR), both the single detector and the multi-filter/detector (MFRSR) versions to replace the MASP. The operational mode of the RSRs is substantially different than the MASP or other traditional sun-tracking radiometers, because, by virtue of the automated rotating shadowband, the total and diffuse irradiance on a horizontal plane are measured and the direct-normal component deduced through computation from the total and diffuse components by the self-contained microprocessor. Because the three irradiance components are measured using the same detector for a given wavelength, the calibration coefficients are identical for each component, thus reducing errors when comparing them. The MFRSR is the primary radiometric instrument in the nine-station Quantitative Links Network (QLN) established in the eastern United States in late 1991. Data from this network are being used to investigate how cloud- and aerosol-induced radiative effects vary in time and with cloud structure and type over a mid-latitude continental region. This work supports the DOE Quantitative Links Program to quantify linkages between changes in atmospheric composition and climate forcing. In this paper we describe the setup of the QLN and present aerosol optical depth results from the on-going measurements at PNL/RMO, as well as preliminary results from the QLN. From the time-series of data at each site, we compare seasonal variability and geographical differences, as well as the effect of the perturbation to the stratosphere by Mt. Pinatubo. Analysis of the wavelength dependence of optical depth also provides information on the evolution and changes in the size distribution of the aerosols.
Date: January 1, 1994
Creator: Laulainen, N. S.; Larson, N. R.; Michalsky, J. J. & Harrison, L. C.
Partner: UNT Libraries Government Documents Department

HIC-1: a first approach to the calculation of heavy-ion reactions at energies greater than or equal to 50 MeV/nucleon

Description: A preliminary version of a heavy-ion-interaction model is described in detail. The basic assumption of the model is that heavy-ion reactions can be described by the interactions of the individual nucleons of the projectile and target with one another. Transitions to the eigenstates of the target and projectile are ignored. Encouraging results are obtained when comparisons with experimental data are made on an absolute basis, even though there are differences of factors of three or more in these comparisons for some of the data. Several ways of improving the model amd extending its applicability to lower energies are also presented. (5 figures, 4 tables) (auth)
Date: January 1, 1974
Creator: Bertini, H. W.; Gabriel, T. A.; Santoro, R. T.; Hermann, O. W.; Larson, N. M. & Hunt, J. M.
Partner: UNT Libraries Government Documents Department

Evaluation of the silicon isotopes for ENDF/B-VI

Description: Isotopic evaluations for {sup 28,29,30}Si performed for ENDF/B-VI are briefly reviewed. The evaluations are based on analysis of experimental data and results of model calculations. Evaluated data are given for neutron induced reaction cross sections, angular and energy distributions, and gamma-ray production cross sections. All necessary data are given to allow KERMA (Kinetic Energy Released in MAterials) and displacement cross sections to be calculated directly from information available in the evaluations. These quantities are fundamental to studies of neutron heating and radiation damage. 20 refs., 4 figs.
Date: January 1, 1991
Creator: Hetrick, D.M.; Larson, D.C.; Larson, N.M.; Fu, C.Y. & Epperson, S.J.
Partner: UNT Libraries Government Documents Department

sup 56 Fe and sup 60 Ni resonance parameters

Description: High-resolution neutron transmission and differential elastic-scattering measurements were made for a {sup 56}Fe-enriched iron target at the Oak Ridge Electron Linear Accelerator (ORELA). A natural iron target was used for transmission measurements below 160 keV. The data were analyzed from 5 to 850 keV. Parameters were obtained for 33 {ell} = 0 and 242 {ell} > 0 resonances. New {sup 6}Li-glass transmission data were acquired for two {sup 60}Ni-enriched sample thicknesses. The neutron width for the 2.253-keV resonance was determined to be 59.3 {plus minus} 0.6 meV and the radiation width 553 {plus minus} 50 meV. 9 refs., 3 figs., 2 tabs.
Date: January 1, 1991
Creator: Perey, C.M.; Perey, F.G.; Harvey, J.A.; Hill, N.W. & Larson, N.M.
Partner: UNT Libraries Government Documents Department

R-matrix evaluation of {sup 28}Si, {sup 29}Si and {sup 30}Si up to 1.8 MeV

Description: The intent of this paper is to present and describe the procedures used to evaluate the silicon cross sections in the resolved resonance region up to 1.8 MeV with the multilevel Reich-Moore R-matrix formalism and to present the results. The resonance analyses were performed with the SAMMY code which utilizes a generalized least squares technique (i.e., Bayes` method).
Date: June 1, 1997
Creator: Leal, L.C.; Larson, N.M.; Larson, D.C. & Hetrick, D.M.
Partner: UNT Libraries Government Documents Department

Efficient use of Bayes` equations for fitting neutron-induced cross section and integral data

Description: Analysis of differential and integral neutron data requires the use of a fitting procedure such as Bayes` method, used in the analysis code SAMMY. In this paper, techniques for more efficient use of Bayes` method are described. A reformulation of Bayes` equations permits truly simultaneous fitting to multiple measurements without overhead costs required for calculating theoretical values simultaneously. Several techniques for properly including data covariances are also described.
Date: December 31, 1998
Creator: Larson, N.M.; Leal, L.C. & Derrien, H.
Partner: UNT Libraries Government Documents Department

R-matrix analysis of the {sup 240}Pu neutron cross sections in the thermal to 5700 eV energy range

Description: Resonance analysis of high resolution neutron transmission data and of fission cross sections were performed in the neutron energy range from the thermal regions to 5,700 eV by using the Reich-Moore Bayesian code SAMMY. The experimental data base is described and the method of analysis is given. The experimental data were carefully examined in order to identify more resonances than those found in the current evaluated data files. The statistical properties of the resonance parameters are given. A new set of the average values of the parameters is proposed, which could be used for calculation of the average cross sections in the unresolved resonance region. The resonance parameters are available IN ENDF-6 format at the national or international data centers.
Date: August 1, 1997
Creator: Derrien, H.; Bouland, O.; Larson, N.M. & Leal, L.C.
Partner: UNT Libraries Government Documents Department

Evaluation of {sup 28,29,30}Si neutron induced cross sections for ENDF/B-VI

Description: Separate evaluations have been done for the three stable isotopes of silicon for ENDF/B-VI. The evaluations are based on analysis of experimental data, supplemented by results of nuclear model calculations. The computational methods and the parameters required as input to the nuclear model codes are reviewed. Discussion of the evaluated data given for resonance parameters, neutron induced reaction cross sections, associated angular and energy distributions, and gamma-ray production cross sections is included. Extensive comparisons of the evaluated cross sections to measured data are shown in this report. The evaluations include all necessary data to allow KERMA (Kinetic Energy Released in MAterials) and displacement cross sections to be calculated directly. These quantities are fundamental to studies of neutron heating and radiation damage.
Date: April 1, 1997
Creator: Hetrick, D.M.; Larson, D.C.; Larson, N.M.; Leal, L.C. & Epperson, S.J.
Partner: UNT Libraries Government Documents Department

Integral data analysis for resonance parameters determination

Description: Neutron time-of-flight experiments have long been used to determine resonance parameters. Those resonance parameters have then been used in calculations of integral quantities such as Maxwellian averages or resonance integrals, and results of those calculations in turn have been used as a criterion for acceptability of the resonance analysis. However, the calculations were inadequate because covariances on the parameter values were not included in the calculations. In this report an effort to correct for that deficiency is documented: (1) the R-matrix analysis code SAMMY has been modified to include integral quantities of importance, (2) directly within the resonance parameter analysis, and (3) to determine the best fit to both differential (microscopic) and integral (macroscopic) data simultaneously. This modification was implemented because it is expected to have an impact on the intermediate-energy range that is important for criticality safety applications.
Date: September 1, 1997
Creator: Larson, N.M.; Leal, L.C. & Derrien, H.
Partner: UNT Libraries Government Documents Department