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PSR-0158 SAMMY.

SAMMY, Multilevel R-Matrix Fits to Neutron and Charged-Particle Cross-Section Data Using Bayes' Equations

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1. NAME OR DESIGNATION OF PROGRAM:  SAMMY-8.0.0
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2. COMPUTERS
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Program name Package id Status Status date
SAMMY-8.0.0 PSR-0158/17 Arrived 15-DEC-2008

Machines used:

Package ID Orig. computer Test computer
PSR-0158/17 Linux-based PC,PC Windows
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3. DESCRIPTION OF PROBLEM OR FUNCTION

The purpose of the code is to analyze time-of-flight cross section data in the resolved and unresolved resonance regions, where the incident particle is either a neutron or a charged particle (p, alpha, d, ...). Energy-differential cross sections and angular-distribution data are treated, as are certain forms of energy-integrated data.
  
In the resolved resonance region (RRR), theoretical cross sections are generated using the Reich-Moore approximation to R-matrix theory (and extensions thereof). Sophisticated models are used to describe the experimental situation: Data-reduction parameters (e.g. normalization, background, sample thickness) are included. Several options are available for both resolution and Doppler broadening, including a crystal-lattice model for Doppler broadening. Self-shielding and multiple-scattering correction options are available for analysis of capture cross sections. Multiple isotopes and impurities within a sample are handled accurately.
  
Cross sections in the unresolved resonance region (URR) can also be analyzed using SAMMY. The capability was borrowed from Froehner's FITACS code; SAMMY modifications for the URR include more exact calculation of partial derivatives, normalization options for the experimental data, increased flexibility for input of experimental data, introduction of user-friendly input options.
  
In both energy regions, values for resonance parameters and for data-related parameters (such as normalization, sample thickness, effective temperature, resolution parameters) are determined via fits to the experimental data using Bayes' method (see below). Final results may be reported in ENDF format for inclusion in the evaluated nuclear data files.
  
The new features added to SAMMY include:
1. The value of NU for ETA calculations can now be energy dependent.
2. Extensive revisions have been made to the self-shielding multiple-scattering (ssm) module.
3. Tabulated values (from Monte Carlo calculations) can be used instead of SAMMY-generated double-plus scattering corrections.
4. The "simple" resolution function may include a Gaussian whose width is a linear function of energy.
5. Input resonance parameters can now be presented as reduced width amplitudes gamma instead of partial widths GAMMA = 2Pgamma2.
6. For transmission measurements, the sample thickness may be non-uniform.
7. SAMMY now produces a third type of output file from which plots may be made-an ASCII file (with extension "LST") is created.
  
Please see the home page http://www.ornl.gov/sci/nuclear_science_technology/nuclear_data/ for the ORNL Nuclear Data Group and links from there to the SAMMY homepage.
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4. METHOD OF SOLUTION

Bayes' Theorem (generalized least squares) is used to find the 'best fit' values of parameters and the associated parameter covariance matrix. In the RRR, different data sets, or different energy ranges of the same data set, may be analyzed either simultaneously (though the implementation is somewhat awkward) or sequentially with results effectively equivalent to those which would be obtained via a simultaneous analysis, provided the output parameter values and covariance matrix from the first analysis are used as input to the second analysis. Also included are expeditious methods (the 'propagated uncertainty parameter' and 'implicit data covariance' procedures) of including the correct data covariance matrix within the fitting procedure. In the RRR, sequential analysis is the default mode though analyses can also be performed simultaneously. In the URR, the default mode is simultaneous analysis, though capability for sequential analyses is also available.
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5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM:  None noted.
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6. TYPICAL RUNNING TIME

Run time varies with the number of resonances and the number of channels per resonance, the number of flagged parameters, the number of data points to be fitted, the number and type of corrections for experimental conditions that must be applied, and the particular computer system on which the code is run. Each of the nine runs in test case tr001 took less than 0.15 second on a Dec Alpha computer under UNIX. The longest run in test case tr039, involving full multiple-scattering corrections plus Doppler broadening for 1751 data points, 123 resonances, and 36 varied parameters,  required 73 seconds of cpu time.  Under 200 seconds were needed for the longest run in test case tr071, with 3193 resonances, 590 varied parameters, and 3021 data points with both Doppler and resolution broadening.
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8. RELATED AND AUXILIARY PROGRAMS

Seventeen auxiliary codes are provided along with the SAMMY code. These codes aid with such processes as preparing input, plotting results, or studying statistical properties of resonance parameters. A complete list and description of the auxiliary codes is provided in Section X of the SAMMY users' manual.
  
ANGODF Convert PLOT file from energy/angle to angle/energy
CONVRT Convert from REFIT input to SAMMY or vice versa
SAMAMR Add, mix, or recover variables in COVariance file
SAMAMX Alter the value of one non-varied parameter in the COVariance file after completion of an analysis
SAMCPR Compare SAMMY calculations to those from other sources
SAMDIS Calculate statistical distributions for resonance parameters
SAMFTZ Modify the experimental energies with t0 and L0
SAMORT Plot the ORR resolution function
SAMPLT Alternative form for plot files
SAMQUA Generate resonance quantum numbers for particle pairs
SAMRML Read ENDF File 2; calculate cross sections and derivatives
SAMRPT Plot RPI resolution function
SAMRST Plot Gaussian plus exponential resolution function
SAMSMC Monte Carlo calculation of multiple scattering corrections
SAMSTA Generate staircase plots of resonance widths
SAMTHN Thin experimental data
SUGGEL Estimate quantum numbers for resonances
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9. STATUS
Package ID Status date Status
PSR-0158/17 15-DEC-2008 Masterfiled Arrived
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10. REFERENCES

Background references: Please see references cited in the SAMMY users' manual (ORNL/TM-9179/R8).
PSR-0158/17, included references:
- N. M. Larson: INSTALL.pdf (2008)
- N. M. Larson:
Updated Users' Guide for SAMMY: Multilevel R-Matrix Fits to Neutron Data
Using Bayes' Equations, ORNL/TM-9179/R8 (October 2008)
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11. MACHINE REQUIREMENTS

SAMMY 8.0.0 was tested on PC under Linux or Windows. Earlier versions of SAMMY were tested on IBM RS/6000 under AIX and on DEC Alpha, on which this version is expected to run. However, these systems were not available for testing of the current release.
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12. PROGRAMMING LANGUAGE(S) USED
Package ID Computer language
PSR-0158/17 FORTRAN-77
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13. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED

All Unix and Linux systems require a Fortran compiler to create executables. Windows users may run included PC executables (found in subdirectory /Windows), which were created on a Dell Dimension 4100 operating under Windows 2000 SP4 with Compaq Visual Fortran Professional Edition 6.6.B; alternatively, they may create their own executables using information provided in that same subdirectory. SAMMY-8.0.0 was tested on the following machines:
- Pentium running Windows 2000 SP2 with Compaq Visual Fortran Professional Ed. 6.6B
- Pentium under WindowsXP using included executables
- AMD Athlon with G77 Version 3.4.6 20060404 (RedHat 3.4.6-8)
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14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS

WinZIP 8.0 or newer is required to expand the provided compressed Unix tar file under Windows.
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15. NAME AND ESTABLISHMENT OF AUTHOR

Contributed by:
                Radiation Safety Information Computational Center
                Oak Ridge National Laboratory
                Oak Ridge, Tennessee, U. S. A.

Developed by:   Nancy M. Larson
                Oak Ridge National Laboratory
                Oak Ridge, Tennessee, U. S. A.
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16. MATERIAL AVAILABLE
PSR-0158/17
SAMMY and auxiliary code source files
Windows executable files
Unix and Windows scripts
exercises, test cases, and simulations
electronic documentation
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17. CATEGORIES
  • A. Cross Section and Resonance Integral Calculations
  • O. Experimental Data Processing

Keywords: ENDF, R matrix, neutron cross sections, nuclear models, reich-moore formula, resolved region, resonance.