RSICC COMPUTER CODE PSR-158

 

1.   NAME AND TITLE

SAMMY 8.1.0:        Code System for Multilevel R‑Matrix Fits to Neutron and Charged‑Particle Cross‑Section Data Using Bayes’Equations.

 

AUXILIARY CODES:

Eighteen auxiliary codes are provided along with the SAMMY code. These codes aid with such processes as preparing input, plotting results, studying statistical properties of resonance parameters, or including integral benchmark data as part of the experimental data set in the resolved resonance region (RRR). A complete list and description of the auxiliary codes are provided in Section X of the Updated Users’ Guide for SAMMY [1]

     

 

 

2.   CONTRIBUTOR

Oak Ridge National Laboratory, Oak Ridge, Tennessee.

 

3.   CODING LANGUAGE AND COMPUTER

FORTRAN, CMAKE; PC, Mac; Linux, MacOS or Windows (P00158MNYCP13).

 

4.   NATURE OF PROBLEM SOLVED

Please see the home page https://www.ornl.gov/division/rnsd/nuclear-data-and-criticality-safety  for the ORNL Nuclear Data Group and links from there to the SAMMY homepage.

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, α, 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 8.1.0 include:

            1. The auxiliary code SAMINT is now distributed with SAMMY. SAMINT can be used to include the information in integral benchmark experiments in the analysis of the RRR along with differential experimental data.

            2. New detector resolution functions based on MCNP simulations for liquid scintillator detector EJ-301, and for lithium glass detector NE-110..

            3. Updated physical constants in SAMMY to make results identical to SAMRML’s.

            4. Improved SQA by modernized build, test, version control, and bug tracking processes.

 

5.   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.

 

6.   RESTRICTIONS OR LIMITATIONS

None noted.

 

7.   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.

 

8.   COMPUTER HARDWARE REQUIREMENTS

SAMMY 8.1.0 was compiled by gfortran and ifort, and tested on Mac, Windows, and Linux.

 

9.   COMPUTER SOFTWARE REQUIREMENTS

8.1.0: GNU gfortran compiler v. 4.8.* and 4.9.* were used to compile SAMMY on Mac OS X 10.9.5 and on GNU/Linux 2.6.9, while Intel ifort compiler v. 15 was used to compile SAMMY on Linux 2.6.9 and Windows Server 2012.

 

10.  REFERENCES

a) Included in documentation:

[1] N. M. Larson, “Updated Users’ Guide for SAMMY: Multilevel R-Matrix Fits to Neutron Data Using Bayes’ Equations,” ORNL/TM-9179/R8 ENDF-364/R2 (October 2008).

[2] V. Sobes, L. Leal, G. Arbanas, “Updated Users’ Guide for SAMINT: A Code for Resonance Parameter Adjustment with Sammy Based on Integral Experiments,” ORNL/TM-2014/245 (August 2014).

[3] A. Youmans, L. Leal, R. Bahran, D. Yaron, G. Arbanas, “Improving Neutron Cross Section Data Analysis via Accurate Detector Resolution Functions from Monte-Carlo Simulations”

 

b) Background references:

[4] Please see references cited in the SAMMY users’ manual (ORNL/TM-9179/R8).

 

11.  CONTENTS OF CODE PACKAGE

The package is distributed on CD which contains the referenced documentation, source and test cases.

 

12.  DATE OF ABSTRACT

      April 1984, revised June 1994, February 1996, December 1996, April 1997, February 1999, September 1999, December 2000, January 2002, May 2002, May 2003, November 2006,  June 2007, and November 2008, April 2016, March 2017

 

KEYWORDS:   ENDF FORMAT; NUCLEAR MODELS; R-MATRIX THEORY; RESONANCES