RSICC CODE PACKAGE PSR-508

1. NAME AND TITLE

SUGGEL: Program Suggesting the Orbital Angular Momentum of a Neutron Resonance from the Magnitude of Its Neutron Width.

2. CONTRIBUTORS

Oak Ridge National Laboratory, Oak Ridge, Tennessee, and Nuclear Data Evaluation Laboratory, Korea Atomic Energy Research Institute, Taejon, Korea.

3. CODING LANGUAGE AND COMPUTER

Fortran 77; DEC Alpha and IBM RS/6000 (P00508MNYWS00).

4. NATURE OF THE PROBLEM SOLVED

The SUGGEL computer code produces a "suggested value" for the orbital angular momentum (l) of a resonance from the magnitude of its g_n. SUGGEL also either suggests the most probable resonance spin (J), or assigns the spin value randomly, according to user preference. The suggested value is based on the probability calculated by using the Bayesian approach.

The method (as well as the calculation of the probability density functions) could be incorporated into the SAMMY code. An effective alternate procedure would be to run the three codes RSAP, SUGGEL, and then SAMMY. In this procedure, the RSAP peak search of the measured total or scattering cross sections will first provide approximate resonance energy and g_n values; then SUGGEL will generate a priori parameter file with suggested spin group identification. Finally, SAMMY will be used to perform the detailed analysis. SUGGEL is included in the P00158MNYCP09/SAMMY-M6 code package.

5. METHOD OF SOLUTION

The suggestion is based on the probability that a resonance having a certain value of g_n is an l-wave resonance. The probability is calculated by using Bayes' theorem on the conditional probability. The probability density functions (pdf's) of g_n for up to d-wave (l=2) have been derived from the ² distribution of Porter and Thomas. The pdf's take two possible channel spins into account. This code is a tool which evaluators will use to construct resonance parameters and help to assign resonance spin. The use of this tool is expected to reduce time and effort in the evaluation procedure, since the number of repeated runs of the fitting code (e.g., SAMMY) may be reduced.

The SUGGEL computer code was developed and tested on both resonance parameters taken from actual evaluations and on artificially-generated parameters. Test results show that SUGGEL is capable of providing a reasonable first estimate for the orbital angular momentum quantum numbers for many resonances. By using SUGGEL as a pre-analysis tool before running SAMMY, the analyst can expect a reduction in the time and effort required for proper spin group assignments.

6. RESTRICTIONS OR LIMITATIONS

This Bayesian approach is unfortunately not appropriate for some resonances at high energy region, higher than ~hundred keV, where the magnitudes of g_n's of s-wave and higher l-waves are comparable. This was anticipated initially and is observed in a test for ²⁷Al with SUGGEL. There is another kind of deficiency: The Bayesian approach fails in distinguishing the total angular momentum. However, in spite of deficiencies in the l assignment for higher energy resonances as well as in the J assignment, SUGGEL is still effective in providing a good initial guess of spin group for a detailed analysis.

7. TYPICAL RUNNING TIME

It takes only a few seconds to run the sample cases.

8. COMPUTER HARDWARE REQUIREMENTS SUGGEL was installed and tested on DEC Alpha and IBM workstations.

9. COMPUTER SOFTWARE REQUIREMENTS

A Fortran compiler is required on Unix operating systems.

10. REFERENCES

a) included in document:

S. Y. Oh and L. C. Leal, "SUGGEL: A Program Suggesting the Orbital Angular Momentum of A Neutron Resonance from the Magnitude of its Neutron Width," ORNL/TM-2000/314 (February 2001).

b) background information:

N. M. Larson, "Updated Users' Guide for SAMMY: Multilevel R-Matrix Fits to Neutron Data Using Bayes' Equations," ORNL/TM-9179 (August 1984), ORNL/TM-9179/R1 (July 1985), ORNL/TM-9179/R2 (June 1989), ORNL/TM-9179/R3 (September 1996), ORNL/TM-9179/R4 (December 1998), ORNL/TM-9179/R5 (October 2000).

11. CONTENTS OF CODE PACKAGE

Included are the referenced document in 10.a and a Unix tar file which is transmitted on a DOS formatted diskette.

12. DATE OF ABSTRACT

August 2001.

KEYWORD: NEUTRON CROSS SECTIONS