**1. NAME AND TITLE**

SIOB: Calculation of Least-Squares Shape Fitting Several Neutron Transmission Measurements
Using the Breit-Wigner Multilevel Formula.

**2. CONTRIBUTOR**

Computer Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee.

**3. CODING LANGUAGE AND COMPUTER**

Fortran IV; IBM 360/370.

**4. NATURE OF PROBLEM SOLVED**

SIOB was developed to least-square fit the shape of neutron transmission curves. It was designed
for the simultaneous analysis of transmissions on the same energy scale through several thicknesses.
It was also successfully applied to the analysis of transmission data through samples composed of
medium and lightweight nuclei.

**5. METHOD OF SOLUTION**

Any number of measurements on a common energy scale for different sample thicknesses can be
simultaneously fitted. The computed transmission curves can be broadened with either a Gaussian or
a rectangular resolution function, or both, with the resolution width a function of energy. The total
cross section is expressed as a sum of single-level or multilevel Breit-Wigner terms and Doppler
broadened using a fast interpolation routine.

**6. RESTRICTIONS OR LIMITATIONS**

The number of data points, resonance levels and variables which can be handled simultaneously
is limited only by the overall dimensions of two arrays in the program and by the stability of the matrix
inversion.

**7. TYPICAL RUNNING TIME**

In a test problem, seven transmissions with 3750 data points each were simultaneously fitted using
74 resonances and 110 variable parameters. On an IBM 360/91 computer, this problem took 47 min
of CPU time for 3 iterations.

**8. COMPUTER HARDWARE REQUIREMENTS**

SIOB is operable on the IBM 360/370 computers.

**9. COMPUTER SOFTWARE REQUIREMENTS**

A Fortran IV compiler is required.

**10. REFERENCE**

G. de Saussure, D. K. Olsen, and R. B. Perez, "SIOB: A Fortran Code for Least-Squares Shape
Fitting Several Neutron Transmission Measurements Using the Breit-Wigner Multilevel Formula,"
ORNL/TM-6286 (ENDF-261) (May 1978).

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced document and one (1.2MB) DOS diskette which contains the source
code and sample problem input and output.

**12. DATE OF ABSTRACT**

March 1984.

**KEYWORDS: ** EXPERIMENTAL DATA ANALYSIS; NUCLEAR MODELS