RSIC COMPUTER CODE PSR-092

1. NAME AND TITLE

FORIST: Neutron Spectrum Unfolding Code System -- Iterative Smoothing Technique.

FORIST is a modification of PSR-17/COOLC. The smoothing function used in COOLC has been redefined and an iterative procedure for selecting the widths of the smoothing functions has been added. This iterative procedure optimizes the energy resolution for a given statistical error of the unfolded spectrum.

2. CONTRIBUTORS

Nuclear Engineering Program, University of Illinois at Urbana-Champaign, Urbana, Illinois.

McMaster University, Hamilton, Ontario, Canada.

3. CODING LANGUAGE AND COMPUTER

Fortran IV; IBM 360/370 (A), CYBER (B).

4. NATURE OF PROBLEM SOLVED

FORIST solves the matrix unfolding problem for neutron spectrum measurements using NE-213 proton-recoil spectrometry.

5. METHOD OF SOLUTION

A constrained least-squares unfolding procedure is used. The response function used in unfolding includes the resolution of the spectrometer; therefore, the unfolded spectrum has large errors initially. The unfolded spectrum must be smoothed to reduce these errors. The smoothing functions are determined iteratively to optimize energy resolution.

6. RESTRICTIONS OR LIMITATIONS

FORIST is currently dimensioned for a 113 by 77 response matrix. It is written for measurements consisting of two different gain runs. The iterative procedure used in smoothing is applicable for unfolding neutron spectra; a slight change in the smoothing procedure may be necessary to apply this iterative procedure to unfolding gamma-ray spectra.

7. TYPICAL RUNNING TIME

The sample problem, which contains two spectra, takes approximately 30 seconds on an IBM 360/91.

8. COMPUTER HARDWARE REQUIREMENTS

FORIST is operable on the IBM 360/370 or the CYBER computers. Approximately 270 K bytes of storage are needed. A scratch disc or tape, printer, and punch are required.

9. COMPUTER SOFTWARE REQUIREMENTS

A Fortran IV compiler is required.

10. REFERENCES

R. H. Johnson, D. T. Ingersoll, B. W. Wehring, and J. J. Dorning, "NE-213, Neutron Spectrometry System for Measurements from 1.0 to 20 MeV," Nucl. Instr. and Meth. 145 (1977) 337-346.

R. H. Johnson, "A User's Manual for COOLC and FORIST," PNE-75-107 (December 1975).

R. H. Johnson, J. J. Dorning, and B. W. Wehring, "Integral Test of Cross Sections Using Neutron Leakage Spectra from Spheres of Iron, Niobium, Beryllium, and Polyethylene," Proceedings of the Conference on Nuclear Cross Sections and Technology, Washington, D.C. (March 1975). [To be published by National Bureau of Standards.]

D. T. Ingersoll and B. W. Wehring, "Gamma-Ray Pulse-Height Response of an NE-213 Scintillation Detector," Nucl. Instr. and Meth. 147 (1977) 551-561.

D. T. Ingersoll, Informal Note on FORIST (July 12, 1976).

11. CONTENTS OF CODE PACKAGE

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

12. DATE OF ABSTRACT

March 1984; reviewed May 1984, updated August 1991.