RSIC COMPUTER CODE PSR-031

1. NAME AND TITLE

SWIFT: Monte Carlo Neutron Spectra Unfolding Code.

2. CONTRIBUTOR

USAEC Health and Safety Laboratory, New York, New York.

3. CODING LANGUAGE AND COMPUTER

Fortran IV; CDC 6600.

4. NATURE OF PROBLEM SOLVED

SWIFT obtains unfolded spectra from measurement distributions obtained with the multi-sphere spectrometer. The program as written can handle as many as nine spectra simultaneously; it can also unfold spectra from detector arrays consisting of as many as seven detectors.

The use of SWIFT is not restricted to neutron spectrometry using the multi-sphere spectrometer. In theory, it can be used to unfold spectra from any spectrometer system.

5. METHOD OF SOLUTION

SWIFT uses a random number generator to generate neutron spectra whose measurement distributions for a given spectrometer are calculated using appropriate response data. These calculated distributions are then compared with actual measurements. This process is repeated a large number of times and the spectrum whose calculated distribution best agrees with the measurements is said to be the unfolded neutron spectrum. The first collision and maximum specific doses are then calculated for the neutron spectra.

6. RESTRICTIONS OR LIMITATIONS

None noted.

7. TYPICAL RUNNING TIME

SWIFT takes about 1500 seconds to run 1,000,000 tries for a single spectrum on the CDC-6600 computer. It takes little additional time to run multiple sets of data and is, therefore, recommended for processing batches of data from the same spectrometer. As the number of spectral channels increases, the computer time required to run a given number of tries will increase rapidly and the probability of obtaining good results will decrease.

8. COMPUTER HARDWARE REQUIREMENTS

SWIFT is operable on the CDC-6600 computer. The answers obtained for a given set of input data will depend on the random number generator used.

9. COMPUTER SOFTWARE REQUIREMENTS

A Fortran IV compiler is required.

10. REFERENCES

R. S. Sanna, "A User's Guide to SWIFT, A Monte Carlo Technique for Unfolding Neutron Spectra," HASL-244 (July 1971).

R. Sanna and K. O'Brien, "Monte-Carlo Unfolding of Neutron Spectra," Nucl. Inst. Meth., 91 (1971) 573-576.

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.

12. DATE OF ABSTRACT

November 1983.