RSIC COMPUTER CODE PSR-099

1. NAME AND TITLE

SPEC-4: Calculated Recoil Proton Energy Distributions from Monoenergetic and Continuous Spectrum Neutrons.

2. CONTRIBUTORS

Atomic Weapons Research Establishment, Aldermaston, England.

Oak Ridge National Laboratory, Oak Ridge, Tennessee.

3. CODING LANGUAGE AND COMPUTER

Fortran IV; IBM 360/370.

4. NATURE OF PROBLEM SOLVED

SPEC-4 calculates the neutron spectrum incident on a spherical proportional counter containing hydrogen. It allows a complete analysis of an experimental recoil proton spectrum obtained from a spherical gas filled proportional counter. The only input data required in addition to the experimental spectrum are the counter parameters and an estimate of the neutron spectrum above the highest energy to be analyzed. The answer is presented as neutron flux per unit lethargy interval in groups of width equal to the counter resolution.

5. METHOD OF SOLUTION

The basis of the method is a knowledge of the pulse height distribution produced in the counter by mono-energetic neutrons (including "wall effect"). An analytical expression is used to generate this "response function" for the given neutron energy. The integrated response to neutrons above EMAX can now be calculated and subtracted from the measured pulse height distribution. The neutron spectrum in defined energy groups is then found by unfolding a matrix of response functions at the specified energies, using "back substitution." To reduce oscillations, the response function matrix is differentiated and unfolded from the differentiated data.

6. RESTRICTIONS OR LIMITATIONS

The neutron spectrum above a maximum energy EMAX (depending on gas pressure) must be known. The measured proton range v energy data is also required.

Storage and time restrictions can be neglected compared with the need to get reasonable statistical accuracy on the input data. This has been found to restrict the number of energy groups to approximately 30.

7. TYPICAL RUNNING TIMES

SPEC-4 ran in 45 seconds on the IBM 360.

8. COMPUTER HARDWARE REQUIREMENTS

SPEC-4 is operable on the IBM 360/370 computers. A card or tape reader and printer are required; auxiliary storage is not.

9. COMPUTER SOFTWARE REQUIREMENTS

A Fortran IV compiler is required.

10. REFERENCES

P. W. Benjamin, C. D. Kemshall, and A. Brickstock, "The Analysis of Recoil Proton Spectra," AWRE 09/68.

C. D. Kemshall, "The Use of Spherical Proportional Counters for Neutron Spectrum Measurements," AWRE 031/73.

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.