RSIC COMPUTER CODE PSR-090

1. NAME AND TITLE

NPTXS: Data Generator: Neutron Point Cross Sections from ENDF/B Resolved and Unresolved Resonance Parameters.

AUXILIARY ROUTINE

ICLOCK: Non-standard Subroutine.

2. CONTRIBUTOR

Oak Ridge National Laboratory, Oak Ridge, Tennessee.

3. CODING LANGUAGE AND COMPUTER

Fortran IV and Assembler Language; IBM 360/370.

4. NATURE OF PROBLEM SOLVED

NPTXS permits the "pre-processing" of ENDF resonance nuclides and the creating of pointwise files for the total, elastic scattering, fission, and (n,gamma) cross sections at a given input temperature.

5. METHOD OF SOLUTION

The single-level or the multilevel Breit-Wigner formalism is used for calculation of cross sections in the resolved resonance region. Pointwise cross sections in the unresolved resonance region are computed by taking averages over suitable Porter-Thomas distributions of the neutron and fission widths. Cross sections can be Doppler-broadened using numerical integration techniques or by using PSI and CHI functions. Unnecessary points, which can be reproduced by interpolation between adjacent points, within a desired input tolerance, are eliminated. Infinite dilution resonance integrals are computed and serve as a gross check on the accuracy of the calculation.

6. RESTRICTIONS OR LIMITATIONS

The principal restriction is the availability of adequate core storage. NPTXS is flexibly dimensioned which means that array sizes may be set for a particular problem at execution time. Problems with up to ~15,000 points can be run in 540 K bytes of core storage; core storage requirements are not affected by the number of nuclides in a case.

7. TYPICAL RUNNING TIME

Running times for NPTXS are a function of several parameters and vary greatly from one nuclide to another. The sample problem, ²³³U, ENDF/B-IV MAT 1260, required 1.9 minutes on the IBM 360/91 computer. ²³⁸U, ENDF/B-IV MAT 1262, requires about 16 minutes CPU time on the IBM 360/91 computer.

8. COMPUTER HARDWARE REQUIREMENTS

NPTXS was designed to operate on computers of the IBM 360/50/65/75/91 and CDC 6600/7600 class. Approximately 540 K bytes of directly addressable core are required. External storage such as magnetic tape or disk devices must be available. The clock is sampled.

9. COMPUTER SOFTWARE REQUIREMENTS

Fortran IV--level H and Assembler Language compilers are required.

10. REFERENCES

"NPTXS: AMPX Module to Produce Point Data from ENDF/B for Resonance Nuclides."

"Exact Doppler Broadening of Evaluated Neutron Cross Sections," by D. E. Cullen, O. Ozer, and C. R. Weisbin (paper).

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, updated December 1991.