1. NAME AND TITLE

SPECTRA: Determination of Neutron Spectra from Activation

SPECTRA was placed in RSIC through interaction with the American Society for Testing and Materials (ASTM) Standards Committee E10. Nuclear Technology and Applications and Subcommittee E10.05 Nuclear Radiation Metrology. The SPECTRA code package is included in the ASTM Proposed Standard Recommended Practices for the Application of Neutron Spectrum Adjusted Methods in Reactor Surveillance.

2. CONTRIBUTOR

Sandia Laboratories, Albuquerque, New Mexico.

3. CODING LANGUAGE AND COMPUTER

FORTRAN 63; CDC 1604/3600. FORTRAN IV; CYBER 73.

4. NATURE OF PROBLEM SOLVED

Neutron energy spectra are determined by an analysis of experimental activation detector data.

5. METHOD OF SOLUTION

A technique is used for solving the Fredholm integral equations describing neutron activation spectroscopy measurements. Through the representation of the spectrum and cross sections as piecewise linear functions of energy, the set of activation integral equations is reduced to a matrix equation. By introducing a constraint involving a ``best'' trial spectrum, it is shown that certain additional physical information usually available to an experimenter can be utilized. Based upon this constraint, a unique solution to the matrix equation can be obtained.

The user of the code has the option of obtaining the closed form exact solution and/or an approximate solution arbitrarily close to the exact solution through an iterative procedure.

The code is accompanied by a cross section library of 28 specific reactions and a complete data handling program which allows the removal, addition, and/or editing of the data on the cross section tape.

6. RESTRICTIONS OR LIMITATIONS

Number of energy points < 50.

7. TYPICAL RUNNING TIME

Estimated running time of the sample problem on the CDC 1604:

Cross Section Handling: 5 minutes

SPECTRA: 4 minutes

8. COMPUTER HARDWARE REQUIREMENTS

At least a 32K memory is required. The code was designed for the CDC 3600. It was converted for use on the CDC 1604 and on CDC CYBER 73, and uses standard I-O and 2 tapes.

9. COMPUTER SOFTWARE REQUIREMENTS

CDC compilers.

10. REFERENCE

C. R. Greer, J. A. Halbleib, and J. V. Walker, "A Technique for Unfolding Neutron Spectra from Activation Measurements," SC-RR-67-746 (December 1967).

11. CONTENTS OF CODE PACKAGE

Included are the referenced document and one (1.2MB) DOS diskette which contains for each of three hardware versions the source codes and a cross-section data library, and input and output for a sample problem.

12. DATE OF ABSTRACT

May 1969; updated July 1981.