RSIC COMPUTER CODE PSR-028

1. NAME AND TITLE

AMUSE: Gamma-Ray Spectra Unfolding Code.

2. CONTRIBUTOR

Los Alamos National Laboratory, Los Alamos, New Mexico.

3. CODING LANGUAGE AND COMPUTER

Fortran 63; CDC-6600.

4. NATURE OF PROBLEM SOLVED

AMUSE unfolds complex gamma-ray spectra obtained with Ge(Li) detectors. It will analyze 20 independent regions in a spectrum with up to 350 data points and 11 full-energy lines in each region. Gaussian and exponential functions represent the data analytically. The best least-squares values of the energy, area, and width can be obtained for each full-energy peak.

5. METHOD OF SOLUTION

AMUSE determines the number of counts in the full-energy peaks of complex gamma-ray spectra. A sequence of related spectra is recorded on magnetic tape, along with identification information. For unfolding, the first spectrum in the series is divided into regions that contain the peaks to be analyzed. Estimates of certain parameters are made and then each region is analyzed separately. If subsequent spectra use the same regional divisions, it is possible to use the results of one spectrum as the estimates for parameters in the following spectrum.

A Gaussian function with two exponential tails on its low-energy side is fitted to each full-energy peak. A single exponential function is then fitted to the entire region to represent contributions from higher-energy lines and background. The sign and magnitude of each parameter are checked after each iteration to prevent the least-squares analysis from diverging.

Spectra are taken in sequence from different positions on the element. Then a preparatory program is used to edit the data from the analyzer and to rewrite them into a format compatible with the CDC-6600 computer. This computer is used for the spectral unfolding code. Finally, another program is used to extract data from the sequence of unfolded spectra to infer the spatial distributions of selected radionuclides.

6. RESTRICTIONS AND LIMITATIONS

Analyses of spectra by this code are not influenced by the source geometry and no library of spectra is required. However, it is necessary to apply attenuation corrections to the results. These corrections are normally applied by other codes after the results of this code have been obtained.

AMUSE can analyze up to 220 peaks in a single pass through one spectrum.

7. TYPICAL RUNNING TIME

No study has been made by RSIC of typical running times for AMUSE.

8. COMPUTER HARDWARE REQUIREMENTS

AMUSE is operable on the CDC 6600 computer.

9. COMPUTER SOFTWARE REQUIREMENTS

A Fortran 63 compiler is required.

10. REFERENCE

W. M. Sanders and D. M. Holm, "An Analytical Method for Unfolding Gamma-Ray Spectra," LA-4030 (July 1968).

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.

12. DATE OF ABSTRACT

November 1983.