RSIC COMPUTER CODE PSR-089

1. NAME AND TITLE

SKEWGAUS: Skewed-Gaussian Line Peak Fitting Code -- Multichannel Analyzer (MCA) Spectra -- Ge(Li) and Semiconductor Detectors.

2. CONTRIBUTOR

Ames Laboratory, USDOE, Iowa State University, Ames, Iowa.

3. CODING LANGUAGE AND COMPUTER

Fortran IV, PL/1; IBM 360/370.

4. NATURE OF PROBLEM SOLVED

SKEWGAUS fits a skewed-Gaussian line shape to peaks in multichannel analyzer (MCA) spectra obtained with Ge(Li) and Si(Li) semiconductor detectors.

5. METHOD OF SOLUTION

SKEWGAUS reads an entire multichannel analyzer (MCA) spectrum and retains this spectrum in core while all fits are being performed on it. Any number of fits may be performed on a spectrum and any number of spectra may be included in a single execution of the program. Each fit may include a superposition of up to nine peaks in addition to a linear or (optionally) quadratic background. Parameters of different peaks may be constrained to vary proportionately during the fit. Different convergence criteria are applied to different peak parameters. Several options are available for handling the background, permitting it to be fit either concurrently with the peaks or separately. A modified statistical weighting of the MCA data points takes into account the differential non-linearity of the analyzer. SKEWGAUS was designed to supply its own initial estimates for nearly all parameters so that the amount of input data which must be supplied is minimal.

6. RESTRICTIONS OR LIMITATIONS

The maximum number of channels included in the channel-by-channel output listing is 210; the maximum number of variable parameters in a fit is 40. It is possible to change these numbers following instructions in the documentation.

The maximum number of peaks in a fit is 9. This number cannot be changed easily.

7. TYPICAL RUNNING TIME

On an IBM 360/65 system, a sample problem involving 7 fits with an average of 36 data points and 10 variable parameters per fit and requiring an average of 11 iterations per fit took a total of 16 seconds of CPU time (exclusive of the plot step).

8. COMPUTER HARDWARE REQUIREMENTS

SKEWGAUS is operable on the IBM 360/370 computers. It was designed to fit into 128 K bytes (32 K words) of main core storage. Alternatively, the MCA data array may be placed in bulk (LCS) core storage to reduce the main core size to 96 K bytes.

9. COMPUTER SOFTWARE REQUIREMENTS

A Fortran IV compiler is required.

10. REFERENCE

W. C. Schick, Jr., "SKEWGAUS: A Fortran Program for Fitting Peaks in Semiconductor Detector Spectra," IS-3460 (October 1974).

11. CONTENTS OF CODE PACKAGE

Included are the referenced document and one (1.2MB) DOS diskette which contains the source code input.

12. DATE OF ABSTRACT

March 1984.