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.
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.
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
12. DATE OF ABSTRACT
KEYWORDS: DATA PROCESSING, SPECTRA; GAMMA-RAY SPECTRUM ANALYSIS; UNFOLDING