THE GUELPH-PIXE SOFTWARE PACKAGE-II

Modifications and improvements made to the software package GUPIX in the period since it was first described in 1989 are reported. The code now handles thin, intermediate, thick and multi-layer specimens, and permits the inclusion of ''invisible'' elements and complexes that may be independent or stoichiometrically related to elements whose X-rays are visible in the spectrum. M X-rays have been added to the data base, and are included in secondary fluorescence computation. The nonlinear least squares spectrum fitting procedure has been altered to conclude with a linear least-squares section which provides better reproducibility. The conventional statistical weighting has been augmented by a systematic weighting scheme that deals with uncertainties in low-energy tailing features on the spectral peaks. A new, exact treatment of peak area errors gives good agreement with the earlier approximate approach. The influence of the digital filter used to remove spectrum background upon errors and detection limits is examined, and recommendations provided on the appropriate filter dimensions. Input and output options have been expanded, and various minor changes made.