THE GUELPH-PIXE SOFTWARE PACKAGE-II

Modifications and improvements made to the software package GUPIX in t he period since it was first described in 1989 are reported. The code now handles thin, intermediate, thick and multi-layer specimens, and p ermits 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 nonlinea r least squares spectrum fitting procedure has been altered to conclud e with a linear least-squares section which provides better reproducib ility. The conventional statistical weighting has been augmented by a systematic weighting scheme that deals with uncertainties in low-energ y tailing features on the spectral peaks. A new, exact treatment of pe ak area errors gives good agreement with the earlier approximate appro ach. The influence of the digital filter used to remove spectrum backg round upon errors and detection limits is examined, and recommendation s provided on the appropriate filter dimensions. Input and output opti ons have been expanded, and various minor changes made.