COMPENSATION SCHEMES FOR PEAK-TAILING UNCERTAINTIES IN PIXE SPECTRA, USING THE GUPIX CODE

Many specimen types give rise to very intense peaks in the low-energy X-ray region of PIXE spectra. The tailing components of these peaks, arising in part from radiative Auger bands and from detector imperfections, are not perfectly known, and in the second case may exhibit dependence upon time and upon counting rate. A least-squares fit to the spectrum may therefore produce a channel versus energy relationship that is slightly in error; this in turn results in mis-fitting of the weak trace element peaks in the high-energy region of the spectrum. Two schemes are shown to avert this problem in the overall context of our GUPIX fitting code. One involves including X-rays from a weak radioactive source in the spectrum, which assists the code to converge to accurate energy calibration parameters. The other is a weighting scheme incorporated in GUPIX to de-emphasise the contribution of tailing features to the overall goodness-of-fit. Both are tested in some detail.