The principle of PIXE method consists in an ionization of the levels
near the atomic nucleus. This ionization is followed by a rearrangement
of the electronic architecture with emission of characteristic X-ray. The
detection of this radiation is realized by Si(Li) or intrinsic Ge semi-conductor
detectors. A typical spectrum is shown in the following picture. It is the
elementary analysis of vegetals that were contamined by water from a forbidden
stocking of industrial wastes.
The computing treatment of this spectrum gives the elementary concentration
of more than 20 elements with a detection limit near the ppm. The reality
or the confidence in these absolute values given by the PIXE method depends
on many factors as the counting statistics, the importance of the background
and the spectrum interpretation. When analysing a spectrum, secondary fluorescence,
auto-absorption of X-rays by the target and filters, escape peaks and electronic
pile-up have to be taken into account. By the way, it is extraordinary that
although all these possible errors, the confidence in the results is near
5% in the case of thick targets for which the slowdown of incident particles
when they penetrate the target is another error source. Indeed, the probability
of X-ray production depends on the incident particle energy and it is not
always evident to precisely know the energy lost per unity of charged particle
penetration in the analysed matter.
The characteristics of the method are the following:
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