Multilayer target PIXE spectral simulation (X,X) secondary fluorescence correction algorithm

Abstract

Simulation of particle induced X-ray emission (PIXE) spectra is not a recent subject. Still, when samples are not homogeneous, problems emerge even in the simplest case of layered samples. If it is necessary to consider the presence of the same chemical element in more than one physically distinct layer the number of available simulation codes is very small. In addition, although X-ray emission spectra from PIXE experiments are much less prone to significant secondary fluorescence issues than their X-ray fluorescence spectrometry (XRF) counterpart, cases do emerge where secondary fluorescence calculations are necessary to ensure good PIXE spectral simulations, even if corrections are small. The case of secondary fluorescence induced by primary X-rays in thick homogeneous samples was solved long ago by various authors. In the case of non-homogenous targets, the problem becomes much more complex and, although also addressed long ago, a general solution cannot be found in the standard accessible literature on the PIXE technique. In the present work we revise a secondary fluorescence correction method presented in 1996 to handle homogeneous targets and extend it to be applicable to multilayered targets. Its implementation in the DT2 code allows simulation of PIXE spectra taking into account this type of matrix effect correction in complex multilayer targets. Fluorescence between different physical layers, the possibility of the presence of one chemical element in more than one layer, and the potential “illusional” presence of a chemical element in a given layer due to secondary fluorescence effects, when its real concentration in that layer is null, are dealt with. This is the first of what is intended to be a series of three papers. In this part I work, the model is presented for the case of secondary X-rays induced by primary X-rays produced by particle collisions. Applications and potentially demanding experimental conditions will be dealt with in part II, and the case of secondary X-rays induced by primary radiation from non-radiative transitions of fast electrons will be addressed in part III.