hkl] are found to depend on the direction of the primary beam, however, to a different extent for the different parameters.
040] measured with three different directions of the primary beam (17).
With a flatbed scanner (the line scanner typically used for the analysis of x-ray films does not permit to collect area scans), the complete reconstruction of the intensity profile of the primary beam is then possible (2).
The uneven intensity distribution along the lens radius induces a non linearity in the transfer function of the lens-slit assembly; in other words, the integrated intensity of the primary beam does not follow the increase of the area selected by the cross-slits collimator.
A simple treatment of this case follows by using a square opening for the slits (horizontal and vertical dimensions of the primary beam are therefore equal to w) and supposing beam, polycapillary collimator and crossed-slits setup being concentric.
The non-uniformity of the primary beam can be introduced via a function describing the distribution of intensity through the section of the beam.
A set of random rays is generated, possessing the characteristics (intensity/divergence) known for the primary beam, and their path followed from the source to the detector (if the latter is reached).
The non-uniform intensity distribution in the primary beam and complex movements of the specimen can be thus considered.
The electrons scattered out of the beam by elastic interactions with the atoms of the gas form a broad, non-focused "skirt" around the unscattered, focused portion of the primary beam.
The choice of a high primary beam energy, 20 keV or more, provides efficient excitation of the upper part of the photon energy range, and is a good choice for the VPSEM-ESEM since a high beam energy also serves to minimize gas scattering.
Bilde-Sorenson and Appel have described a method to estimate the contribution of the skirt based upon comparing two measurements, the first with the primary beam and the skirt striking the specimen and the second after intercepting the primary beam with a beam stop (9,10).
The most serious is the action of gas scattering of the primary beam to degrade the effective spatial resolution through remote excitation of x rays.
Nockolds, Quantitative EDS Analysis in the Environmental Scanning Electron Microscope (ESEM) Using a Bremsstrahlung Intensity-Based Correction for Primary Beam Variation and Scatter, Microsc.