Backscattering Corrections

Backscattering Corrections. The backscattering correction factor Fb is given by  

The overall correction factor is given by the product of these individual factors  

Iteration. Matrix correction factors are dependent on the composition of the specimen, which is not known initially. Estimated concentrations are initially used in the correction factor calculations and, having applied the corrections thus obtained the calculations are repeated until convergence is obtained, i.e. when the concentrations do not change significantly between successive calculations. 

Current commercial systems normally provide proprietary computer software which general incorporates the correction methods outlined above. 

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Figure 5.13. Backscattering correction factor R as a function of atomic number and W0 (= Ec/E0)...

A backscattering correction should be applied to alpha counting in 27t counters (Fig. 8.86). It has been determined that the number of backscat-... 

Since final revision of the manuscript for this chapter, NIST has released an additional database to those fisted in Section 3.2.3.3. The new database is the NIST Backscattering-Correction-Factor Database for Auger Electron Spectroscopy [138]. This database provides values of backscattering correction factors (BCFs) of... 

Ema data can be quantitated to provide elemental concentrations, but several corrections are necessary to account for matrix effects adequately. One weU-known method for matrix correction is the 2af method (7,31). This approach is based on calculated corrections for major matrix-dependent effects which alter the intensity of x-rays observed at a particular energy after being emitted from the corresponding atoms. The 2af method corrects for differences between elements in electron stopping power and backscattering (the correction), self-absorption of x-rays by the matrix (the a correction), and the excitation of x-rays from one element by x-rays emitted from a different element, or in other words, secondary fluorescence (the f correction). 

A correction for matrix effects is usually required. Difficulties in PIXE quantitation may be relieved by complementary information from RBS [290], or FTIR and elastic backscattering (EBS) analysis [291], FTIR can give a rough estimation of the elemental composition, while EBS or RBS can deliver information on the major-element composition. 

A straightforward Fourier transform of the EXAFS signal does not yield the true radial distribution function. First, the phase shift causes each coordination shell to peak at the incorrect distance second, due to the element-specific backscattering amplitude, the intensity may not be correct. The appropriate corrections can be made, however, when phase shift and amplitude functions are derived from reference samples or from theoretical calculations. The phase- and amplitude-corrected Fourier transform becomes ... 

In the squeezed position, the B radiation is trapped in the gap between the two surfaces and the electrons are backscattered from both of them (J 9). The larger contribution comes from the scattering from the high density material of the metal electrode (due to the Z-dependence of the backscattering power). The f correction which accounts for the backscattering is included in Equation 1. 

Z neighbors. Phase correction of the Fourier transform by the backscattering phase shift of one of the absorber—neighbor pairs is also extensively used. This has the effect of correcting the distances observed in the radial structure function as well as emphasizing the contributions from the chosen ab-... 

An example of practical importance in atmospheric physics is the inference of effective optical constants for atmospheric aerosols composed of various kinds of particles and the subsequent use of these optical constants in other ways. One might infer effective n and k from measurements—made either in the laboratory or remotely by, for example, using bistatic lidar—of angular scattering fitting the experimental data with Mie theory would give effective optical constants. But how effectual would they be Would they have more than a limited applicability Would they be more than merely consistent with an experiment of limited scope It is by no means certain that they would lead to correct calculations of extinction or backscattering or absorption. We shall return to these questions in Section 14.2. 

Additional evidence was obtained from Auger surface analysis of the Pt-sapphire specimens. Peak-to-peak heights of the lead line at 94 eV were taken from six spots on the Pt-covered area and from six spots on the adjoining sapphire area after a 24-hr exposure to pulsator exhaust. There was, after correction of the 94-eV line for backscattered electrons, more lead on the Pt-covered area in five out of six comparisons. On the average there was a 50% higher lead content on the Pt-covered areas. At lower lead exposures the differences are difficult to discern, since the accumulation of the ubiquitous particulate lead is not expected to vary from one kind of surface to another. Such behavior is essentially in accord with the findings of Williams and Baron (95). At present, however, we still must consider the preferential association of lead with Pt or Pd only as eminently plausible but in need of further, still more direct confirmation. 

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