Dot mapping

There are three modes of analysis commonly used spectrum acquisition spatial distribution, or dot, mapping of the elements and elemental line scans. 

Often, more detailed information is needed on the distribution of a constituent. The technique of X-ray area scanning, or dot mappings can provide a qualirative view of elemental distributions. As the beam is scanned in a raster pattern on the specimen, a cathode ray rube scanned in synchronism is used to display a full white dot whenever the X-ray detector (WDS or EDS) detects an X ray within a certain narrow energy range. The pattern of dots is recorded on film to produce the dot map. Dot maps are subject to the following limitations ... 

Figure 5 X-ray area scan (dot map) showing the distribution of zinc at the grain boundaries of copper.

Mapping of major constituents can be carried out in approximately 15-30 minutes of scanning per image. Minor constituents require 0.5-3 hours, and trace constituents require 3-10 hours. An example of a dot map of zinc at concentrations in copper as low as 1% is shown in Figure 5 6 hours of scan time was needed to produce a dot map at this level. 

Since no background correction can be made, dot maps of minor and trace constituents are subject to possible artifacts caused by the dependence of the bremsstrahlung on composition, particularly with EDS X-ray measurement. 

The surface of this face is analyzed for silicon by obtaining what is called a silicon dot map. This technique analyzes the whole surface for silicon to a depth of one micron. The resulting photo shows the distribution of silicon on the face of the particle. 

Figure 1. Cross-section of a membrane functionalized with MPE functional groups imaged by x-ray dot mapping of phosphorous. The sparse black dots represent the background level of the epoxy used to mount the sample, while the concentrated band represents the membrane cross-section.

The distribution of geochemical data may be presented, in their most basic form, through the use of dot maps in which dots, or other symbols selected by the operator, of a size proportional to concentration are plotted at geographical coordinates for each sampled site. Dot sizes may be classified by means of concentration intervals based on percentiles or other statistical methods. Dot maps are often the most suitable method to represent isolated points of a discrete set of geochemical data. 

For each sampled site, radioactivity was measured by a portable scintillometer (Lima et al., 2005). The data set was used to produce various types of geochemical maps, including dot maps, baseline maps, factor analysis association maps, risk, partial and total radioactivity maps. 

FIGURE 8.2 Backscattered electron image of surface soil and corresponding x-ray elemental dot maps. White colors indicate highest concentration of target elements, and dark spots indicate low concentration. 

Figure 2. Elemental dot map of Paracas hair fiber indicating distribution of sulfur (left) and potassium (right).

Figure 6. Elemental dot map of bast fiber, Etowah Mound C 1145 core, indicating distribution of iron (left) and copper (right).

Figure 7.22. Elemental dot-maps. Shown is (a) elemental concentrations of Si, O, and F (as white pixels) overlaid onto the SEM image of a Nafion resin/sihca composite[33l (b) bright-held STEM image of a GaN/AlN/AlGaN nanowire cross section, with elemental mapping of Ga, N, and A1 (scale bar is 50nm).[34l...

FIGURE 34.25 SEM-XRF dot-map of Na in a cross-section of (a) Nafion 117 and (b) lonac MC 3470. It may be noted that the charged sites are more uniformly distributed in the homogeneous membrane Nafion 117, while the heterogeneous membrane lonac MC 3470 has nonconducting pockets shown by dark space. 

Examination and comparison of these ratio plots and dot maps for each of the two fields indicate that the more anomalous magnitude sites (large dots) match the composition of the known underlying reservoirs. The areal groupings and Pixler ratio plots of these specific components with their appropriate reservoirs lends confidence to the deduction that these soil-gas anomalies are the result of migration of petrogenic hydrocarbons from the underlying sedimentary sources. 

An alternative approach to contour maps is to generate a colour compositional dot map (Fig. 5-37), in which the size of each dot is proportional to the ethane magnitude and the colour is selected from the Pixler ratio plot (Fig. 5-37, inset, upper left). 

Fig. 5-37. Ethane colour compositional dot map for 1984 regional soil-gas data. Railroad Valley, Nevada inset, Pixler ratio composition.

Fig. 5-40. a) Ethane colour compositional dot map for 1985 Currant detailed soil-gas data. Railroad Valley, Nevada b) Pixler-type diagram characterisation of anomalous soil-gas hydrocarbons associated with known oil fields in Railroad Valley, Nevada c) methane/ethane scatter plot for 1985 Currant detailed soil-gas data. Railroad Valley, Nevada. 

Fig. 5-42. Comparison of ethane colour dot maps for Currant area. Railroad Valley, Nevada, illustrating repeatability of soil-gas compositional data a) 1984 regional survey and b) 1985 detailed survey.

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