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1
Maps for additional elements, that may be present at
low or trace levels, can also be added to the map group,
but care is needed to correctly interpret the presence
of a trace element.
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2
In this example, a map for Mn has also been added. A
first look suggests that there are several regions of
the field of view that contain Mn.
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3
However, further inspection of the spectra
reconstructed from two regions show a Manganese peak in
only one of them.
The apparent presence of Mn in the middle and top
regions of the field is due to increased background
X-ray counts because the average atomic number in these
regions is higher. The map can be corrected by
subtracting a background map.
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4
First make a background window: Select 'Background'
tab in Element Setup, set the cursor at the beginning of
the window you want to make, hold down 'Shift' and
'click and drag' through the window. Select 'Add' and
save the background window. The position of the
background window should be close to the window of
interest and in a region where there are no other
overlapping elements.
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5
Comparing the Mn map and the 'background for
Manganese' map, we see significant variation in the
background intensity.
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6
To subtract the background map, click and drag the
background map over the element map - it doesn't have to
be perfectly aligned. The 'Process' window is displayed,
press 'Subtract'. The scaling factor is automatically
calculated to account for the difference in width
between the element and background windows.
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7
The background subtracted map is now displayed,
showing Mn is only present in one region. The
distribution of Mn can now be correctly interpreted.
The map label contains ‘*’ to indicate it has been
processed. When the project is saved the processed maps
are stored. However the original maps can always be
reconstructed from the Smartmap data by reselecting the
elements in the Element Setup step.
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8
Background subtraction of maps is important for
correct interpretation of maps for trace elements.
An alternative approach is to use QuantMap to process
and display SmartMap data. QuantMap uses the full
'filter and fit' routines of Inca Quantitative analysis
and therefore the effects of variation in background
intensity is automatically corrected.
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