Trace Element mapping Without Off-Peak Measurements (MAN)

[John Donovan]

This topic is for discussing the new CalcImage capability to acquire trace element maps in *literally* half the time and with *better* precision than traditional off-peak measurements...

Of course there is a caveat, and that is: although precision is improved with the MAN background method, at trace levels, accuracy becomes the dominant issue. The solution is to use a suitable "blank" standard to adjust accuracy during the matrix iteration. Of course that means you're *not* going to be using this method for monazite mapping!

This blank correction method for improving accuracy in off-peak and/or MAN background corrected acquisitions is discussed in several topics such as:

http://probesoftware.com/smf/index.php?topic=4.0

http://probesoftware.com/smf/index.php?topic=307.0

http://probesoftware.com/smf/index.php?topic=29.0

http://probesoftware.com/smf/index.php?topic=204.0

This topic is reserved for discussion of the MAN method for trace element mapping in materials where a suitable blank standard can be obtained, e.g., pure metal, pure oxides and some simple silicates (ZrSiO4) and some simple sulfides (FeS2).

A nice example of how sensitive the MAN background correction is for quant mapping is seen here:



Note that because the Hf concentration in this zircon is changing slightly, the MAN calculated bgd intensities also vary (as they should), since the average Z is also changing.

Unlike what one sees in the off-peak measured data where the precision in the off-peak intensities is not sufficient to detect the variation in the continuum:

[John Donovan]

In the above example, we can also compare the quant elemental concentrations and see that the off-peak data is significantly less sensitive which is visibly affecting accuracy:

Off-peak quant:



MAN quant (same data without off-peak measurements):

[Probeman]

Here is a nice comparison between off-peak and MAN methods.



The two line profiles above were calculated using the *same* data set for both off-peak and MAN background methods for the U concentration maps shown in the above posts (note the maps are labeled Johnstones Camp zircon, but actually they are SIMS zircon oxygen standard AS3). Here we can easily see that accuracy is maintained and precision is significantly improved, while in practice, the MAN method acquisition would take ½ the acquisition time of the off-peak trace element maps.