Using one off-peak background and a slope to get the peak background counts

[Joe Boesenberg]

Both Cameca and JEOL software have an option for dealing with backgrounds, which involves measuring the counts of one background (either high or low) and using the slope of a line to calculate the background counts under the peak. For Cameca, the "slope" value was a simple multiplier on the counts from the off-peak background therefore the values were almost always near 1 (0.9 to 1.2 typically). In JEOL, there is a rise over run calculation employed to determine the count rate under the peak. PfE appears to have this background-slope option as well, but how does it function, like Cameca or JEOL or some other way?

Thanks. Joe

[John Donovan]

Both Cameca and JEOL software have an option for dealing with backgrounds, which involves measuring the counts of one background (either high or low) and using the slope of a line to calculate the background counts under the peak. For Cameca, the "slope" value was a simple multiplier on the counts from the off-peak background therefore the values were almost always near 1 (0.9 to 1.2 typically). In JEOL, there is a rise over run calculation employed to determine the count rate under the peak. PfE appears to have this background-slope option as well, but how does it function, like Cameca or JEOL or some other way?

Thanks. Joe

Probe for EPMA always acquires two off-peak backgrounds when using the Off-peak background acquisition method:



Of course with the mean atomic number (MAN) background method, only the on-peak intensities are acquired and with multi-point background (MPB) method, more than two backgrounds are acquired. Here is a nice explanation of the various background methods in Probe for EPMA:

https://smf.probesoftware.com/index.php?topic=1378.0

The MAN background method is usually the choice for geologists:

https://smf.probesoftware.com/index.php?topic=4.msg499#msg499

unless one is working with extremely complex materials (e.g., monazite or other uranium or REE materials) or extreme accuracy for trace elements is required, when the MPB method is useful.

But back to your question on using a single background and a slope... yes, you can do that in Probe for EPMA as described here:

https://smf.probesoftware.com/index.php?topic=68.msg11595#msg11595

showing how one can model the high or low off-peak background slope to a wavescan sample for best accuracy.  The idea being that although the absolute value of the background may change with different compositions, the slope will remain the same.