calcimage and multipoint backgrounds

[Philipp Poeml]

Hi John,

is the multipoint background method already implemented in calcimage? And if not, any plans to implent this soon?

Cheers
Philipp

[Probeman]

Hi John,

is the multipoint background method already implemented in calcimage? And if not, any plans to implent this soon?

Cheers
Philipp

Hi Phillip,
Use of the multi-point bgd in Calcimage (I was wondering when someone would ask about this!), would require the acquisition of multiple (more than two!) off-peak x-ray maps. The problem is that the precision of these maps will be insufficient to benefit from the MLB method.

So we will probably never implement it because of this precision limitation.
john

[Philipp Poeml]

That is very bad news for mapping actinides and other M-lines... In fact I have acquired the background maps exactly at the position of the multi point background positions, in theory it should work.

All right then, let's go for standard off peak maps then.

Cheers
Philipp

[John Donovan]

That is very bad news for mapping actinides and other M-lines... In fact I have acquired the background maps exactly at the position of the multi point background positions, in theory it should work.

All right then, let's go for standard off peak maps then.

Cheers
Philipp

Hi Philipp,
Yes, I already said I agree that it will work, but that the precision of xray map pixels is insufficient for the method.

To explain further I mean that the difference in accuracy between normal off peak and multi-point bad methods is smaller than the precision of the map pixels.

Think of it this way: what is your typical off peak pixel dwell time for mapping?  Let's say you are crazy like me and have used offpeak dwell times of 500 msec or so...  to see the difference between normal off peaks and multi point off peaks you might need off peak dwell times of tens or hundreds of seconds.

You can test this for yourself. Acquire some MPB data in PFE and then process it both ways, first using MPB and then subsequently using a normal off peak method. You can do this on the same dataset by selecting the different background methods from the Elements/Cations dialog. See how short an off peak acquisition time you can use and obtain statistically significantly differrent results on the same data.
john

[John Donovan]

As already posted here:

https://smf.probesoftware.com/index.php?topic=249.msg12670#msg12670

we have implemented a method to utilize Multi-Point Background (MPB) x-ray maps as "shared" off-peak maps in CalcImage.   That is one can acquire 2, 1 or no off-peak images per on-peak element map in Probe Image, and then utilize the off-peak maps from other elements to perform the off-peak background fit for an on-peak element.  Assuming of course that one has more than a single element (and off-peak maps) per spectrometer/crystal combination.

Now we have also implemented a method to display these MPB background intensities for selected pixels in your x-ray maps from the Run menu in CalcImage as shown here:



In addition one can display only a single pixel and see the fit: