What's a sample for Nth point bkgds

[dawncruth]

What is considered a sample for this? We have to assign a new sample when we open a new run/when the run finishes etc. But we also make new samples in the digitize sample window. If we want to test bkgds every 5 points, is that for the samples in the digitize window?

[John Donovan]

What is considered a sample for this? We have to assign a new sample when we open a new run/when the run finishes etc.

I do not know what you mean by this question.

But we also make new samples in the digitize sample window. If we want to test bkgds every 5 points, is that for the samples in the digitize window?

The Nth point bgd method was developed by Mike Jercinovic, Julien Allaz and myself to deal with beam sensitive samples that require high beam currents and long counting times, but are relatively homogeneous. In this example, the Nth point parameters (in the Acquire! | Acquisition Options dialog were set to "3" for each element:



The idea being that the background is only re-measured every N points.

Nth point samples will work for both manually acquired samples (from the Acquire! window) and also automated acquisitions from the Automate! window. The user's reference manual describes the options in some detail. Also here is a description of Nth point bgds that might be helpful:

https://smf.probesoftware.com/index.php?topic=71.msg7875#msg7875

And here:

https://smf.probesoftware.com/index.php?topic=806.msg8036#msg8036

[Ben Buse]

As I've said before I really like this option. Running it on the standards - so that it only runs the background once for 6 points accumulated on the standards, which speeds up standard acquisition, and was the default for CAMECA. The idea being standard has high peak to background ratio so the error on the background is insignificant. There are cases when this would be a bad idea such as when using the standard for overlap correction.

Anyway back to how to use it and what I recently learnt

I open a file - I add all the elements and set in acquisition options the flag to use nth point for standards only, then when I run standards using last unknown from acquisition window it acquires them with nth point turned on.

What I recently learnt was that if I later add elements to the setup - to enable nth point for the standard for these elements - I need to create any standard using 'New Sample/Setup' and select nth point for the new elements. If I do it on an unknown setup it doesn't update it for the standards. Therefore it needs to be done on a standard setup to update it for the standards, reflecting the standards and unknowns able to have different setting for nth point

Hope this is helpful

[John Donovan]

As I've said before I really like this option. Running it on the standards - so that it only runs the background once for 6 points accumulated on the standards, which speeds up standard acquisition, and was the default for CAMECA. The idea being standard has high peak to background ratio so the error on the background is insignificant. There are cases when this would be a bad idea such as when using the standard for overlap correction.

Anyway back to how to use it and what I recently learnt

I open a file - I add all the elements and set in acquisition options the flag to use nth point for standards only, then when I run standards using last unknown from acquisition window it acquires them with nth point turned on.

What I recently learnt was that if I later add elements to the setup - to enable nth point for the standard for these elements - I need to create any standard using 'New Sample/Setup' and select nth point for the new elements. If I do it on an unknown setup it doesn't update it for the standards. Therefore it needs to be done on a standard setup to update it for the standards, reflecting the standards and unknowns able to have different setting for nth point

Hope this is helpful

Ben makes a good point about setting Nth point parameters for unknowns vs. standards. You can set the Nth point parameters for standards vs. unknowns as Ben describes above by making samples of each type, but one can also do this from the Acquisition Options dialog.

In fact it's worth pointing out that a similar situation appears for standards vs. unknowns for the background acquisition type as well.  This visual may help:



Note however that if one adds an element to a sample, the default is no Nth point and off-peak, so those need to be changed for the standards and/or unknowns if desired.

[John Donovan]

Note however that if one adds an element to a sample, the default is no Nth point and off-peak, so those need to be changed for the standards and/or unknowns if desired.

So this story is more interesting than I originally thought.

It turns out that the PFE software actually handles the Nth point parameters differently than I had assumed and it's a little unintuitive...

Basically one simply creates an unknown sample, then one opens the Acquisition Options dialog and chooses the Nth option:

1. Use Nth point for Stds and Unks
2. Use Nth point for Unks only
3. Use Nth point for Stds only

Then click each element and turn on the Use Nth point for each element as desired.

So even if you select Use Nth point for Stds only, and the unknown sample shows Use Nth point, it is OK. Because the program will properly assign the Nth point flags when the acquisition starts.

But then, if you add a new element to the run (by starting a new unknown sample), you'll want to go into the Acquisition Options and turn on the Nth point flag for the new element (even though it's an unknown), so when the next standard is created, it will use the Nth point flag for the new element!