Testing new multi-channel analyser PHA capability for Cameca SX

[Karsten Goemann]

Hi John,

I tested the new Cameca PHA MCA feature a bit (http://probesoftware.com/smf/index.php?topic=42.msg883#msg883).

It's great, 1 second PHA scans!

However, I noticed that when PHA differential is specified, the x axis range of the PHA window reflects that PHA window, but the PHA scan data is actually for the full window (.56 to 5.5V) so the x axis range is wrong, see attached two images for S Ka on PET, identical conditions but PHA diff switched on for the first one (base .75, window 2.09V) and PHA integral for the second one.

Cheers,

Karsten

[John Donovan]

Ok, I see this.

Interesting that I got it to work correctly in demo mode!

[John Donovan]

Hi Karsten,
OK, I got it working.  But here's something I don't understand...

So here is a MCA PHA acquired using the new MCA PHA hardware:



It looks just like the display on the PeakSight software. And here is the same x-ray line acquired using the traditional PHA scanning method:



Why are they different?  Where is the Ar escape peak in the MCA PHA acquisition?

[Karsten Goemann]

Not sure.

I do normally see the escape peak using PeakSight's MCA and usually it has more separation between the main and the escape peak, but that's obviously energy dependent.

Which x-ray line did you use for that PHA scan?

[Gseward]

here is an MCA PHA scan and a traditional PHA scan of the Fe ka peak from my SX100.





the peak position appears different, Is the x-axis wrong for one of the plots?

[Gseward]

Testing the new MCA PHA acquisition I increased the time to 1s with 40 intervals, I get this error:

PHA MCA Test on spectro  1 timed out. This is usually caused by too low an x-ray intensity. Please try the PHA MCA Test again using a material with a higher concentration or uncheck the Use MCA PHA Acquisition checkbox in Acquisition Options dialog and instead utilize the traditional PHA acquisition method.

 I did a bit more messing around and discovered that if:

 count time * intervals >= ~30

the error occurs. count time * intervals < 30  and all is good.

Gareth

[John Donovan]

Not sure.

I do normally see the escape peak using PeakSight's MCA and usually it has more separation between the main and the escape peak, but that's obviously energy dependent.

Which x-ray line did you use for that PHA scan?

Fe Ka.

Gareth's Fe scan looks more like my traditional one!

I wonder if these MCA PHA electronics ever need to get recalibrated?

[Gseward]

John,

If I move to lower gain so that the peak is at a similar V to yours, then I see similar results to you, I don't know why yet either:

MCA


Traditional


BUT note again that the peak has an apparent shift - I have a feeling that the Cameca MCA data is returned as 0-5V not 0.5-5.5V as it is being plotted by PFE.

Gareth

[John Donovan]

That makes some sense.  I was just going by the PeakSight data display which I thought shows a blue line for the PHA data going from 0.5 to 5.5 and yes:



but I have a pretty old version of PeakSight. What do you see?

[Gseward]

Well, what about that - Mine shows 0-5V!



p.s. I have no idea how I managed to turn the background black, and I can't figure out how to make it white again!

EDIT by GSeward: this plot has no smoothing applied

[Probeman]

You know what this means?

We can't demonstrate the escape peak any longer using this new MCA PHA hardware!
john

[John Donovan]

So I tried PeakSight again with checking the smoothing option off and get a slightly better escape peak:



and now my acquisition looks pretty much the same:



So I guess the MCA method is not quite as good energy resolution...?

[Karsten Goemann]

Our SX is in use right now so I can't collect examples for comparison before Monday.

But I seem to remember that the "traditional" PHA scans we collected with PFE on our system were looking extremely jagged and asymmetrical. Back then I thought it was because the electronics can't keep up with the fast baseline/window changes. Or the count rates are just too low, or both. The minimum PHA window setting I needed to get an acceptable PHA peak shape was 0.6V.

Gareth, to change the background colour in PeakSight, double left-click into the background of the graph. A window should open where you can adjust the colour.

[Probeman]

So in my quick testing, I can see we are getting back 256 intensities, but what voltage range do these intensities represent?  I ask because my PeakSight display shows them going from 0.5 to 5.5, but on Gareth's PeakSight display they go from 0 to 5 volts.

The test PHA return packet seems to *always* return 805 and 5637 millivolts for the baseline and window respectively,  but if I set the PHA window *before* the pha acquisition to 3 volts, I can see that the instrument window is 3 volts in the PeakSight display during the test PHA acquisition, but the test PHA function still returns the same exact range of intensities no matter what window setting I specify.

[John Donovan]

Here is what one sees when running a MCA PHA "test" in DebugMode (from the Output menu)...

Setting spectro  2 PHA (BWGBMD):  .5 3 1003 1250 -1 .0000038
Moving to crystal and on-peak spectrometer positions...
SX100MoveMotor: 2 to 27644 at speed 3000
Moving motor  2 from  32295 to  27644
Setting column conditions (TKCS)...
Inserting faraday cup or blanking beam
Faraday cup inserted or beam blanked
Setting operating conditions (TKCS):  40 15 50 0
Setting operating conditions (TKCS):  40 15 50 0
Setting operating conditions (TKCS):  40 15 50 0, getting current conditions...
SX100SetConditions: current conditions (TKCS) =  40 15 51.5915 0
SX100SetConditions: static variables (TKCS) =  40 15 50 0
SX100SetConditions: ForceAnalyticalConditions =  0
SX100SetConditions: OperatingVoltageTolerance =  .002, BeamCurrentTolerance =  .01
SX100SetConditions: beam current error = 51.5915 / 50 =  3.18300 %
Setting operating conditions (TKCS):  40 15 50 0, setting beam current...
SX100SetConditions: set beam current =  50
Setting operating conditions (TKCS):  40 15 50 0, setting beam size...
SX100SetConditions: set beam size =  0
Operating conditions set (TKCS)

Setting beam mode (Analog  Spot)...
Setting beam mode (Analog  Spot)...

Setting magnification:  40000
Setting magnification to  40000...
Magnification set to 40000

Removing faraday cup or unblanking beam
Faraday cup removed or beam unblanked
Acquiring PHA acquisition...
Setting spectro  2 PHA (BWGBMD):  .5 3 1003 1250 -1 .0000038

SX100GetPHADistributionMCA2: Motor= 2, Status= 1, MaxTries= 0
SX100GetPHADistributionMCA2: Motor= 2, Status= 0, MaxTries= 1
SX100GetPHADistributionMCA2: Motor= 2, Acquisition number=1
SX100GetPHADistributionMCA2: Baseline= 804
SX100GetPHADistributionMCA2: Window= 5627
SX100GetPHADistributionMCA2: Alignment= 0
SX100GetPHADistributionMCA2: Index= 256
SX100GetPHADistributionMCA2 (Byte): Min= 0, Max= 246, CountTime= 0.035
SX100GetPHADistributionMCA2 (PHA Sum): Min= 0, Max= 236.5714
SX100GetPHADistributionMCA2 (Averaged): Min= 0, Max= 236.5714
SX100GetPHADistributionMCA2 (Normalized): Min= 0, Max= 6759.184

Note that the returned "baseline" and "window" from the MCA PHA acquisition are 0.804 and 5.627 volts respectively.