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1
Do the different sessions use different bias voltages on the detectors?

What happens if you change the bias voltage manually?  Do the counts visibly change? 

Can you monitor the detector bias power supply?
john
2
We are not seeing short-term changes, it changes session by session.

One session took more than 1-2 days and the background level is constant within a session. (Checked by chart recorder in JEOL software)

In a session when background intensity increased peak intensity also increased, so background increase does not affect net intensities.

That's why we're thinking this is related to detectors (probably bias voltage or gain?). Our 3, 4, 5 spectrometer has sealed Xe counter so P-10 may not be a problem, I think.
3
OK, that has to be a high voltage power supply for the bias voltage for the flow detectors.

Or maybe a bad P-10 bottle?

Are the intensities changing minute by minute?  It's only around 30-50% more counts at background level. Probably you wouldn't notice it when counting peak intensities I assume?

Weird.
4
Hi John,

No, we are seeing this in all five spectrometers.




Hwayoung
5
Hi Hwayoung,
Are you only seeing this "dichotomy" in intensities on spectrometer 2?
john
6
Hi all,

I would like to ask for a help or comment about sudden increase of off-peak X-ray background intensities from samples of similar mean atomic number range under same analytical conditions.

The issue is.. we have been measuring trace elements from olivines of varying compositions through 4 different sessions with single conditions and settings:
  - 13 elements : Si, Mg (EDS)  /  Na, Al, K, Ca, P, Fe, Mn, Zn, Ti, Cr, Ni (WDS)
  - 15kV, 500nA, 3um beam
  - 360s for peak, 180s for upper and lower background (off-peak)
  - exponential modeling for background, +-2mm background positions

and these are measured and interpolated background intensities at Al Ka position with TAP crystal:

(Time interval of 3 weeks between 1st and 2nd sessions, 2days between 2nd and 3rd sessions, and 6 hours between 3rd and 4th sessions)

You can see the background level at 2nd & 4th sessions are higher than those of 1st & 3rd sessions. (Beam, spectrometer and detector settings are *exactly same* for all sessions, except minor change of peak position). And this increase in seen for all WDS elements, not only for Al.

And this is background X-ray intensities vs. calculated mean atomic number (Z-BAR) of olivines:


Mean atomic number (MAN) range from 10.5 to 13.5 is due to different olivine compositions. And background level between 1.2 and 1.4 (cps/nA) of 1st and 3rd session seems normal, because they sat on a range of past background measurements using our probe from other matrices of similar mean atomic numbers. Why are there two different correlation lines of background vs MAN even though we used same analytical settings?

All olivine grains were in a single mount and vacuum conditions were constantly good through entire sessions. There are daily temperature variations in our lab but the 3rd session took 3 days, so we can rule out possible problems in coating, vacuum and temperature.

So far, we can not find any reasons for this dichotomy. Any comments would be helpful.
Thank you.
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Just in case you thought you were going crazy, I have the cursed hump too...

Hi Ben,
Thanks. That is good to know. And your SXFive instrument is quite a bit newer than my SX100 (so maybe it's not a Bragg crystal degradation, but more a secondary diffraction artifact).  Does the "hump" seem to be related to Fe content? Maybe also scan a gold or other high Z std and see if the "hump" disappears.  You should also scan the region around Hf La on an LiF crystal too, on an Fe std. 

By the way, please move your in-line images to the user forum gallery:

https://probesoftware.com/smf/index.php?topic=2.msg4040#msg4040

Using external image hosting sites means that the links to your images will eventually break.  Some users that were using TinyPics to host their images lost all their images when TinyPic shutdown recently.

Just use the Gallery feature from your user forum login and your image links will be permanent.
8
Hi Mike,
Yeah, that's a different thing.

PFE locks the database when ever it performs a "transaction". That is updating the database.  This is to prevent any possibility of data corruption.

https://en.wikipedia.org/wiki/Transaction_processing

You might notice a .LDB file at times in the folder. That is Microsoft's file locking mechanism, but it doesn't work fast enough over a network connection, so yes, copy the database to a local drive and all is well.
john
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I’ve been getting a similar behaviour (but for a different reason I think). When opening a PfE database file over a network connection I sometimes get a ‘database already open locked for access’ error message. Copying the database file to the desktop solves the problem so I suspect it’s something to do with the slightly slower connection over the network causing a false error. Took me a while to work out that the database files weren’t getting randomly corrupted.
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Just in case you thought you were going crazy, I have the cursed hump too...
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