Julien,

Also make sure to use the largest objective lens aperture when doing quantitative analyses, regardless of beam current.  This will give the best linearity in beam current.

Pete


Peter McSwiggen
McSwiggen & Associates, P.A.
2855 Anthony Lane South, Suite B15
St. Anthony, MN  55418-2883        USA
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> On Jul 9, 2020, at 11:06 AM, Joe Geller <[log in to unmask]> wrote:
> 
> I’d suggests using a sample as a Faraday cup and measure sample current vs. column Faraday cup. See if they track.
> You might also use an independent microammeter to check on linearity.
>  
> Joe Geller
> Geller MicroAnalytical Laboratory, Inc.
> 426e Boston St.
> Topsfield, Ma 01983 (USA)
> 978 887-7000, fax 978 887-6671
> www.GellerMicro.com <http://www.gellermicro.com/>
>  
>  
>  
> From: JEOL-Focused Probe Users List <[log in to unmask] <mailto:[log in to unmask]>> On Behalf Of Allaz Julien
> Sent: Thursday, July 9, 2020 11:44 AM
> To: [log in to unmask] <mailto:[log in to unmask]>
> Subject: [PROBEUSERS] Non linearity of beam current?
>  
> Dear all, 
>  
> I hope you are all safe and healthy…
>  
> Ever since JEOL installed our new 8230 last year, I’m having issues with the count rate at low vs. high beam current. At first, I thought this was a dead time issue (still set to the original value of 1.1 µs), but I can ensure you it is not...
>  
> My most recent test was done from 10 nA to 200 nA, looking at a LOW QUANTITY element (Ti in hornblende ~1.4 wt% TiO2). With this test, even the highest beam current yields a relatively low count rate (around 6000 to 8000 counts per second), and therefore I can almost for sure eliminate a dead time issue. As you can see from the attached PDF, ALL five spectrometers show the same behaviour, with an increase in count rate with beam current, around 4 to 6% at 70 nA (reference = measure done at 10 nA), and a whooping 8 to 12% at 100 and 200 nA!!!
>  
> This result let me think that there is a non-linearity in the beam current measurement (i.e., when the instrument measures 200 nA with the Faraday cup, it is in reality 220 or 225 nA…). Or maybe something else???
>  
> Did anyone observe such a behaviour on their 8230 or 8530? Is it possible to adjust this, and if so, how?
>  
> I know that Cameca acknowledge this issue; in their case, the “jump” occurs around 50 nA (and there is possibly another “jump” at much lower current; these jumps are due to different “loops” measuring either a low, medium, or high current or something like this...). Cameca “solves” this issue by adding to the dead time correction a linearity coefficient that is applied beyond a certain current threshold (this factor can be found in the dead time setting of Peak Sight). Does JEOL has the same thing somewhere (maybe not accessible unless logged in as a JEOL engineer)???
>  
> Best,
>  
> Julien
>  
>  
> 
> ########################### 
> Dr. Julien Allaz
> Head assistant for SEM/EPMA
> Inst. für Geochemie und Petrologie
> ETH Zürich
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