Hi Julien,

Is it possible your sample is building a charge at the higher currents. If
you have an EDS detector you
might be able to verify this by monitoring the Dwayne-Hunt limit.

Cheers,
Bill

On Thu, Jul 9, 2020 at 11:44 AM Allaz Julien <[log in to unmask]>
wrote:

> 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
>
>
>
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