To build on this there is an alignment procedure for the column faraday cup
where you put a faraday cup in the chamber, record it's current, then
insert the column one and align it in x and y until you're reading a
similar amount of current. This being said you can't always take the
reading from the column cup as a ground truth due to the possibility of it
being misaligned.
Adam McCombs
On Thu, Jul 9, 2020, 9:06 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
>
>
>
>
>
>
>
> *From:* JEOL-Focused Probe Users List <[log in to unmask]> *On
> Behalf Of *Allaz Julien
> *Sent:* Thursday, July 9, 2020 11:44 AM
> *To:* [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
> NW E 84
> Clausiusstrasse 25
> 8092 Zürich
> Switzerland
>
>
>
> Tel: +41 44 632 37 20
>
> Fax: +41 44 632 16 36
>
> Email: [log in to unmask] <[log in to unmask]>
>
> ###########################
>
>
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