Thanks for the additional suggestion!

The W filament is actually pretty new with less than 100 hours, and I’ve seen this behaviour of change in count rate with beam current (not purely related to a bad DT correction) with other filament.

We have the LaB6 option, and I have yet to load such a crystal on this EPMA. We just received a bunch and I will likely load it after the next maintenance.

We have the JEOL PC-SEM and PC-EPMA on Windows 10 with the following versions:

- PC-SEM 3.0.1.26

- PC-EPMA 1.16.0.2

- EOS sub system 1.15.3.0

I believe these where the version accessible to JEOL Germany as of April 2019 (update at installation).

So far it’s running smoothly beside some known software and other minor hardware issues. However, I should say that I prefer Probe for EPMA for most of my analysis and mapping, and only use the JEOL software for beam alignment, imaging, combined EDS-WDS mapping, and leave most of my quant analysis and complex cases to PfE. However, all test I sent so far were exclusively run with the JEOL software.

I’ll try to hook my ammeter we have at the SEM later this week if I have time (and when the SEM is not in use)…

I’ll also check the DH limit on the EDS at high current, although I have observed this issue in many samples (test shown here made on our permanent standard block, other sample tested are several thin sections freshly coated).

Best,

J.

On 14 Jul 2020, at 19:31, William J Mushock <[log in to unmask]> wrote:

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

###########################

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]

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