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] <[log in to unmask]> > ########################### > > **** JEOL Probe Users Listserver > > Moderator: Anette von der Handt, [log in to unmask], Electron Microprobe > Lab, University of Minnesota > > Post a message: send your message to [log in to unmask] > > Unsubscribe: send "SIGNOFF PROBEUSERS" to [log in to unmask] > > On-line help and FAQ: http://probelab.geo.umn.edu/jeoluserlist.html > > * > **** JEOL Probe Users Listserver Moderator: Anette von der Handt, [log in to unmask], Electron Microprobe Lab, University of Minnesota Post a message: send your message to [log in to unmask] Unsubscribe: send "SIGNOFF PROBEUSERS" to [log in to unmask] On-line help and FAQ: http://probelab.geo.umn.edu/jeoluserlist.html *