WDS preamplifier design

[John Donovan]

I'd just point to the peak shifts and window placement discussion in the "improving accuracy" thread to point to yet another issue that a solid state detectors would eliminate.  I do believe solid state detectors are the hardware improvement that will bring the next level of accuracy.  They will solve problems that microanalysts don't even realize exist.

I could not agree more!

I am reminded of the story I heard where, back in the day JEOL was contacted by the Seiko (watch) company, who asked JEOL to develop a FEG for their EPMA instrument. Apparently a few million dollars were provided to JEOL Japan for this!

Seems to me that a solid state detector and fast pulse counting electronics should be a much smaller and easier project, right?

Have you got a spare million bucks to be an angel investor on this?

[Les Moore]

There's an added factor that would favor SDD over FC, recovery time.  Try mapping something with SiC in it with a Si Ka at 200nA with bidirectional mapping and you will see a saw tooth effect on the boundaries. The massive change in countrate must be saturating the detector such that it won't reliably measure the Si Ka when it drops back down.
 

[sem-geologist]

There's an added factor that would favor SDD over FC, recovery time.  Try mapping something with SiC in it with a Si Ka at 200nA with bidirectional mapping and you will see a saw tooth effect on the boundaries. The massive change in countrate must be saturating the detector such that it won't reliably measure the Si Ka when it drops back down.
 

Could you share a picture?

Excellent observation about saturation... but completely wrong tree to bark. What you are saturating is rather the preamplifier and not the gas flow chamber itself. Also, did this observation happened with correct PHA settings to compensate the PHA shift? The PHA shift will happen gradually at transition of grain boundary, as discharging the feedback capacitor (which gets near-full charged during very high count rate) of preamplifier needs some time.
This thread is about preamplifier design which is the weakest part in currently used GFPC. Replace the outdated preamplifier + shapping oamps and discrete pulse counters, and give modern electronics to GFPC and it will leave SDD in the dust with the performance.