Author Topic: Minimum dwell times and 'searchmap' style acquisitions  (Read 142 times)

orlandin

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Minimum dwell times and 'searchmap' style acquisitions
« on: November 13, 2019, 11:59:32 am »
Hello, all! I am trying to promote the use of our fabulous JEOL 8200 for in-situ enthusiasts among the apatite+zircon+rutile crowd by providing 'searchmaps' that I was first exposed to at UMass looking for monazites. I am sure that this is quite common: running very quick, coarse stage maps over the whole section with the spectrometers tuned to the characteristic element of each mineral; then the few bright pixels on the Zr, P, and Ti maps can be overlain onto the BSE and bonus Si/Al/Ca maps from the spare spectrometers for context and navigation. I particularly love doing these, because then the user has a whole suite of spatial data stimulating future investigations that they may have otherwise never noticed!

Since the quicker we can do these maps the more attractive it is, I've been trying to figure out what exactly I can get away with in terms of stage speed. PI thinks that the minimum dwell time for a 20 micron step is 3 ms and a 50 micron step is 4 ms, which I am deeply impressed by. In practice though, I've noticed that maps seem to take about 1.5-1.6 times longer than PI predicts, and my automated runs are occasionally killed at 1am by a JEOL -206 'floating point' error that may or may not be related (JEOL is getting back to me).

It all has me wondering what other folks do for these sorts of applications, what sort of speeds are typically possible, and if I can make some improvements to this method. If anyone would like to share any tips or alternate approaches, I would love to hear them!

orlandin

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Re: Minimum dwell times and 'searchmap' style acquisitions
« Reply #1 on: December 09, 2019, 12:48:24 pm »
Here is an example of this type of map, for someone who would need to navigate by BSE alone to find in-situ zircon, apatite, and rutile. This was collected as two 1014x588 and 920x569 pixel maps and then stitched together in Adobe Illustrator. ~110 nA, 3 ms dwell time, 20 micron beam, 20 micron step. So, about two hours to collect and then about 30 minutes of post-processing to threshold levels, stitch, and annotate. I think you'll probably have to click on each inline image to get them closer to full resolution to make out anything useful in several of them.

BSE:


Ca:


P:


S (creates lots of false positives in BSE for this rock type):


Ti:


Zr:


Completed map to be used for navigation: