Renaud Geological houses two electron microprobes. The first probe was purchased in May 2005 from CalTech (Probe #1), the second was purchased in July 2007 from SGS Lakefield (Probe #2).
The microprobe has a total of 5-wavelength-dispersive spectrometers, of which four are two-crystal spectrometers equipped with two analyzing crystals, and the remaining spectrometer is a special four-crystal spectrometer equipped with four analyzing crystals. The crystal inventory is listed below:
Spectrometer Crystal Inventory:
Spectrometer Analyzing Crystal
Spectrometer 1 TAP/PET/LDE1/LDEB
Spectrometer 2 TAP/LDEC
Spectrometer 3 LIF/PET
Spectrometer 4 PET/TAP
Spectrometer 5 LIF/PET
Because this instrument is equipped with two turbomolecular pumps (rather than a single oil-diffusion pump), it routinely achieves a 1X10-7 torr vacuum in an oil-free environment with very low carbon contamination rate. It is also equipped with a liquid nitrogen anti-contamination cold fin). These capabilities make the instrument highly desirable for light element x-ray analysis. The instrument has a very good electronic and analytical stability, vacuum cleanliness, and capability to perform analysis with high precision and accuracy.
The microprobe has a Tracor Northern energy-dispersive spectrometer and a TN-5000 x-ray analyzer that is used to simultaneously acquire x-rays over a wide energy range. The EDS detector can be used to perform energy-dispersive quantitative analysis if so desired.
Our JEOL JXA-733 currently uses the Tracor Northern TN-5600 spectrometer and stage automation system. It is the first JXA-733 to use the “Probe for Windows” operating system from “Advanced Microbeam” to drive the TN-5600 automation package.
The “Probe for Windows” and related programs are essentially advanced front-end programs that store their data in Microsoft Access database files. All standard compositions are maintained in a standard database and read in by “Probe for Windows” during correction. The “Probe for Windows” program performs all spectrometer and stage automation activities and handles operations during an automated microprobe run.
The unit was acquired from IBM in 1998 after two years of deployment at California Institute of Technology and then purchased by SGS Lakefield Research.
The microprobe has a total of 4-wavelength-dispersive spectrometers, equipped with two-crystals each. The crystal inventory is listed below.
Spectrometer Crystal Inventory:
Spectrometer 1 LIF/PET
Spectrometer 2 LIF/PET
Spectrometer 3 TAP/LDE1
Spectrometer 4 LIF/PET
JEOL-733 operating software was upgraded in 2000 from the original NT-5600 operating system by the addition of Geller MicroAnalytical Laboratory, Inc. dQant (microprobe analyses) and dPict (BEI-SEI-X-ray imaging) software packages. These run in parallel with Princeton Gamma Tech’s Avalon PGT eXcaliber EDS controller. Geller and PGT hardware and software are widely used at many microprobe facilities around the globe. Minor e-beam current variations are permanently monitored by Geller dQant software and incorporated into the ZAF correction procedure.
PROBE #1 and PROBE #2: Precision and Accuracy:
The precision of measurements on the electron microprobe is a function of x-ray counting statistics, which depends on the total number of x-ray counts collected on both the standard used for calibration, and also on the counts collected on the unknown sample. The minimum precision attainable on the instrument is in the vicinity of 0.5% relative. Spectrometer mechanical reproducibility is considered to be the limiting factor in precise measurements on the instrument. Therefore, at low total counts
collected, counting statistic errors dominate, and at high total counts collected, instrument reproducibility dominates. Precision also depends on the chemical homogeneity of both the standard used for calibration and that of the unknown sample.
The accuracy of measurements on the electron microprobe depends on accurate knowledge of the composition of the primary calibration standard, and the “correctness” of the algorithm used to convert from x-ray intensity to concentration units (i.e. the ZAF correction). A global accuracy statement cannot be made. However, the accuracy is typically better than 5%, but may be worse for elements subject to peak interferences, or where there is a large compositional difference between the standard and sample and a large correction factor is observed (i.e. x-ray absorption, for example).
Polishing wheels for removing saw marks from the rock samples for photographic purposes.