ROM Based Peaking Scan:
- fine scan uses peaking time divided by 4 times 1.0
- coarse scan uses peaking time divided by 4 divided by 2.0
- fine scan uses peaking time divided by 4 times 1.5
Several ROM based peak center fit types are available. Applies only to Cameca SX100/SXFive and JEOL 8200/8900 microprobes.
0 = Internal (the instrument ROM peak method which applies only to Cameca)
1 = Parabolic (spectrometer scan data is fit to a parabolic fit)
2 = Maxima (spectrometer scan data is fit to Brent’s Maxima function)
3 = Gaussian (spectrometer scan data is fit to a Gaussian fit)
The internal ROM type is available only on Cameca instruments. The other options are only available on JEOL 8200/8900 and Cameca SX100/SXFive instruments. The parabolic and maxima fits require at least 3 data points above the threshold (see below). The parabolic and maxima methods have a user defined threshold that can be specified in the INI file and the program.
The ROM peaking thresholds are designed to allow the user to define the intensity values above which are used for one of the three ROM fitting methods (parabolic, maxima or Gaussian). The default is 0.33 which means that all intensity values 1/3 above the minimum to maximum intensity range are used in the fit.
ROM Based Peaking Scan Range
The ROM peak scan range is related to the crystal 2d and spectrometer position peaking start size parameter as shown here:
where:
ScalLiFPeakingStartSize is from line 19 of the SCALERS.DAT file
and:
Factor is calculated from the following expression:
where:
is the spectrometer on-peak position
is the spectrometer high limit
is the spectrometer low limit
is the 2d spacing of the analyzing crystal
is the 2d spacing for LiF (4.0267)
Note that if the analyzing crystal 2d is greater than 30 (for LDE analyzers) the scaling factor is increased by an additional factor of three. The actual ROM peakscan range is further adjusted based on the expression:
where:
ScalPeakScanSizeFactor is from line 16 of the SCALERS.DAT file
ScalLIFPeakingStartSize is from line 19 of the SCALERS.DAT file
PeakingStartSize is the calculated from above and is user adjustable within the application
is the spectrometer high limit
is the spectrometer low limit
Note that the SCALERS.DAT parameters are designed to place these parameters in approximate relative scale for normal and high intensity spectrometers while the PeakingStartSize can be edited by the user from the Peak/Scan Options dialog for a specific analytical situation to increase or decrease the ROM peaking scan range.
The Manual method peak center is very simple, utilizing only a pre-scan, P/B check and post-scan. The peakscan range for post and prescan peakscans is based on the peakscan range calculated above but the counting time is further modified as shown here:
PreScanCounTime = PeakingCountTime /4
PostScanCountTime = PeakingCountTime
Where:
PeakingCountTime is from the PROBEWIN.INI [counting] section.
The program will automatically select elements in the element list that were not peaked in the previous peak center when the window is re-opened again. Note that the element list is multi-select so that any combination of elements can be peaked. If more than one element on the same spectrometer was selected, then the program will automatically peak center them one at a time. The Plot Selected Peak Center button may be used to display the last peak center count-position data for the selected element.
The move to on-peak option is useful for moving a spectrometer (and setting the PHA conditions) to its on-peak position for imaging purposes. Remember : the elements to peak center (or move to on-peaks) must be highlighted before closing the dialog.