Peak Spectrometers
Clicking the “Peaking” button opens the peak center window. All currently analyzed elements are listed. The Peak Center method can be specified. A choice of Interval Halving, Parabolic and ROM based (if supported by the hardware) is available. The default peak center method can be specified from the PROBEWIN.INI file. With all methods the program will perform a peak to background measurement to determine if the peak is statistically significant enough to attempt a peak center.
Three options are offered, the first an option move the spectrometers to their on-peak positions if selected in the element list. This option is useful for moving the spectrometers to calibrated peak positions for x-ray mapping purposes.
The second option forces the program to acquire a "pre-scan" wavescan just prior to the peak center procedure to allow the user to select an initial peak center start position. This last option is particularly useful in cases where the nominal spectrometer position is badly out of mechanical calibration and the actual peak position is some distance from the theoretical peak position. One can also specify as a third option a "post scan" to be executed after a peak center to confirm that the peak center method was properly performed. This option gives the operator maximum control over the automated determination of the peak "center". Here the peak center found by one of the 3 methods can be verified, by a slow step across the top of the centroid.
The Plot Selected Peak Center button will display graphically, the last peak center attempted for the selected element. The points displayed are numbered in the order acquired. Therefore, for example, if the parabolic peak center was performed, and an optimum peak center was obtained, there will be four points displayed: the three (on, hi, lo) for the parabolic fit and a fourth new on-peak based on the calculated peak center.
The Interval Halving method is the most accurate, but the slowest. It is based on a peak crawl that changes direction and halves the step size whenever the count intensity drops by more than a standard deviation.
The Parabolic method peak center uses a moving three point fit on the peak top that is fit to a 2nd order polynomial. The centroid of the parabola is returned as the new peak center. This method is the fastest, if the spectrometer position is already close to the actual on-peak position.
The ROM Based method peak center is available if the hardware interface supports a ROM peak center. The actual method used for the ROM Based peak center depends on the microprobe hardware.
Several 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 available on JEOL 8200/8900/8500/8x30 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.
The Manual method peak center is very simple utilizing only a pre-scan, P/B check and post-scan.
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.
Spectrometer Peak Center Scans
Initial Peak-To-Background Measurements
Spectrometer Peak Center Procedure
Final Peak-To-Background Measurements