ROM Based Peaking
For the ROM based peak centering (if available), the peaking start size is again utilized for best results, depending on the interface type. Note the following parameters apply to non-ROM based and ROM based peak scan parameters:
Non-ROM scan based
1. Wavescan: # of points, wave count time
2. Quickscan: Spectro scan speed (%), quick count time
ROM scan based
1. Wavescan: # of points, wave count time
2. Quickscan: Spectro scan speed (%), quick count time
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 8200/8900/8500/8x30 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 8200/8900/8500/8x30 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.
JEOL 8900/8200/8500/8x30 Direct (InterfaceType=2)- The "Peaking Start Size" is used to calculate the spectrometer scan width for the peak scan procedure. The coarse scan width is 3 times larger than the fine scan width.
Where
:
is the calculated peaking scan width
is the spectrometer high limit (from MOTORS.DAT)
is the spectrometer low limit (from MOTORS.DAT)
is the peak scan size factor (from SCALERS.DAT)
is the crystal spectrometer peaking size (calculated for 2d and position)
is the LIF spectrometer peaking size (from SCALERS.DAT)
SX100/SXFive (InterfaceType=5)- The "Peaking Start Size" is modified to produce a number between 0 and 4 by utilizing the following expression :
where pw is the SX100 peak center width
Mhigh is the motor high limit
Mlow is the motor low limit
P is the Peaking Start Size
The program uses a larger start and stop size for lower thetas and larger crystal 2d spacings. A smaller stop peaking step size will force the program to more carefully adjust the spectrometer position, however this will require more time to achieve. Be sure that the start peaking size is large enough for the program to measure a significant count change. The start values must be larger than 1/6000th of the total spectrometer range. The stop peaking size must be less than the start peaking size. The actual calculation for a specific peak position for a specific crystal is shown here :
Where :
is the actual calculated step size
is the spectrometer default start or stop size
is the spectrometer high limit
is the spectrometer low limit
is the spectrometer on-peak position
is the 2d spacing of the analyzing crystal
is the 2d spacing for LiF (4.0267)