Example of the windows interface of the AgeMap program

Main Window

     The main window consists in four sub-groups:
                  - 'Image and Probe Set Up' where the user input the image and probe characteristics used to display and calibrate the X-ray maps and to calculate the age map. These information include the elements mapped, the size of the image, beam current, counting time per pixel, backgrounds values, ZAF and calibration factor for each element and the correction coefficient for ray interferences.
                  - 'Files' where are displayed the input files, raw images (pixel value = cps) or the calibrated images (pixel value = ppm).
                  - 'Age Map' where is displayed the calculated Age Map.
                  - 'Results' where are displayed the average pixel value from selected sub-areas in the compositional map or age map.

Threshold Window, map calibration and age map calculation

     Creation of a mask

     The calibration and age calculation procedure requires to build a separate mask image to avoid calculation using matrix pixels, in order to eliminate "unrealistic ages". The mask is created by applying a threshold processing, included with the Age Map program, on one of the raw element images selected by the user.
     Consequently, calculations for image manipulation are carried out only on pixels corresponding to white pixels in the threshold map.

     Calibration of the compositional maps

     The values of each pixel in raw X-ray maps, as they are stored from the microprobe, represent total accumulated counts (peak + background). For calibrated age maps, these total counts are converted to concentration in ppm:
          1) First, background intensities (in counts per second) are subtracted from total counts. We apply a constant, previously determined or estimated, background value to the full map.
          2) After background subtraction, pixel intensities are adjusted using a ZAF factor determined from previous quantitative analysis.
          3) Finally, concentrations are obtained by referencing the intensities in counts per second per nanoampere (c/s/nA) of each pixel to standard intensities according to the equation
                       Conc(unk) = I(unk) * (Conc(std) / I(std))
where Conc is in ppm and I in c/s/nA. The ratio Concstd / Istd is denominated as the 'Calibration Factor' in our AgeMap program.

   Age map calculation

     Before calculating the age map, an empirical correction for two interelement interferences (Pb Ma- Y Lg and Th Mg - U Mb ) is applied using the general equation:
                      Correc(peak) = Meas(peak) - Meas(peak-interf)
      An age map is calculated using the intensity of each pixel (in ppm) in the equation of Montel (1996), which is solved iteratively. Each calculated "age" (in millions of years) is stored in the corresponding pixels of the new age map.

     AgeMap program includes several image analysis functions that can be applied to all image types (raw images, calibrated compositional maps and age maps). At runtime, the user has access to pixel coordinates and the associated pixel values (total counts, ppm or age) at the pointer location.
     Areas within maps can be selected and average pixel values, mimimal and maximal pixel value within that area are in the window results).

     AgeMap program also includes a profile tool that displays in a graph the intensities of pixels (counts, ppm or age) along a line within the image. To limit noise, the width of the profile can be set to values greater than one pixel (see below).