Intro: GeoPIXE: Using the x-ray spectrum fit window

Video

Coming soon!

Steps

1. We recommend that you begin your fitting process in the X-ray Spectrum Fit window by loading an existing fit setup (.pcm file). We can help you locate an appropriate setup for your sample if you do not already have one. Examples may be viewed in home/maiauser/Demo/setup.

2. In order for changes to the fit setup to be processed, you must press "fit one" (or "fit all" if you have multiple spectra in the spectrum display window). Otherwise, the red line you see represents just a preview of the fit. (The default is that the green line is the data, and the purple line is the background fit.)

3. Check the elements in the fit. Click on elements to add them to the fit. Click multiple times to change between K, L, and M lines. Use the Window > Identify X-rays tools to help identify lines (see spectrum display tutorial.)

4. Check the yields file. Set up a new one or load an appropriate .yield file.

5. Adjust the energy range manually, or set the view cursors are the region of interest and click "Use View."

6. Check that the filter is set correctly- usually Air 5mm or Air + 6.5 um polymer.

7. Under Advanced > General, check that the desired cuts file (.cuts) is loaded, and/or that no unwanted .cuts file is loaded.

8. Under Advanced > Back, tweak the number of SNIP passes to better fit the background, if needed.

9. Parameters under Advanced > SXRF can be useful for improving the fit to the elastic/Compton scattering peaks.

10. Turn on or off the "Cal On" (applies energy calibration), "FWHM" (restricts full width half max of the peak fitting), "Tail on" (tries to fit low energy tails- not always helpful), and "Boost" buttons as desired (see Tips below).

11. Remember to click "Fit one" or "Fit all" to take the changes into account. When happy with the fit, save the fit setup and click "Generate DA matrix," then "normal single DA matrix." Save the .damx file to your setup folder.

Tips

• It's nice for the first passes to fit with just "Cal On" and "Tail On," "FWHM," and "Boost" all off. When the fit is looking good, try turning off "Cal On" and turn on "FWHM" and fit again. Iterating these can improve the fit, with the goal being to have a good fit with both "Cal On" and "FWHM" on.
• If the fit gets really strange, try restricting the fit region using the view cursors, fitting, and then re-increasing the energy range of the fit. If this doesn't work, try reloading your fit setup and starting over.
• With the above in mind, save your fit setup often as it improves.
• Save the final fit setup (.pcm) and corresponding DA matrix (.damx) with the same file names so you can easily match them up later.

-- LouisaSmieska - 16 May 2016