Intro: GeoPIXE: Setting up a yields file
1. It makes sense to set up a yields file as part of the fitting process. Normally at this point, you will have a spectrum open in the Spectrum Display window
and a fit setup loaded in the X-ray Spectrum Fit window
2. If you just want to load an existing yields file, click "Load" next to the "Yields" field, navigate to the desired .yield file, and press Open.
3. If you need to set up or modify a yields file, click "New" next to the "Yields" field. This will open a new window, PIXE/SXRF Yield Calculation. You will usually set up a new yields file for every sample.
4. The first step is to load some Maia-specific parameters by clicking "Load" and navigating to a yields setup (.lcm) file. You can look at examples in the home/maiauser/Demo/setup/ directory. This will set up the Energy Range and Detector fields for the Maia detector.
5. The Beam Particle should be set to Photons by loading a .lcm file, but you will need to change the beam energy for your experiment. The units are keV.
6. The other critical part of the yields is to set up the Target Layer Selection field. This section contributes to how GeoPIXE models the expected x-ray attenuation due to your sample, and also serves as the concentration reference to which all your elemental maps will be relative.
- For a calibration foil, this setup is straightforward: enter the areal density (mass/area) of the film, which can be found in the Maia binder, making sure the units are set correctly (usually mg/cm2)- ignore the density, leaving it set to 1 is fine- and entire the chemical formula of the foil (gold, copper, etc.).
- For a heterogeneous sample, this setup is more complicated. If the thickness and density are known, these can be entered, but it is often simpler to estimate an areal density (from a mass and the sample area, or from the x-ray transmission map). For the chemical formula, the best one can usually do is estimate the overall composition- the exact chemical formula of a shrimp, for example, is impossible to know precisely!
7. Change the Output path to a new .yield file name. Edit the title of the setup file and save the set-up as a .lcm file of the same name.
8. Press "Calculate Yields." When the calculation is complete, the yields will be saved in your .yield file. You can then close the PIXE/SXRF Yield Calculation window. Your new .yield file should have automatically loaded in the X-ray Spectrum Fit Window Yields field.
- 16 May 2016