[B._Beckhoff,_et_al.]_Handbook_of_Practical_X-Ray_(b-ok.org).pdf

For this reason the photon microprobe is a quite

Info icon This preview shows pages 507–510. Sign up to view the full content.

For this reason the photon microprobe is a quite unique tool due to the variety of interaction processes with matter. In particular the possible corre- lation brought to evidence, will show the exact position on the sample where absorption (EXAFS or XANES) or diffraction measurements would bring in- valuable information on the chemical state or structural environment of an element. We thus recommend that micro-XRF be associated, on the same beamline, without removing the sample, to simultaneous or subsequent ab- sorption or diffraction measurements. As an example we present in Fig. 7.27 the map of the distribution of iron and manganese in a polluted soil sample. The dark area represents high el- 0 200 400 600 800 1000 1200 1400 1600 1800 0 200 400 600 800 1000 0 200 400 600 800 1000 (a) 3 2 1 Fe 0 200 400 600 800 100012001400 16001800 (b) 5 4 3 2 1 Mn Position in m m Position in m m Position in ( m m) Position in ( m m) Fig. 7.27. Fe (a) and Mn (b) maps in a soil sample using ROIs
Image of page 507

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

Methodological Developments and Applications 487 0 200 400 600 800 1000 1200 1400 1600 1800 0 200 400 600 800 1000 5 4 (b) Mn 0 200 400 600 800 1000 1200 1400 1600 1800 0 200 400 600 800 1000 3 1 2 (a) Fe Position in m m Position in m m Position in ( m m) Position in ( m m) Fig. 7.28. Fe (a) and Mn (b) maps in a soil sample using fitted lines emental concentrations. In map (a), Fe seems concentrated in three distinct regions marked 1, 2 and 3. In map (b), Mn appears to be concentrated in the same regions (1,2,3) plus two other marked 4 and 5 (very intense). This suggests that in this sample at least two different forms of Mn cohabit: one as- sociated to iron (1,2,3) and another uncorrelated with this element (4 and 5). Now if we look at Fig. 7.28, which represents the same map but generated from the true areas of the fitted K α lines of Fe and Mn on each spectrum the situation is completely different. Iron still appears at positions 1, 2 and 3 but manganese is now only found in regions 4 and 5. What has happened is obviously explained in Fig. 7.29, which is the fluorescence spectrum of a pure iron sample. We see that the fluorescence peak recorded with a Si(Li) detector shows a low energy tail that extends quite far from the main peak and in particular in the ROI devoted to Mn. Consequently, there is always a given fraction of the Fe intensity in the Mn ROI. This is why Fe and Mn seem so strongly correlated in regions 1, 2 1 10 5 6 7 8 100 1000 10000 Escape K b K a Mn ROI Counts Energy (keV) 4 Fig. 7.29. Fe spectrum in a soil sample
Image of page 508
488 A. Simionovici and P. Chevallier and 3 of Fig. 7.27, whereas Mn has completely disappeared from these regions in Fig. 7.28. Another interesting feature is seen in the lower right corner of the iron map of Fig. 7.27 where we can observe a slight iron concentration corresponding to region 5 of the Mn map. In regions 1, 2 and 3 Fe is dominant and Mn in low concentration while it is the opposite in region 5. In Fig. 7.28, this has disappeared because there is effectively no iron in region 5. If there is a high concentration of Mn in this area its K β line, which falls in the Fe K α ROI will misleadingly suggest the presence of iron in this position.
Image of page 509

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

Image of page 510
This is the end of the preview. Sign up to access the rest of the document.
  • Spring '14
  • MichaelDudley

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern