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

721 here the source is a mo micro focus x ray tube

Info icon This preview shows pages 488–490. Sign up to view the full content.

View Full Document Right Arrow Icon
3D micro-XRF set-up, which is shown in the photographs of Fig. 7.21. Here, the source is a Mo micro-focus X-ray tube combined with a polycapillary full lens in the excitation channel. The micro-focus tube has a FWHM spot size of 100 µ m; the polycapillary lens has an 80 µ m FWHM spot size with a working distance of 22 mm. In the detection channel the same poly CCC and the same Si(Li) detector is used as was used for the set-up at the synchrotron source BESSY. A second Si(Li) detector is positioned downstream on the optical axis of the polycapillary lens to ensure the alignment of the lens and to monitor the alignment of the two foci of the X-ray optics to produce the microvolume.
Image of page 488

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

View Full Document Right Arrow Icon
468 B. Kanngießer and M. Haschke Polycapillary full lens Poly CCC + detector Monitor detector Fig. 7.21. Photographs of the 3D micro-XRF set-up, depicting a closer view on the confocal set-up on the left hand side and a top-view of the whole set-up on the right-hand side The whole set-up is located in a vacuum chamber which facilitates the mea- surement of light elements. Both X-ray tube and Si(Li) detector are equipped with thin windows for the same reason. With the tabletop 3D micro-XRF set-up pigment layers have been investi- gated for their homogeneity [36]. Now it is possible to image the elemental dis- tribution in a certain depth of the sample, which helps to differentiate between various kinds of inhomogeneities, like inclusions and particles. Figure 7.22 shows the intensity depth profiles of a green chrysocolla (CuSiO 3 · n H 2 O) pigment layer on a lead white (2PbCO 3 · Pb(OH) 2 ) ground layer painted on paper. The depth profiles are scaled to the same height. The pigment layers were scanned with a step width of 10 µ m. The measurement lifetime at each step was 100 s with a tube current of 0.6 mA and a voltage of 35 kV. The two pigment layers are clearly distinguishable in the intensity depth profiles of their characteristic elements Cu and Pb. Both curves have a FWHM of about 100 µ m, which correspond to the layer thickness. Furthermore, the depth profiles for Si and Fe indicate inhomogeneities in and on the green chrysocolla pigment layer. The fact that the main part of the two curves is lying in the Cu intensity curves indicates inhomogeneities rather than a thin top layer. The different FWHMs of 30 µ m for Fe and 77 µ m for Si, respec- tively, are another indicator for inhomogeneities in a layer. And indeed the chrysocolla pigment is known to have inclusions containing iron and quartz particles. A full 3D scan, that is, a lateral scan in addition to the depth pro- files, corroborates the results. The 3D scan clearly demonstrated that the fluorescence was coming from an Fe particle of about 30 µ m in diameter. The contour plot of the Si fluores- cence showed furthermore that the Fe particle is partly embedded in a quartz inclusion of the top pigment layer. At the site of the Fe particle the Si fluores- cence is diminished due to the absorption of the particle. The latter finding could only be stated unambiguously with the lateral scan in combination with the Fe depth profiles.
Image of page 489
Image of page 490
This is the end of the preview. Sign up to access the rest of the document.

{[ 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