Refraction contrast imaging at LNLS

ROCHA, H.S.; GILES, C.; C. CUSATIS; HÖNNICKE, M.G.; MAZZARO, I.; TIRAO, G.; PESSÔA, L.M.; LOPES, R.T.

LNLS

Congreso; XIV Reunión Anual de Usuarios del LNLS; 2004

LNLS

The real part of the refraction index (n = nr +ini) can and has been used to enhance contrast and details of radiographic images instead of absorption contrast, that is, the imaginary part ni, normally used for imaging. Refraction, diffraction and phase contrast can improve the quality of radiographic imagery by increasing details, edges and differentiating points with the same absorption but with different nr, very useful for biological/medical samples. The XRD2 beamline was used to test the feasibility of refraction contrast imaging with the synchrotron light at LNLS. In this beamline we can not use the white beam of the LNLS, so the beamline mirror were used in defocusing set-up in order to improve a parallel beam on the vertical direction (qy=10-4 rad) at 14keV. This is fundamental for refraction contrast imaging, but this condition was not fulfilled for the two directions (vertical and horizontal). The beamline double crystal monochromator was used in defocusing set-up too. To improve a parallel beam in the horizontal a two crystals set-up was used in this direction. The two crystals were put on the double axis diffractometer. On the first axis an asymmetric crystal Si(220) that expand the horizontal beam and on the second axis a symmetric Si(1200) that analyze the beam horizontally. The horizontal divergence with this set-up is qx=3.10-6 rad. After this crystals the beam is 23mm wide and 2mm height. For imaging of samples with 20x 20 mm the set-up was completed with two vertical translators: one for the sample and the other for the CCD detector (direct conversion with 1242x1152 pixels and spatial resolution of 25mm). Images of biological samples as bat fetus were made with the samples after the crystals and the detector far from the sample. These images were compared with absorption radiographs made with conventional sources. The low photon flux of this low energy (14keV) at LNLS takes our measurements very long.