Dalton Abdala's webpage

IMX beamline

 

Tomography

Tomography is a non-invasive imaging technique that allows to examine slices of a sample without damaging it. While radiography provides an image from a single orientation of the sample, tomography provides many images of the sample from different orientations, resulting in a set of projections or sinograms. Essentially, each sinogram column corresponds to the X-ray projection at one angle. This data can then be reconstructed by basically solving the inverse Radon transformation. In our case, filtered back projection is used to reconstruct 3D images from a series of 2D projections. The projection values are smeared back across the 2D projections and integrated across all angles. To reduce blurring effects, the images are filtered in Fourier space before being back projected.

 

Important to note that the experimenter can choose between white beam, with its greater flux and energy spectrum for imaging dense samples (rocks, fossils, meteorites), and monochromatic beam, which will deliver a much lower radiation dose to the sample, particularly useful for sensitive biological samples.

 

Phase Contrast – Propagation Based

Similar to tomography, this method involves placing the detector some distance from the sample, so that the radiation refracted from the sample can interfere with the unchanged beam. Given the high degree of coherence available in synchrotron radiation, interference patterns or Fresnel fringes can be observed some distance away from the sample. Using this technique allows us to enhance the contrast observed in absorption images or separate entirely the phase (phase retrival) and attenuation components. This method is particularly useful when investigating light materials or biological samples or even composites made from similar materials.

Other techniques currently under development include Phase Contrast – Talbot Interferometry and Differential Absorption Tomography.

 

Endstations

 

Microscope

Optique Peter have designed a novel modular based indirect detector for X-Ray microimaging. It can be adapted for different cameras, i.e. different sensor sizes and can be tailored to work either with monochromatic illumination and the correspondingly lower absorbed dose or with intense white beam irradiation. In order to allow for a high level of compatibility, a common camera support represents the backbone of the microscope. It consists of a tube lens, a motorized camera rotation, a camera mount and a flexible interface system. A so-called low-dose head or high-dose head can be mounted to this common support. The difference between the two being the removal of the microscope objective from the x-ray path.

 

The camera head and the objective head can be motorized. The objective head can be equipped with 3 different high-quality objectives, allowing quick change between different field of views and spatial resolution. The microscope has been tested and used in several beamlines already – TopoTomo (ANKA light source, Germany); 2-BM (Advanced Photon Source, APS, USA) aswell as BM05 and ID15a (ESRF, France).

 

Camera

The microscope is currently used in combination with the PCO.2000 camera. The PCO.2000 is a high resolution 14-bit CCD cooled camera. This camera has a sensor size of 2048 x 2048 pixels, where each pixel is 7.4µm. For the low-dose configuration, this results in a FOV of 3.8mm x 3.8mm for the 4x objective; 1.52 mm x 1.52 mm for the 10x objective and 0.76mm x 0.76mm for the 20x objective. In high-dose configuration a 5x objective can be used to obtain a FOV of 3.4mm x 3.4mm and a 10x objective can achieve 1.7mm x 1.7 mm.