College Park, Maryland      June 6 - 10 , 2004

MP16: Application of double crystal diffractometers for the tomographic reconstruction of macroscopic structures

M. Strobl, W. Treimer (University of Applied Sciences (TFH) Berlin; Hahn-Meitner-Institut Berlin), A. Hilger (Hahn-Meitner-Institut Berlin)

Double crystal diffractometers (DCD) conventionally are applied for small angle scattering investigations in the ultra small angle range. In the case of neutrons (USANS) the q-range (app. 10-4-10-1nm-1) overlaps and exceeds the range of small angle neutron scattering (SANS) experiments and enables the characterisation of structures with sizes up to some 10 μm. It can be shown that such a high angular (momentum) resolution achieved by two perfect single crystals provides the possibility to investigate macroscopic structures in a range (in real space) between approximately 100 μm up to several cm as well. Smallest beam deviations caused by refraction i.e. by phase gradients can be recorded. Combined with tomographic methods which means recording such data under several projection angles the macroscopic inner structure of test objects could be reconstructed with respect to different interactions within the sample. From the angular intensity distributions recorded in the DCD (stemming from defined beam paths) three sets of parameters could be deduced. The conventional parameter for tomographic imaging, the beam attenuation could be defined as well as a refraction and a USANS parameter. From each of them an independent reconstruction of the sample could be achieved containing redundant and/or complimentary (additional) (image) information about the sample. While the reconstruction from the beam attenuation parameter provides an image in terms of the attenuation coefficients, the refraction parameter enables to reconstruct in terms of refractive index and the USANS parameter images areas of different scattering behaviour (different microscopic structure). The contrast behaviour is therefore not only dependent on the sample attenuation anymore as two more contrast methods could be introduced. Several examples will be given.

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