Moosmann J., Altapova V., Hanschke D., Hofmann R., Baumbach T.
in AIP Conference Proceedings, 1437 (2012) 57-62. DOI:10.1063/1.3703343
For coherent X-ray imaging, based on phase contrast through free-space Fresnel propagation, we discuss two noniterative, nonlinear approaches to the phase-retrieval problem from a single-distance intensity map of a pure-phase object. On one hand, a perturbative set-up is proposed where nonlinear corrections to the linearized transport-of-intensity situation are expanded in powers of the object-detector distance z and are evaluated in terms of the linear estimate. On the other hand, a nonperturbative projection algorithm, which is based on the (linear and local) contrast-transfer function (CTF), works with an effective phase in Fourier space. This effective phase obeys a modified CTF relation between intensity contrast at z > 0 and phase contrast at z = 0: Unphysical singularities of the local CTF model are cut off to yield ‘quasiparticles’ in analogy to the theory of the Fermi liquid. By identifying the positions of the zeros of the Fourier transformed intensity contrast as order parameters for the dynamical breaking of scaling symmetry we investigate the phase structure of the forward-propagation problem when interpreted as a statistical system. Results justify the quasiparticle approach for a wide range of intermediary phase variations. The latter algorithm is applied to data from biological samples recorded at the beamlines TopoTomo and ID19 at ANKA and ESRF, respectively. © 2012 American Institute of Physics.
Myagotin A., Ershov A., Helfen L., Verdejo R., Belyaev A., Baumbach T.
in Journal of Synchrotron Radiation, 19 (2012) 483-491. DOI:10.1107/S0909049512015099
A novel image-processing procedure is proposed for the analysis of sequences of two-dimensional projection images. Sudden events like the merging of bubbles in an evolving foam can be detected and spatio-temporally located in a given projection image sequence. The procedure is based on optical flow computations extended by a forward-backward check for each time step. Compared with prior methods, efficient suppression of noise or false events is achieved owing to uniform foam motion, and the reliability of detection is thus increased. The applicability of the proposed procedure in combination with synchrotron radiography is illustrated by a series of characteristic studies of foams of different kind. First, the detection of single-bubble collapses in aqueous foams is considered. Second, a spatial distribution of coalescence events in metals foamed in casting molds is estimated. Finally, the structural stability of polymer foams containing admixed solid nanoparticles is examined. © 2012 International Union of Crystallography.
Altapova V.R., Ershov A., Rolo T.d.S., Reznikova E., Mohr J., Pivovarov Y.L., Pichugin V.F., Baumbach G.T.
in Journal of Surface Investigation, 6 (2012) 394-397. DOI:10.1134/S1027451012050035
The imaging methods used at the ANKA Synchrotron Light Source (Institute for Synchrotron Radiation, Karlsruhe Institute of Technology) are briefly reviewed. Examples of recent applications of the phase-contrast imaging method using a grating interferometer and fast radiography with optic flow data analysis to study static and moving biological objects are presented. © 2012 Pleiades Publishing, Ltd.
Alaribe L., Disch C., Fauler A., Engels R., Keller E., Cecilia A., Rolo T.D.S., Hamann E., Fiederle M.
in IEEE Nuclear Science Symposium Conference Record (2012) 1567-1571, 6154633. DOI:10.1109/NSSMIC.2011.6154633
Currently, there is a great interest in the research and development of SrI 2:Eu 2+ scintillating crystals. The high light yield, high density (4.6 g/cm 3) and high effective atomic number (49.4) make the Eu 2+-activated SrI 2 suitable for use as x-ray and gamma ray detector. SrI 2:Eu 2+-single crystals were grown with the vertical Bridgman technique in silica ampoules to prevent melt hydration and oxygen contamination during the crystal growth. For measurements, crystals were hermetically encapsulated in aluminum containers with quartz glass optical windows. The radioluminescence spectra of the SrI 2:Eu 2+-samples show maximum at 431 nm and 432 nm for the 5% and 6% dopant concentrations respectively. The light yield of the bulk samples was up to 80 000 photons/MeV and up to 119 000 photons/MeV for a 360 μm sample integrated in an x-ray imaging setup. © 2011 IEEE.
Altapova V., Helfen L., Myagotin A., Hanschke D., Moosmann J., Gunneweg J., Baumbach T.
in Optics Express, 20 (2012) 6496-6508. DOI:10.1364/OE.20.006496
Synchrotron laminography is combined with Talbot grating interferometry to address weakly absorbing specimens. Integrating both methods into one set-up provides a powerful x-ray diagnostical technique for multiple contrast screening of macroscopically large flat specimen and a subsequent non-destructive three-dimensional (3-D) inspection of regions of interest. The technique simultaneously yields the reconstruction of the 3-D absorption, phase, and the so-called dark-field contrast maps. We report on the theoretical and instrumental implementation of of this novel technique. Its broad application potential is exemplarily demonstrated for the field of cultural heritage, namely study of the historical Dead Sea parchment. © 2012 Optical Society of America.
Alaribe L., Disch C., Fauler A., Engels R., Keller E., Cecilia A., Dos Santos Rolo T., Fiederle M.
in Materials Research Society Symposium Proceedings, 1341 (2012) 21-26. DOI:10.1557/opl.2011.1275
Eu 2+- activated strontium iodide is a promising material for x-ray and gamma ray detector. A lot of difficulties are though encountered growing strontium iodide crystals due to the high oxygen-sensitivity, hygroscopic property and high impurity concentration. Single crystals of Srl 2:Eu were grown from zone refined starting materials in silica ampoules. The crystals showed good optical qualities. The light yield of two samples cut from the same ingot was determined to be 53 000 photons/MeV and 119±22 photons/keV for a 0.4 cm 3 sample and a 360 μm sample respectively, indicating some level of light trapping in the bulk sample. Keywords: scintillator, Bridgman growth method, energy resolution. © 2011 Materials Research Society.
Balzer M., Caselle M., Chilingaryian S., Herth A., Kopmann A., Stevanovic U., Vogelgesang M., Rolo T.D.S.
in SEI 2012 – 103. Tagung der Studiengruppe Elektronische Instrumentierung im Fruhjahr 2012 (2012) 121-132.
Haas D., Mexner W., Spangenberg T., Cecilia A., Vagovic P., Kopmann A., Balzer M., Vogelgesang M., Pasic H., Chilingaryan S.
in PCaPAC 2012 – 9th International Workshop on Personal Computers and Particle Accelerator Controls (2012) 103-105.
X-ray imaging permits to spatially resolve the 2D and 3D structure in materials and organisms, which is crucial for the understanding of their properties. Additional temporal resolution of structure evolution gives access to dynamics of processes and allows to understand functionality of devices and organisms with the goal to optimize technological processes. Such time-resolved dynamic analysis of micro-sized structures is now possible by aid of ultrafast tomography, as being developed at the TopoTomo beamline of the synchrotron light source ANKA. At TopoTomo, the whole experimental workflow has been significantly improved in order to decrease the total duration of a tomography experiment down to the range of minutes. To meet these requirements, detectors and the computing infrastructure have been optimized, comprising a Tango-based control system for ultra fast tomography with a data throughput of several 100 MB/s. Multi-GPU based computing allows for high speed data processing by using a special reconstruction scheme. Furthermore the data management infrastructure will allow for a life cycle management of data sets accumulating several TByte/day. The final concept will also be part of the IMAGE beamline, which is going to be installed in 2013. © 2012 by the respective authors.