Alumni

Current research / employment

The new generation of pixelated photon counting X-ray detectors like the Medipix2 and the Medipix3 does not measure energy deposition directly. Instead of this the measured observable is the number of photons, which deposited an energy larger than a given threshold.

To understand the response of these detectors we developed a new detector class for use in the Monte-Carlo-Simulation ROSI, which is based on the C++ library LSCAT-GISMO, including the well-established EGS4 algorithms with its low energy extension LSCAT.

The implementations in the detector class are the physics processes in the sensor layer, diffusion and repulsion of charge carriers during drift and lifetime of the charge carriers, all taking into account intrinsic doping of the sensor material. The drift of charge carriers induces mirror charges at the electrodes leading to a signal even if not all electrons and holes reach the electrode. This results in partial charge collection and therefore has impact on energy resolution. Noise is modelled with Fano noise during energy deposition, and several noise contributions of the pixel electronics. Further, the charge summing mode of the Medipix3 is available in the detector class.

Due to the hybrid design of the Medipix detectors several combinations of ASIC and sensor are possible. With the implemented physics it is possible to simulate the response of high-Z sensor materials like CdTe or GaAs in addition to silicon.

The detector class allows an arbitrary positioning and orientation of the detector with respect to the incoming beam. Therefore it is possible to simulate complex imaging systems containing several units of pixelated photon counting X-ray detectors taking into account a detailed implementation of the processes inside each detector unit.

Due to the effect of Charge Sharing several pixels can be triggered by a single X-ray photon which interacts in the sensor volume. Therefore the total number of counts does not follow Poisson noise anymore. In my research the multiplicity framework was developed, including a formula to calculate or measure the zero frequency detective quantum efficiency (DQE). The detection efficiency is reduced by a factor containing the averaged multiplicity and its noise.

Currently I am working on different applications of pixelated photon counting X-ray detectors like Phase Contrast Computed Tomography (PHACT), active personal dosimetry or the search for double beta decay (COBRA).

Current employment: ECAP


Publications M. Filipenko, T. Gleixner, G. Anton, J. Durst, T. Michel, Characterization of the energy resolution and the tracking capabilities of a hybrid pixel detector with CdTe-sensor layer for a possible use in a neutrinoless double beta decay experiment, Europ. Phys. Journal C, 73, , (2013)

T. Michel, T. Gleixner, J. Durst, M. Filipenko, S. Geißelsöder, The Potential of Hybrid Pixel Detectors in the Search for the Neutrinoless Double-Beta Decay of Cd-116, Adv. in High Energy Phys., , , (2013)

T. Michel, B. Bergmann, J. Durst, M. Filipenko, T. Gleixner, K. Zuber, Measurement of the double K-shell vacancy creation probability in the electroncapture decay of 55Fe with active-pixel detectors, Phys Rev. C, 89, , (2013)

A. Ritter, F. Bayer, J. Durst, K. C. Gödel, W. Haas, T. Michel, J. Rieger, T. Weber, L. Wucherer, G. Anton, Simultaneous maximum-likelihood reconstruction for x-ray grating based phase-contrast tomography avoiding intermediate phase retrieval, arXiv.org, [physics.med-ph], arXiv:1307.7912, (2013)

A. Ritter, F. Bayer, J. Durst, K. C. Gödel, W. Haas, T. Michel, T. Weber, G. Anton, Investigations on the origin of the darkfield signal, Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2011 IEEE, , 2314-2315, (2011)

A. Ritter, P. Bartl, F. Bayer, J. Durst, W. Haas, T. Michel, G. Pelzer, T. Weber, G. Anton, Optimization of differential phase-contrast imaging setups using simulative approaches, Proceedings of SPIE, 7961, , (2011)

M. Schwenke, K. Zuber, B. Janutta, Z. He, F. Zeng, G. Anton, T. Michel, J. Durst, F. Lück, T. Gleixner, C. Gössling, O. Schulz, Exploration of Pixelated detectors for double beta decay searches within the COBRA experiment, Nucl. Instr. and Meth. in Phys. Res. Sec. A, 650, , (2011)

E. Guni, J. Durst, T. Michel, G. Anton, Material reconstruction with the Medipix2 detector with CdTe sensor, submitted to JINST, , , (2010)

E. Guni, J. Durst, T. Michel, G. Anton, M. Fiederle, A. Fauler, A. Zwerger, The influence of pixel pitch and electrode size on the spectroscopic performance of a photon counting pixel detector with CdTe sensor, submitted to Trans. Nucl. Sci., , , (2010)

J. Giersch, J. Durst, Monte Carlo simulations in X-ray imaging, NIM A, 591, 300-305, (2008)

B. Kreisler, J. Durst, T. Michel, G. Anton, Generalised adjoint simulation of induced signals in semiconductor X-ray pixel detectors, JINST, 3, P11002, (2008)

J. Durst, G. Anton, T. Michel, Discriminator threshold dependency of the zero-frequency DQE of photon-counting pixel detectors, NIM A, 576, 235-238, (2007)

T. Michel, G. Anton, M. Böhnel, J. Durst, M. Firsching, A. Korn, B. Kreisler, A. Loehr, F. Nachtrab, D. Niederlöhner, F. Sukowski, P. Takoukam Talla, A fundamental method to determine the signal-to-noise ratio (SNR) and detective quantum efficiency (DQE) for a photon counting pixel detector, NIM A, 568(2), 799-802, (2006)