D. Greiffenberg

Energy resolution and transport properties of CdTe-Timepix-Assemblies

CdTe is a promising material for the detection of γ- and X-rays as 1 mm thick CdTe sensors offer an absorption efficiency that is higher than 50 {%} for photon energies up to 120 keV. Therefore 1mm thick CdTe from Acrorad has been flip-chipped as the sensor material on a Timepix readout-electronics ASIC at the Freiburg Materials Research Center (FMF). The transport properties of the CdTe material are investigated by determining the μτ-product of the charge carriers by illuminating the non-collecting electrode with alpha particles. The method commonly used to determine the μτ-product for non-pixelated devices was adapted for the Medipix pixelated readout-electronics. The position of the alpha particles on the pixel matrix provides spatial information, which was used to create a mapping of the μτ-product. The energy resolutions and the positions of the noise edge of two CdTe-Timepix assemblies, one with a pixel pitch of 110 x 110 μm2 and another one with a pixel pitch of 55 x 55 μm2 were investigated by performing a threshold scan of a 241Am source. A comparison of the energy spectra obtained with the two assemblies with different pixel pitches confirms the strong dependence of charge sharing on the energy spectra, as expected.

Investigation of Growth Conditions of CdTe Thick Films on Properties and Demands for X-Ray Detector Applications

CdTe thick films were prepared by vacuum deposition on amorphous substrates using MBE technique. The growth was performed at different temperatures to investigate the development of the growth rate, surface morphology, structure and optical properties. Properties of films deposited with a single CdTe source are compared with films grown with an additional Cd source. The growth experiments are discussed with regard to demands for X-ray detector applications.

Investigation of growth conditions of CdTe thick films on properties and demands for X-ray detector applications

CdTe thick films were prepared by vacuum deposition on amorphous substrates using MBE technique. The growth was performed at different temperatures to investigate the development of the growth rate, surface morphology, structure and optical properties. Properties of films deposited with a single CdTe source are compared with films grown with an additional Cd source. The growth experiments are discussed with regard to demands for X-ray detector applications.

Evaluation of the ATLAS-MPX devices for neutron field spectral composition measurement in the ATLAS experiment

A network of 15 Medipix2-based devices (ATLAS-MPX devices) has been installed at various positions in the ATLAS detector within the framework of the ATLAS-MPX collaboration. The aim of the network is to perform real-time measurement of spectral characteristics and composition of the main radiation types in the experiment including slow and fast neutrons, especially during the initial low luminosity LHC operation. This contribution describes the network structure and focuses on the neutron efficiency calibration process of the ATLAS-MPX devices and its simulation in order to predict the behavior of the device in complex neutron fields.

Investigations of the high flux behavior of CdTe-Medipix2 assemblies at the synchrotron ANKA

CdTe is a promising sensor material for the detection of γ-Rays and X-Rays as it offers an absorption efficiency higher than 50 % for photon energies up to 120 keV for 1 mm thick sensors. Connected to the pixilated, single-photon counting readout electronics Timepix, its application at a synchrotron source was investigated. The focus of the investigations was on the high flux behavior of the CdTe-Timepix assemblies, as CdTe is known to suffer from a degradation of the count-rates when being illuminated with high photon fluxes. Moreover, the high flux behavior of the readout electronics itself was investigated by measuring an assembly with a silicon sensor, which is not known to suffer from a degradation effect at high photon fluxes.

Characterization of Medipix2 assemblies with CdTe sensor using synchrotron radiation

Medipix2 assemblies with CdTe sensors have been characterized using synchrotron radiation. Processing of the assemblies has been done at the Freiburg material research center (FMF), the characterization has been performed at the ANKA at the Forschungszentrum Karlsruhe. The following paper reports the first results of the research of efficient pixelarray detectors for application in a synchrotron providing high energetic photons. Examinations on the homogeneity of the sensor, charge sharing and an energy scan will be shown.

Applications of Medipix2 single photon detectors at the ANKA synchrotron facility

Medipix2 single photon-counting pixel detectors are nowadays confirmed as a valuable concept in different X-ray analysis and imaging techniques using either X-ray tubes or synchrotron sources. Recently, the detector pool of the ANKA synchrotron source was equipped with a set of these detectors. In this work we describe the main results obtained by applying Medipix2 single photon counting detectors to synchrotron radiation methods. The results were obtained at the TopoTomo beamline whose X-ray tuneability in energy and flux allows a detailed characterization of different sensor materials, the energy calibration of detector arrays and the application of different imaging methods.

Spectroscopic imaging with an X-ray microscopy setup using a pixelated detector with single photon processing

Energy resolving X-ray imaging opens up new perspectives for applications within the fields of medical X-ray diagnosis and industrial X-ray quality control. Single photon processing X-ray imaging systems with a pixel size of 55 × 55 μm2 have been developed within the MEDIPIX collaboration. These systems show excellent images without any background noise. However the spectral properties of the device are deteriorated by significant charge sharing between neighbouring pixels. This is a main objective for the recently started development of the MEDIPIX3 readout chip with charge summing between neighbouring pixels. In order to study the effects of improved spectral resolution on image quality before the MEIDPIX3 chip is available we have developed a detector with a pixel size of 220 × 220 μm2 and connected it to a MEDIPIX2 readout chip, using only a limited number of the available pixels. Using larger pixels will improve the spectral resolution since a smaller fraction of the detected photons are subject to charge sharing. By placing this detector in the X-ray microscope and using a magnification of four times we can estimate the response of a detector with 55 × 55 μm2 pixels and good spectroscopic resolution.