[en] The methodology of Coincidence Instrumental Activation Analysis (CIAA) based on a three-parameter gamma-gamma coincidence spectrometer with two high-purity Ge detectors is presented. A flexible coincidence system was built on standard NIM spectrometric modules connected to a VME or CAMAC data acquisition system. The detailed setup of the system optimized for the maximum energy resolution, maximum data throughput (dead time correction, pile-up rejection) and maximum flexibility is described. The use of different data acquisition platforms is discussed (VME bus with several different controllers, CAMAC bus). The software developed for reading and basic processing of measured data is also described. The possibilities of off-line data evaluation are discussed. The system was tested with respect to its compliance with the criteria of the CIAA method. Some results of measurement by this method are also presented. The flexibility of the system is demonstrated on its ability to measure the time characteristics of different detectors. (author)

[en] The application of the Medipix-1 hybrid pixel detector device for direct non-destructive observation of damage development in gradually stressed materials by means of X-ray transmission measurements (so-called X-ray Dynamic Defectoscopy or XRDD) has been recently successfully demonstrated. It was found that both the sensitivity and the spatial resolution of the XRDD method depend significantly on the stability of the detecting device and on the quality of the X-ray beam. This paper is a study of the imaging quality and the temperature-dependent behaviour of the Medipix-1 device. In XRDD tests we observed that on the edge of a sample slit, where an extremely sharp contrast takes place, the slit image is expanded and broadened. Results of the study of contrast influence on the image quality are presented in this paper. The dependency of the electronic noise on the device temperature was measured with respect to the XRDD accuracy

[en] The Medipix1 chip is a prototype (digital) CMOS imaging chip that emerged from particle detection in high energy physics experiments. It was designed at CERN following specifications from the Medipix1 Collaboration. This contribution aims at demonstrating the applicability of Medipix1 Si and GaAs pixel devices for alpha and X-ray particle detection. A study of 'charge sharing' between pixels and test of 'spatial resolution' using narrow beam and 'edge' image contrast was performed. For photons with energy <35 keV charge sharing between neighbouring pixels is negligible. On the contrary alpha-particles are detected in the form of clusters of adjacent pixels with typical cluster diameter of about 2.5 pixels. Possible applications of the device for position sensitive heavy charged particle detection (e.g. for surface analysis or for neutron detection) are considered

[en] The hybrid particle counting pixel detectors of Medipix family are well known. In this contribution we present new USB 3.0 based interface AdvaDAQ for Timepix3 detector. The AdvaDAQ interface is designed with a maximal emphasis to the flexibility. It is successor of FitPIX interface developed in IEAP CTU in Prague. Its modular architecture supports all Medipix/Timepix chips and all their different readout modes: Medipix2, Timepix (serial and parallel), Medipix3 and Timepix3. The high bandwidth of USB 3.0 permits readout of 1700 full frames per second with Timepix or 8 channel data acquisition from Timepix3 at frequency of 320 MHz. The control and data acquisition is integrated in a multiplatform PiXet software (MS Windows, Mac OS, Linux). In the second part of the publication a new method for correction of the time-walk effect in Timepix3 is described. Moreover, a fully spectroscopic X-ray imaging with Timepix3 detector operated in the ToT mode (Time-over-Threshold) is presented. It is shown that the AdvaDAQ's readout speed is sufficient to perform spectroscopic measurement at full intensity of radiographic setups equipped with nano- or micro-focus X-ray tubes.

[en] Position sensitive detectors are evolving towards higher segmentation geometries from 0D (single pad) over 1D (strip) to 2D (pixel) detectors. Each step has brought up substantial expansion in the field of applications. The next logical step in this evolution is to design a 3D, i.e. voxel detector. The voxel detector can be constructed from 2D volume element detectors arranged in layers forming a 3D matrix of sensitive elements - voxels. Such detectors can effectively record tracks of energetic particles. By proper analysis of these tracks it is possible to determine the type, direction and energy of the primary particle. One of the prominent applications of such device is in the localization and identification of gamma and neutron sources in the environment. It can be also used for emission and transmission radiography in many fields where standard imagers are currently utilized. The qualitative properties of current imagers such as: spatial resolution, efficiency, directional sensitivity, energy sensitivity and selectivity (background suppression) can be improved. The first prototype of a voxel detector was built using a number of Timepix devices. Timepix is hybrid semiconductor detector consisting of a segmented semiconductor sensor bump-bonded to a readout chip. Each sensor contains 256x256 square pixels of 55 μm size. The voxel detector prototype was successfully tested to prove the concept functionality. The detector has a modular architecture with a daisy chain connection of the individual detector layers. This permits easy rearrangement due to its modularity, while keeping a single readout system for a variable number of detector layers. A limitation of this approach is the relatively large inter-layer distance (4 mm) compared to the pixel thickness (0.3 mm). Therefore the next step in the design is to decrease the space between the 2D detectors.

[en] In recent years phase-contrast has become a much investigated modality in radiographic imaging. The radiographic setups employed in phase-contrast imaging are typically rather costly and complex, e.g. high performance Talbot-Laue interferometers operated at synchrotron light sources. In-line phase-contrast imaging states the most pedestrian approach towards phase-contrast enhancement. Utilizing small angle deflection within the imaged sample and the entailed interference of the deflected and un-deflected beam during spatial propagation, in-line phase-contrast imaging only requires a well collimated X-ray source with a high contrast and high resolution detector. Employing high magnification the above conditions are intrinsically fulfilled in cone-beam micro-tomography. As opposed of 2D imaging, where contrast enhancement is generally considered beneficial, in tomographic modalities the in-line phase-contrast effect can be quite a nuisance since it renders the inverse problem posed by tomographic reconstruction inconsistent, thus causing reconstruction artifacts. We present an experimentally enhanced model-based approach to disentangle absorption and in-line phase-contrast. The approach employs comparison of transmission data to a system model computed iteratively on-line. By comparison of the forward model to absorption data acquired in continuous rotation strong local deviations of the data residual are successively identified as likely candidates for in-line phase-contrast. By inducing minimal vibrations (few mrad) to the sample around the peaks of such deviations the transmission signal can be decomposed into a constant absorptive fraction and an oscillating signal caused by phase-contrast which again allows to generate separate maps for absorption and phase-contrast. The contributions of phase-contrast and the corresponding artifacts are subsequently removed from the tomographic dataset. In principle, if a 3D handling of the sample is available, this method also allows to track discontinuities throughout the volume and therefore states a powerful tool in 3D defectoscopy.

[en] The single photon counting pixel detector Medipix2 is a powerful tool for energy resolved X-ray imaging. It allows the energies of incoming X-rays to be discriminated by setting an energy threshold common to all pixels. As the parameters of individual pixels vary, each pixel further contains a 3-bit digital-to-analogue converter (DAC) adjustment. Values of these DACs are traditionally determined by finding the noise floor in each pixel. Our approach is based on a polychromatic X-ray beam attenuation measurement. An attenuation curve is measured using varying thickness of aluminium foil. The attenuation curve is fitted in each pixel with a function calculating the detected signal. Free parameters of the fit are the beam intensity and the energy threshold. The measurement is done twice, with the threshold adjustment set to minimum resp. maximum value in all pixels. The result is a calibration of the adjustment DACs, allowing the value of the adjustment DAC in each pixel to be found such that the dispersion of energy thresholds between pixels is minimized. It is a fast and simple to use method that does not require modification of the imaging setup. It will be shown that it reduces the dispersion of threshold values by up to 40% compared to the noise-floor based technique of equalization.

[en] The semiconductor pixel detector Timepix (matrix of 256 × 256 pixels with 55 μm pitch) can be used for measurements of energies of radiation quanta. For this purpose knowledge of the energy calibration of each pixel is required. Such a calibration is nonlinear. Two calibration methods already exist that use either monochromatic radiation sources or the internal test pulse capability. In the work we compare the calibrated response of the detector with the source method and for different temperatures and detector settings. Furthermore in this work we also explore the possibility of calibrating the detector under new conditions (temperature, detector settings) by adjusting an already existing calibration for different conditions. The new cross-temperature and cross-threshold calibration is calculated based on 3 original calibrations. This approach is advantageous, because it allows improving the detector response for different conditions without the need to make a whole new calibration. It is also the only appropriate method for particular applications where the detector is for instance placed in environments beyond direct physical access such as in a nuclear reactor vessel, the LHC ATLAS detector or in outer space. The method was applied and tested on a Timepix chip equipped with a 300 μm thick Si sensor.

[en] High resolution radiography is a powerful imaging technique for real time and nondestructive visualization of ne internal structure of materials and biomedical samples. X-ray imaging is based on attenuation, but this may be a dicult task for visualization of structures with similar elemental compositions. However, high performance electronic imagers are able to resolve these similarities in attenuation by utilising and improving their properties. In addition to conventional beam attenuation contrast imaging techniques, additional information may be further improved by X-ray d raction techniques (phase-contrast) [1] which require either a coherent X-ray source (synchrotron accelerator) or a highly sensitive detector (Medipix [2]). This phase contrast is complementary to absorption contrast produced solely by attenuation. In this study radiographs of d erent samples were obtained using a microfocus X-ray tube, a hybrid semiconductor (silicon) pixel detector, Medipix2, and a commercial at panel (scintillator-GOS) detector. High quality microradiographs were produced for biological samples such as a small y, wasp and others. Phase-contrast enhanced images were acquired and evaluated. The analysis was performed regarding edge-enhancement relative to background, the contrast, and the signal-to-noise ratio (SNR) of the images acquired with both devices. The edge-enhancement was obtained from the image intensity pro le using oversampling techniques [3]. Superior quality radiographs were obtained with the hybrid semiconductor pixel detector Medipix2, con rming that direct photon detection is preferable for high spatial resolution and contrast enhanced microradiography

[en] Recent advances in semiconductor technology allow construction of highly efficient and low noise pixel detectors of ionizing radiation. Steadily improving quality of front end electronics enables fast digital signal processing in each pixel which offers recording of more complete information about each detected quantum (energy, time, number of particles). All these features improve an extend applicability of pixel technology in different fields. Some applications of this technology especially for imaging in life sciences will be shown (energy and phase sensitive X-ray radiography and tomography, radiography with heavy charged particles, neutron radiography, etc). On the other hand a number of obstacles can limit the detector performance if not handled. The pixel detector is in fact an array of individual detectors (pixels), each of them has its own efficiency, energy calibration and also noise. The common effort is to make all these parameters uniform for all pixels. However an ideal uniformity can be never reached. Moreover, it is often seen that the signal in one pixel can affect the neighbouring pixels due to various reasons (e.g. charge sharing). All such effects have to be taken into account during data processing to avoid false data interpretation. A brief view into the future of pixel detectors and their applications including also spectroscopy, tracking and dosimetry is given too. Special attention is paid to the problem of detector segmentation in context of the charge sharing effect.