A geometrical calibration method for the PIXSCAN micro-CT scanner

Reconstruction in Cone-Beam Tomography can suffer from artifacts due to geometrical misalignments of the source-detector system. They can be avoided by a complete and precise description of the system. We present a high precision method for the geometric calibration for the PIXSCAN, a small animal X-ray CT scanner demonstrator based on hybrid pixel detectors (XPAD2). The specificities of the XPAD2 detectors (dead pixels, tilts and gaps between modules...) made the calibration of the PIXSCAN quite difficult. The method uses a calibration object consisting of a hollow cylinder of polycarbonate on which we positioned four metallic balls. It requires 360 X-ray images (1° increments). An analytic expression of the 3 image ellipses has been derived. It is used for a least square regression of the 13 alignment parameters after a correction of the internal XPAD2 geometry. Our method is fast and completely automated, achieving a precision of about 30 μm

3D electronics for hybrid pixel detectors – TWEPP-09

Future hybrid pixel detectors are asking for smaller pixels in order to improve spatial resolution and to deal with an increasing counting rate. Facing these requirements is foreseen to be done by microelectronics technology shrinking. However, this straightforward approach presents some disadvantages in term of performances and cost. New 3D technologies offer an alternative way with the advantage of technology mixing. For the upgrade of ATLAS pixel detector, a 3D conception of the read-out chip appeared as an interesting solution. Splitting the pixel functionalities into two separate levels will reduce pixel size and open the opportunity to take benefit of technology's mixing. Based on a previous prototype of the read-out chip FE-I4 (IBM 130nm), this paper presents the design of a hybrid pixel read-out chip using threedimensional Tezzaron-Chartered technology. In order to disentangle effects due to Chartered 130nm technology from effects involved by 3D architecture, a first translation of FEI4 prototype had been designed at the beginning of this year in Chartered 2D technology, and first test results will be presented in the last part of this paper

Neutron imaging with the XPAD3-s hybrid pixel detector

The X-ray photon counting hybrid pixel camera XPAD3-S is a promising detector for small animal X-ray radiography and tomography. The increasing interest in neutron imaging as a complementary approach to X-ray imaging motivates the study of the potentialities of this device for neutrons. To investigate this issue, we have studied the response of XPAD3-S to alpha particles and cold neutrons. The neutron detection was obtained with passive converters placed in front of the sensor. This choice permits to easily assemble 2D neutron sensitive imagers without size constraints; it penalizes however the detector efficiency with respect to other solutions. In this paper, we first analyze the detector response to alpha particles under several conditions, then we investigate its imaging performances and its detection efficiency for cold neutrons. Finally, we present the first XPAD3-S neutron tomography. Most of the results are validated by Monte Carlo simulations that will also permit to extrapolate the detector response to thermal neutrons

Study of the charge sharing effect in the photon-counting pixel detector XPAD3-S

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