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Abstract: Since the beginning of the 1990s, the CEA is being involved in the development of compact gamma cameras based on a pinhole collimator, a scintillator and an intensified CCD. In collaboration with the Kurchatov Institute, the CEA has recently developed a miniature coded mask, which significantly improves sensitivity and angular resolution. Laboratory tests have demonstrated excellent performance. They are summarized, accompanied with on-site test results. We also present preliminary results of Medipix2/CdTe, a semiconductor pixel detector. [Copyright &y& Elsevier]

In the framework of the Medipix2 Collaboration, a new photon-counting chip is being developed made of a 256×256 array of 55 μm-side square pixels. Although the chip was primarily developed for semiconductor X-ray imagers, we think that this type of device could be used in applications such as decommissioning of nuclear facilities where typical sources have γ-ray energies in the range of a few hundred keV. In order to enhance the detection efficiency in this energy range, we envisage connecting the Medipix2 chip to a CdTe or CdZnTe substrate (at least 1 mm thick).The small pixel size, the thickness of the Cd(Zn)Te substrate and the high photon energy motivate us to estimate first the spatial energy spreading following a photon interaction inside the detector. Estimations were made using the MCNP Monte Carlo package by simulating the individual energy distribution for each primary photon interaction. As an illustration of our results, simulating a 660 keV γ source, we found that there are two pixels on average, for each primary interaction, on which the deposited energy exceeds 50 keV.We have also made more accurate simulations using sub-pixels of side 11 μm, in order to evaluate the distance between the barycentre of the deposited energy and the photon impact point. As an example, with a 660 keV γ source, we found that the average of this distance reaches 67 μm when restricted to the events depositing more than 400 keV. If all events are taken into account, the mean distance is 26 μm, even though there is a small proportion of interactions where the scattered photon interacts somewhere else in the detector.Results are presented for different photon energies (60 keV, 660 keV, 1.25 MeV) and different materials (CdTe, GaAs). [Copyright &y& Elsevier]

Abstract: The objective of the paper is to present characterization tools for specific metallic foams objects. As a first step, the objective is to obtain the geometric model of the foam as an input for computed fluid dynamics code. In a second stage, the water behavior in foam samples is studied in free conditions. To address these objectives, an X-ray microtomograph system based on a microfocus X-ray generator and the Medipix2 detector has been implemented. Such X-ray generator has a focal spot size in the magnitude of 1μm that allows a geometric magnification of the sample without blurring images. Experimental constraints are details to observe in the foams in the magnitude of a few tens of micrometers or less, which implies very low contrast. For these reasons the Medipix2 detector is well suited as a very low noise detector. Two-dimensional images are acquired for 360 projections of the foam. The three-dimensional image is obtained by using an algebraic algorithm Ordered Subset Expectation Maximization (OSEM). Two spatial scales are studied in dry and wet conditions for the foams. Images acquired on a 10mm2 sample of foam with pixel size equal to 50μm are used to make the analysis at a macroscopic scale of geometry and water kinetics. Images acquired on a 1mm2 sample of foam with pixel sizes equal to 5μm are used for a thin characterization of the geometry and to reconstruct the water distribution along the struts of the foam. [Copyright &y& Elsevier]