No abstract available

[en] The ''GYRAC'' concept is based on cyclotron resonance in a magnetic field that is increasing slowly in time. Others have shown that this results in an autoresonance in which the wave provides a synchronous acceleration of the electrons. Using a simple model makes it possible to design a particularly compact, cyclic electron accelerator; in a cavity with a 1-m radius and final magnetic field of 5 T, electron energy reaches 680 MeV, giving rise to synchrotron radiation at 1keV. Assuming uniform fields and rescaling time, the authors arrive at a Hamiltonian system which has one degree of freedom and which, in a first order approximation, is time independent. In a second-order approximation, the authors find a slow damping of autoresonant oscillation. A paraxial model for beam and fields enables us to evaluate the charge effects-the GYRAC then resembles the betatron. Finally, these results are illustrated by numerical 3-D simulations

[en] We have tested the high-energy imaging capabilities of detectors made of a Medipix1 pixel photon-counting chip hybridized with a 300 μm thick Si or a 200 μm thick GaAs substrate. The results presented in this paper show that an important part of the signal is due to secondary particles coming from γ-ray diffusion in the detector surroundings. According to simulation studies realized with the Monte-Carlo code PENELOPE, the contribution of a 2 mm thick Pyrex screen placed between the source (⁶⁰Co) and the Si detector can reach 75% of the total number of counts. The main reason for this high relative sensitivity of the substrate to the secondary particles is its very poor detection efficiency at high γ-ray energies. We also present results for imaging with a double-cone pinhole collimator, through comprehensive comparisons between experiment and simulation. The first prototypes of a Medipix2 chip hybridized with a 1 mm thick pixel CdTe substrate have been carried out and we present experimental tests done with γ-ray sources at high energies (up to 1.33 MeV). We also present results obtained with a dedicated pseudo-Monte-Carlo 3D simulation code. This simulation code, whose first stage is the single-event energy-deposition distribution, processes the charge-carrier transport taking into account trapping and diffusion and, at the same time, registers the induced signal on pixels. The first confrontations with experimental measurements are shown

No abstract available

[en] The Cartogram system has been specially designed for measurements and control of gamma rays during dismantling and/or maintenance of nuclear sites. It performs real time and accurate diagnosis on localisation of radionuclides, thus reducing time of radiation exposure for personnel in accordance with ALARA principles

No abstract available

[en] This report presents the results of measurements of absorbed doses axial and radial distribution in the vertical experimental channels of the RA reactor. Measurements were done in channels VK-5, VK-7, VK-9 and GF-36. Results were compared to the results of calorimetry measurements and measured neutron flux values performed by other laboratories. Fricke and oxalate dosemeters were used in addition to the cobalt indicators

No abstract available

[en] In the framework of the MEDIPIX Collaboration, a hybrid pixel detector has been developed primarily for X-ray radiography. This detector consists of a 64x64 pixel photon counting chip (PCC), bump bonded to a 200 μm thick GaAs substrate. The PCC is optimised for energy depositions in the range of a few keV to a few tens of keV. The aim of this study is to evaluate the detector for applications in decommissioning of nuclear power plants where typical sources have energies in range of a few hundred keV. Tests were realised using a ¹³⁷Cs gamma source (660 keV). At this energy, Monte-Carlo simulations predict that, on average, for more than 60% of primary interactions, there is at least one pixel on which the deposited energy exceeds 100 keV. Simulations also allow modelling of the spatial energy spreading. The comparison of the simulation results with experimental data should indicate if there is a significant contribution of electrical cross-coupling between pixels to the cluster size of the detected hits. The results obtained demonstrate promising perspectives for this kind of detector towards gamma imaging applications

No abstract available