Les CATs (Compteurs A Trous), Étude et développement d'un nouveau type de compteur proportionnel pour le rayonnement synchrotron

The gas detectors have been used for a long time in physics experiments, particularly those around the synchrotron radiation. The previous detectors have certain limitations (fragility, saturation with X-ray flux, images modulation...) which could be useful to be overcome. In that context appeared the CATs (Compteurs A Trous) in 1994. These proportional counters can resolve mainly of the disadvantages of the other gas detectors. Our work concerned the measurements and the analytic modelisation of the behaviour of CATs. We have performed measurements using conventional X-ray source and synchrotron radiation. We compared results of counting and current mode measurements with regard to the X-ray flux. The record of the energy resolution curves indicates that the multiplication of electrons must occur along a tube very closed of the symmetry axis. Introducing the electric field formula along the symmetry axis in the expression of the gain in the Townsend model we gave an analytical expression of the gain for this electron multiplier filled with the following pure gases: : Argon, Xenon, CH4 and CO2. The comparison between the model prediction and experimental results proved the pertinence of the approach. We remarked some discrepancy between the calculation and the measurements when the pressure varies. We improved the agreement between the model and the experiment using an expression of the ionization differential cross section which linearly depends on the reduced electric field E/N. We also tried to extend the model to the mixtures of the cited gases. Then, we shown the great quality of the CATs proportional counters, which certainly can be used for experiments using the synchrotron radiation produced by the third-generation synchrotron sources, and proposed an analytical model to predict their gain.