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Dielectric materials can be used in radiative environment that is why it is of major importance to determine their properties modifications with time. In this paper we focus our attention on PolyTetraFluoroEthylene (PTFE) films submitted to gamma radiations. We investigate the FTIR spectra and show that after exposure to Co 60 the crystallinity of the material is increasing. This result is confirmed by Differential Scanning Calorimetry (DSC) analysis. Some space charge distribution profiles obtained by the Pulse Electro Acoustic (PEA) method show that the irradiation favours the drift of injected charges toward the bulk. Obviously the dose of radiation must be carefully chosen in order to be able to perform electrical measurements. Indeed, we observed that if the radiation dose is too high the sample becomes fragile and most of the characterisation tools cannot be used.

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The kinetics of interstitial iron precipitation in p-type silicon are investigated. During annealing, the iron charge state is controlled by the applied reverse voltage and its effect on the precipitation is studied. We observe that iron in the neutral charge state (Fe0i) precipitates preferentially in three-dimensional nucleation centers while Fe+ivanishes in the dislocation lines (rod-like nucleation centers). These centers are created during the fast cooling procedure necessary to dissolve iron in the silicon matrix.

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The aim of the present work is to study the dynamics of the space charge in cross-linked polyethylene (XLPE) irradiated by gamma rays. For this purpose, film samples peeled from cables have been irradiated with gamma rays at total dose up to 100 kGy, in air at room temperature. To investigate the impact of the irradiation on the electrical behavior, space charge measurements were achieved in ambient conditions after the irradiation using Pulsed Electro Acoustic (PEA) method. The space charge measurements on the irradiated XLPE under an electric field of 40 kV/mm show the development of twoheterocharge regions adjacent to the electrodes. This is in mark contrast with the behavior of un-irradiated XLPE with space charge pattern dominated by charge injection. The charge accumulated during the polarization step persists during the relaxation and is stable after 1 hour.

The aim of the present work is to study the dynamics of the space charge in crosslinked polyethylene (XLPE) induced by electron beam irradiation. For this purpose three energies have been chosen so as to implant charges in a controlled way, in the volume, at different depths not too close to the electrodes. Pulsed Electro Acoustic (PEA) method was used to measure space charge in each sample, at the end of the irradiation process, in ambient conditions. The space charge measurements show the existence of two electron implantation sites after irradiation, one in the bulk at a depth depending on the irradiation energy and the other near the irradiated surface and a fixed position (25 µm). The application of the electric field shows that the charge implanted in the volume tends to be evacuated during the polarization. The charge accumulated persists during the relaxation and is stable after 1 hour. The current measurements reveal the impact of the irradiation in XLPE sample: the steady current measured on the irradiated sample is substantially higher compared to the one recorded on the non-irradiated specimens. Also a change in conduction mechanism is observed. The current recorded on XLPE irradiated weakly diverges from linearity with the electric field in the field range up to 40 kV/mm.