Publications

Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) have been used to evidence the occurrence, morphology and microcomposition of the superconducting phases (Bi,Pb)(2)Sr2Ca2Cu3O10+delta (2223) and (Bi,Pb)(2)Sr2CaCu2O8+delta (2212), and of other non-superconducting phases, in the sintered pellets obtained from nitrate solution by spray frozen, freeze drying technique. For decomposition of the nitrate powder four different heat treatments were used. Superconducting and structure properties of the pellets have been tested by AC susceptibility measurements (610 Hz, 0.5 Oe) and X-ray diffraction analysis, respectively. A correlation between the SEM and EDS observations and the superconducting properties has been established. (C) 1997 Elsevier Science B.V.

Electron spin resonance investigations on ion beam irradiated polymers are reviewed from a critical point of view. The nature of free radicals produced by heavy ion bombardment is discussed in detail, in connection with the main hypotheses (thermal spikes and secondary electrons). ESR investigations on cellulose nitrate irradiated with accelerated oxygen ions are reported. From the temperature dependence of resonance line parameters, the presence of exchange interaction is noticed and the generation of free radicals at 200 degrees C is studied. (C) 1997 Elsevier Science B.V.

The effect of electron beams on polyoctenamer is investigated by viscosimetry, swelling and electron spin resonance spectroscopy. From these experimental investigations it has been deduced that the main degradation process in polyoctenamer is its crosslinking during electron beam irradiation in air, at room temperature. (C) 1997 Elsevier Science B.V.

The thermal stability of amorphous Se/CdSe multilayers has been investigated by X-ray diffraction. The multilayer structure is stable up to similar to 60 degrees C. After annealing at higher temperatures hexagonal selenium and hexagonal CdSe phases with nanometric crystallite size were revealed. (C) 1997 Elsevier Science Ltd.

Electron spin resonance and optical studies reveal the presence of both Cu2+ and Cu+ centers in Rb2ZnCl4:Cu single crystals grown from melt and their conversion by X- or gamma-irradiation. Two types of paramagnetic Cu2+ centers with different concentrations and production properties have been identified. The more abundant Cu2+(I) center consists of a Cu2+ ion substituting for Zn2+ at the center of a ZnC42- tetrahedron. The less abundant Cu2+(II) center seems to be situated at a Rb site. Production experiments strongly suggest that during the crystal growth copper enters the Rb2ZnCl4 lattice as Cu2+, mainly at Zn2+ sites, part of it being afterwards converted to Cu+ precursor centers. The presence of a neighboring-charge compensating anion vacancy and its departure during the radiolytic Cu+(I) --> Cu2+(I) conversion seems to play an essential role in the stabilization of the Cu+(I) and Cu2+(I) centers, respectively.

Anomalies occurring in irradiated polymers within the glass transition range, as reported by various authors are critically reviewed. A theoretical description for such processes, is developed within the free volume approximation. The discrepancies between the temperature at which such anomalies are noticed and the glass transition temperature have been ascribed to the fact that the volume of radiation-induced radicals is not equal with the segmental one. The agreement between experiment and theory is good. (C) 1997 Elsevier Science B.V.

Lanthanum stearate films were prepared by the conventional Langmuir-Blodgett method and by a dragging procedure. Multilayers have been obtained and studied by X-ray diffraction. The electron density distribution normal to the bilayer plane has been calculated. (C) 1997 Elsevier Science S.A.

The light induced modifications in thin films of Fe:PVA were studied by optical and Mossbauer spectroscopy. Under the UV exposure both the refractive index and the absorption coefficient are changing. The real part of the refractive index is measured using m-line Spectroscopy. As a function of UV exposure, the optical absorption as well as the Mossbauer spectra were measured. A correlation between the optical and the measured Fe2+/Fe3+ ratio is discussed. (C) 1997 Elsevier Science S.A.

The concept of NIEL (Non Ionising Energy Loss) is usually considered to correlate the effects of the displacement damage produced in the material bulk by different particles in different energy ranges. An evaluation of the NIEL is especially important for those semiconductors which are planned to be used in the extreme radiation environment of the new generation of colliders as LHC. In the present work, a calculation of the pion NIEL in silicon and GaAs, in the energy region up to 50 GeV is reported and discussed. The energy dependence of the NIEL is found to follow the resonant structures of the pion-nuclei interactions, where the strongest effect is due to the Delta(33) resonance. Above 1 GeV a slight monotonic decreasing behaviour of the NIEL has been found, both for Si and GaAs.

The Fe:PVA thin films were studied by optical and Mossbauer spectroscopy. Both the absorption and Mossbauer spectra are dependent on the PVA dilution and ferric chloride concentration. A strong correlation between the optical and Mossbauer results was found, indicating the major role of the iron electronic local levels in the optical phenomena. A relation between the various absorption probabilities and also indirect information about the Debye temperatures were obtained. (C) 1997 Elsevier Science S.A.