Search

It is now well known that during high-energy heavy-ion irradiation, the very high-energy deposition in electronic excitation induces a spectacular damage creation in some types of metallic targets. A selected number of pure metals has been irradiated by GeV ions in order to test some possible criteria which might be pertinent to explain such effects: electron-phonon interaction, electrical conductivity, existence of various allotropic phases,.... The present results show that the latter criterion or more precisely that the existence of a displacive transformation associated with a soft mode in the phonon spectrum seems to favour efficient energy transfers between highly excited electrons and target atoms. For titanium targets, electron microscopy observations show striations which are parallel to the incident ion beam direction.

A sodium borosilicate glass was irradiated sequentially and simultaneously with alpha particles and gold ions. Alpha particles induced partial recovery of the network damage and mechanical properties in the gold pre-irradiated glass, while no such recovery effect was observed during gold irradiation of the alpha pre-irradiated glass. The damage capacity of the gold ions was significantly reduced during simultaneous irradiation with alpha particles and gold ions. These results highlight that the irradiation sequence of the ions plays an important role in controlling the final damage level; and if properly employed, irradiation can be employed to induce defect recovery. Such results are of paramount importance to understand the radiation damage in nuclear reactor components and in nuclear waste glass matrices which are subjected to multiple particle irradiations.

The CIRIL: 30 years of interdisciplinary research at GANIL meeting was held in Caen, France, in October 2013. The meeting provided an excellent opportunity to present the research performed with ion beams delivered by the GANIL facility (Grand Accelerateur National d'Ions Lourds, Caen, France). This proceedings volume comprises a series of reviews from different disciplines (physics, chemistry, biology, medicine, etc) of the results obtained with GANIL ion beams. Unfortunately, the issue is missing two major research domains concerning the induced damage in metals and insulators. Therefore, we refer the interested readers to the following publications: metals [1] and insulators [2].

First measurements of angular distributions of Uranium dioxide (UO2) sputtering induced by slow highly charged Xenon ions (81 keV, v < 0.16 a.u.) have been performed using a catcher technique. The angular distributions are found to be non-isotropic. A clear projectile charge state effect on the sputtering process is observed. From the angular distributions, the total sputtering yield can be deduced. It increases with the projectile potential energy. Varying the projectile incidence angle from 0° with respect to the surface normal to 60°, the sputtering yield increases in the beam forward direction. The projectile charge effect on the angular distribution becomes less prominent at 60° than at 0°. In addition, angular sputtering distributions were studied with Xe25+ at 8 keV (v < 0.02 a.u.), where the potential and kinetic energies of the projectile are equal.

The variations in the transport and magnetic properties on irradiation are now well established for quasi-one-dimensional organic conductors. However, the study of (TMTSF)2ClO4 gives some new results in this field. Indeed, at low temperatures, (TMTSF)2ClO4 belongs to the class of two-dimensional compounds; the influence of irradiation-induced defects at low doses is of the same type as in classical metals. As the disorder increases, the molecular stacks become increasingly decoupled from the point of view of the transverse coherence of the electron wavefunction: the electronic gas becomes quasi-one-dimensional. At the same time the anion ordering after slow cooling is destroyed by the presence of defects as well as the long-range ordering of the spin-density waves for quenched samples.

The comparison between the disordered metallic state created by irradiation and the metallic regime stabilised by high pressure in TMTSF-DMTCNQ ands TMTSF2-PF6 establishes the existence of a contribution from superconducting fluctuations to the conductivity below 50K. A calculation using Ginzburg-Landau theory is in very good agreement with the experimental temperature dependence of the paraconductivity. The authors show that the metal-insulator transition in TMTSF2-PF6 is shifted by the disorder to a lower temperature. However, the effect is less for the spin-density-wave transition in TMTSF-PF6 than for the charge-density-wave ordering in TMTSF-DMTCNQ. Finally they show that the superconductivity transition is strongly depressed by irradiation-induced defects.

The critical temperature of La2CuO4 specimens showing a grain surface superconductivity after annealing under normal O2 pressure can be improved by 2.9 GeV krypton ion bombardment. The midpoint temperature has thus been raised from 32.5 to 35.0 K by a fluence of 4 · 1012 cm-2. Such a result probably enhanced by the high value of the electronic stopping power might be related to the pressure effect of the defects induced by irradiation and/or the existence of a spin density wave phase.