Radiation damage in the target area shielding of a facility for Selective Production of Exotic Species ( SPES Project )
The advancement of radioactive ion beam (RIB) science since its advent in the last few decades calls for the development of so-called next generation facilities, able to provide beam intensities several orders of magnitude higher than presently available. Two of them are planned by the European roadmap and are representative of the two main methods by means of which RIBs are produced nowadays: projectile fragmentation and isotope separation on-line (ISOL); the latter, based on the ISOL technique, is the EURISOL project: the plan encompasses the construction of three intermediate facilities, one of which is expected to be built at Legnaro (Padua) INFN Laboratories: the SPES Project (Selective Production of Exotic Species).
Possibility of Radiation-Induced Degradation of Concrete by Alkali-Silica Reaction of Aggregates
The effect of Ar ion irradiation on the reactivity of crystalline and amorphous quartz to alkali has been examined for clarifying whether radiation from nuclear reactors accelerates the degradation of concrete by inducing alkali-silica reaction of aggregates. Distorted amorphous quartz generated on the surface of quartz by irradiation of a 200 keV Ar ion beam is at least 700 times and 2.5 times more reactive to alkali than crystalline and regular amorphous quartz, respectively. The high reactivity of the distorted amorphous quartz indicates that the degradation of concrete by alkalsilica reaction is possible to be induced by nuclear radiation even the aggregates are inert to alkali before the irradiation. The critical radiation doses for the degradation of aggregates containing crystalline quartz are estimated to be 5 × 1019 n/cm2 for fast neutrons with energy >0.1 MeV, and 5×1011 Gy for beta and gamma rays. They are 1×1019 n/cm2 and 0.5tiems;1011 Gy, respectively for aggregates containing amorphous quartz.
Ion beam induced amorphization in α quartz
The amorphization of α quartz induced by light and medium mass ion bombardment has been investigated by means of Rutherford backscattering spectrometry in channeling geometry, resonant nuclear reaction analysis and mechanical surface profiling. The single crystalline samples were irradiated at 77 K with H+, N+, Ne+ and Na+ ions at energies of 10–100 keV and fluences up to 5×1016 ions/cm2. Disordering of α quartz by ion bombardment was found to occur by three-dimensional nucleation and growth of defect agglomerates and, possibly, small, spatially separated amorphous zones in the still crystalline surrounding. The nucleation rate scales with the energy density FD in elastic collisions. Above a critical energy density EC=1.92(7)eV/at deposited by nuclear collisions (corresponding to a displacement rate of 0.04 dpa) a coherent amorphous layer forms at the depth of maximum energy deposition, which then grows towards the surface and into larger depths during continued ion bombardment. Mechanical surface profili...