Spatially resolved magnetic resonance studies of swift heavy ion induced defects and radiolysis products in LiF crystals

摘要

Spatially resolved NMR (F-19 and Li-7) spin-lattice relaxation rates were measured on LiF single crystals irradiated with swift heavy ions of about 10 MeV per nucleon corresponding to several tens of micrometer range. Beyond the ion penetration depth, where the relaxation rate is small enough, also the relaxation dispersion was studied by a spatially resolved mechanical field cycling technique. Experiments were performed on crystals exposed to a variety of beam parameters (ion species, projectile energies and fluences) as well as for varying thermal annealing conditions. In addition to NMR, Q-band EPR was applied to study radiolysis products as produced by annealing. The most important findings are a dose dependent defect region within the ion range and an enhanced relaxation rate beyond the ion range due to characteristic X-ray emission (in case of heavy projectile ions) or nuclear reactions (in case of light projectile ions). Moreover, under certain irradiation conditions molecular fluorine F-2 is produced, and thermal annealing involves the formation of metallic lithium, F-center clusters and impurity aggregates.