Mossbauer spectroscopy at ISOLDE

Applications of radioactive ion beams produced at the ISOLDE facility for M ossbauer studies of probe atoms in solids are presented. Examples are given for a site-selective incorporation on different substitutional sites in co mpound semiconductors by ion implantation and thermal annealing of the radi ation damage resulting from the implantation. The interactions of the probe atoms with lattice defects created in the implantation process have been s tudied to elucidate likely causes for the site-selective implantation mecha nism. The technique has enabled to determine the electronic densities at el ectrically active substitutional probe atoms, having shallow donor or accep tor states as well as states deeper in the band gap. The results are in goo d agreement with theoretical results from local density calculations. Metho dological aspects of the Mossbauer emission techniques employed at ISOLDE a re compared to alternative accelerator based techniques and the consequence s of the application of different precursor isotopes to the Fe-57 Mossbauer isotope are treated in detail for Fe-57 in silicon. Finally, results obtai ned for the magnetic hyperfine interactions of 5 sp impurities associated w ith vacancies in ferromagnetic metals are discussed.