In-beam Mössbauer spectroscopy using an unstable nuclear probe or an energetic radioactive isotope (RI) beam is one of the most powerful technique that is used to observe the site occupations, dynamic atomic jump processes, and exotic chemical states of extremely diluted atoms in a material. The on-line Mössbauer technique offers unique information of the probe atoms under non-equilibrium or metastable conditions in the Mössbauer lifetime. Here, the outlines of recent results of ⁵⁷Mn implantation experiment and the facility of RIKEN RI-beam Factory are explained.