Muonic x-ray spectroscopy uses muons to obtain information about the structure of the atom and the nucleus. In muonic atoms, the energy levels of atomic orbitals are significantly more sensitive to the finite size correction. By probing these orbitals using x-ray spectroscopy, the nuclear size correction can be extracted, providing valuable input for laser spectroscopy in the form of absolute charge radii with a relative precision better than 10^-3. Continuing on developments that allowed measurements on target quantities of about 5 μg, we showed the feasibility of using implanted targets. In the future, this will allow the measurement of absolute charge radii of long-lived radioactive isotopes that are not available in sufficient enrichment or large quantities. In this contribution, we shall report on the target preparation, involving high-fluence implantation, and on the preliminary results of the muX experimental campaign.