Muonic Atoms of Unstable Nuclei Available to Purchase

New intense muon beams with flux several orders of magnitude higher than at present muon facilities would allow many novel experimental studies that were until now statistically not feasible. The investigation of the nuclear properties of short‐lived nuclei using muonic atom spectroscopy would become possible. A feasibility study at RIKEN‐RAL muon facility using the cold hydrogen film method to produce radioactive muonic atoms is in progress. This method would allow studies of the nuclear properties and nuclear sizes of unstable nuclei by means of the muonic X‐ray method at facilities where both intense negative muon and RI beams would be available. Encouraging experimental results were obtained with stable argon ions implanted in solid deuterium films. In this paper, we present a compilation of the recent progress of this project that were previously reported in several shorter publications, and discuss future perspectives at the new Muon Experimental Facility in the J‐PARC project.