Observation of Muonic X-rays of Cosmic-Ray Muons Stopped in Al and Fe Targets

We successfully measured muonic X-rays of cosmic-ray muons stopped in Al and Fe targets. In order to identify the events that incoming cosmic-ray muons were stopped in the targets, a coincidence and anticoincidence system of three plastic scintillators was used. The X-rays associated with the atomic muon captures were measured with germanium detectors. Measurements using the Al and Fe targets were carried out for 33 and 16 days, respectively. A sufficient number of muonic X-ray events for identifying the elemental compositions of the target materials were clearly observed. This technique provides a means of nondestructive elemental analysis that does not require the use of particle accelerators.