Experimental evidence for muonicX-rays from fission fragments

In the spectrum of muonic X-rays of238U measured in coincidence with prompt fission events a structure has been found which is attributed to 2p→1s transitions of the muon attached to heavy fragments. The intensityIs of this structure relative to the strengthIpf observed for prompt fission has been determined to beIs/Ipf=(6.0± 2.1) %. Although the experimental significance for the appeareance of this phenomenon is weak, this is the first experimental indication for its occuxence.