free neutrons are unstable: would a muon in say uranium be "stable"? free neutrons are unstable: would a muon in say uranium be "stable"? free neutrons decompose and have a half-life of about 15 minutes. neutrons bound in a nucleus, especially in a magic shell configuration like helium-4 or iron, have an indefinite lifespan. muons are unstable with 4.4 msec half-life. muon decay can be lengthen near-light speeds due to special relativity time dilation would a muon in an extremely heavy nucleous like uranium where 1S electrons have near-light speeds be stable, or have a long half-life? such muons might serve as a basis for cold fusion. remove 1 electron from a uranium atom (or other stable heavy isotope) replace with muon.