Simulation of muonium formation in liquid hydrocarbons

Muonium formation in liquid hexane is examined by computer simulation. In t rack-end competition between muonium formation and cation-electron recombin ation, the muon is found to react with electrons from a significant part of the track end, corresponding to an energy attenuation of several tens of k eV and a length of several microns. This muonium formation extends to micro seconds following muon implantation. Delayed muonium formation leads to a m uch smaller amplitude of the muonium asymmetry than for prompt muonium form ation during slowing down of the muon, and in this way may account for the missing polarization in transverse magnetic field experiments. If reaction of muons with electrons from their radiolysis tracks contributes to the exp erimentally observed muonium yield, the muon must thermalize between 60 and 150 nm from the last ionization of the track to reproduce the amplitudes o f the muon and muonium asymmetries. For the smallest distance, 60 nm, the e xperimentally observed muonium asymmetry results from delayed muonium only. As the muon thermalization distance increases, prompt muonium formation al so contributes, so that at 150 nm the observed asymmetry is almost entirely due to prompt muonium formation. (C) 1999 American Institute of Physics. [ S0021-9606(99)50540-0].