MUONIUM FORMATION IN XENON AND ARGON UP TO 60 ATMOSPHERES

Results of muon polarization studies in xenon and argon up to 60 atm are reported. In argon for pressures up to 10 atm, the muon polarization is best explained by an epithermal-charge exchange model. Above this pressure, the decrease in P(D) and increase in P(L) are ascribed to charge neutralization and spin exchange reactions, respectively, in the radiolysis track. Measurements with Xe/He mixtures with a xenon pressure of 1 atm indicate that the lost polarization in the pure xenon at this pressure is due to inefficient moderation of the muon. As the pressure in pure xenon is increased above 10 atm, we find that P(L) remains roughly constant and P(D) begins to increase. The lost fraction may be due to the formation of a XeMu Van der Waals type complex, while P(D) is ascribed to XeMu+ formation. This suggests that spur processes appear to be less important in xenon than in argon.