Temperature dependence of positronium decay rates in gases

The decay rate of orthopositronium (o-Ps) formed and thermalized in eight d ifferent gases is systematically investigated as a function of temperature. The o-Ps collisional quenching rate is observed to increase with temperatu re, T, for He, Ne, Ar, N-2, ethane, methane, isobutane and neopentane. All of the gases except ethane and methane increase linearly over the investiga ted temperature range, 300 K < T < 600 K. Recent theoretical work for noble gases at elevated temperatures suggests a linear increase in the collision al quenching rate with temperature at the low densities used herein where c ollective phenomena such as bubble formation and density fluctuations are n ot present. When comparisons can be made with previous experimental results the agreement is generally poor. Precision o-Ps decay rate measurements us ing gases are also discussed concerning systematic effects due to the energ y dependence of the collisional quenching rate.