Temperature dependence of positronium decay rates in gases

The decay rate of orthopositronium (o-Ps) formed and thermalized in eight different gases is systematically investigated as a function of temperature. The o-Ps collisional quenching rate is observed to increase with temperature, T , for He, Ne, Ar, N2, ethane, methane, isobutane and neopentane. All of the gases except ethane and methane increase linearly over the investigated temperature range, 300 K < T < 600 K. Recent theoretical work for noble gases at elevated temperatures suggests a linear increase in the collisional quenching rate with temperature at the low densities used herein where collective phenomena such as bubble formation and density fluctuations are not present. When comparisons can be made with previous experimental results the agreement is generally poor. Precision o-Ps decay rate measurements using gases are also discussed concerning systematic effects due to the energy dependence of the collisional quenching rate.