Positronium in α-Quartz. I. Observed Temperature Dependence of the Positronium Effective Mass and the Probability of Annihilation from Singlet Positronium State

The momentum distribution of photon pairs from positrons annihilating in synthetic crystalline quartz has been measured over a wide temperature range. The width of the narrow component in the distribution was analyzed to yield the positronium effective mass. The effective mass is found to be (1.6 7 ±0.15)×2 m e at low temperature, but appears to increase as the temperature is raised. This result will be discussed in Part II from the view-point of positronium-phonon interaction. The probability of annihilation from singlet positronium state (i.e., the intensity of the narrow component) also increases as the temperature is raised, and tends to approach to a constant value at sufficiently high temperatures. This result might be attributable to possible temperature dependence of positronium formation probability in quartz.