Study of the Positronium Peak in the Angular Correlation Curve of NaF Crystal

Abstract

Positron annihilation 2γ angular correlation curve of NaF has been measured at temperatures ranging from 4.5 K to 300 K. The temperature dependence of the narrow peaks originating from the self-annihilation of singlet positronium (Ps) is analysed. In the lower temperature region, the peak width increases in a rate that shows the Ps is in free state with the effective mass 1.5±0.2 times heavier than the bare mass. At temperatures higher than 150 K, tlae peak width increases more rapidly than in the lower termperature region, which indicates that a number of the Ps are trapped in some localized state.