On the Existence of Delocalized Positronium in NaF at Room Temperature

Abstract

The angular correlation of two gamma-rays from positrons annihilating in NaF crystal has been measured at several temperatures from 89 K to 300 K. The narrow component in the angular correlation curve resulting from the self-annihilation of delocalized positronium, which has already been reported to be obvious at liquid nitrogen temperature, is still noticeable at temperatures up to about 200 K. Though it becomes much blurred at temperatures above this, qualitative examination of the data indicates that it does exist even at room temperature.