Measurement of positron lifetime to probe the mixed molecular states of   liquid water
  Positron lifetime spectra were measured in liquid water at temperatures between 0c and 50c. The long lifetime of ortho-positronium atoms (o-Ps) determined by electron pick-off in molecular substances decreases smoothly by 10% as the temperature is raised. This lifetime temperature dependence can be explained by combining the Ps-bubble model and the mixture state model of liquid water. 
Katsushige Kotera, Tadashi Saito and Taku Yamanaka