Pressure Effects in ortho-Positronium Annihilation

In the literature on positron annihilation lifetime spectroscopy (PALS) numerous papers are devoted to the temperature dependence of annihilation parameters: lifetime and relative intensity of various modes of decay. The number of studies on pressure dependence of the same parameters is in great contrast to the previously mentioned: the number is very low. The pressure studies certainly deserve more attention. Using quite moderate pressures one can observe many interesting effects. In this paper we want to describe some of them. The data presented below were obtained in positron laboratory at Marie Curie-SkÃlodowska University in Lublin. All the spectra were measured on standard fast-slow spectrometers (BaF2 crystals, dynode output) and processed using the LT programme [1].