Positron Age-Momentum-Correlation (AMOC) Measurements on Organic Liquids

Abstract

By means of correlated measurements of the individual lifetimes of positrons (called positron ages) and of the Doppler shifts of their 2γ-annihilation radiation (Age-Momentum Correlation, acronym AMOC) the room-temperature behaviour of positrons and positronium in n-hexane, tetramethylsilane, benzene, methanol, ethanol, nbutanol, n-hexanol, n-octanol, and water has been investigated. The annihilation parameters of “free” positrons and of para- and orthopositronium (lifetimes and Doppler-broadened lines) have been deduced from a two-dimensional analysis of the AMOC data. The lifetimes of positrons are found to be related to the electronic polarizability of the investigated liquid. The behaviour of the Doppler-broadened free-positron and orthopositronium linewidths is explained in terms of structural and dipolar properties of the liquid molecules.