Abstract
Correlated measurement of the lifetime and of the lineshape of the 511 keV annihilation radiation of positrons (age-momentum correlation, AMOC) has become a powerful tool for investigating reactions of positron or positronium in condensed matter as a function of time. The beam-based β + gDE AMOC method installed at the Stuttgart relativistic positron beam facility (E e+ kin 4MeV) offers substantial advantages over the conventional γγΔE coincidence technique resulting in a fast data taking due to the unity detection efficiency of the β + scintillator which provides the start signal for the lifetime measurement. In this paper the application of AMOC to positron-ium chemistry is illustrated by the study of spin conversion of positronium in the system methanol/HTEMPO as a function of HTEMPO (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, a paramagnetic solute) concentration. The same technique can be applied to other systems and other reactions in positronium chemistry, e.g., oxidation or complex formation
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