Spin conversation of positronium in paramagnetic solutions studied by age-momentum-correlation method

Correlated measurement of the lifetime and of the lineshape off the 511 keV annihilation radiation off 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+γΔE AMOC method installed at the Stuttgart relativistic positron beam facility (EKine+ ∼ 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. Tn this paper the application of AMOC to positronium 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. (author) 17 refs.; 4 figs.; 1 tab