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Number of results
1993 | 83 | 3 | 349-358
Article title

The Kinetics of the Spin-Conversion of Positronium Measured by β^{+}γ∆E Age-Momentum Correlation

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Languages of publication
EN
Abstracts
EN
Age-momentum correlation (AMOC) measurements provide time-resolved information on the momentum distribution of annihilating electron-positron pairs through correlated determination of Doppler broadening (∆E) of the 511 keV annihilation radiation line and positron age. In the β^{+}γ∆E AMOC technique implemented at the Stuttgart pelletron accelerator the start signals for the age measurements are generated when the relativistic positrons pass through a fast plastic scintillator, which has a detection efficiency close to unity. Beam-based β^{+}γ∆E AMOC measurements thus combine high β^{+}γ∆E triple-coincidence rates with low background. From a practical point of view this constitutes a major progress compared to conventional (source-based) γγ∆E AMOC measurements. The AMOC technique permits direct access to a wide variety of time-dependent processes, among them the reaction kinetics in positronium chemistry. As an example, we present a β^{+}γ∆E AMOC investigation of the kinetics of a spin-conversion reaction of positronium in methanol induced by the presence of a nitrosyl free-radical paramagnetic solute (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl , HTEMPO). The AMOC measurements allowed the time-resolved observation of the spin-conversion process, which had been investigated before by uncorrelated positron lifetime and Doppler-broadening measurements. It is found that within the concentration range investigated (≤ 0.1 mol/l) the spin-conversion reaction rate at room temperature depends linearly on the HTEMPO concentration with a reaction-rate constant k_{conv} = (22.5 ± 0.5) × 10^{9} l mol^{-1} s^{-1}.
Keywords
EN
Contributors
author
  • Max-Planck-Institut für Metallforschung, Institut für Physik, Postfach 800665, 7000 Stuttgart 80, Germany
author
  • Max-Planck-Institut für Metallforschung, Institut für Physik, Postfach 800665, 7000 Stuttgart 80, Germany
author
  • Max-Planck-Institut für Metallforschung, Institut für Physik, Postfach 800665, 7000 Stuttgart 80, Germany
author
  • Max-Planck-Institut für Metallforschung, Institut für Physik, Postfach 800665, 7000 Stuttgart 80, Germany
author
  • Max-Planck-Institut für Metallforschung, Institut für Physik, Postfach 800665, 7000 Stuttgart 80, Germany
  • Max-Planck-Institut für Metallforschung, Institut für Physik, Postfach 800665, 7000 Stuttgart 80, Germany
author
  • Max-Planck-Institut für Metallforschung, Institut für Physik, Postfach 800665, 7000 Stuttgart 80, Germany
author
  • Centre de Recherches Nucléaires, Laboratoire de Chimie Nucléaire, B.P. 20 67037 Strasbourg Cedex, France
author
  • Centre de Recherches Nucléaires, Laboratoire de Chimie Nucléaire, B.P. 20 67037 Strasbourg Cedex, France
author
  • Centre de Recherches Nucléaires, Laboratoire de Chimie Nucléaire, B.P. 20 67037 Strasbourg Cedex, France
References
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Publication order reference
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bwmeta1.element.bwnjournal-article-appv83z319kz
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