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

• Authors: U. Lauff , K. Maier , J. Major , A. Seeger , H. Stoll , P. Wesołowski , M. Koch , I. Bilard , J. Abbé , G. Duplâtre
• 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

78.70.Bj

Discipline

• 78.70.Bj: Positron annihilation(for positron states, see 71.60.+z in electronic structure of bulk materials; for positronium chemistry, see 82.30.Gg in physical chemistry and chemical physics)

• Journal: Acta Physica Polonica A
• Year: 1993
• Volume: 83
• Issue: 3
• Pages: 349-358

Dates

published

1993-03

Contributors

author

U. Lauff

• Max-Planck-Institut für Metallforschung, Institut für Physik, Postfach 800665, 7000 Stuttgart 80, Germany

author

K. Maier

• Max-Planck-Institut für Metallforschung, Institut für Physik, Postfach 800665, 7000 Stuttgart 80, Germany

author

J. Major

• Max-Planck-Institut für Metallforschung, Institut für Physik, Postfach 800665, 7000 Stuttgart 80, Germany

author

A. Seeger

• Max-Planck-Institut für Metallforschung, Institut für Physik, Postfach 800665, 7000 Stuttgart 80, Germany

author

H. Stoll

• Max-Planck-Institut für Metallforschung, Institut für Physik, Postfach 800665, 7000 Stuttgart 80, Germany

author

P. Wesołowski

• Max-Planck-Institut für Metallforschung, Institut für Physik, Postfach 800665, 7000 Stuttgart 80, Germany

author

M. Koch

• Max-Planck-Institut für Metallforschung, Institut für Physik, Postfach 800665, 7000 Stuttgart 80, Germany

author

I. Bilard

• Centre de Recherches Nucléaires, Laboratoire de Chimie Nucléaire, B.P. 20 67037 Strasbourg Cedex, France

author

J. Abbé

• Centre de Recherches Nucléaires, Laboratoire de Chimie Nucléaire, B.P. 20 67037 Strasbourg Cedex, France

author

G. Duplâtre

• Centre de Recherches Nucléaires, Laboratoire de Chimie Nucléaire, B.P. 20 67037 Strasbourg Cedex, France

Identifiers

DOI

10.12693/APhysPolA.83.349