Abstract
A monoenergetic positron beam (6 × 10 4 e + s −1) in the energy range of 0.5 MeV ⩽ E ⩽ 6.5 MeV ( ΔE E ≈ 10 −4 FWHM) has been installed at the Stuttgart Pelletron accelerator. Besides experiments on e + e − scattering (Bhabha scattering) and e + e − annihilation-in-flight experiments, β + γ positron-lifetime measurements in solids and melts have been performed. Substantially increased count rates and virtually eliminated background are among the advantages of the beam-based β +γ technique over the conventional γγ coincidence technique. Measurements under difficult conditions (e.g., in high-temperature melts) are simplified. Time-resolved information on the evolution of the positron states (e.g., trapping of positrons at defects) and a sensitive detection of positronium formation are obtained by measuring the lifetime of a positron together with the energy of one of the annihilation quanta in a triple-coincidence setup (age-momentum correlation). In contrast to the conventional γγE age-momentum-correlation technique, the beam-based β + γE technique permits high count rates and almost completely eliminates the deterioration of the measured spectra by pileup effects and by random coincidences.
Published Version
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