The Stuttgart positron beam, its performance and recent experiments

Abstract

A monoenergetic MeV positron (e +) beam, with a flux at present of 6 × 10 4 e +/s in the energy range of 0.5 to 6.5 MeV, has been installed at the Stuttgart Pelletron accelerator. The stabilization and the absolute calibration of the energy E is monitored by a Ge detector with real-time feedback; a relative energy stability of Δ E E ⩽ 10 −4 is obtained. So far, e +e − scattering and annihilation-in-flight experiments for investigating the low-energy e +e − interaction as well as β + γ positron lifetime measurements in condensed matter have been performed. The advantages of the β + γ method compared to the conventional γγ coincidence technique have been demonstrated. Recently, triple-coincidence positron “age-momentum correlation” measurements have been carried out on fused quartz. A brief account is given on the development of a “positron clock” aiming at a substantial improvement of the time resolution of the β + γ positron lifetime measurements.