Positronium time of flight spectrum from NEG surface obtained by high-intensity slow-positron beam

A new slow positron beamline based on a dedicated linac is described. A positron beam is a useful probe for investigating the electronic states in solids, especially concerning the surface phenomena. However, such studies as low-energy positron diffraction, positronium spectroscopy and positron microscopy, which require high intensity slow-positron beams, are very limited due to the poor intensity normally obtained from a conventional radioactive-isotope-based positron source, compared with electron source. We started slow-positron beam experiments with linac based high intensity beam last year. The pulsed beam is used for positronium time-of-flight (Ps-TOF) spectroscopy. This method is applied for a study of non-evaporable getters (NEG). Positronium emission from the surface is obtained. Different process is found when the injection energy of the positron beam increase. (author)