A simple positron lifetime spectrometer for a magnetically guided low-energy beam

Abstract

We present a new, simple, and inexpensive positron lifetime spectrometer intended for the depth-resolved characterization of thin films and buried interfaces. The spectrometer operates on a conventional magnetically guided positron beam with energies ranging from 1 to ∼50 keV. Given is a detailed description of the performance of the apparatus, built on thorough experimental investigations and computer simulations. A timing resolution of 350±13 ps at full-width-at-half-maximum was obtained. The count rate for thin films (low positron energies) was of the order of 1000 s−1. A maximum peak-to-background ratio>105, aiding the measurements of long-living (10–100 ns) positronium in voids, was achieved by constant beam rate reduction and by beam chopping. Examples are presented for measured lifetimes in well-characterized systems.