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

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 similar 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 > 10(5), 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. (C) 2002 American Institute of Physics.