DETERMINATION OF PS LIFETIMES BY THE BEAM-FOIL TECHNIQUE AT MEV ENERGIES

With the new experimental set-up for beam-foil spectroscopy at the University of Lund atomic lifetimes down to about 10 ps are straight forward to measure at MeV energies. In this paper we discuss the modelling of the observed decay curves, including the effects of the finite spatial resolution of the monochromator and shadowing by the foil, that is necessary to obtain ps or even sub-ps lifetimes. The detailed model presented is based on measureable geometric quantities only and is found to accurately reproduce observed data. We conclude that the uncertainty in the shape of the foil surface is an important factor setting the low-lifetime limit for this method of analysis.