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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.

The spectrum of seven times ionized sulfur, S VIII, has been observed in the wavelength range 50-1200 A. Both beam-foil and laser-produced plasma light sources have been used. 71 new Lines representing the transitions 2p5-2p43d, 2p43s-3p, 3 p 3 d , 3d-4J 4f-5g and 5g-6h have been identified and 100 energy levels, of which 46 are new, are now accurately established. The spectral analysis is supported by isoelectronic comparisons along the F I-sequence and by parametric least-squares fits of Slater integrals to the observed levels. The ionization potential in S VI11 is determined to 2651 899 * 6Ocm-' and estimated ionization energjes are derived for the isoelectronic elements between F I and Ar X.

We have determined lifetimes of the 12 4d95p fine-structure levels of AgII, using the beam-foil excitation method. The results are compared with various theoretical predictions. Fairly good agreement is found with recent superposition-of-configurations (SOC) calculations which have included relativistic corrections. r] Ld8 5s2Ld9 5p