Beam-foil lifetimes of highly ionized silicon

Electronically excited states of Si ions are created by passing a 20 MeV Si⁵⁺ beam through a thin carbon foil. The EUV-radiation (λ=13–61 nm) emitted by the beam is analyzed using a grazing-incidence spectrometer. From the decay curves, lifetimes of 24 low lying levels in Si VIII to Si XII and of the 4f and 5g levels of Si XI and Si XII are derived. Cascades from doubly excited states turn out to be an important contribution to the radiation observed. The lifetime values of this work are compared to theoretical data mainly of Wiese, Sinanoλu and Dankwort/Trefftz. Most experimental values agree with at least one of the theoretical values. The decay time 560 ps of the 2s2p ^{3 3} D ₃ ⁰ state of Si IX is clearly longer than the theoretical prediction (highest value 455 ps by Sinanoglu).