Beam-foil spectroscopy for ions of lead and bismuth

Abstract

The beam-foil technique is used to measure the lifetimes of levels in Pb III, Pb IV, Bi III and Bi IV. The problem of the energy loss incurred by heavy ions at the foil is discussed. Intensity decay curves including the region around the foil are analysed using VNET, a multiexponential fitting routine which includes the instrumental window function. These analyses are found to give results virtually identical with those obtained using normal curve-fitting of the data excluding the foil region in our case, where the window region only extends over one or two primary lifetimes. A comparison of the experimental and theoretical ƒ-values trends for the resonance transitions of the ions belonging to the gold and mercury isoelectronic sequences shows that the model potential used by Migdalek and Baylis in 1985 to allow for valence-core correlation gives good agreement with observation for the mercury sequence, whereas their similar calculation in 1979 for the gold sequence appears to give ƒ-values lower than those found by experiment for Tl III and Pb IV.