Suppression of Cascade Effects in Beam-Foil Mean-Life Measurements

Using the spatial decay of quantum beats, we have succeeded in suppressing optical cascading effects in the mean-life measurements of levels in foil-excited O II ions. This straightforward technique may be applied to any excited level with total angular momentum $J>\mathrm{}\frac{1}{2}$ and a lifetime within the range of the beam-foil technique. With the present method, mean lives are obtained in terms of the Landé $g$ factors and an external magnetic field, instead of the customary particle speed and decay length.