In Na- through Ca-like ions of Fe, rather low-lying 3d levels feature level lifetimes in the range from picoseconds to many seconds. This lifetime range is somewhat wider than that of the 3p resonance levels of the same ions. When trying to measure such level lifetimes, the width of the range exceeds the capabilities of a single measurement scheme. However, there also is the fundamental problem of multi-exponential decay curves and the reliability of their analysis. This problem has arisen afresh for the analysis of long-lived 3p levels in the ground configurations of many isoelectronic sequences that are replenished by cascades from long-lived 3d levels that have no E1 decay channels, but consequently feature lifetimes of the same order of magnitude as those in the ground configuration. This tutorial addresses the measurement situation for lifetimes of 3d levels in a number of ions of Fe and nearby elements.
E. Träbert (Fri,) studied this question.