Measurements of long atomic lifetimes at an ion storage ring

Millisecond lifetimes of excited levels in multicharged ions may be measured at ion storage rings. At the Heidelberg storage ring TSR, particle detection after collisions between the circulating ions and electrons of the cooler has been used to obtain dielectronic recombination spectra as well as time curves of ionization and recombination for four-electron ions, with the aim of measuring transition probabilities for magnetic dipole and for electric dipole intercombination decays. The measurements on the 2s2p 3P01 level in the Be-like ions of N and O indicate lifetime values of τ=(1.6±0.2) ms for N3+ and of τ=(0.5±0.1) ms for O4+. Problems of these experiments are discussed as well as the prospects for improved measurements on other such ions of astrophysical interest, planning for state-specific optical detection. (orig.)