Metastable level lifetimes from electron-shelving measurements with ion clouds and single ions M. Knoop, C. Champenois, G. Hagel, M. Houssin, C. Lisowski, M. Vedel and F. Vedel Eur. Phys. J. D, 29 2 (2004) 163-171 Published online: 24 February 2004 DOI: 10.1140/epjd/e2004-00022-6