Lifetime measurement of He- using an electrostatic ion trap

The lifetimes of the metastable 1s2s2p P-4(5/2), level of He-, as well as t he lifetime of the average of the P-4(3/2) and P-4(1/2) levels, have been m easured using a new type of ion trap that stores keV ion beams using electr ostatic fields only. The use of a pure electrostatic field avoids the compl ication of magnetic-field-induced mixing effects, which can interfere with the measurement of the spontaneous decay. The measured lifetime for the P-4 (5/2) state, after correction for decay;induced by blackbody radiation, is 343+/-10 mu s. This value is consistent with previous experiments, and in e xcellent agreement with the most recent theoretical calculations. The avera ge lifetime of the P-4(3/2) and P-4(1/2) is 8.9+/-0.2 mu s, which is about 20% lower than the weighted theoretical value. [S1050-2947(99)09501-3].