Effect of satellites on the 1s2p 3P20 level lifetime in He-like ions

Full text: Hyperfine fields (HFS) cause a small admixture of the 1s2p 1,3P10 states to the 1s2p 3P0,20 wave functions for He-like ions. This HFS enables the transitions from 1s2p 3P0,20 to 1s21S0 state allowed which is other wise forbidden. Therefore the lifetimes of the 1s2p 3P0,20 states are reduced by hyperfine quenching (HFQ) [1]. Lifetime measurements of highly charged ions are mostly done with beam-foil type of experiments. During beam-foil interactions, He-like ions are produced along with several neighboring charge states due to ion-atom collisions involving electron capture and loss processes. As a result, transitions of the type 1snln 'l' - 1snln' 'l' (n', n' ≥ 2) from K-shell excited configuration in Li-like ions give rise to satellite lines near the 1s2 - 1snl lines of the corresponding He-like ions. Resonance line in He-like systems (1s21S0-1s2p 1P10) is very fast and therefore satellite lines being forbidden could not affect it. However, satellite line does affect the slower M2 line during lifetime measurements. Experimental techniques do not always resolve such satellite line from the line of interest (say, He-like M1 and M2 lines) in the spectra. If the satellite line is not taken into consideration, the lifetime measured from the unresolved peak may well deviate from its true value [2,3]. In fact one sees a combined effect of the two or more lines originating from different ionic states. Effects of hyperfine quenching and satellite maybe indistinguishable if the upper level of satellite is shorter lived than that of the M2 line (Z ≤ 40). Co-existence of these two effects complicates the measurements. The present study concerns this problem. In the present work it is shown that an unresolved Li-like 1s22s 2S1/2 - 1s2s2p 4P5/20 satellite line affects the lifetimes deduced for the He-like 1s2p 3P20 level. To include the effect of this satellite line we derive a simple but novel semi-empirical formula and estimate the 'effective' lifetime of the 1s2p 3P20 level if the satellite line is unresolved [4]