Lifetimes for the Be- and B-like Fe intercombination lines

Abstract

The 2s(sup 2)(S(sub 0))-1-2s2p(P(sub 1))-3 intercombination line in Be-like ions is of considerable interest. The main reason for the interest is due to the fact that the intercombination lines in C III and O V are used in the diagnostics of astrophysical plasmas. The 2s2p(P(sub 1))-3 lifetime was measured for only four ions in the sequence, namely C III, Fe XXIII, Kr XXXIII, and Xe LI. The measurement for Fe XXIII was not in agreement with the currently recommended theoretical result. A remeasurement of the 2s2p(P(sub 1))-3 lifetime was initiated for Fe XXIII. The measurement was made using a beam of 2.5 MeV/nucleon Fe ions provided by the RILAC (RIKEN Linear Accelerator). The experimentally determined lifetime was found to be 17.5 +/- 1.5 ns which was in reasonable agreement with the recommended theoretical value of 19.6 +/- 0.8 ns. Using the same ion beam a measurement was made for the 2s2p(sup 2)(P(sub 5/2))-4 lifetime in B-like Fe. The experimentally determined value for the (P(sub 5/2))-4 lifetime was 14.8 +/-1 ns which was in good agreement with the most recent theoretical result of 13.4 ns.

Be-型イオンの2s(sup 2)(S(sub 0))-1-2s2p(P(sub 1))-3異重項間遷移線はかなりの関心を集めている。関心の主な理由は、CIIIとOVの異重項間遷移線が天体物理学的プラズマ診断に使用されるという事実に基づいている。2s2pP(sub 1)-3寿命は、C III、FeXXIII、KrXXXIII、XeLIのわずか4つのイオンについてのみ測定されている。FeXXIIIの測定結果は最近推奨された理論的結果と一致していない。FeXXIIIの2s2p(P(sub 1))-3寿命を再測定した。RILAC(理研線型加速器)からの2.5MeV/核子のFeイオンビームを使って測定した。実験的に決定した寿命は17.5±1.5nsであったが、これは推奨される理論値19.6±0.8nsとうまく一致していた。同じイオンビームを使って、B-型Feの2s2p(sup 2)(P(sub 5/2))-4寿命を測定した。実験的に決定した寿命は14.8±1nsであり、極最近の理論値13.4nsと良く一致した。