New laboratory lifetime measurements of U II for the uranium cosmochronometer

Details New laboratory lifetime measurements of U II for the uranium cosmochronometer New laboratory lifetime measurements of U II for the uranium cosmochronometer

Jun 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001a%26a...372l..50l&link_type=abstract

Astronomy and Astrophysics, v.372, p.L50-L52 (2001)

Astronomy and Astrophysics

Astrophysics

10

Atomic Data, Stars: Evolution, Galaxy: Evolution

Scientific paper

We present new measurements of radiative lifetimes for six energy levels of singly ionized uranium, U II, using laser-induced fluorescence technique. One of the levels, 5f36d7p6M13/2 at 26191 cm-1, decays by a transition at 3859.6 Å. This line has recently been observed in the spectrum of the metal-poor star CS1082-001, the first detection of uranium outside the solar system. The lambda 3859 line can be used as the presently most accurate cosmochronometer (Cayrel et al. \cite{Cayrel}). Our value of the lifetime of the 6M13/2 level is 18.6+/-0.7 ns, and it confirms the f-value used in the Nature article by Cayrel et al. (\cite{Cayrel}), which is based on an experimental lifetime of 20+/-5 ns (Chen & Borzileri \cite{Chen}). The new measurement also removes the doubt about the choice between that value and other f-values in the literature, differing by a factor of 3. Adopting the same branching fraction as Chen & Borzileri (\cite{Chen}) for the 3859.6 Å line, we derive a gf-value of 0.68, which is 8% higher than the value used by Cayrel et al. (\cite{Cayrel}). Of significance for the chronometer is also the reduced uncertainty of the radiative lifetime, 4% compared to 25%, and consequently of the f-value, which should decrease the uncertainty in the determination of the stellar age considerably.

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