/sup 186,187,188/Os(n,γ) cross sections and galactic nucleosynthesis

The /sup 186,187,188/Os(n,γ) cross sections were measured over the incident neutron energy range 2.6--800 keV. Optimized statistical model fits to the average cross sections were made employing estimates of the 186Os, 187Os, and 188Os p-wave strength functions 0.29 x 10-4, 0.45 x 10-4, and 0.33 x 10-4, respectively, d-wave strength functions 1.3 x 10-4, 4.0 x 10-4, and 1.5 x 10-4, respectively, and gamma ray strength functions (Gamma-bar/sub γ//D0) 26.8 x 10-4, 176 x 10-4, and 20.8 x 10-4, respectively. A lower bound for the 187Os neutron inelastic cross section is estimated as 0.25(20) b at 30 keV. The Maxwellian-averaged capture cross sections are presented as a function of temperature. The ratio of 30 keV Maxwellian-averaged cross sections /=0.504(17) is reported and the lack of agreement with earlier measurements of this ratio is discussed. The use of this cross section ratio in estimating, via the 187Re-187Os beta decay, the duration of galactic nucleosynthesis is discussed. The cross section ratio from this work yields an estimate of 10.4(25) x 109 yr for the duration of galactic nucleosynthesis, a result higher than but still consistent with the estimate 7(2) x 109 yr derived from U/Th decay