[en] Measurements of neutron capture and total cross sections for ¹⁸⁶Os, ¹⁸⁷Os, and ¹⁸⁸Os, neutron inelastic scattering cross sections for ¹⁸⁷Os and ²³⁸U, and total cross sections for ³²S + n are reported. This report is administrative in nature, with few data. 7 figures

[en] The averaged total neutron cross sections in the energy range 1.9-144 keV and the elastic and inelastic scattering cross sections of neutrons of energy E = 24.4 keV have been measured for ¹⁸⁷Os. All the experimental data on the neutron cross sections of ¹⁸⁷Os in the energy range E ≤ 150 keV have been analyzed, taking into account a possible correlation of the elastic and inelastic scattering channels. The average resonance parameters of ¹⁸⁷Os have been determined and are S₀ = 2.44(21) x 10^-4 eV^-1/2, S₁ = 0.368(41) x 10^-4 eV^-1/2, R^∞₀ = -0.243(25), and bar Γ_γ0 = 78.6(4.9) meV. The best approximation of the experimental data is obtained when the coefficient describing the correlation of the elastic and inelastic channel amplitude is ρ = 0.65. 19 refs., 8 figs., 3 tabs

[en] The inelastic neutron scattering cross section of ¹⁸⁷Os for the first excited level (9.75 keV above the ground state) is important for evaluating the age of the universe via the Re/Os cosmochronometer. This information is required for calculating the competition between neutron capture and scattering under stellar conditions. The ⁷Li(p,n)⁷Be reaction at threshold has been used for producing 30 keV neutrons with less than 10 keV FWHM. Inelastic scattering events were detected by three ⁶Li glass detectors at 90, 120 and 270 degree with respect to the neutron beam. The measurement has been performed with isotopically enriched ¹⁸⁷Os and ¹⁸⁸Os samples. Detailed GEANT simulations of the full experiment setup were employed for the determination of various corrections. The results are compared to previous data and to theoretical predictions. (orig.)

[en] The cross sections for radiative capture of neutrons by ^186,187Os in the energy interval 1-150 keV have been determined through an analysis of experimental data on the neutron cross sections of these nuclei under steller conditions. Capture from excited states is taken into account. Mean steller temperatures [kT] = 20-40 keV are considered. For [kT] = 30 keV the total capture cross sections are [σ_γ]_st = 0.414 ± 0.021 and 1.076 ± 0.045 b for ^186,187Os, respectively. The possible systematic errors in the calculations are ≤ 2%. 17 refs., 7 figs

[en] Osmium nuclei lie between the axially deformed prolate rare earth and spherical Pb nuclei. Many of the even-even Os isotopes are known to be γ-soft and odd-A Os isotopes show rotational bands based on different multi-quasiparticle configurations. The study of the dependence of different properties of these bands, e.g. the signature splitting, band crossing frequency, gain in alignment, etc., as a function of neutron and/or proton Fermi level is an important aspect in nuclear structure physics. The neutron Fermi levels in light Os nuclei lie in the mid-upper part of the i_13/2 orbital, so their shapes tend to take appreciable prolate deformation. However, as the Fermi level moves up to the upper part of the i_13/2 orbital, the oblate deformations are expected for the heavier ones. But the experimental data for heavier odd A Os isotopes are very scarce. We have performed an experiment to study the high spin state of ¹⁸⁷Os and have extended its earlier established level scheme through the observation of several new bands and band crossings for the first time. The band built on 7/2^-(503) configuration and its band crossing phenomenon have been discussed here

[en] The cross sections of elastic and inelastic scattering of 45-keV neutrons by ¹⁸⁷Os are measured by the technique of filtered neutron beams at the Kiev VVR-M reactor and are found to be σ_e1 = 11.90 ± 0.50 b and σ_inel = 1.51 ± 0.45 b, respectively. These results confirm the existence of a nonstatistical enhancement of the inelastic-scattering channel due to a noticeable contribution of a preequilibrium state involving two particles and a hole. 8 refs., 1 fig

[en] The Re/Os cosmo-chronometer requires a precise determination of the neutron capture cross section of ¹⁸⁷Os at the stellar conditions of s-process nucleosynthesis, i.e., the effective stellar values for thermal energies between 8 and 25 keV. This implies a correction to the cross section measured in the laboratory, because at these temperatures most of the ¹⁸⁷Os nuclei are in the first exited state at 9.75 keV. In order to support the necessary Hauser-Feshbach calculations of the capture cross section for the excited states, it is important to consider the competition by the inelastic channels, including the so-called super-elastic scattering, where the neutron gains in energy. In this context, the inelastic scattering cross section of ¹⁸⁷Os has been measured using a pulsed neutron beam with an energy of (30 ± 9) keV (FWHM) and a repetition rate of 1 MHz. Neutrons were produced directly at the threshold of the ⁷Li(p,n)⁷Be reaction in order to take advantage of the sharp collimation from reaction kinematics. To compensate for the low neutron yield close to the threshold, scattered neutrons were recorded with 3 efficient ⁶Li-glass scintillators 11 cm in diameter, located at 90 and 120 deg with respect to the neutron beam. Data have been taken with isotopically enriched ¹⁸⁷Os and ¹⁸⁸Os, the latter for measuring the elastic component separately. The analysis of the data was performed by a complete Monte Carlo simulation of the experiment. The results for the inelastic cross section are compared to previous data and are discussed with respect to the stellar (n,γ) rates, which are instrumental for an evaluation of the Re/Os cosmo-chronometer. (authors)

No abstract available

[en] A measurement of the ¹⁸⁷Os inelastic neutron cross section to the 3/2^- 9.75 keV excited state with 34 +- 2 keV incident neutrons gives 1.5 +- 0.2 barns. Pulsed neutron time of flight and a short anisotropic iron-aluminum filter allowed separation of the inelastic yield from the 1/2^- ground-state elastic yield at 24 keV. The influence of the result on r-process galactic age calculations via the Re-Os decay chronometer is discussed, and the need for further theoretical calculations is emphasized

No abstract available