412 research outputs found

    Direct measurements of neutron capture on radioactive isotopes

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    We simulated the response of a 4p calorimetric g-detector array to decays of radioactive isotopes on the s-process path. The GEANT 3.21 simulation package was used. The main table contains estimates on the maximum sample size and required neutron flux based on the latest available neutron capture cross section at 30 keV. The results are intended to be used to estimate the feasibility of neutron capture measurements with 4p arrays using the time of flight technique

    The 14C(n,g) cross section between 10 keV and 1 MeV

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    The neutron capture cross section of 14C is of relevance for several nucleosynthesis scenarios such as inhomogeneous Big Bang models, neutron induced CNO cycles, and neutrino driven wind models for the r process. The 14C(n,g) reaction is also important for the validation of the Coulomb dissociation method, where the (n,g) cross section can be indirectly obtained via the time-reversed process. So far, the example of 14C is the only case with neutrons where both, direct measurement and indirect Coulomb dissociation, have been applied. Unfortunately, the interpretation is obscured by discrepancies between several experiments and theory. Therefore, we report on new direct measurements of the 14C(n,g) reaction with neutron energies ranging from 20 to 800 keV

    Neutron capture cross section of 139 La

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    The neutron capture cross section of 139La{}^{139}\mathrm{La} has been measured relative to that of 197Au{}^{197}\mathrm{Au} by means of the activation method. The sample was irradiated in a quasistellar neutron spectrum for kT=25keVkT=25\mathrm{keV} generated via the 7Li(p,n)7Be{}^{7}\mathrm{Li}{(p,n)}^{7}\mathrm{Be} reaction with the proton energy adjusted 30 keV above the threshold. Maxwellian averaged neutron capture cross sections were calculated for energies kT=5‚ąí‚ąí100keV.kT=5--100\mathrm{keV}. The new value for kT=30keVkT=30\mathrm{keV} is found to be 31.6\ifmmode\pm\else\textpm\fi{}0.8\mathrm{mb}, 18% lower and considerably less uncertain than the previously recommended value of 38.4\ifmmode\pm\else\textpm\fi{}2.7\mathrm{mb}. With these results the s- and r-process components could be more accurately determined, making lanthanum a reliable s- and r-process indicator in stellar spectroscopy
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