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Neutron Capture Measurements of Bismuth and Lead Isotopes

The n_TOF Collaboration. Neutron Capture Measurements of Bismuth and Lead Isotopes. Jose L. Tain Instituto de Fisica Corpuscular CSIC-Univ.Valencia. Layout: Motivation Experimental details 209 Bi(n, ) and 207 Pb(n, ) results Conclusions. Motivation:. Astrophysics.

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Neutron Capture Measurements of Bismuth and Lead Isotopes

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  1. The n_TOF Collaboration Neutron Capture Measurements of Bismuth and Lead Isotopes Jose L. Tain Instituto de Fisica Corpuscular CSIC-Univ.Valencia • Layout: • Motivation • Experimental details • 209Bi(n,) and 207Pb(n,) results • Conclusions

  2. Motivation: Astrophysics • Termination region of the s-process path: • stellar site • r-process abundances • Th/U cosmo-chronometers (n,) -decay -decay

  3. Motivation: ADS Sub-critical system for the transmutation of nuclear waste with Pb or Pb/Bi spallation-target/coolant Neutron balance: Radio-toxicity: • 210mBi (3x106 y) • 210Po (138 d)

  4. Set-up sample changer C6D6 C6D6 n-beam Experimental details: • Challenges: • very small capture cross section • large scattering to capture ratio • few percent accuracy Use C6D6 detectors and setup with reduced neutron sensitivity Samples & beam-time:

  5. 1.15keV @56Fe Experimental details: Accuracy of the Pulse Height Weighting Technique? (used to count properly capture cascades) Use of detailed MC simulations of detector response with the full setup + Use of the nuclear statistical model to make systematic corrections … accuracy < 2%

  6. RK=18.2(5%) meV RK=12(7%) meV 209Bi(n,) Results: neutron sensitivity! n_TOF vs. previous experiments

  7. RK=18.2(5%) meV RK=12(7%) meV 209Bi(n,) Results: neutron sensitivity! n_TOF vs. Evaluated Data Files and compilations

  8. 207Pb(n,) Results: n_TOF vs. previous experiments incorrect WF ! not included …

  9. 207Pb(n,) Results: n_TOF vs. Evaluated Data Files and compilations incorrect WF ! not included …

  10. 204Pb under progress … 206Pb under progress … poor peak/background ratio due to sample scattered in-beam -rays 208Pb

  11. Conclusions: • Cross sections with improved accuracy have been obtained and they point out to the need of updating Evaluated Data Bases • Astrophysics implications: slight reduction of Bi abundance calculated in low metallicity TP-AGB stars • ADS implications: larger production of long term radiotoxic210mBi • Extension of the measurements with this improved setup to higher energies are very desirable and possible with a reduction of in-beam -ray background

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