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Neutron Sensitivity Analysis of 62Ni and 63Ni Reactions at CERN

Analysis of 62Ni(n,g) and 63Ni(n,g) proposals by Claudia Lederer from University of Vienna at a n_TOF analysis meeting in 2010 at CERN. The analysis includes normalization, flux shape considerations, and neutron sensitivity evaluation.

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Neutron Sensitivity Analysis of 62Ni and 63Ni Reactions at CERN

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  1. Analysis of 62Ni(n,g) + 63Ni (n,g) proposal Claudia Lederer University of Vienna n_TOF analysis meeting, 23-24th november 2010, CERN

  2. 62Ni(n,g) analysis Claudia Lederer

  3. Status • all data processed  weighted spectra available • 2 Wf (threshold biased ) by Nicola (GEANT3) and Frank (MCNPX) are in very good agreement • Flight path calibration by fitting resonance energy of well known Au resonances (L=186.97 m) Things to discuss • normalization & flux shape • neutron sensitivity Claudia Lederer

  4. Normalization and flux shape • normalization to 4.9 eV saturated resonance in Au: Nicola Wf: N=0.596 ± 0.002 Frank Wf: N=0.590 ± 0.002 • Agreement within 1% Flux: MGAS (10B) (normalization 0.598 for MCNPX flux) Claudia Lederer

  5. SAMMY calculation with fitted normalization

  6. Normalization and flux shape • normalization to 4.9 eV saturated resonance in Au: Nicola Wf: N=0.596 ± 0.002 Frank Wf: N=0.590 ± 0.002 • Agreement within 1% Flux: MGAS (10B) (normalization 0.598 for MCNPX flux) • normalization to 1.15 keV resonance in Fe MGAS flux: N=0.598 ± 0.005 MCNPX flux: N=0.567  5% change!! Claudia Lederer

  7. Fit of normalization at Fe resonance at 1.15 keV • Picture FE

  8. Comparison Flux 2009: • Picture fluxes

  9. Comparison Flux 2009 + ‚official‘ flux 2003 • Picture fluxes

  10. Resonance-analysis: neutron sensitivity • 62Ni: ER= 4.6 keV, Gn=2.026 keV, Gg=2.374 eV • Contributes around 50% to MACS at 30 keV •  Gn/ Gg = 853 Estimation of neutron background: Nibg= Niel_yield*Carbon/Carbonel_yield Elastic yield of Ni calculated with SAMMY Claudia Lederer

  11. Resonance-analysis: neutron sensitivity

  12. Resonance-analysis: neutron sensitivity • Fitting the 4.6 keV resonance with pointwise BG Claudia Lederer

  13. Resonance-analysis: neutron sensitivity • Problem: Carbon spectrum is a mixture of ‚time-correlated‘ and ‚time-uncorrelated‘ neutron scattering • Fitting the 4.6 keV resonance • including background: Gg=1.800 eV, Gn= 2026 eV • no background: Gg=2.860 eV, Gn=2026 eV JENDL parameters: Gg=2.376 eV, Gn=2026 eV  This would result in a neutron-sensitivity around 5x10-4 Claudia Lederer

  14. Resonance-analysis: neutron sensitivity • procedure overestimates the neutron scattering background • measurement of neutron sensitivity of setup is important • simulations of time-of-flight from scattering to capture event could possibly help Claudia Lederer

  15. Resonance-analysis: narrow resonances • assumption: resonant neutron scattering loses time-correlation • other background (e.g. in-beam-gammas) smooth • fit of each resonance individually plus fit of background in SAMMY • ER: 9.420  9.535 keV • l=1 • Gn: 350  689 meV • Gg: 1000 meV Claudia Lederer

  16. Cross section at thermal • Extrapolation of 62Ni data to thermal point: • 1/v fit from 1eV to 100 eV • s(0.025 eV) = 14.1 b (with n-scattering BG subtraction) • s(0.025 eV) = 15.3 b (without n-scattering BG subtraction) Experimental values: 14.0 - 15.9 barn Claudia Lederer

  17. Conclusions Simulation of time correlation of scattered neutrons necessary: • Verify that narrow HE-resonances are not affected • Try to estimate scattered resonance shape for 4.6 keV Problem in flux-shape above 200 eV for 2009 Claudia Lederer

  18. Proposal: 63Ni(n,g) at n_TOF Claudia Lederer

  19. The case of 63Ni: role in stellar nucleosynthesis • t1/2=100.1 yr • decay: b- to 63Cu (no g-emission  no radioactive background) • t1/2 reduced under stellar conditions - for kT=91 keV, t1/2= 0.4 yr ! (Pignatari et al. Ap.J. 710 (2010)) Courtesy of I. Dillmann s-process core He burning, kT=25 keV, Nn~106 cm-3 s-process C shell burning, kT=91 keV, Nn~1011 cm-3

  20. The case of 63Ni: role in stellar nucleosynthesis • t1/2=100.1 yr • decay: b- to 63Cu (no g-emission  no radioactive background) • t1/2 reduced under stellar conditions - for kT=91 keV, t1/2= 0.4 yr ! (Pignatari et al. Ap.J. 710 (2010)) • 63Ni represents first branching point in s-process reaction path • Highest uncertainty in 63,65Cu abundances comes from unknown 63Ni(n,g) cross section Courtesy of I. Dillmann s-process core He burning, kT=25 keV, Nn~106 cm-3 s-process C shell burning, kT=91 keV, Nn~1011 cm-3

  21. Present situation on 63Ni(n,g) • measurements so far ONLY at thermal energies • MACS are based on extrapolation of these cross sections  theoretical assumptions could be affected by big uncertainties • MACS at 30 keV: KADoNiS: 31± 6 mb TENDL(2009): 68.9 mb this work: 90.8 mb Claudia Lederer

  22. 63Ni sample • 3 metal discs (2 foils produced 1984, 1 foil produced 1992) • total mass: 955 mg • diameter: 10 mm • enrichment in 63Ni: 11.7 % (= 112 mg) • contaminants: 18.3 mg 63Cu  will be removed chemically at PSI • sample will be sent to PSI middle of december Claudia Lederer

  23. Measurement • measurement with C6D6 detection system (high elastic scattering background expected) • sample geometry will ideally be changed to 2 cm diameter • remeasurement of 62Ni necessary (main contaminant) • goal: few percent uncertainty Claudia Lederer

  24. 5x1018 protons 4x1018 - 63Ni 1x1018 - 62Ni, Au, C

  25. Approved by INTC 5x1018 protons 4x1018 - 63Ni 1x1018 - 62Ni, Au, C

  26. Additional slides Claudia Lederer

  27. Comparison Wf by Nicola vs. Wf by Frank: Au

  28. Comparison Wf by Nicola vs. Wf by Frank: Ni

  29. Comparison Wf by Nicola vs. Wf by Frank: Pb

  30. Claudia Lederer

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