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Neutron capture cross section measurements for nuclear astrophysics at n_TOF

Neutron capture cross section measurements for nuclear astrophysics at n_TOF. Outline The CERN n_TOF Facility Motivation Basic parameters Experimental Setup Experimental campaigns in 2002-2004 Neutron capture measurements for astrophysics Perspectives. Michael Heil

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Neutron capture cross section measurements for nuclear astrophysics at n_TOF

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  1. Neutron capture cross section measurements for nuclear astrophysics at n_TOF • Outline • The CERN n_TOF Facility Motivation Basic parameters Experimental Setup • Experimental campaigns in 2002-2004 Neutron capture measurements for astrophysics • Perspectives Michael Heil on behalf of the n_TOF collaboration Michael Heil NIC IX, June 2006, Geneva

  2. The n_TOF collaboration 41 Research Groups 120 researchers Michael Heil NIC IX, June 2006, Geneva

  3. Neutron physics at n_TOF • Nuclear Data for ADS • n_TOFidea (C. Rubbia et al., 1998): • Measurements of neutron cross sections relevant for • Nuclear Waste Transmutation and related Nuclear Technologies • Nuclear Astrophysics • Neutron capture cross section measurements • relevant for Nuclear Astrophysics • Basic nuclear Physics with neutrons n_TOF-ND-ADS: EC FP5 project running from November 2000 to December 2004 coordinated by CERN spokespersons: Noulis Pavlopoulos, Alberto Mengoni Michael Heil NIC IX, June 2006, Geneva

  4. The n_TOF facility at CERN

  5. Basic parameters of n_TOF Michael Heil NIC IX, June 2006, Geneva

  6. Characteristics of the neutron beam

  7. Sample changer C6D6 C6D6 sample Neutron beam Experimental setup and detectors Silicon detectors viewing a thin 6LiF foil Since 2004 BaF2 detector is operational Pulse height weighting technique: Correction of the -response by weighting function to make the detector efficiency proportional to -ray energy -ray detection via C6D6 scintillators Neutron flux monitor 4p BaF2 detector array • 40 BaF2 crystals • High detection efficiency ≈100% • Good energy resolution • so far, only used for (n,g) • measurements of actinides Sample changer and beam pipe made out of carbon fibre Michael Heil NIC IX, June 2006, Geneva

  8. Astrophysics at n_TOF Michael Heil NIC IX, June 2006, Geneva

  9. Neutron capture measurements Mg Zr La Sm Os Pb Bi see poster 22.03 by Giuseppe Tagliente see poster 20.38 by Stefano Marrone see talk by Marita Mosconi today at 9 am see talk by C. Domingo Pardo today at 10:15 am Michael Heil NIC IX, June 2006, Geneva

  10. 90,91,92,93,94,96Zr(n,g) measurements • 90Zr is neutron magic (N=50) • small x-section (resonance dominated) bottleneck in the s-process flow • Zr abundances are sensitive to neutron flux in AGB models • s-process branching at 95Zr Mg Zr La Sm Os Pb Bi Michael Heil NIC IX, June 2006, Geneva

  11. 90,91,92,93,94,96Zr(n,g) measurements • Samples • Isotopically enriched samples • diameter 2.2 cm • mass: 1.3 – 3.4 g • Al can Mg Zr La Sm Os Pb Bi Michael Heil NIC IX, June 2006, Geneva

  12. 90,91,92,93,94,96Zr(n,g) measurements Mg Zr La Sm Os Pb Bi L Marques, et al. - The n_TOF Collaboration The extracted resonance parameters were compared with a previous measurement (Boldeman et al., 1976) Michael Heil NIC IX, June 2006, Geneva

  13. 90,91,92,93,94,96Zr(n,g) measurements Mg Zr La Sm Os Pb Bi C Moreau, et al. - The n_TOF Collaboration ND2004 Conference, Santa Fe, NM – Sept. 2004 96Zr ≈20% lower than previous data Michael Heil NIC IX, June 2006, Geneva

  14. 90,91,92,93,94,96Zr(n,g) measurements Mg Zr La Sm Os Pb Bi Analysis 93Zr in progress! Michael Heil NIC IX, June 2006, Geneva

  15. 139La(n,g) measurement • Neutron magic N=82 • small x-section (resonance dominated) bottleneck in the s-process flow • 139La is mono-isotopic and easier to detect in stellar spectroscopy than Ba • On the basis of accurate neutron capture cross sections 139La can be used as s-process indicator (complement to Eu as r-process indicator) Mg Zr La Sm Os Pb Bi 139La Michael Heil NIC IX, June 2006, Geneva

  16. 139La(n,g) measurement R. Terlizzi et al. (INFN) Mg Zr La Sm Os Pb Bi Remarkable energy resolution and background conditions have allowed to determine the resonance parameters up to 9 keV In the past, the best experimental data did not exceed 2.7 keV. Up to 2.7 KeV: <capture strength> n_TOF < 10% of Nakajima + Musgrove < 20% of databases MACS-30 in agreement with the FZK activation measurement(s) Michael Heil NIC IX, June 2006, Geneva

  17. 152Gd 153Gd 154Gd 155Gd 156Gd 157Gd Gd Eu 151Eu 152Eu 153Eu 154Eu 155Eu 156Eu 150Sm 151Sm 93 a 152Sm 153Sm 154Sm Sm 151Sm(n,g) measurement • Sample: • 206 mg 151Sm2O3 (Oak Ridge) • 90 % enrichment • t1/2 = 93a, activity: 156 GBq • encapsulated in Ti-can • Branchings can be used to determine • neutron density • temperature • mass density • convection time scales • in the interior of stars Mg Zr La Sm Os Pb Bi First s-process branch point which was directly measured via TOF Michael Heil NIC IX, June 2006, Geneva

  18. 151Sm(n,g) measurement Mg Zr La Sm Os Pb Bi Michael Heil NIC IX, June 2006, Geneva

  19. 151Sm(n,g) measurement Mg Zr La Sm Os Pb Bi U Abbondanno et al. Phys. Rev. Lett. 93 (2004), 161103 S. Marrone et al. Phys. Rev. C 73 (2006) 03604 n_TOF MACS-30 = 3100 ± 160 mb <D0> = 1.48 ± 0.04 eV, S0 = (3.87 ± 0.20)×10-4 Michael Heil NIC IX, June 2006, Geneva

  20. 24,25,26Mg(n,g) measurements Mg Zr La Sm Os Pb Bi • Motivation: • Neutron poison for s process • Strength of 22Ne(a,n)25Mg neutron source • Magnesium anomalies in presolar grains • 26Mg excess from in situ decay of radioactive 26Al Michael Heil NIC IX, June 2006, Geneva

  21. 24,25,26Mg(n,g) measurements Mg Zr La Sm Os Pb Bi Fitting of resonance parameter in progress! first known Mg resonance at 24 keV Impurities In, Sb Michael Heil NIC IX, June 2006, Geneva

  22. Outlook - Plan for measurements in Phase-2 n_TOF will continue: Letter of Intent signed by 24 research labs of the n_TOF Collaboration + 4 newcomers (January 2005) Michael Heil NIC IX, June 2006, Geneva

  23. Second n_TOF beam line & EAR-2 NewExperimentalArea (EAR-2) ~ 20 m n_TOF target EAR-1 (at 185 m) • Flight-path length : ~20 m at 90° with respect to p-beam • expected neutron flux enhancement: ~ 100 • drastic reduction of the t0 flash • duty factor improved by factor of 10 Michael Heil NIC IX, June 2006, Geneva

  24. Use of D2O moderator Photon time distribution (E>1MeV) Michael Heil NIC IX, June 2006, Geneva

  25. problems of sample production and safety issues relaxed EAR-2: Optimized sensitivity Improvements (ex: 151Sm case) • sample mass / 3 s/bkgd=1 • use BaF2 TAC e x 10 • use D2O F30 x 5 • use 20 m flight path F30 x 100 consequences for sample mass 50 mg 5 mg 1 mg 10 mg boosts sensitivity by a factor of 5000 ! (a factor of 100 ONLY from higher flux) Michael Heil NIC IX, June 2006, Geneva

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