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Astrophysics with spallation sources

Explore the current status and future options of spallation facilities for studying the s-process in astrophysics. Learn about the challenges and remaining questions in s-process nucleosynthesis, and discover the model tests and reactions involved in this field.

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Astrophysics with spallation sources

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  1. Astrophysics with spallation sources Franz Käppeler Karlsruhe Institute of Technology • (n,g) cross sections for the s process • operating spallation facilities: LANSCE, J-PARC, n_TOF & examples for time-of-flight studies • comparison of spallation facilities and future options

  2. status of s-process(n,g)cross sections and remaining quests • current quests in s-process nucleosynthesis • model tests:16 s-only isotopes ± 1% • nn,T, r via branchings • ~20 unstable isotopes ± 5% • presolar grains:anomalies in ~20 elements • with 75 isotopes ± 1% • bottle neck15 n-magic nuclei ± 5% • reactions: • neutron poisons:abundant light elements • neutron sources:(a,n) reactions on 13C • and 22Ne • thermally excitedel. and inel. scattering • states: • yields at A < 60:(n,a) and (n,p) cross • sections even-even nuclei

  3. status and requests needed: cross sections with uncertainties between 1 and 5% for complete set of isotopes from 12C to 210Po, including unstable samples

  4. Maxwellian averaged cross sections s(En) measured by time of flight and folded with stellar neutron spectrum ‹sv› 2 ∫ s(En) En exp(-En/kT) dEn ‹s› == vT √π ∫ En exp(−En/kT) dEn • MACS directly measured via activation

  5. s-process energies s(En) via TOF for 1 < En < 300 keV • low mass stars: kT = 8 keV and 25 keV massive stars: kT = 25 and 90 keV

  6. high energy with moderator (spallation sources, e-linacs) pulsed neutron sources En = ½ m v2resolution DEn/En = 2Dt/t + 2Ds/s g low energy (VdG, FRANZ) g

  7. LANSCE @ Los Alamos 800 MeV proton linac plus PSR 17 n/p Luhan Neutron Scattering Center: pulsed, moderated spallation source for time-of-flight studies thermal < En < 300 keV, Dt = 250 ns WNR: unmoderated tungsten spallation target using the 800 MeV pulsed proton beam from the LANSCE linac 0.5 < En < 750 MeV, Dt ~150 ps

  8. DANCE @ Luhan (FP 14) „designed for neutron capture reactions on small quantities, of order 1 mg, of radioactive or rare stable nuclei“ • pulse width: 250 ns • rep rate: 20 Hz • moderator: water • neutron energy: th – 300 keV • flight path: 20 m • neutron beam diameter: 10 mm • equipment: BaF2 calorimeter, • 160 modules http://lansce.lanl.gov/about.shtml Nucl. Sci. Eng. 106 (1990) 208

  9. DANCE array: 160 BaF2 modules (n,g) reactions →small samples, small cross sections the 62Ni problem: integrated neutron flux in massive stars too small, reaction flow NOT in equilibrium → strong impact of single cross sections

  10. 62Ni(n,g)63Ni 35 abundance ratio 22.6 12.5 mass number • TOF 25.8 ± 3.7 (2008) 37.0 ± 3.2 (2005) 12.5 ± 4.0 (1983) 26.8 ± 5.0 (1975) (courtesy I. Dillmann) • activation 20.2 ± 2.1 (2009) 23.4 ± 4.6 (2008) 26.1 ± 2.6 (2005) the 62Ni problem

  11. smallest sample ever used in TOF 237Np, 400 mg

  12. J-PARC in Japan Japan Proton Accelerator Research Complex Japan Spallation Neutron Source

  13. J-PARC beam parameters LINAC 3 GeV synchrotron 50 n/p 50 GeV synchrotron

  14. ANNRI @ J-PARC Accurate Neutron-Nucleus Reaction measurement Instrument

  15. ANNRI – inside/outside

  16. ANNRI specifications • proton beam power: 17.5 kW → 120 kW (→ 1 MW) • pulse width: double pulse (100 ns separated by 600 ns) • rep rate: 25 Hz • moderator: coupled hydrogen moderator • neutron energy: 0.0015 eV < En < 50 keV • intensity at 1 MW at 21.5 m: 4.3×107 n/cm2/s (1.5 < En < 25 meV) 9.3×105 n/cm2/s (0.9 < En < 1.1 eV) 6.0×106 n/cm2/s (0.9 < En < 1.1 keV) • beam diameter: 3, 7, 22 mm • equipment: Ge spectrometer at 21.5 m NaI spectrometer at 27.9 m http://j-parc.jp/MatLife/en/instrumentation/ns_spec.html JKPS 59 1781, 2011

  17. ANNRI: intensity and beam profile

  18. 107Pd(n,g) with Ge spectrometer sample mass 137 mg

  19. n_TOF - the CERN spallation neutron source • 20 GeV protons on lead block • 300 neutrons per proton • most luminous n-source worldwide • high resolution TOF facility

  20. J-PARC in Japan Neutron detection Neutron creation 1.4 GeV 50 MeV

  21. 1st collimator (Ø=11 cm) halo cleaning and first shaping  + filter station 2nd collimator (Ø=1.8/8 cm) beam shaping • Experimental Area • 185 m from the spallation target • location of samples and detectors neutrons from spallation target

  22. n_TOF coordinates • proton beam power: 20 GeV, 9 kW • pulse width: 6 ns • rep rate: 0.4 Hz • moderator: (borated) water • neutron energy: th < En < 1 GeV • intensity at 185 m: 0.2 – 2·105 n/s/decade • energy resolution: 0.4% @ 1 MeV • neutron beam diameter: 30 (70) mm • equipment: TAC, C6D6 for (n,g) FIC, PPAC for (n,f) pCVD, Mgas for (n,cp) https://twiki.cern.ch/twiki/bin/view/NTOF/ CERN / INTC-O-011

  23. -ray detection: C6D6 scintillators Sample changer C6D6 C6D6 Neutron beam high resolution in neutron energy • 186Os (2 g, 79 %) • 187Os (2 g, 70 %) • 188Os (2 g, 95 %) • Al can environmental background • 197Au (1.2g) flux normalization (using Ratynski and Macklin high accuracy cross section data) • natPb (2 g) in-beam gamma background • natC (0.5 g) neutron scattering background

  24. n_TOF n_TOF n_TOF results for 62Ni previous TOF measurements (courtesy Iris Dillmann) n_TOF campaign to determine (n, g) cross sections of all stable Fe and Ni isotopes and of 63Ni

  25. x13 x1.2 2009: new target with separate moderator in-beam g rays from 1H(n,g) substantially reduced (borated water in saturated conditions, 1.28% H3BO3) gravitational cut-off at 0.02 eV

  26. borated water moderator

  27. 63Ni(n,g) – first results from n_TOF (2011) courtesy by Claudia Lederer

  28. TAC with 40 BaF2 modules

  29. TAC data for 241Am(n,g) present URR limit about 320 keV Increase of the RRR limit above 150 eV

  30. astrophysics measurements at n_TOF campaign 2009-13 (n,g) 54,56,57Fe 58,60,62,63Ni 33S(n,a) 26Al(n,p) 59Ni(n,p) campaign 2002-4 (n,g) 151Sm 204,206,207,208Pb, 209Bi 24,25,26Mg 90,91,92,94,96Zr, 93Zr 186,187,188Os, 139La 19 isotopes (2 radioactive) 19 full publications

  31. n_TOF upgrade NewExperimentalArea (EAR-2) EAR-2 ~ 20 m 10 m n_TOF target EAR-1 (at 185 m) Flight-path length : ~20 m at 90° respect to p-beam direction expected neutron flux enhancement drastic reduction of the t0 flash

  32. Feb 2, 2012 Dear Colleagues, I'm very proud to announce that this morning the INTC committee "strongly recommended " to the Research Board our proposal for EAR-2. Sergio Bertolucci, Director for Research and Computing, was present during the discussion and gave a positive reaction. Kind regards Enrico EAR2 @20 m from pit, above ground To be built ISR Technical gallery (@10 m from pit) Existing hole n_TOF target pit proposed EAR-2 n-flux x25, n-rate x10, lower background

  33. Upgrades Neutron flux at sample FRANZ 1∙107 Lansce 5∙107 J-PARC 3·107 n_TOF 2·106 Facility n/p Lansce 17 J-PARC 45 n_TOF 300 comparison of pulsed neutron sources

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