The n_TOF project and its results Paolo Maria MILAZZO (on behalf of the n_TOF collaboration)

1. The n_TOF project and its results Paolo Maria MILAZZO (on behalf of the n_TOFcollaboration)

2. The n_TOF collaboration CERN TechnischeUniversitat Wien Austria IRMM EC-Joint Research Center, GeelBelgium IN2P3 – IPN – Orsay, IN2P3 - IReS - Strasbourg, CEA – SaclayFrance FZK – KarlsruheGermany AstroParticle Consortium (Athens, Thessaloniki, Thrace …) Greece INFN and DipartimentoFisica –Bari, Bologna, LNL, Trieste ENEA – Bologna, Universitàdi Pavia Italy LIP - Universitade de Coimbra, ITN Lisbona Portugal INR – Dubna, IPPE – ObninskRussia CIEMAT - Madrid, IFIC – Valencia, University of Santiago de Compostela, University of CatalunaSpain Universityof Basel Switzerland UniversityofNotre Dame, LNL, ORNL USA

3. Objectives Cross sections relevant for Nuclear Astrophysics (but also) Measurements of neutron cross sections for Nuclear Waste Transmutation and related Nuclear Technology purposes (and) Neutrons as probes for fundamental Nuclear Physics

4. To study Nuclear Astrophysics (@ n_TOF) means to investigate: Stellar nucleosynthesis Stellar thermal conditions Cosmochronology

5. a-nuclei12C,16O,20Ne,24Mg, …. 40Ca GapB,Be,Li Elements heavier than Fe are the result of neutron capture processes NEUTRONS r-process peaks (nuclear shell closures) s-process peaks (nuclear shell closures) Th, U Fe peak Au Pb

6. n_TOF is a CERN fecility

7. The n_TOF facility @ CERN n_TOF is a spallation neutron source based on 20 GeV/cprotons from the CERN PS hitting aPb block (~360 neutrons per proton). Experimental area at 200 m.

8. The n_TOF facility @ CERN A 7x1012protons/bunch beam @ 20 GeV/c from the PS accelerator, with a short pulse width of 6 ns and a low duty cycle of 0.4 Hz produces for spallation on a lead block a neutron beam, running on a base of flight of ≈200 m

10. N_TOF Vs Other facilities Average flux Instantaneous flux • n_TOFallows: • The measurementofradioactiveisotopes • The extensionof the resolvedresonanceregiontohigherenergies

11. neutron magic nuclei A<120 unstable branching isotopes A lot of work to do!

12. Setupforcapture Setupforfission Flux monitor The Experimental Area

13. Detector The neutron capture reactions g fn Capturereactions are measuredbydetectingγ-raysemitted in the de-excitationprocess. At n_TOF, builttwodifferent detection systems.

14. Capture experimental set-up (1): Liquid scintillators C6D6 detector neutrons C6D6 (deuteratedliquidscintillators) Specificallydesigned low neutronsensitivitydevice Samples

15. sample Capture experimental set-up (2): Total Absorption Calorimeter • 42 BaF2crystals, 15 cm in length • High efficiencytoγ-raysfromcaptureevents • Gooddiscriminationfrom the background • Discriminationbetweenγ-rayscascadesfromcapture and => idealforcapturemeasurements on fissile samples and/or samplesavailable in smallquantities 10B loaded Carbon Fibre Capsules Neutron Beam C12H20O4(6Li)2 Neutron Absorber

16. The s-process branching at A=151 (n,γ) x-sections of 151Sm 152Gd 154Gd • 151Sm usedasstellar thermometer 152Eu 151Eu 153Eu 154Eu s-Process 153Sm 151Sm 152Sm 150Sm laboratory half-life of 93 yr reduced to t1/2 = 3 yr at s-process site a probe for the temperature at s-process site

17. The s-process branching at A=151 (n,γ) x-sections of 151Sm Measured for the first time at a time-of-flight facility Resonance analysis with SAMMY code (≈ 500 resonances, mostly new) Maxwellian averaged cross-section experimentally determined for the first time s-process in AGB stars produces 77% of 152Gd, 23% from p process Maxwellian averaged (n,γ) cross section of the 151Sm and previous calculation (symbol) NO PREVIOUS MEASUREMENTS!

18. Bottlenecks in the s-process at N=50,82 (n,γ) x-sections of 90Zr, 139La Zr La

19. The border between main and weak component (n,γ) x-sections of 90Zr, 91Zr, 92Zr, 93Zr, 94Zr, 96Zr • The branching point at 95Zrdepends on • Thermodinamicstellar conditions • Zr(n,γ) cross sections T½ = 35 d 95 97 Mo T½ = 72 m Probing the neutron exposure and neutron flux in Red Giant Stars 93 95 97 Nb 90 91 92 93 94 95 96 97 Zr Sprocess T½ = 16 h T½ = 1.5 Myr T½ = 64 d Rprocess

20. The border between main and weak component (n,γ) x-sections of 90Zr, 91Zr, 92Zr, 93Zr, 94Zr, 96Zr Sntof 14%lowerthan previous data Weaker kernels reflects in lower MACS 90Zr

21. Cosmocronology (n,γ) x-sections of 186Os, 187Os, 188Os Tnucleosynthesis BANG! 4.5 Gyr Now Galaxies Solar system • nuclear clocks • 235U / 238U • 232Th /238U • 187Re / 187Os

22. The Re/Os cosmochronometer (n,γ) x-sections of 186Os, 187Os, 188Os s-only σNs(186Os) = σNs(187Os) Os 184 0.02 Os 185 94 d Os 186 1.58 Os 187 1.6 Os 188 13.3 Os 189 16.1 Os 190 26.4 Os 191 15.4 d Os 192 41.0 Re 183 71 d Re 184 38 d Re 185 37.4 Re 186 90.64 h Re 187 62.6 Re 188 16.98 h Re 189 24.3 h Re 190 3.1 m 42.3x109 a W 182 26.3 W 183 14.3 W 184 30.67 W 185 75.1 d W 186 28.6 W 187 23.8 h W 188 69 d s-process r-only r-process the β-decayhalf-lifeof187Re (42.3 Gyr) contributes to the abundance of the daughter 187Os

23. The Re/Os cosmochronometer (n,γ) x-sections of 186Os, 187Os

24. The Re/Os cosmochronometer (n,γ) x-sections of 186Os, 187Os The useofRe/Osabundancepairas a clock addressfewcomplications: The β-decayhalf-lifeof187Re isstronglydependent on temperature The stellar (n, γ) cross sectionof187Os isinfluencedbylow-lyingexcitedlevels (strong populationof 1st state at 9.8 keV, competitionbyinelasticchannels) Branching(s) at 185W and/or at 186Re Destructionof187Re in laterstars (Astration) The chemicalevolutionof the galaxywasnotuniform Re and Osabundanceuncertainties Ages • Cosmological way13.7 ± 0.2 Gyr • based on the Hubble time definition (“expansion age”) • Astronomical way14. ± 2. Gyrbased on observations of globular clusters • Nuclear way15.3 ± 2.(*)Gyrbased on abundances & decay properties of long-lived radioactive species (*) 0.4 Gyr uncertainty due to x-sections http://physics.aps.org/synopsis-for/10.1103/PhysRevC.82.015802

25. The end of the s-process (n,γ) x-sections of 204Pb, 206Pb, 207Pb, 208Pb, 209Bi -recycling Normalization of s-process abundances Discrimination between stellar models (accuracies of 3-5% are needed)

26. The end of the s-process (n,γ) x-sections of 204Pb, 206Pb, 207Pb, 208Pb, 209Bi 207Pb 206Pb Reduction of neutron background sel>>sg 209Bi 209Bi

27. neutron poison in the s process, constraints for the 22Ne(a,n)25Mg reaction (n,γ) x-sections of 24Mg, 25Mg, 26Mg Main component 22Ne(,n)25Mg is a neutron source in AGB stars: 1Msun < M < 3Msun kT=8 keV and kT=25 keV Weak component 22Ne(,n)25Mg is the mainneutron source in massive stars: M > 10 – 12Msun kT=25 keV and kT=90 keV

28. neutron poison in the s process, constraints for the 22Ne(a,n)25Mg reaction (n,γ) x-sections of 24Mg, 25Mg, 26Mg Resonance shape analysis: Capture &Transmission ORELA Result: reduced poisoning effect Lower MACS of 25Mg higher neutron density

29. Seeds of the s-process (n,γ) x-sections of 54Fe, 56Fe, 57Fe, 58Fe, 58Ni, 60Ni, 61Ni, 62Ni, 63Ni 63Cu 69.17 64Cu 12.7 h 60Ni 26.223 61Ni 1.140 62Ni 3.634 63Ni 100 a 64Ni 0.926 59Co 100 60Co 5.272 a 61Co 1.65 h 56Fe 91.72 57Fe 2.2 58Fe 0.28 59Fe 44.503 d 60Fe 1.5 106 a 61Fe 6 m s-process

30. Seeds of the s-process - (n,γ) x-sections of 62Ni Preliminary results

31. First branching point along the s-processpath (n,γ) x-sections of 63Ni

32. First branching point along the s-processpath (n,γ) x-sections of 63Ni • Sample prepared at Paul Scherrer Institute • NiO powder • Total mass: 1156 mg • Diameter: 20 mm • Enrichment in 63Ni: ~ 11 % (= 108.4 mg) • 63Ni / 62Ni content ~ 12 % • encapsulated in a cylinder made of PEEK (Polyetheretherketone) • Activity: 470 GBq

33. First branching point along the s-processpath (n,γ) x-sections of 63Ni 63Ni: First (n,γ) measurement in the resonance region Yield = nat∙s(n,g) 63Ni-sample 62Ni-sample Preliminary results

34. First branching point along the s-processpath (n,γ) x-sections of 63Ni Maxwellian Averaged Cross Sections [combination of RRR (<10 keV, n_TOF) and URR (> 10 keV, JENDL)] Submitted to PRL

35. Now opening ! (n,α) x-sections of 33S, 59Ni First (n,α) measurement at n_TOF ! with a Chemical Vapor Deposition (CVD) diamond or MicroMegas detectors CVD diamond detector a n Isotope of interest 59Ni, 10B, 33S, 149Sm, etc.

36. Now opening ! (n,α) x-sections of 33S, 59Ni Last week a measurement of the 59Ni(n, α) reaction has been completed with a mosaic-detector. Sample:516 kBq (174 mg 59Ni), 1.5 cm diameter 59Ni sample Neutrons

37. Future EAR-2 flight-path ≈19 m at 90⁰ with respect to the proton beam Newexperimentalarea at 19 m (EAR-2) n_TOF target Experimental area at 185 m

38. Future EAR-2 The main advantages of EAR-2 will be: • Neutrons fluxes on average increased by a factor 25 • (with respect to EAR-1) • Very small mass samples (< 1 mg) • Very small cross-sections • Much shorter time scales measurement

39. Future EAR-2 • very small samples importantcandidates: 79Se, 90Sr, 93Zr, 107Pd, 135Cs, 147Pm, 163Ho,171Tm, 182Hf, 204Tl • very small cross sections important candidates 86Kr, 88Sr, 138Ba, 140Ce, 208Pb; isotopes of C, O, Ne, Mg • short measuring times important candidates 64Zn, 70Ge, 76Ge, 80,82Kr, 86,87Sr, 95,96Mo, 104Pd, 164,166Er, 198Hg

40. EAR-2, when? n_TOF EAR1 will restart after LS1

41. EAR-2, experiments “in preparation” Measurement of the 25Mg(n,α)22Ne cross section Neutron capture measurement of the s-process branching point 79Se Destruction of the cosmic γ-ray emitter 26Al by neutron induced reactions Measurement of 7Be(n,p)7Li and 7Be(n,α)4He cross sections, for the cosmological Li problem ...

42. Summary Neutron cross sections are key quantities for studying stellar evolution and nucleosynthesis. n_TOFoffers the best conditions to obtain these nuclear physics quantities with the required accuracy. The n_TOF Collaboration is carrying on an extensive plan to measure cross sections relevant for nuclear astrophysics, in particular for s-process nucleosynthesisstudies. Opportunities for obtaining new data for presently inaccessible nuclei (using extremely low quantities of material) will be soon open.

43. Publications