Nuclear Astrophysics at the n_TOF facility at CERN M. Barbagallo, INFN Bari and CERN, on behalf of the n_TOF Collaboration 101o Congresso Nazionale della Societa’ Italiana di Fisica, Roma, 21-25 Settembre 2015

Outline Stellar Nucleosynthesis The facility The experimental program 151Sm(n,g) and 63Ni(n,g) Conclusions M. Barbagallo, Nuclear Astrophysics at the n_TOF facility at CERN, SIF 2015, Roma 21-25 Settembre 2015

The n_TOF Collaboration CERN Technische Universitat Wien Austria IRMM EC-Joint Research Center, Geel Belgium IN2P3-Orsay, CEA-Saclay France KIT – Karlsruhe, Goethe University, Frankfurt Germany Univ. of Athens, Ioannina, Demokritos Greece INFN Bari, Bologna, LNL, LNS, Trieste, ENEA – Bologna Italy Tokyo Institute of Technology, JAEA Japan ITN Lisbon Portugal Charles Univ. (Prague) Czech Republic Univ. of Lodz Poland IFIN – Bucarest Rumania INR – Dubna *, IPPE – Obninsk * Russian Fed. CIEMAT, Univ. of Valencia, Santiago de Compostela, University of Cataluna, Sevilla Spain University of Basel, PSI Switzerland Univ. of Manchester, Univ. of York UK ~ 30 Institutions >100 Researchers + Newcomers Hig haccuracy measurements of neutron induced reaction cross-sections (n,f), (n,cp), (n,g) M. Barbagallo, Nuclear Astrophysics at the n_TOF facility at CERN, SIF 2015, Roma 21-25 Settembre 2015

Stellar Nucleosynthesis s-process (Red Giants) r-process (Supernovae) Neutron beams Radioactive beam facilities s-process (slow process): Capture times long relative to decay time Involves mostly stable isotopes Nn = 108 n/cm3 , kT = 0.3 – 300 keV r-process (rapid process): Capture times short relative to decay times Produces unstable isotopes (neutron-rich) Nn = 1020-30 n/cm3 M. Barbagallo, Nuclear Astrophysics at the n_TOF facility at CERN, SIF 2015, Roma 21-25 Settembre 2015

capture rate: ln = Nn<s(n,g)·v>kT s-process s-process nucleosynthesis: neutron captures and successive b-decays capture rate: ln = Nn<s(n,g)·v>kT Along the b-stability valley The abundance of elements in the Universe depends on: thermodinamic conditions in stars (temperture and neutron density) neutron capture cross-sections 62Cu 9.74 m 63Cu 69.2% 64Cu 12.7 h 60Ni 26.2% 61Ni 1.14% 62Ni 3.63% 63Ni 100 y 64Ni 0.93% 58Co 70.86 d 59Co 100% 60Co 5.272 y 61Co 1.65 h s(n,g) is a key quantity s-process 56Fe 91.7% 57Fe 2.2% 58Fe 0.28% 59Fe 44.5 d 60Fe 1.5·106 y 61Fe 6 m Need of new and accurate neutron capture cross-sections: refine models of stellar nucleosynthesis in the Universe; obtain information on the stellar environment and evolution M. Barbagallo, Nuclear Astrophysics at the n_TOF facility at CERN, SIF 2015, Roma 21-25 Settembre 2015

Uncertainties in Nuclear Data Huge amount of data collected on many isotopes, mostly stable. Main features of s-process now well understood. However, cross-section uncertainties in some cases remain high, in particular if compared with progresses in: observations of abundances (i.e. in meteorite grains) models of stellar evolution Bao et al. ADNDT 76 (2000) For three classes of nuclei data are lacking or need substantial improvements: 1. Nuclei with low cross-section, in particular neutron magic nuclei (s-process bottleneck) N=50 86Kr, 87Rb, 88Sr, 90Zr N=82 138Ba, 139La, 140Ce 2. Isotopes unavailable in large amount, such as rare or expensive isotopes: 186,187Os, 180W, etc… 3. Radioactive branching isotopes (“stellar thermometers”): 79Se, 85Kr, 151Sm, 163Ho, 204Tl, 205Pb M. Barbagallo, Nuclear Astrophysics at the n_TOF facility at CERN, SIF 2015, Roma 21-25 Settembre 2015

The n_TOF facility Neutron Time Of Flight The advange of n_TOF are a direct consequence of the characteristics of the PS proton beam: high energy, high peak current, low duty cycle. Neutron Time Of Flight See “Commissioning of the n_TOF second experimental area at CERN”, today at 12.00, Aula Amaldi EAR2 20 m EAR1 20 GeV/c protons Spallation Target 185 m M. Barbagallo, Nuclear Astrophysics at the n_TOF facility at CERN, SIF 2015, Roma 21-25 Settembre 2015

The experimental program so far Phase 1 (2001-2004) Phase 2 (2009-2012) Phase 3 (2014-today) Capture 151Sm 232Th 204,206,207,208Pb, 209Bi 24,25,26Mg 90,91,92,94,96Zr, 93Zr 186,187,188Os 233,234U 237Np,240Pu,243Am Fission 233,234,235,236,238U 232Th, 209Bi, 237Np 241,243Am, 245Cm Capture 25Mg, 88Sr 58,60,62Ni,63Ni 54,56,57Fe 236,238U, 241Am Fission 240,242Pu 235U(n,/f) 232Th, 234U 237Np (FF ang.distr.) (n,) 33S,59Ni Capture 171Pm EAR2 Ge EAR1 242Pu EAR1 171Tm EAR1 203,204Tl EAR2 Fission 240Pu EAR2 237Np EAR1&2 Reactions (n,cp) 7Be(n,a) EAR2 33S(n,a) EAR2 M. Barbagallo, Nuclear Astrophysics at the n_TOF facility at CERN, SIF 2015, Roma 21-25 Settembre 2015

Measurements relevant for Astrophysics The combination of excellent resolution, unique brightness and low background has allowed to collect high-accuracy data, in some cases for the first time ever. Cross sections relevant for Nuclear Astrophysics branching point isotopes 151Sm, 63Ni, 147Pm, 171Tm, 203Tl abundancies in presolar grains 91,92, 93,94,96Zr magic nuclei and end-point 139La, 90Zr, 204,206,207,208Pb,209Bi seeds isotopes 54,56,57Fe, 58,60,62Ni isotopes of special interest 186,187,188Os (cosmocronometer), 24,25,26Mg (neutron poison), 7Be (CLiP) 7Be(n,a) and 7Be(n,p) cross section measurement for the Cosmological Lithium Problem at the n_TOF facility Today at 11.45, aula Amaldi M. Barbagallo, Nuclear Astrophysics at the n_TOF facility at CERN, SIF 2015, Roma 21-25 Settembre 2015

Capture setups at n_TOF Capture reactions are measured by detecting g-rays emitted in the de-excitation process. At n_TOF, two detection systems are used, for different purposes. Total Absorption Calorimeter (TAC) High-efficiency 4p detector (40 BaF2 scintillators) Mostly used for fissile isotopes (actinides) C6D6 (deuterated liquid scintillators) Low neutron sensitivity device Total energy method (+Pulse Height Weighting Technicque) Neutron beam Neutron beam C12H20O4(6Li)2 By combining the results, it is possible to reduce systematic uncertainties and to reach accuracy as low as few percent. M. Barbagallo, Nuclear Astrophysics at the n_TOF facility at CERN, SIF 2015, Roma 21-25 Settembre 2015

Branching point isotopes: the 151Sm case 151Sm (T1/2=90 y) causes a branching of the s-process nucleosynthesis 152Gd 154Gd 151Eu 152Eu 153Eu 154Eu s-Process 150Sm 151Sm 152Sm 153Sm The branching ratio for 151Sm depends on: Termodynamical condition of the stellar site (temperature, neutron density, etc…) Cross-section of 151Sm(n,g) 151Sm used as stellar thermometer !! M. Barbagallo, Nuclear Astrophysics at the n_TOF facility at CERN, SIF 2015, Roma 21-25 Settembre 2015

Branching point isotopes: the 151Sm case First measurement ever of the Maxwellian-Averaged Cross Section (MACS) of 151Sm (5% accuracy). Results quite different from model predictions Background 1000 1500 2000 2500 3000 3500 1970 1975 1980 1985 1990 1995 2005 Year MACS [mb] n_TOF Models n_TOF results provide confirmation of the model of Thermal Pulsing AGB stars M. Barbagallo, Nuclear Astrophysics at the n_TOF facility at CERN, SIF 2015, Roma 21-25 Settembre 2015

Branching point isotopes: the 63Ni case 63Ni (t1/2=100 y) represents the first branching point in the s- process, and determines the abundance of 63,65Cu 62Ni sample (1g) irradiated in thermal reactor (1984 and 1992), leading to enrichment in 63Ni of ~13 % (131 mg) In 2011 ~15.4 mg 63Cu in the sample (from 63Ni decay). After chemical separation at PSI, 63Cu contamination <0.01 mg First high-resolution measurement of 63Ni(n,g) in the astrophysical energy range. M. Barbagallo, Nuclear Astrophysics at the n_TOF facility at CERN, SIF 2015, Roma 21-25 Settembre 2015

Conclusions There is need of accurate new data on neutron cross-section both for nuclear astrophysics (and advanced nuclear technology, nuclear medicine, fundamental physics) Since 2001, n_TOF@CERN has provided an important contribution to the field, with an intense activity on capture and n-charged particle measurements. Several results of interest for stellar nucleosynthesis (Sm, Os, Zr, Ni, Fe, etc…). To date, high resolution measurements performed in EAR1 in optimal conditions (borated water moderator, Class-A experimental area, etc…). A second new (and more intense flux) experimental area is now available. EAR2 opens new perspectives for frontier measurements on short-lived radionuclides. A rich experimental program related to nuclear astrophysics is foreseen both in EAR1 and EAR2. M. Barbagallo, Nuclear Astrophysics at the n_TOF facility at CERN, SIF 2015, Roma 21-25 Settembre 2015