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Nuclear Astrophysics at the n_TOF facility at CERN

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

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Nuclear Astrophysics at the n_TOF facility at CERN

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  1. 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

  2. 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

  3. The n_TOF Collaboration CERN TechnischeUniversitat 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 – BolognaItaly Tokyo Institute of Technology, JAEA Japan ITN LisbonPortugal Charles Univ. (Prague) Czech Republic Univ. of LodzPoland IFIN – BucarestRumania INR – Dubna*, IPPE – Obninsk* Russian Fed. CIEMAT, Univ. of Valencia, Santiago de Compostela, University of Cataluna, Sevilla Spain University of Basel, PSISwitzerland 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

  4. Stellar Nucleosynthesis s-process(Red Giants) Neutronbeams Radioactivebeamfacilities r-process(Supernovae) • s-process(slow process): • Capturetimes long relative todecaytime • Involvesmostlystableisotopes • Nn = 108 n/cm3 , kT = 0.3 – 300 keV • r-process(rapidprocess): • Capturetimesshort relative todecaytimes • Producesunstableisotopes(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

  5. s-process s-processnucleosynthesis: neutroncapturesand successive b-decays capture rate: ln = Nn<s(n,g)·v>kT Along the b-stability valley • The abundance of elements in the Universedepends on: • thermodinamicconditions in stars(temperture and neutron density) • neutroncapturecross-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 neutroncapturecross-sections: • refinemodelsof 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

  6. Uncertainties in Nuclear Data • Hugeamountof data collected on manyisotopes, mostlystable. Mainfeaturesofs-processnowwellunderstood. • However, cross-sectionuncertainties in some casesremainhigh, in particularifcomparedwithprogresses in: • observationsofabundances (i.e. in meteorite grains) • modelsof stellar evolution Bao et al. ADNDT 76 (2000) • Forthreeclassesof nuclei data are lacking or needsubstantialimprovements: • 1. Nuclei withlow cross-section, in particularneutronmagic nuclei (s-processbottleneck) • N=50 86Kr, 87Rb, 88Sr, 90Zr • N=82 138Ba, 139La, 140Ce • 2. Isotopesunavailable in largeamount, suchas rare or expensiveisotopes: • 186,187Os, 180W, etc… • 3. Radioactivebranchingisotopes (“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

  7. The n_TOF facility Neutron Time Of Flight The advangeofn_TOF are a directconsequenceof the characteristicsof the PS protonbeam: high energy, high peakcurrent, low duty cycle. 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

  8. 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 171Pm EAR2 Ge EAR1 242Pu EAR1 171Tm EAR1 203,204TlEAR2 Fission 240Pu EAR2 237Np EAR1&2 Reactions (n,cp) 7Be(n,a) EAR2 33S(n,a) EAR2 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 M. Barbagallo, Nuclear Astrophysics at the n_TOF facility at CERN, SIF 2015, Roma 21-25 Settembre 2015

  9. Measurements relevant for Astrophysics The combination of excellent resolution, unique brightnessand low backgroundhas 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

  10. 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

  11. Branching point isotopes: the 151Sm case 151Sm (T1/2=90 y) causes a branching of the s-processnucleosynthesis 152Gd 154Gd 151Eu 153Eu 152Eu 154Eu s-Process 153Sm 152Sm 150Sm 151Sm • The branching ratiofor151Smdepends on: • Termodynamicalconditionof the stellar site (temperature, neutron density, etc…) • Cross-sectionof151Sm(n,g) • 151Sm usedasstellar thermometer !! M. Barbagallo, Nuclear Astrophysics at the n_TOF facility at CERN, SIF 2015, Roma 21-25 Settembre 2015

  12. 3500 n_TOF Models 3000 2500 MACS [mb] 2000 1500 1000 1970 1975 1980 1985 1990 1995 2000 2005 Year Branching point isotopes: the 151Sm case First measurementever of the Maxwellian-Averaged Cross Section (MACS) of 151Sm (5% accuracy). Resultsquitedifferentfrommodelpredictions Background n_TOFresultsprovideconfirmation of the model of ThermalPulsing AGB stars M. Barbagallo, Nuclear Astrophysics at the n_TOF facility at CERN, SIF 2015, Roma 21-25 Settembre 2015

  13. 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

  14. Conclusions • There is need of accurate new dataon neutron cross-section both for nuclearastrophysics (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

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