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n _TOF ( n eutron Time-of-flight @ CERN)

n _TOF ( n eutron Time-of-flight @ CERN). Neutron cross-section measurements with high accuracy at high resolution in a wide energy range for Nuclear Astrophysics and for Nuclear Technology. Nuclear Data for Science, Technology and … Society (Hans Blix, ND 2008). Nicola Colonna

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n _TOF ( n eutron Time-of-flight @ CERN)

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  1. n_TOF (neutron Time-of-flight @ CERN) Neutron cross-section measurements with high accuracy at high resolution in a wide energy range for Nuclear Astrophysics and for Nuclear Technology Nuclear Data for Science, Technology and … Society (Hans Blix, ND 2008) • Nicola Colonna • IstitutoNazionaleFisicaNucleare, Sez. di Bari • nicola.colonna@ba.infn.it

  2. Outline • Motivations(15’) • The n_TOFfacility and experimentalsetups(10’) • Results(15’) • Status and perspectives(5’) Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  3. n_TOF in the Chart ofNuclides Nuclearenergy (fissionproducts & Structural material) NuclearAstrophysics (stellar nucleosynthesis) Astrophysics Advancednuclearreactors (actinides) Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  4. BB Neutron capture Fusion NeutronstudiesforNuclearAstrophysics Fe Abundance s s r r Massnumber

  5. The stellar nucleosynthesis Neutronbeams s-process(Red Giants) Radioactivebeamfacilities r-process(Supernovae) • s-process(slow process): • Capturetimes long relative todecaytime • Involvesmostlystableisotopes • Nn= 108n/cm3 , kT = 0.3 – 300 keV • r-process(rapidprocess): • Capturetimesshort relative todecaytimes • Producesunstableisotopes(neutron-rich) • Nn= 1020-30n/cm3 Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  6. The s-processnucleosynthesis Along the b-stabilityvalley • s-processnucleosynthesisproceedsthroughneutroncapturesand successive b-decay. • The abundanceofelements in the Universedepends on thermodinamicconditions(temperture and neutron density) and on the neutroncapturecross-sections. 62Cu 9.74 m 63Cu 69.17 64Cu 12.7 h 60Ni 26.223 61Ni 1.140 62Ni 3.634 63Ni 100 a 64Ni 0.926 capture rate: ln = Nn<s(n,g)·v>kT 58Co 70.86 d 59Co 100 60Co 5.272 a 61Co 1.65 h s(n,g) is a key quantity 56Fe 91.72 57Fe 2.2 58Fe 0.28 59Fe 44.503 d 60Fe 1.5 106 a 61Fe 6 m s-process • Neutroncross-sections are neededto: • refinemodelsof stellar nucleosynthesis in the Universe; • obtain information on the stellar environment and evolution Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  7. The neutroncapturecross-section Bao et al. ADNDT 76 (2000) • 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 • 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 Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  8. Neutronstudiesforenergyapplications

  9. The energyproblem Recently, renewed interest in nuclearenergy due to: • continouslyincreasingenergydemand; • growingconcernover production ofgreenhousegasesand relatedclimatechanges More than80 % of the energyconsumed in the world comesfromfossilfuels Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  10. CO2 and climate changes , Report of the IntergovernmentalPanel on ClimateChanges (IPCC), 2007 www.ipcc-wg1.unibe.ch/publications/wg1-ar4/wg1-ar4.html Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  11. The emission of CO2 Tosatisfy the world energydemand (in particularfromdevelopingcountries), minimizing the impact on the climate, itisnecessary a mix ofenergysourceswhichincludesnuclearenergy(Intergov. Panel on ClimaticChange, IPCC-ONU, Valencia, 17 Nov. 2007). Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  12. Main problems of current nuclear reactors Existingreactorshave low burn-upefficiencyand produce largeamountofradioactivewaste. 4%Fissionproducts 3% 235U 1%Pu and Minor Actinides Currentreactorsuseonlyfewpercentof U resources. Availabilityof U resourcesmaybecome a problem in the medium term (100 y). 96% potential fuel 97% 238U 94% 238U 1%235U Fuel (LWR) Spentfuel Closedcycle (recycling) wouldmake U resourcessufficientforthousandsofyears !! Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  13. The nuclear waste problem 244, 245Cm 1.5 Kg/yr Figura Nucleosintesi (frecce che si muovono) Foto FIC 241Am:11.6 Kg/yr 243Am: 4.8 Kg/yr 239Pu: 125 Kg/yr 237Np: 16 Kg/yr LLFP 76.2 Kg/yr LLFP Quantities refer to yearly production in 1 GWe LW reactor Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  14. The actinides problem • Main problem in the nuclear waste are the transuranic actinides: Pu and MA (Np, Am, Cm,...) • 1.5% in mass but give the biggest contribution to radiotoxicity and heat after 100 y • problem persists for more than 105 y • some isotopes are fissionable (proliferation and criticality concern). , At present, onlysolutionto the high radiotoxicitynuclearwasteisgeologicalrepositories Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  15. Geologicalrepositories Withcurrentreactors, itwouldbenecessarytofind a newgeologicalrepositorylike Yucca Mountain every20 years. Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  16. The Th/U fuel cycle Figura Nucleosintesi (frecce che si muovono) Foto FIC b-, t1/2=22 m b-, t1/2=27 d 232Th(n,g)233Th 233Pa 233U LLFP LLFP Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  17. New generation reactors The revolutionaryidea ofGeneration IVreactorsis the recyclingof thespentfuel (including minor actinides). Recycling Once through • Otheroptionsnowbeingconsidered: • AcceleratorDrivenSystems (nuclearwasteincineration) • Useof the Th/U fuelcycle (currentlybeingdevoloped in India forenergy production) Otheradvantagesof Generation IV (fast breeder) reactors: • improvedsafety, proliferation-resistence, lowercosts and constructiontime • hydrogenproduction (tosubstitute fossile fuels in transport) The developmentofGen IV (fast breader) reactorsrequires accurate neutrondata tominimize design uncertainty and optimizesafetyparameters. Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  18. Data needsfornuclearenergy • Nuclear fuel (U/Pu and Th/U cycles) Th, U, Pu, Np, Am, Cm(n,f), (n,) … • Long-lived Fission Products 99Tc, 103Rh, 135Xe, 135Cs, 149Sm (n,) • Structural and cooling material Fe, Cr, Ni, Zr, Pb, Na, ... all Data on a largenumberofisotopes are neededfor design ofadvancedsystems and forimprovingsafetyofcurrentreactors. NEA/WPEC-26 (ISBN 978-92-64-99053-1) • The overall list of requirements is rather long: • capture cross sections of235,238U, 237Np, 238-242Pu, 241,242m,243Am, 244Cm • fission cross sections of 234U, 237Np, 238,240-242Pu, 241,242m,243Am, 242-246Cm FP VII EURATOM Topic: Fission-2009-2.3.2: Improved nuclear data for advanced reactor systems. The combination of advanced simulation systems and more precise nuclear data will allow optimising the use of and need for experimental and demonstration facilities in the design and deployment of new reactors. A concerted effort including new nuclear data measurements, dedicated benchmarks (i.e. integral experiments) and improved evaluation and modelling is needed in order to achieve the required accuracies. The project shall aim to obtain high precision nuclear data for the major actinides present in advanced reactor fuels, to reduce uncertainties in new isotopes in closed cycles with waste minimisation and to better assess the uncertainties and correlations in their evaluation. Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  19. Target AccuraciesforGen IV Fast Reactors Necessary to reduce uncertaintied to ~3-7 %for most Pu isotopes and Minor Actinides, in the energy range from a few keV to several MeV. Source: Aliberti, Palmiotti, Salvatores, NEMEA-4 workshop, Prague 2007

  20. The n_TOF facility at CERN n_TOF is a spallation neutron source based on 20 GeV/cprotons from the CERN PSon aPb target (~360 neutrons per proton). Experimental area at 200 m. Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  21. Technical details p n • 80x80x80 cm3Pb target surrounded by 5 cm water for moderation (isolethargic flux) and cooling • 200 mt time-of-flight tunnel • several iron and concrete walls for shielding (from n, g, m, etc…) • sweeping magnet for charged particle deflection • 2 collimators Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  22. The n_TOF facility n_TOFis at presentoneof the mostimportantfacilitiesforneutrontime-of-flight in the world (other TOF facilities are GELINA and LANSCE). • Mainfeatureofn_TOFis the extremely high instantaneousneutronflux (105 n/cm2/pulse). • Uniquefacilityformeasurementsofradioactiveisotopes (maximizesignal-to-backgroundratio): • branch-pointisotopes (Astrophysics) • actinides (nucleartechnology) • Other features of the neutron beam: • high resolution in energy (DE/E = 10-4) …………….. study resonances • large energy range (25 meV<En<1GeV) ………………. measure fission up to 1 GeV • low repetition rate (< 0.8 Hz) ……………………………… no wrap-around Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  23. The detectorsforcapturereactions Capturereactions are studiedbydetectingg-raysemitted in the de-excitationof the compoundnucleus. • Twotypesofbackground (source ofsystematicerrors): • g-raysfromneutronscatteredby the sample and captured in the setup (“neutronsensitivity”) • g-raysfromenvironmental background, radioactivityof the sample, or competingreactions • Neutronsensitivitybig problemforisotopeswith low capturecross-sections (Astrophysics) (n,n) (n,g) • Background fromnaturalradioactivitybig problemforactinides (applications) A uniquesolutionforallproblemsdoesnotexist. At n_TOF, twodifferentdetectorsbuilttominimize the twotypesof background. Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari 24

  24. Detectorswith low neutronsensitivity Apparatusused at ORELA in the pastforcapturemeasurements. High neutronsensitivity, difficultto estimate and correct. At n_TOF, neutronsensitivityenormouslyreduced, relative to the past. Problemofthissetup: low efficiency and selectivity Verysmallamountof material, and extensiveuseofcarbonfiber. Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari 25

  25. The calorimetricmethod In measurementsofcapture on actinides, the mainproblemis the g-raybackgroundassociatedto the naturalradioactivityof the sample, aswellastofissionreactions. Calorimetro(BaF2) The calorimetricmethodallowsto discriminate the background on the basisoftotal energyofdetectedg-rays. bersaglio neutroni The Total AbsorptionCalorimeter (TAC) fundamentalforneutroncapturemeasurementsofactinides Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  26. The n_TOFcalorimeter • The n_TOF TAC: • 4parrayof40 BaF2scintillators (15 cm thick) • High efficiencyallowstoreconstruct the entiredeexcitationcascade. Neutroni Problemwith TAC: badneutronsensitivity (detectors and heavysupportstructure) At n_TOF, minimizedneutronsensitivitywithinnersphereofabsorbing material, and capsules in carbon fibre with10B. C12H20O4(6Li)2 Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari 27

  27. The fission detectors The mainproblem in fissionmeasurementsis the background due toa-decay. At n_TOF, minimizedby the very high instantanousneutronflux. • La “Fission Ionization Chamber” • Standard detector, with fast gas and electronics neutroni neutroni • ParallelPlateAvalancheCounters (PPAC): • Fissionfragmentsdetectedin coincidence • Verygoodrejectionofa-background Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  28. The Data Acquisition System High instantaneous neutron flux several events for each neutron pulse + pile-up between signals Standard DAQ methods are largely inadequate • n_TOF DAQ entirely based on Flash ADC • Up to 1 GSample/s (500 MHz bandwidth), 16 MB buffer memory • Software Zero suppression • Commercially available in compact_PCI standard (Acqiris) • Offline signal reconstruction for time and charge information • Simple algorithm for a single signal • Fitting procedure for pile-up events Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  29. The Fissionsetup Neutron beam M. Calviani et al., Nucl. Instr. Meth. A 594, 220 (2008) Fission chamber (single fragment) : 235U, 238U ……..……… reference (standad) 236U ……………… U/Pu fuel cycle 232Th …………… Th/U fuel cycle 233U, 234U ………… Th/U fuel cycle 237Np…..……… Gen IV and ADS 241,243Am …..………… Gen IV and ADS 245Cm ……………… Gen IV and ADS PPAC (coincidence method): 235U, 238U ………..… reference (standad) 232Th …………Th/U fuel cycle 233U, 234U ……………Th/U fuel cycle 237Np …………..… Gen IV and ADS 209Bi, natPb…………….. ADS Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari 30

  30. The n_TOF activity Cattura 151Sm 204,206,207,208Pb, 209Bi 24,25,26Mg 90,91,92,94,96Zr, 93Zr 186,187,188Os, 139La 232Th, 233,234U 237Np,240Pu,243Am Fissione 233,234,235,236U 232Th, 209Bi 237Np 241,243Am, 245Cm n_TOF phase 1 (2002-2004) • Misurementsof capture reactions: • 25 Isotopes (8 of which radioactive) • Often of double interest (Astrophysics and applications) • Several publication • Measurements of fission cross-sections: • 11 isotopes (10 radioactive) • MainlylinkedtoTh/U cycle e transmutation • strong interestbyInternational NuclearAgencies • results are stillbeingpublished EC Contracts FP5: n-TOF-ND-ADS FP6: EUROTRANS FP7: ANDES 40 articles, 100 ConferenceProceedings, 26 PhDthesis Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  31. Then_TOFCollaboration (80 Researchers from 30 European Institutes) CERN TechnischeUniversitat Wien Austria IRMM EC-Joint Research Center, Geel Belgium IN2P3-Orsay, IN2P3-Strasbourg, CEA-Saclay France FZK – KarlsruheGermany Univ. of Athens, Ioannina, Demokritos Greece INFN Bari, Bologna, LNL, Trieste ENEA – Bologna Italy Univ. of Tokio Japan ITN LisbonPortugal Charles Univ. (Prague), Univ. ofLodzPoland IFINRumania INR – Dubna, IPPE – ObninskRussian Fed. CIEMAT, Univ. of Valencia, Santiago de Compostela, University of Cataluna, Sevilla Spain Universityof BaselSwitzerland Univ. of Manchester, Univ. of York UK Notre Dame, Los Alamos, OakRidgeUSA

  32. The capturecross-sectionof151Sm 151Sm is a branching point isotope (T1/2=90 y) 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 !! Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  33. 3500 n_TOF Models 3000 2500 MACS [mb] 2000 1500 1000 1970 1975 1980 1985 1990 1995 2000 2005 Year The n_TOFresults on 151Sm n_TOFresultsconfirmedmodelofThermalPulsing AGB stars Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  34. The capturecross-sectionofPb/Bi Importantimplications on the originofSolar System Past n_TOF Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  35. The Zr saga New valuesfor the neutron density in Heburningshellsof Red Giants Past n_TOF Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari 36

  36. The Ostrilogy Ageof the Universefromnuclearcosmocronometer: 14.9±2 Gyr Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  37. The capturecross-sectionof232Th • Very accurate data collected at n_TOF on neutron capture for 232Th: • clear advantage over GELINA in the Resolved Resonance Region. • important results also at high energy, (previous data off by 40 %). Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  38. The fissioncross-sectionof233U PRC referee report The experiment and the data obtained are ofhigh quality and clearlysuperiortoearliermeasurements. The resultisof major importancefornucleartechnology, in particularfor the neutronicsofnuclearreactorsusing the Th/U breedingcycle. …. In conclusion the qualityof the article and of the obtained data are exceptionally high. A publication in a journal on nuclearengineeringwouldalsobeadequate, butpersonally I recommend the articleforpublication in Phys.Rev. C. Thus the results are more visiblefor the scientific community. Important data for Th/U cycle ! Fission cross-section on 233U measured for the first time from thermal to 50 MeV, with 5 % accuracy, and high resolution. Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  39. The cross-sectionsof237Np 237Np(n,g) Previous data scatteredallover. Accuracyofn_TOFresultsbetterthan 4% (up to 10 keV). Solvedlargediscrepancy in the UnresolvedResonanceRegion D=50% C. Guerreroetal., Phys. Rev. C, in preparation 237Np(n,F) C. Paradelaet al., sub. to PRC n_TOFresults6% higherthanprevious data and evaluations (all normalized to ONEmeasurements of 1983). Very important result for design of future generationreactors (Npis the mostabundant MA produced in currentreactors) Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  40. The cross-sectionsof240Pu 240Pu(n,g) First capturemeasurement in resolvedresonanceregion. Accuracy 6% (up to 10 keV). Extractednuclearproperties (levelspacing, average gamma widths, etc…). C. Guerreroetal., Phys. Rev. C, in preparation Ti(n,n) 240Pu(n,F) Tobeperformed in 2011 Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  41. The cross-sectionsof241Am 241Am(n,g) Tobeperformed in 2010 241Am(n,F) Largediscrepancies in databasesforseveralresonances. Overalluncertaintytoo high fornuclearenergyapplications. M. Calviani etal., Phys. Rev. C, in preparation Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  42. Cross-sectionsof243Am 243Am(n,g) Uniquemeasurement (not easy toperform). High-resolution and high-accuracyresults up to a fewkeV (becauseofthick Ti capsule). Improvements and newmeasurements are needed. Ti resonance E. Mendoza etal., Phys. Rev. C, in preparation 243Am(n,F) Clarified a long-standing discrepancy of more than 15 % ! n_TOF data (3% accuracy) confirm current evaluations, against previous results (even of 2004 !!). 244Pu(3He,tf) F. Bellonietal., Nucl. Sci. Eng., in preparation Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  43. Cross-sectionsof245Cm 245Cm(n,g) Tobeperformed in the future 245Cm(n,F) Very few measurements available on this isotope (difference up to a factor of 2, with evaluation in between). New data from n_TOF clarify that one of the two previous measurements is completely wrong. M. Calviani etal., Phys. Rev. C Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari 44

  44. n_TOFPhase 2 Some isotopesrequire a muchhigherflux (x100) New Experimental Area at 20 m fromspallation target. Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari 45

  45. The newspallation target Moderator (4 cm) New pressure vessel Cooling water (1 cm) Pb Ø = 60 cm L = 40 cm protonis Existing Pool Existingretention vessel Itisnowpossibletousedifferentmoderators (tooptimizeneutronspectrum or minimize background) Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  46. Commissioningof the new target Profilo Withborated water, background reducedby a factor 10 more ! Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  47. The newexperimental area • Twopossibilitiestomeasureradioactive isotopes at CERN: • Encapsulatedsamples, with ISO2919 certification; • Suitableexperimental area (hot lab). • In the past, wehaveused Ti/Al capsules, whichhowever induce a large background. Area sperimentale Dressing room Duringshut-down, experimental area transformed in “Work Sector Type A” (forhandlingnotcertifiedradioactivesamples). Variousmodifications: sealed area, controlledventilation, underpressure, fire-proofdoors, fire detection systems, radioactivity monitor, etc… Access: dressingroom, hand/footcontamination monitor, decontamination area, etc… Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  48. The newfacility The n_TOF access tunnel n_TOF changing room The escape lane The experimental area Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

  49. Nextmeasurements • Esperiments approved by INTC: • n_TOF-10: Capture of 242Pu, 241Am and 245Cm with a TAC at n_TOF • n_TOF-12: New target commissioning and beam characterization : Borated water : Fluence, Resolution Function, Background • n_TOF-13: The role of Fe and Ni for s-process nucleosynthesis in the early Universe and for innovative nuclear technologies : 54,57,58Fe, 58,60,61,64Ni with C6D6 measurements • n_TOF-14: Angular distributions in the neutron-induced fission of actinides: Fission Measurements of 232Th, 235,238U with PPAC • n_TOF-16: Neutron capture cross section measurements of 238U, 241Am and 243Am (+197Au, natC, natPb, Empty) with TAC+C6D6at n_TOF • New proposals: • Measurement of fissioncross-section of 240Pu, 242Pu and 245Cm with a MGAS or FIC0 detector • Experimental test of a fission tagging neutron capture measurement combining the n_TOFTAC with a MGAS detector (233U) • The 33S(n,a) cross-section: implications for neutron capture therapy and Astrophysics • n_ToFdumpas a facility for neutron detector testing Isolde – CERN, July 14th, 2010 N. Colonna – INFN Bari

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