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Short Baseline Reactor Experiments

Short Baseline Reactor Experiments. STERILE NEUTRINOS at the CROSSROADS VirginiaTech, September 25-28, 2011. Yves Déclais, Lyon university. Short Baseline Reactor Experiments. Introduction to reactor experiments First batch of reactor neutrino anomalies : 1975-1985

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Short Baseline Reactor Experiments

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  1. Short Baseline Reactor Experiments STERILE NEUTRINOS at the CROSSROADS VirginiaTech, September 25-28, 2011 Short Baseline Reactor Experiments(Yves Déclais) Yves Déclais, Lyon university

  2. Short Baseline Reactor Experiments • Introduction to reactor experiments • First batch of reactor neutrino anomalies : 1975-1985 • Savannah River deuterium experiment • ILL neutrino experiment • Bugey I experiment • Systematical studies : 1985-1996 • Gosgen, Rovno, Krasnoyarsk, SRP, Bugey 3 • High precision benchmark : • Bugey 3 : shape of the neutrino energy spectrum • Bugey 4 : absolute neutrino flux from reactors • Application to the long baseline experiments : CHOOZ • Conclusions Short Baseline Reactor Experiments(Yves Déclais)

  3. Nuclear reactors : best source for detecting neutrinos • fission bomb : ~8 1023 /Kt • nuclear reactor : ~2 1020  /Gwth /sec As you recall, we planned to use a nuclear explosion for the source because of background difficulties. Only last week it occurred to us that background problems could be reduced to the point where a Hanford pile would suffice by counting only delayed coincidences between the positron pulse and neutron capture pulse. Fred Reines: Letter to E. Fermi , October 4, 1952 Answer from Fermi, October 8 Certainly your new method should be much simpler to carry out and the great advantage that the measurement can be repeated any number of times Large R&D for PMTs and Liquid Scintillator production Short Baseline Reactor Experiments(Yves Déclais)

  4. Reactor Anti-neutrinos detection • Signature: Delayed coincidence • prompt signal : β+ • delayed signal : neutron capture Detectected spectrum X section • Background: • γ interactions • fast neutrons from μ spallation Production spectrum Short Baseline Reactor Experiments(Yves Déclais)

  5. First Attempt of Reactor Anti-neutrinos detection Hanford experiment : 1953 first homogeneous detector 300 l Cd loaded liquid scintillator  neutron capture time 2.2 μsec Viewed by 90 2-inch PMTs Passive shielding : lead, paraffin, water Active shielding : Geiger Mueller counters Correlated bkgd studied with emulsion plates Pile up : 2.55  0.15 evts/min Pile down : 2.14  0.13 evts/min Signal : 0.41  0.20 evts/min Expected : 0.2 ( assuming σ = 6 10-20 barns ) Also used as : ‘ ‘ whole body radiation detector : HUMCO I & II ‘’ Ref: Los Alamos Science 23, p 276, 1995 Short Baseline Reactor Experiments(Yves Déclais)

  6. First Detection of Reactor Anti-neutrinos Reactor power 700 Mw Distance from reactor : 11m Overburden : 12m Better passive shielding Liquid scintillator cosmic veto Cd loaded water target: 2x200 l. Overall efficiency : 10% Savannah River experiment : starting 1955 New approach with a more selective detector for better β+ and neutron signature ( decreasing n detection efficiency by 1/3 ) Neutrino signal : 3  0.2 /hour Replacing Water target by Cd Loaded LS 1.4 m3 : rate : 364 evts/hour S/B : 1/5 Short Baseline Reactor Experiments(Yves Déclais)

  7. Knowledge of the of the Expected Reactor Anti-neutrinos Rate Reactor operation ( σ 1% ) Nexpected =(Pth)x(E/fission)-1x(N/fission)x(Δ)x(σ)x(Nprotons)x(Eff.) 238U, 235U, 239Pu, 241Pu from Reactor Operation For power reactor The uncertainty on N/fission is the dominant term:  cancelled by comparing the flux at 2 distances Short Baseline Reactor Experiments(Yves Déclais)

  8. First Batch of Reactor Anti-neutrinos Anomalies 1975-1985 • SRP  deuterium experiment • ILL  experiment • Bugey I experiment • Further verifications Short Baseline Reactor Experiments(Yves Déclais)

  9. allowed 1) SRP  deuterium experiment (1975-1980) Normalization through the ‘ncd’ reaction: Less sensitive to the knowledge of the  flux (1st order !) R= (ccd/ncd)measured / (ccd/ncd)expected • distance 11.2 m • Pth 2000 MWth RSRP = 0.62  0.16 (1980) Short Baseline Reactor Experiments(Yves Déclais)

  10. 2) ILL  experiment ( 1980-1981) ILL  experiment 1980-1981 • distance 8.76 m • Pth ’57’ ‘ MWth • 93.5% enriched 235U reactor core Short Baseline Reactor Experiments(Yves Déclais)

  11. Mostly used to disprove d result from Reines Short Baseline Reactor Experiments(Yves Déclais)

  12. First Common Fit by a theorist … 1981-1983 Indications Of Neutrino Oscillations From An Analysis Of Reactor Experiments Performed at Different Distances.D. Silverman, (UC, Irvine) , A. Soni, (UCLA) UCI-81-35, UCLA/81/TEP/15, Nov 1981 Phys.Rev.D27:58,1983 • Fitting: • SRP (6.5 m & 11.2 m) on proton • ILL (8.7 m ) on proton • SRP (1.2 m ) on deuteron Short Baseline Reactor Experiments(Yves Déclais)

  13. Pth 2800 MW 13.6 m 18.3 m 3) Bugey I experiment ( 1982-1984) He3 chambers • carbon copy of the ILL detector • He3 chamber from ILL • improved shielding (?) • internal layer of low activity Pb Target cells Movable detector Short Baseline Reactor Experiments(Yves Déclais)

  14. Common solution with Silverman’s analysis !? Excluded through The shape analysis R18.3/13.6 = 0.907 .014stat .028syst Allowed through the rate analysis Short Baseline Reactor Experiments(Yves Déclais)

  15. 4) Further experimental verifications : • Bugey II program •  d setup • ILL reanalysis Short Baseline Reactor Experiments(Yves Déclais)

  16. a) Bugey II program ( 1985-1988) Bugey I bkgd >> ILL bkgd !!  internal lead suspected to produce spallation neutron (veto inefficiencies, photo-production) • internal lead removed • measurement campaign with various shielding configuration •  no reactor correlated bkgd observed • Burnup measurement  model validated R18.3/13.6 = 0.993 .021stat .021syst Rmeasured/expected = 0.995 .005stat .069syst • M. Talby Thesis Marseille University, 5/5/88 • H. de Kerret, Moriond jan. 88 / LPC-88-09 Using Schreckenbach 1985 ( At 13.6 m ) Short Baseline Reactor Experiments(Yves Déclais)

  17. Background Signal (rate per day ) SRP 346.0  2.7 63.8  4.1 Single neutron (ncd) BUGEY 25.3  0.7 37.7  2.0 SRP 49.7  1.0 3.66  1.67 Double neutrons (ccd) BUGEY 1.4  0.2 2.45  0.48 RBugey = 0.96  0.23 (1995) b)  Deuterium improved analysis and setup • Improving the analysis ( Nucl. Phys. A396(1983)469 ) • Anticoincidnce selection for ccd • Using the measurement with protons at SRP (11.2 m) RSRP = 0.62  0.16  0.69  0.18 • Improving the bkgd rejection SRP shutdown  detector moved to Bugey (18m) Short Baseline Reactor Experiments(Yves Déclais) Phys Rev C, 59, 1780, 1999

  18. c) ILL reanalysis • thesis M. L. Sanaa, Rabat University • Appl. Radiat. Isot. Vol46, n°6/7, 449, 1995 • 1990: • correction for Pth underestimated (1.095) • new βspectra (Schrekenbach 1984) : +5% • neutron lifetime (926 sec  889 sec) : +4% • Xsection correction (P. Vogel) : - 2% • Full simulation of the detector with the Bugey tools R= 0.955  3.35 % 0.832  3.35 % • Integrated neutron efficiency: • ILL 25.6  2.0 % • Bugey1 : 26.2  0.9 % • (same detectors) • Ongoing test of the reactor-detector distance • Reactor core evolution < 2cm • Geodesic measurement in progress Short Baseline Reactor Experiments(Yves Déclais)

  19. Conclusions on the first batch of anomalies: • Deuterium and Bugey I : improving the experimental setup led to vanishing the anomalies • ILL becomes an intriguing anomaly: • parameters mostly defined by the wiggles observed on the energy spectrum ratio • reinforced by the normalization correction Short Baseline Reactor Experiments(Yves Déclais)

  20. Systematical studies Search for oscillation at larger distances 1985-1996 Measurements performed at several distances to cancel uncertainties from the reactor neutrinos spectrum • Gosgen • Krasnoyarsk • Rovno • SRP mobile experiment • Bugey 3 & 4 Short Baseline Reactor Experiments(Yves Déclais)

  21. ‘carbon copy’ of the ILL detector: • target cells from ILL experiment •  with β+ localisation • new He3 chambers with localisation •  reducing the accidental bkgd • measurements at 37.9m, 45.9m, 64.7m •  dismountable setup Bkgd reduction: 2 1) Gosgen experiment 1981-1986 Phys. Rev. D34,2621 ,1986 Short Baseline Reactor Experiments(Yves Déclais)

  22. 2) Krasnoyarsk experiments 1985-1994 Entrance of the underground facility • 3 reactors: Pu production site  pure 235U fissions • underground site  700 mwe • integral type detector  only neutrons are detected • measurements performed at distances: • 32.8 m and 92.3 m (1987) • 57. m , 57.6 m , 231.4 m (1990) N57m = 114.5  1.09 N231m = 8.07  1.4 Bkgd = 159.4  1.5 Rate ( /105 sec.) R (57m/231m) = 0.86  0.15 Target : 458.4 kg PE 90 3He counters (low bkgd) R (measured/expected) = 0.99  0.05 using Schreck. 1985 and the measurement @ 57m JETP Lett. , 59-6, March 1994 Short Baseline Reactor Experiments(Yves Déclais)

  23. 3) ROVNO experiments 1985-1994 • VVR power plant , ~1400 Mw • 2 detectors at distance : • 12.15 m (12x12 counters) • 18.34 m (16x16 counters) • Integral type detector N12m = 1338 N18m = 1161 Bkgd = 210112m , 293118m Rate ( /105 sec.) R (12m/18m) = 0.976  0.02 (stat)  .015 (syst) R (measured/expected) = 0.985  0.038 using Schreck. 1985 and the measurement @ 18m JETP Lett. , 54-5 , 1991 JETP Lett. , 55-10, 1992 Short Baseline Reactor Experiments(Yves Déclais)

  24. R(1a/1b)= .97 .01(stat) .02(syst) R(d2/d1)= 1.07 .02(stat) .03(syst) 3) Savannah River experiment 1985-1994 • Pu production site (1800 Mw)  pure 235U fissions • homogeneous detector : • Gd Loaded LS (275 l., Xylene based) • mobile setup : • measurements at distances 18m and 24 m. R (mea./expec.) = 0.987  0.6% (stat)  3.7% (syst) = 1.055 1.0% (stat)  3.7% (syst) using Schreck. 1985 Phys. Rev. D, 53-11, 6054, 1996 Short Baseline Reactor Experiments(Yves Déclais)

  25. Neutron capture energy Neutron capture PSD 4) Bugey III program 1985-1994 • Bugey site : 4 power reactors, 2800 Mwth each • segmented, homogeneous 6Li loaded LS detector • 3 identical modules, movable • 1 module installed at 15m from reactor 5 • 2 modules installed at 40m from reactor 5 • (95m from reactor 4) Nucl Phys B434(1995)503 Short Baseline Reactor Experiments(Yves Déclais)

  26. Ratio to the expected spectrum ( syst error : 5% ) R15m = 0.988  0.004 (stat) R40m = 0.994  0.010 (stat) R95m = 0.915  0.132 (stat) using Schreck. 1985, 1989 Short Baseline Reactor Experiments(Yves Déclais)

  27. High precision benchmark 1 : Shape of the energy spectrum ‘Comparison of anti-neutrino reactor spectrum models with the Bugey3 measurements’ B. Achkar et al, Phys. Lett. B 374 (1996) • Model used : • 238U : calculations from Klapdor (1982) • 235U, 239Pu, 241Pu - Schreckenbach 1985, 1989 Energy scale x 1.004 In agreement with the new calculations of the reactor neutrino spectrum Short Baseline Reactor Experiments(Yves Déclais)

  28. CHOOZ proposal : systematical uncertainties. High precision benchmark 2 : Absolute normalisation of the neutrino flux ‘Study of reactor antineutrino interaction with proton at Bugey nuclear power plant Y. Déclais et al, Phys. Lett. B 338 (1994) Bugey 4 Goal : reducing the systematical error related to the neutrino flux for the CHOOZ experiment, avoiding the construction of a near detector Short Baseline Reactor Experiments(Yves Déclais)

  29. R = flux measured/flux expected RRovno = 0.985 .028stat .027syst RBugey = 0.987 .014stat .027syst Error on theoretical predictions Bugey 4 strategy : a) scaling between reactors • Use the same detector (WIND integral detector) near 2 power reactors •  Validation of the scaling procedure between 2 reactors independently of the systematics from the detector (including the Xsection) • Reactor core evolution : Burnup • Thermal power  fission rate • Neutrino spectra Caveat: there could be some compensation/correlation between these 3 parameters Before the RNA era The same procedure will be used for the CHOOZ analysis Short Baseline Reactor Experiments(Yves Déclais)

  30. full simulation package of the neutrino source : • the geometrical structure of the core • the initial configuration & burnup of each fuel element • all the measurements of the neutron flux (every month) • interpolation between measurements based on the data from the external neutron chambers (real time data) Short Baseline Reactor Experiments(Yves Déclais)

  31. Detailed study: ‘Uncertainties in the Anti-neutrino production at Nuclear Reactors’ Djurcic et al , arXiv:0808.0747 • Pth error : 0.51% ( 0.45% systematic, 0.25 % reactor-to-reactor) • errors propagation (correlation, cancellation) in the fission rate calculations  signal rate uncertainty ~0.76%  0.59% Fission rate from Thermal power measurement & Isotopic evolution EDF documentation Pth =  WGv(i) – ΔPr(i) • Enthalpic balance • of each steam generator • (secondary loop) • Measured parameters: • Vapor pressure, Ture & flow • Water Ture & enthalpy Bilan of the losses and intake Inside the primary loop (~12 Mw : 1.3%) Error on WGv(i) : 0.512 %  100% Pmax 0.531 %  50% Pmax 0.752 %  25% Pmax Caveat: substracting the residual power from irradiated fuel components & delayed  emission <<1% Kopeikin et al , IAE-6026/2 Short Baseline Reactor Experiments(Yves Déclais)

  32.  bkgd Bugey 4 strategy : b) scaling from WIND to CHOOZ detectors • The normalisation is defined • by the Detector Calibration: • σ(Np) = 0.5% working volume measured with PU-Li & Sb-Be neutron sources to check the simulation • neutron = 0.549  0.003 (0.5%) using tagged 252Cf source Identical protocol than in the ROVNO exp. Short Baseline Reactor Experiments(Yves Déclais)

  33. CHOOZ detector original concept: ‘the target mass is defined by the mass of the Gd Loaded Liquid Scintillator ‘ now used by all reactor experiments (Double Chooz, Daya Bay, RENO) ~ full β+ efficiency  similar to the integral detector  identical calibration protocol used in Bugey4/ROVNO for the neutron detection efficiency neutron = .796 overall = .698 Implicitly the CHOOZ result is obtained by comparing the measured flux at 15m @ Bugey (Bugey4 , 1.4%) and at 1km • Subtracting automatically the sterile component … if any ! • not sensitive for Δm² > ~ 2eV² Cautiously, the scaling have been applied in a conservative way: CHOOZ publi : Short Baseline Reactor Experiments(Yves Déclais)

  34. Discussing the CHOOZ result In a more optimistic way .. Comparing the measured rate in the CHOOZ & Bugey4 detectors 1.4 % ( Bugey4 stat accuracy) 0.6  0.3 % 2.28 2.22 % Short Baseline Reactor Experiments(Yves Déclais)

  35. New inversion for β- spectra  ~+3% (D. Lhuillier talk ) • Compilation & renormalization : • new fluxes • updated Xsection Best fit : μ = 0.943±0.023 ILL • 3 hypothesis : • common bias in all experiments !!! • short distance oscillation into sterile state • overestimation of the β spectra ? • dispersion of meas. for 235U : 56 % Let’s wait for Klaus Schreckenbach talk Th. Lasserre, EPS meeting this summer Short Baseline Reactor Experiments(Yves Déclais)

  36. Thank you for your attention Short Baseline Reactor Experiments(Yves Déclais)

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