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Antineutrino Detector

This article discusses the overall design and requirements of an antineutrino detector, including mechanics, liquid scintillator, PMTs, electronics, calibration, and performance. Written by Steve Kettell, the Chief Scientist of the Daya Bay Project at BNL.

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Antineutrino Detector

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  1. Antineutrino Detector • Outline • Requirements • Overall Design • Mechanics • Liquid Scintillator • PMTs • Electronics • Calibration • Performance Steve Kettell BNL US Daya Bay Project Chief Scientist

  2. Antineutrino Detector • I will discuss the overall detector design, including some discussion of electronics and calibrations • Bob will show the results of the studies of the systematic uncertainties

  3. Antineutrino Detector Requirements • High statistics large, homogeneous detectors • Identical detectors  precise, redundant measurements • Clean inverse -decay signature with good background separation  Gd-loaded liquid scintillator (LS) (8 MeV/n-capture and 30ms capture time with 0.1% Gd) • Well determined fiducial mass and hydrogen density  precise measurement of Gd-LS volume and mass (no need for vertex cut) • Low threshold to detect e+ at rest  low single g rate • Well-defined neutron detection efficiency g-catcher, energy scale calibration, identical detectors • Good energy resolution for energy scale, spectral distortion  high scintillation output, long Lattn, good photocathode coverage • Enable transport and swapping in a reasonable tunnel size (easy to build multiple modules), manageable muon flux  moderate size

  4. Antineutrino Detector Design 12.2% 13cm Cylindrical three-ZoneStructure: I. Target: 0.1% Gd-loaded liquid scintillator II. g-catcher: liquid scintillator, 45cm III. Buffer shielding: mineral oil, ~45cm 20 t Gd-LS With 224 PMT’s on circumference and diffuse reflector on ends: Oil buffer thickness LS Rate from PMT glass oil 92% g Catcher thickness A 45cm buffer provides ~20cm of shielding against PMT glass g-catcher thickness (cm)

  5. Antineutrino Target Mass 4 x 20 tons target mass at far site Sensitivity after 3 years.

  6. Three zone detector 3-ZONE 2-ZONE cut cut • 2-zones implies simpler design/construction, some cost reduction but with increased risk to systematic effects (neutron e and E spectrum) • 3-zones provides increased confidence in systematic uncert. associated with detection efficiency and fiducial volume, but smaller volume n capture on Gd yields 8 MeV with 3-4 g’s Uncertainty ~ 0.2% Uncertainty ~ 0.4% 40 ton 20 ton • 4 MeV cut can reduce the error by x2, but residual radioactivity in LS volume does not allow us to do so

  7. Rates • spectrum from Aberdeen: same granite as Daya Bay Fast neutron spectrum from MC simulation

  8. Rates Rates are per antineutrino detector module

  9. Mechanical Design • Gd-LS Target: 3.2m () x 3.2m (L)  ~20 tons • LS g-catcher: 4.1m () x 4.1m (L)  ~20 tons • Mineral oil buffer: 5m () x 5m (L)  ~40 tons

  10. Detector Vessel Structure Steel tank Outer acrylic tank Inner acrylic tank PMT Acrylic transparency Dimensions inner outer steel Diameter (mm): 3200 4100 5000 Height (mm): 3200 4100 5000 Wall thickness (mm): 10 15 10-20 Weight (ton):0.6 1.4 10-25 Water

  11. Finite Element Analysis for Steel Tank Load condition: tank structure filled with liquids Constraint condition: bottom annular surface was constrained The max. stress: 108 MPa The max. deformation: 2.8 mm Stress result Unit:Pa Deformation result Unit:m

  12. Moving the Detector • Moving 100t over 0.5% tunnel grade • Down 10% grade when empty (20t) • Lifting 100t into water pool Bridge crane option considered in one of the civil conceptual design reports

  13. Detector Instrumentation Monitoring Goals: - mechanical stability during filling, transport, and movement - liquid levels during filling - acrylic vessel positions mass flow volume flow temperature density CCD camera • Laser reflection for in-situ measurement of: • attenuation length • acrylic vessel movement and position during transport level sensors tilt sensors load sensors Liquid Scintillator sampling

  14. Filling the Detector Detectors are filled in pairs from common storage tanks • I. Target: 0.1% Gd-loaded liquid scintillator • II. g-catcher: liquid scintillator, 45cm • III. Buffer shielding: mineral oil, ~45cm Three Liquids: Mass Measurements: mass + volume flow load sensors Example: Coriolis Mass Flow Measurements Gd-LS LS oil Possible mass flow rates of 1g/hr - 8000kg/hr with 0.1% repeatability. • Flowmeters – 0.02% repeatability • Baseline = 0.2% • Goal = 0.02%

  15. Liquid Scintillator • Gd loading significantly increases the energy of the neutron signal and increases the number of neutron captures (within a given time window) and thereby reduces background • Require stable Gd-loaded liquid scintillator with • high light yield • long attenuation length

  16. Gd-Liquid Scintillator Optical Attenuation: Stable ~700 days • Gd (carboxylate ligands) in pseudocumene (PC) and dodecane • stable for ~2 years • - attenuation Length >15m • - promising alternative scintillator: Linear Alkyl Benzene (LAB)

  17. Determination of H/C and Gd in LS • Combustion Analysis • Gd-LS decomposition in O2: • LS: CxHy + (x + y/4).O2 x. CO2 + y/2.H2O • Gd: 2.Gd +(3/2).O2  Gd2O3 • Potential of measuring C, H and Gd simultaneously with good precision. • Samples were measured by certified, commercial laboratory; achieved C/H measurements at 0.3%. This precision can be improved further. Determination of number of Hydrogen antineutrino targets in the scintillator

  18. Determine H and Gd in LS Prompt Gamma Activation Analysis • Measure 2.2-MeV  from H; 0.18-MeV and other ’s from Gd after thermal neutron capture. • Samples were measured by the Institute of Isotopes, HAS; achieved Gd and H measurement at 1%; the precision needs to be improved.

  19. Performance of Gd in PC and LAB Light Output Spectra Optical Spectra Absorbance over 10 cm Events/nm PC Lab  (nm)  (nm) • Have produced ~1% Gd in LAB and in pseudocumene (PC). (Will dilute to ~0.1% Gd in Daya Bay experiment.) • LAB has lower optical absorption (longer attenuation length). • LAB has better chemical and ESH properties. • LAB and PC have very similar light output efficiency.

  20. PMTs • 224 8” PMTs in 7 rings of 32 • Low-radioactivity glass • Two candidates • Hamamatsu R5912 • Electron Tubes 9354KB • Magnetic shielding under investigation

  21. Electronics (Front-End) Charge Specifications: Dynamic range: 0.025-500 PE Noise: < 0.1photoelecton (PE) Shaping time: 300 ns Sampling freq.: 40 MHz Time Specifications: Resolution < 500 ps Signal split two ways for ADC & TDC

  22. Electronics (Trigger) • Primary Physics Triggers: • Esum: 0.7 MeV • Emult: 10 PMTs • Trigger rate per module: • g < 50 Hz • m = 24 Hz (DB), 14 Hz (LA), 1 Hz (F) • Other triggers: • LED • Radioactive source • Clock • Minbias • Muon system

  23. Electronics (DAQ) • Entire detector is readout on all • physics triggers • Each detector system at each • site is readout independently (8 • antineutrino streams and 9 muon • streams. An event builder • reassembles the streams • Every e+, neutron or m+ will • independently trigger a readout • Primary Physics Triggers: • Antineutrino Detector • Esum: 0.7 MeV • Emult: 10 PMTs • Muon System • Water Pool • Water Tracker • RPC

  24. Calibration • Load sensors, level sensors, thermometers, flow meters, mass flow meters • LED • Radioactive sources: 68Ge (1.022 MeV), 60Co (2.5 MeV), 252Cf • 3-4 locations (with full z travel) • Data (12B, neutrons, Michel electrons) • Determine/maintain energy scale to 1% at 6 MeV throughout detector volume (=> neutron detection efficiency known to 0.2%).

  25. Source Calibration More details in Bob McKeown’s talk • Determination of attenuation length from 2 techniques: • Neutron captures throughout volume relative to center (left) • 60Co source in corner relative to center (right)

  26. LED Calibration Calibration Goal: PMT gains

  27. Detector Performance GEANT simulations Photoelectron yield vs. radius, no mineral oil • 224 PMTs with 12% effective photocathode coverage • ~100 photoelectron/MeV: 12.2%/E Energy resolution

  28. Prototype Performance (1) • 0.5 ton prototype at IHEP (currently unloaded liquid scintillator) • 45 8” EMI 9350 PMTs with 14% effective photocathode coverage • ~240 photoelectron/MeV and 9%/E Linearity Energy Resolution

  29. Prototype Performance (2) Comparison of data and MC • 0.5ton IHEP prototype • L=1.0m, =0.9m 137Cs 137Cs 60Co

  30. Summary • Conceptual design of the antineutrino detector is well advanced • Simulation of the detector response is well developed (Geant3), including several calibration studies (Geant4) • Detailed engineering of the vessels, supports and calibration system is underway • Prototype operational at IHEP, a 2nd prototype to be built at Aberdeen, studies underway of PMTs, electronics, calibration system and LS

  31. Backup

  32. Chooz Data

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