Water-based Antineutrino detector at SONGS Steven Dazeley Oct 11, - - PowerPoint PPT Presentation

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Water-based Antineutrino detector at SONGS Steven Dazeley Oct 11, - - PowerPoint PPT Presentation

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Lawrence Livermore National Laboratory Water-based Antineutrino detector at SONGS Steven Dazeley Oct 11, 2011 This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory in part under

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Lawrence Livermore National Laboratory

LLNL-PRES-503991

Steven Dazeley Oct 11, 2011

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory in part under Contract W-7405-Eng-48 and in part under Contract DE- AC52-07NA27344.

Water-based Antineutrino detector at SONGS

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Lawrence Livermore National Laboratory Sandia National Laboratory

LLNL-PRES-503991

The San Onofre Nuclear Generating Station: Our (nonproliferation) laboratory for over a decade

  • We have cultivated an exceptionally strong and trusting relationship with SONGS:
  • A multitude of access requests have been readily granted since 1999
  • Provide unescorted reactor access, deployment assistance, commercially

sensitive fueling data, introductions to other operators, …..

  • We possess unparalleled operational experience in this industrial environment:
  • Five detector deployments since 2003

Direct Observation of reactor fuel burnup via antineutrino counting

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Lawrence Livermore National Laboratory Sandia National Laboratory

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Tendon Galleries are Ideal Deployment Locations

24m 30mwe

  • High Flux: ~1017 ν/m2/s
  • 130-180m to other reactor
  • Gallery is annular – unfortunately no

possibility to vary baseline

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Lawrence Livermore National Laboratory Sandia National Laboratory

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SONGS Signal and Backgrounds

  • Our SONGS1 detector (20 meters water equiv. underground, 25

meters from core) had S/B of ~4/1

  • Background was primarily:
  • Fast neutron recoil followed by capture
  • Multiple neutron capture
  • Above ground possible?
  • Many more potential deployment sites
  • There may not be a tendon gallery at every reactor
  • Water SONGS particulars
  • Technology choices driven by need to defeat cosmogenic

fast neutrons,

  • Neutron flux ~ up to 103 x below ground site
  • Antineutrino flux (50 meters from core) ~¼ SONGS1 flux
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Lawrence Livermore National Laboratory Sandia National Laboratory

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Above-Ground Water-Detector backgrounds

  • Major background is now – fast (100s MeV) neutron spallating inside an
  • xygen (say) nucleus inside detector  multiple neutron captures
  • Fast neutrons are missed by the muon veto surrounding the detector

n n n Fast n Antineutrino detector Muon veto Poly shield

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Lawrence Livermore National Laboratory Sandia National Laboratory

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Cosmogenic shielding and Muon veto

Fast neutron shield

  • Between 40cm and 60cm poly shielding on all

sides

  • Inner 2.5cm is borated poly

Muon Veto

  • Muon paddles – 5cm thick overlapping plastic

scintillator paddles

  • Muon peak generally fits to a sigmoid

multiplied by an exponential. We use the low energy tail to predict approx efficiency versus energy cut

  • 99% analysis threshold used
  • Veto time – 100 microseconds – 20% dead

time

  • Estimated efficiency (from data)  98.5%
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Lawrence Livermore National Laboratory Sandia National Laboratory

LLNL-PRES-503991

Inner (Water) Detector

  • ~ 1-tonne pure DI water + 0.2% GdCl3
  • 12 x 10-inch Hammatsu PMTs arranged on top of

water looking DOWN

  • Stainless steel tank with baked Teflon interior
  • GORE-DRP diffuse reflective (99%) walls
  • DAQ – PMT signals 23 MHz low-pass filters 

CAEN V975 x10 fast amps  Struck 200MHz SIS3320 waveform digitizers

  • Trigger rate ~ 700Hz inside poly shield (300Hz of

that from muons)

  • Excellent single PE resolution
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Lawrence Livermore National Laboratory Sandia National Laboratory

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Few words about the (important) details

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Shield Construction (Designed and built at Sandia Natl. Lab.)

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Shield Construction

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Installing Inner detector

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Lawrence Livermore National Laboratory Sandia National Laboratory

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Cosmogenic neutron backgrounds

Antineutrino signature is a simple correlated two events - how many correlated neutron pairs are part of a triple? Quadruple? etc

Correlated event pair efficiency as a function of inter-event time after multiple neutron cut Distributions of event times are well understood – simple analytical function fits are very good

Time distribution of any group of 3 uncorrelated events Time distribution of any group of 2 correlated events + 1 uncorrelated event

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Lawrence Livermore National Laboratory Sandia National Laboratory

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Neutron Selection, rates

Selecting Neutrons – detector response

Absolute correlated rate uncertainty versus Expected antineutrino interaction rate (scaling from SONGS1 interaction rate) Correlated events Vs Uncorrelated events Q factor – statistical advantage of applying an analysis cut at some value. Q Factor = Sc/√Bc Sb/ Correlated events tend to have a higher neutron capture component

  • higher detector

response Maximum neutron

sensitivity between 38 and 130 PE

√Bb

Sc, Bc =signal and background

after applying cut Sb, Bb = signal and background before applying cut

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Lawrence Livermore National Laboratory Sandia National Laboratory

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Initial look at data quality…. (ongoing)

  • May 3 2010 – start taking data

…. Some months of inconsistent data quality ….

  • Early July 2010 (1 week) – good physics data

More inconsistencies, temperature troubles, humidity, DAQ…

  • Late August to early Dec 2010 – good data
  • Reactor turns OFF on Oct 10 2010 until mid February 2011
  • Appears to be ~ 5 to 6 weeks good reactor ON/OFF reactor data. But it

remains to be seen how well it stands up to scrutiny/analysis

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Lawrence Livermore National Laboratory Sandia National Laboratory

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Detector Stability (near Reactor shutdown, October time frame)

Reactor ON/OFF transition Period

Gaussian fit to Gd Peak (mean position and width of peak) Reactor ON Reactor OFF Reactor ON Reactor ON Reactor OFF Reactor OFF We see no evidence of any systematically unstable detector response that might lead to fake signals (during this data period (Oct 2 to Oct 17)

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Lawrence Livermore National Laboratory Sandia National Laboratory

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Results: (8 days Reactor ON/OFF)

  • Applying detector response cuts (38 PE to 130 PE), eliminating all triples

and quadruples, etc, get

  • 43768 ± 127.8 Reactor ON per day (October 2 to October 9 2010)
  • 43453 ± 125.7 Reactor OFF per day (October 10 to October 17 2010)
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Lawrence Livermore National Laboratory Sandia National Laboratory

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Future Improvements

  • Wavelength shifting – UV Cherenkov light shifted to blue  Light output ~ x2.

Stable over ~ 2 months Muons neutrons One gives up Cherenkov rings to some extent – which may be a problem in large science experiments

250 liter detector 4-tonne detector Red – no WLS Black – 1ppm 4-Mu Red – no WLS Black – 1ppm 4-Mu

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Lawrence Livermore National Laboratory Sandia National Laboratory

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Gain of CS-124 and Amino-G

CS-124

Low gain

Amino-G

Turns visibly brown at high concentrations

4-MU

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Summary – Preliminary Water Detector results

  • In order to determine the best detector response cuts for positrons, we will use a

MC simulation of the detector response, tuned to match our neutron capture spectrum – in progress…

  • For now, we use the n capture cuts as a proxy for position energy cuts (since the

detector response to positrons (from antineutrinos) is probably higher than for background gamma-rays)

  • Applying detector response cuts (38 PE to 130 PE), eliminating all triples and

quadruples, etc, get

  • 43768 ± 127.8 Reactor ON per day (October 2 to October 9 2010)
  • 43453 ± 125.7 Reactor OFF per day (October 10 to October 17 2010)
  • More data to be analyzed (OTHER 5 weeks ON and OFF data has not been

analyzed yet…watch this space). Conclusion – at these background levels getting a statistically significant positive detection above ground with water detector will be difficult

  • Future improvements – wavelength shifting x2 improvement in light detection
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Lawrence Livermore National Laboratory Sandia National Laboratory

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Bonus Pictures: Shield Construction (Designed and built at Sandia Natl. Lab.)

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Shield Construction

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Shield Construction

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Shield Construction

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Shield Construction

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Filling

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Packing up

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Near the Reactor

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Near The Reactor