LLNL

Alternative Detector Designs for Reactor Antineutrinos

Jim LundSandia National Laboratories

• Goals of our collaboration• Designs under consideration • Progress with the segmented

scintillator concept– Experiments underway– Work remaining to be done

• Summary

Applied Antineutrino Physics Workshop

This work supported by the United States Department of Energy under contract number DE-AC04-94AL85000. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the United States Department of Energy.

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Goals of our development program

• Develop practical anti-neutrino detectors that can be deployed at commercial power reactors

• We are beginning to investigate “above ground” detectors

The tendon gallery

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Alternative anti-neutrino detector designs under study by the LLNL-SNL Collaboration

• Segmented scintillator– Inverse beta

• Water Cerenkov– Inverse beta

• Dual Phase Argon– Nuclear scattering

• Germanium– Nuclear scattering

From Collar group U of Chicago

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Segmented Scintillator Design

• Segmented scintillator– Review of operation– Experimental results

• Time multiplexing• Multiplicity cuts

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ZnS(Ag) scintillator with 6Li loading

Liquid organic scintillator with pulse shape discrimination

~10 cm

~ 1 m

Segmented scintillator design

A single voxel

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Segmented ScintillatorPrinciples of operation

e p e n

ZnS(Ag) scintillator with 6Li loading

e

e p e n

e+

n

• Neutrino interaction signature– Positron

• one cell (discounting annihilation photons)

• Electron-like event in liquid scintillator (fast pulse decay)

– Neutron• Bright ZnS pulse in two adjacent

cells about ~10 s after positron

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Rejection of Background events

Existing Detector• Mimics antineutrino capture

– Pulse from n-p scatter

– Followed by n-capture on Gd

Proposed Detector• Cut because:

– n-p scatter distinguishable from pulse shape

time [s]

0 2 4 6 8 10 12

puls

e am

plitu

de [r

elat

ive

units

]

0.0

0.2

0.4

0.6

0.8

1.0

Neutrino-like event

Background event (fast neutron capture)

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Background eventsslow neutron into detector

coincident with gamma rayExisting Detector

• Mimics antineutrino capture– Pulse from n-p scatter

– Followed be n-cature on Gd

Proposed Detector• Cut because:

Gamma event very unlikely to be in same cell as neutron event

e p e n 6;e n Li

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Background eventstwo chance gamma-rays within time window

Existing Detector• Mimics antineutrino

capture

Proposed Detector• Cut because:

No signal from ZnS scintillator

gammas do not deposit enough energy in ZnS and light from neutron on Li is very large = Q= 4.8 MeV

Light pulses from more than one cell

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Segmented Scintillator DetectorDevelopment Progress

• Recent experiments– Multiplexing scintillator

light– Event identification

with segmentation

ZnS(Ag) scintillator with 6Li loading

e

e p e n

e+

n

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Segmented Scintillator DetectorDesign experiments

Light multiplexing– To minimize number of

PMTs, it would be nice if ZnS signal could be distinguished from liquid scintillator signal by decay time (psd)

ZnS(Ag) scintillator with 6Li loading

e

e p e n

e+

n

2 pmts needed with light multiplexing, 3 (or more) without

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Light MultiplexingExperimental results

Initial experiments by L. Sadler indicate that light multiplexing will probably not work

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Design solution without light multiplexing

Acrylic light guide with LiZnS(Ag) coating

ZnS(Ag) scintillator with 6Li loading

e

e p e n

e+

n

Main PMTs

ZnS readout PMT

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Segmented Scintillator Detector

• Recent experiments– Multiplexing scintillator

light– Even identification

with segmentation

ZnS(Ag) scintillator with 6Li loading

e

e p e n

e+

n

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One of two plastic detectors installed at San Onofre was modified to perfrom

segmentation studies

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Small “scintillator identification” PMTs were added to one of our plastic detectors installed at SONGs

Plastic

Scintillator

Gd containing layer

Scintillator identification PMTs

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Light guide

Main PMTs

Holes in light guide for identification PMTs

Identification PMT configuration

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Identification PMT configuration

View from below (sans main PMTs)

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Event multiplicity physics

• We expect multiple scintillator hits (multiplicity) from energetic neutrons because:– Multi MeV neutrons will

have to undergo several large angle elastic scatters to slow and capture on Gd

– Inelastic scatters on carbon in the scintillator will produce gamma showers

Plastic

Scintillator

Gd containing layer

Scintillator

identification PMTsEnergetic

neutron

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Event multiplicity physics II

• Then again an antineutrino interaction would also have multiplicity

• Positron annihilation could also produce high multiplicity

Plastic

Scintillator

Gd containing layer

Scintillator

identification PMTs

e

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Preliminary multiplicity analysis of SONGS plastic detector data by D. Reyna

Evidence for high multiplicity of fast neutrons!

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Multiplicity analysis of Songs data by D. Reyna

Low multiplicity events are random with respect to Gd capture

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Further studies on segmented scintillatorfor 2008

• Light propagation from LiZnS(Ag)

• Can we get effective PSD from ~1m length segements?

• Monte Carlo studies of neutron slowing down and positron transport

time [s]

0 2 4 6 8 10 12pu

lse

ampl

itude

[rel

ativ

e un

its]

0.0

0.2

0.4

0.6

0.8

1.0

Neutrino-like event

Background event (fast neutron capture)

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Summary and Acknowledgements

• We’ve begun design studies of a highly segmented detector with 6LiF:ZnS(Ag)

• Some discouragement (probably no multiplexing) but we’re still optimistic

• Further experiments in 2008 should complete answers to most important questions

• Like to acknowledge everyone in the LLNL-SNL collaboration for helping out with this study:

• G. Aigeldinger, J. Brennan, A. Bernstein, N Bowden, S. Dazeley, D. Reyna, and L. Sadler