Adam BernsteinLawrence Livermore National Laboratory

Rare Event Detection Group

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Prepared by LLNL under Contract DE-AC52-07NA27344

LLNL-PRES-653915

WATCHMAN: a WATer CHerenkov Monitor for ANtineutrinos

Simulation courtesy Jocher/Usman/Learned NGA and U of Hawaii

Reactors emit huge numbers of antineutrinos

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• 6 antineutrinos per fission

• 1021 fissions per second in a 3,000-MWt reactor

• About 1022 antineutrinos per second from a typical PWR - unattenuated and in all directions

• The catch: mean free path in water is ~300 light years

A look back: Small, deployable near field antineutrino detectors for reactor safeguards

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Determine reactor on/off statuswithin 5 hours with 99.9% C.L.

Measure thermal power to 3% in one week

Detect switch of 70 kg Pu-U with known power and initial fuel content

Rate-based (analysis improves with spectral measurement)• Simple detector design• 25 m from core, outside containment

8’useful for IAEA reactor safeguards• Shipper-receiver differences• Research reactor power• Safeguards by Design and Integrated Safeguards

Long-range reactor monitoring is possible right now– but only for high power reactors with hard-to-scale technology

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1000 tonnes scintillator

1000 m depth

Per month:- 16 reactor antineutrinos- 1 background event

From 130 GWt of reactors

~3% of signal from South Korean reactors @ 400 km standoff

The KamLAND detector

Standoff reactor monitoring is an NNSA Strategic Goal

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Current 3 year scoping project Consider Use Cases Select a Site Create a Preliminary Design, Budget and Schedule Measure of Shallow Depth Backgrounds

2014-15 Decision point to deploy WATCHMAN, a kiloton scale antineutrino detector, ~10 km from a US reactor

Proposed joint funding with Office of Science, High Energy Physics (DOE-SC-HEP)

Ultimate standoff depends on backgrounds from reactors and natural sources

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Global reactor antineutrino fluxessimulation courtesy Jocher/Learned NGA/UH

• Gadolinium-doped (light) wateris the most viable option for scaling to the largest sizes

• Strong synergy with fundamental physics research – Many groups/countries are already investing in this technology

• SuperKamiokande is today’s largest comparable detector - 50,000 tons of H2O

Science & Global Security, 18:127–192, 2010Background 99% confidence level scenarios Detector target mass Standoff in km

Low background Discover 10 MWt reactor in 1 year 1 MT 200

High reactor backgrounds Discover 15 MWt in 6 months 5 MT 100

Possible to extend beyond these limits if antineutrino direction can be recovered

Some current technologies for discovering unknown reactors

• Satellite imaging– Very effective at seeing plumes/heat signature– Non-specific signature– Susceptible to weather, and burial/heat removal countermeasures– Continuous power measurement not practical – Broad area search not practical – Cueing required from other sources of information

• Radionuclide detection– Specific to fissile material production– Cross-border detection possible– Depends on accidental release of activity from reactor– Localization and quantification difficult

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Possible advantages of remote reactor monitoring with antineutrinos

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• For monitoring State/agency– Antineutrinos are highly penetrating and difficult to shield– Continuous long term monitoring is possible– Difficult to mask without another reactor– Some directional information with sufficient statistics (or multiple detectors)

• For the State being monitored– Does not interfere with reactor operations or other activities– Provides limited and specific information about reactor – operational status

and/or thermal power– Willingness to deploy detector indicates likely adherence to any agreement

that restricts undeclared reactors

• For host and monitoring States– Science opportunities facilitate bilateral or multilateral engagements

• Background: Declared reactors near detector can ‘outshine’ small undeclared reactors

• Limited information: (see advantages) – Crude power estimate and operational status only in the far field

• Cost/Complexity: Current technology requires existing underground space (100-1000 meters deep) in the geographical region of interest

Disadvantages and complications

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Why is this work of potential interest ?

• Similar to other joint global nonproliferation and science efforts – CTBT’s International Data Center regularly shares seismic

data with the science community (Intl. Science Ctr.) – infrasound and hydroacoustic also shared

– The SESAME synchroton project in Jordan – “"SESAME…will serve as a beacon, demonstrating how shared scientific initiatives can help light the way towards peace” 45 Nobel Laureates

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• Exclude or discover small undeclared reactors with high confidence in a wide geographical region

• Small reactor 10 MWt standard: 4 kg Pu/year • Alternative technologies

– Radionuclide sensing - depends on accidental release from fuel rods in reactor, ambiguity about location

– Satellite surveillance - requires cueing information

Current Water Cherenkov detectors are large, but can’t identify antineutrinos

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• 20 years of use in neutrino detection

• IMB, Kamiokande, Super-Kamiokande, SNO -1000 – 50,000 tons

• Above the Cerenkov threshold (v>c/n), the number of emitted photons is proportional to the incident neutrino energy.

= q acos(1/n) = 42o

Ekin > 0.26 MeV

~40 m

The SuperKamiokande 50,000 ton water detector

e+ p = e+ + n

For Water Cherenkov antineutrino sensitivity we need Gadolinium doping to efficiently detect neutrons in water

Inverse Beta Decay in Theory

World’s firstGd-H2O detector @ LLNL0.25 ton

Neutron captures in Super-K - 4.3 MeV Evis

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Neutron captures in LLNLGd-H2O detector

n

ep

~ 8 MeV

511 keV

511 keV e+

Gd

t ~ 30 ms

Inverse Beta Decay in A Detector

Neutron sourcebackground

The WATCHMAN collaboration

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UC Davis

UC Berkeley

UC Irvine

U of Hawaii

Hawaii Pacific

A. Bernstein, N. Bowden, S. Dazeley, D. Dobie

P. Marleau, J. Brennan, M. Gerling, K. Hulin, J. Steele, D. Reyna

K. Van Bibber, G. Orebi Gann, C. Roecker, T. Shokair R. Svoboda, M. Askins, M. Bergevin

Students getting WATCHMAN-related Ph.D. s

J. Learned, J. Maricic

S. Dye

M. Vagins, M. Smy

S.D. Rountree, B. Vogelaar, C. Mariani, Patrick Jaffke

World Leaders in the Development and Use of Large Water Cherenkov Detectors

2 National Laboratories6 Universities25 collaborators 15 physicists5 engineers 2 Post-docs3 Ph.Ds

Compared with other large water detector R&D

Detector EGADS WATCHMAN Hyper-K

Status Ongoing 2016 start 2021 or beyond

Mass (ton) 200 1,000 500,000

Type Gd-WCD Gd-WCD Pure H2O or Gd-WCD

Purpose Measure background, material compatibility, energy thresholdToo small to see reactor antineutrinos

Remotely detect reactor antineutrinos – beam and reactor physics potential

Neutrino oscillations, proton decay, supernovae… WATCHMAN would demonstrate Gd option for HyperK or other future bigdetectors

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WATCHMAN Program Plan

4 year Construction and Operation Phase (2016-2019)• Demonstrate sensitivity to reactor ON/OFF transition at ~10 km standoff, with

at most 30 days of ON and OFF data, with at least 99% confidence, with a kiloton scale detector.

• Demonstrate innovative, scalable, cost-effective Gd-H2O Cherenkov technology, pioneered and patented by LLNL staff and WATCHMAN collaborators

• Provide a data-sharing and joint funding model for the scientific community

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3.5 year Scoping Phase (2012-2015)• Consider Use Cases• Find a Site • Create a Preliminary Design, Budget and Schedule• Measure of Shallow Depth Backgrounds

Two Possible Use Cases - Large Detectors

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Ensure no reactors are operating at 10-200 km standoff

Ensure only declared reactors are operating at a known site

•Simplest scenario– Searches for excess antineutrino signal

above background

•Low background levels

•Best suited to excluding new reactors in areas without existing reactors

•Countermeasures are costly– Build a declared reactor near the

detector– Physically attack the detector

•More complex– Requires knowledge of signal from

declared reactors

•Higher backgrounds due to other reactors

•Adjusting power of declared reactors is a potential countermeasure

Not yet claiming significance for any particular Treaty or Agreement

Siting Study: Map of US Power Reactors

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Siting Study: US Reactors + Active Mines

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Preferred and Alternate sites identified

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  Preferred Alternate Reactor Location PERRY Reactor

Perry OhioAdvanced Test Reactor,

Idaho Falls, Idaho

Thermal Power (MWt) 3875 120

Detector Location Morton Salt/IMB mine (!) Painesville, Ohio

New excavationIdaho National Laboratory

Standoff 13 km - the only reactor in the US at a suitable distance from a deep mine

1 km

Overburden (mwe) 1430 ~360

Approval status Morton Salt has approved installation

INL has approved excavation studies

Physics potential Greater physics potential due to greater depth

Antineutrino signal and background

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n (100-200 MeV)

n

n

m

m

9Lib

Signal in 1 kiloton of water

ne

p

~ 8 MeV

511 keV

511 keVe+

Gd

t ~ 30 msprompt e+ signal + n capture on Gd

• Exactly two Cerenkov flashes• within ~100 microseconds • Within a cubic meter voxel

Backgrounds:1. Real antineutrinos 2. Random event pair coincidences3. Muon induced high energy

neutrons4. Long-lived radionuclide decays

Very different from most backgrounds

Full Signal and Background Monte Carloat the PERRY reactor site

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Depth Dependent per day

• Fast Punch-through Neutrons ~1

• Radionuclides not well known ~1-10

Depth-Independent• PMT and Rock Gamma/Neutrons ~1

Other Reactors <1

Geo-antineutrinos negligible ___________________________________________Total Background ~10

Perry Reactor Signal 8-12

Preliminary Design Task

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• Stainless tank assembled in place

• ~3.5 kTon total mass ~1 kTon fiducial region

• ~4800 Target PMTS looking “in”

• 480 Veto PMTs on same frame looking “out”

• Custom recirculation system for Gd-doped water

Drift layout at Morton Salt Mine Close-up of Veto PMT Wall

450

feet

78 feet

Background Measurements at the Kimballton Underground Research Facility

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• Drive in access down to 1500 foot depth

• First-ever continuousmeasurement as a function of depth

• Most important at shallow depths (300 feet, alternative site)

• Final measurement will be at the 1400 foot depth of preferred site

Multiplicity and Recoil Spectrometerfor fast neutron energy spectrum

Small version of WATCHMAN(WATCHBOY) to measure muogenic radionuclide backgrounds

Entering KURF

Physics Synergy

WATCHMAN will provide:

• The U.S.’s only and one of the world’s largest supernova detectors

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Requires nearbyneutrino beam

Requires upgrade to scint.

Science funding agency co-investment is critical to the project’s success‘Positive dual-use’ aspect strengthens the case for long-range monitoring

WATCHMAN may also measure:

• the ordering of the neutrino masses – a major question for 21rst century physics

• a proposed 4th neutrino flavor ( ?)

• non-standard neutrino interactions

• A test facility for future large neutrino detectors (advanced PMTs, water-based scintillator…)

Georg Raffelt, MPI Physics, Munich ISOUPS, Asilomar, 24–27 May 2013

Underground Detectors for Supernova Neutrinos

Super-K (104)KamLAND (400)

WATCHMAN (400 events)

In brackets eventsfor a “fiducial SN”at distance 10 kpc

LVD (400)Borexino (100)

IceCube (106)

Baksan (100)

SNO+ (400)

Daya Bay (100)

~50% chance of Type-II SN occurring before LBNE comes on line.WATCHMAN would be the only detector in the U.S. to see it.Also the only detector in the world with real-time pointingcapability to the supernova source in the sky

• The ISODAR antineutrino source– 60 MEV H2+ cyclotron - strong interest from industry for

isotope production/medical applications– Be neutron production target– 7Li enriched lithium target

Isotope Decay at Rest (ISODAR) neutrino source at 16meters could extend WATCHMAN physics

1. Sterile neutrino searcharXiv:1205.4419v2

ISODAR (green) improves significantlyon previous constraints from LSND (red) and TEXONO (blue)

2. Non-standard interactions/Weinberg angle arXiv:1307.5081v1

ISODAR (solid) has outstanding sensitivity to sterile neutrinos (not affected by the reactor)

• Issues under study:• Accelerator deployment feasiblity

and mine acceptance

• Oil or water-based scintillator may be needed

• 2014 WATCHMAN decision will precede accelerator availabilty

and modifications seenin anomalous rate

Sensitivity of WATCHMAN to sterile neutrino oscillations using the ISODAR beam - examples

Predicted

Expectedmeasurement

Oscillation patterns for a sterile neutrinoISODAR 6 MeV antineutrino source16 meter standoff from detector center

Pure water, 1% scintillator andpure scintillator options

Plots courtesy of Mike Shaevitz, Columbia U.

Conclusions

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• Remote reactor monitoring may fill an important niche – Continued work on use cases, gap analysis, treaty relevance

• WATCHMAN is a natural next step in demonstrating this potential nonproliferation capability

• WATCHMAN also has strong physics potential

• Science community interest in WATCHMAN is strong – 2013 community report mentioned WATCHMAN– April 2014 APS front-page article– Major focus in May 2014 community workshop at LBL– R&D support in 2015 from science funding agencies