Simulation courtesy Jocher/Usman/Learned
NGA and U of Hawaii
WATCHMAN: a WATer CHerenkov Monitor for
ANtineutrinos
Adam Bernstein
Lawrence Livermore National Laboratory
Rare Event Detection Group
Prepared by LLNL under Contract DE-AC52-07NA27344
LLNL-PRES-653915
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Reactors emit huge numbers of antineutrinos
• 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
2
A look back: Small, deployable near field antineutrino detectors
for reactor safeguards
Determine reactor on/off status
Measure thermal
within 5 hours with 99.9% C.L. 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
useful for IAEA reactor safeguards
• Shipper-receiver differences
• Research reactor power
• Safeguards by Design and Integrated Safeguards
8’
3
Long-range reactor monitoring is possible right now– but only for high
power reactors with hard-to-scale technology
~3% of signal from South
Korean reactors
@ 400 km standoff
The KamLAND detector
Per month:
- 16 reactor antineutrinos
- 1 background event
From 130 GWt of reactors
1000 tonnes scintillator
1000 m depth
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Standoff reactor monitoring is an
NNSA Strategic Goal
 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)
5
Ultimate standoff depends on backgrounds from reactors and
natural sources
Science & Global Security, 18:127–192, 2010
Background
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
Global reactor antineutrino fluxes
simulation courtesy Jocher/Learned NGA/UH
•
Gadolinium-doped (light) water
is 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
6
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
7
Possible advantages of remote reactor
monitoring with antineutrinos
• 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
8
Disadvantages and complications
• 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
9
Why is this work of potential interest ?
• 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
• 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
10
Current Water Cherenkov detectors are large, but can’t
identify antineutrinos
20 years of use in neutrino
detection
 IMB, Kamiokande, SuperKamiokande, 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

The SuperKamiokande
50,000 ton water detector
~40 m
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For Water Cherenkov antineutrino sensitivity we need Gadolinium
doping to efficiently detect neutrons in water
Inverse Beta Decay in Theory
e+ p = e+ + n
Inverse Beta Decay 511 keV
in A Detector 511 keV e+
 ~ 8 MeV
e
p
Gd
n
t ~ 30 ms
Neutron captures in LLNL
Gd-H2O detector
World’s first
Gd-H2O
detector @ LLNL
0.25 ton
Neutron captures in SuperK - 4.3 MeV Evis
Neutron source
background
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The WATCHMAN collaboration
A. Bernstein, N. Bowden, S.
Dazeley, D. Dobie
J. Learned, J. Maricic
U of Hawaii
P. Marleau, J. Brennan, M.
Gerling, K. Hulin, J. Steele, D.
Reyna
S. Dye
Hawaii Pacific
M. Vagins, M. Smy
UC Irvine
UC Berkeley
UC Davis
K. Van Bibber, G. Orebi Gann, C.
Roecker, T. Shokair
R. Svoboda, M. Askins, M.
Bergevin
Students getting WATCHMAN-related
Ph.D. s
S.D. Rountree, B. Vogelaar, C.
Mariani, Patrick Jaffke
2 National Laboratories
6 Universities
25 collaborators
15 physicists
5 engineers
2 Post-docs
3 Ph.Ds
World Leaders in the Development and Use of
Large Water Cherenkov Detectors
13
Compared with other large water detector R&D
Detector
Status
Mass (ton)
Type
Purpose
EGADS
WATCHMAN
Hyper-K
Ongoing
2016 start
2021 or beyond
200
1,000
500,000
Gd-WCD
Gd-WCD
Pure H2O or Gd-WCD
Measure background,
material compatibility,
energy threshold
Too 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 big
detectors
14
WATCHMAN Program Plan
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
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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Two Possible Use Cases Large Detectors
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
 More
 Low
 Higher
background levels
complex
• Requires knowledge of signal from
declared reactors
backgrounds due to
other reactors
 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
 Adjusting
power of declared
reactors is a potential
countermeasure
Not yet claiming significance for any particular Treaty or Agreement
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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
Reactor Location
Thermal Power (MWt)
Detector Location
Standoff
Overburden (mwe)
Approval status
Physics potential
Preferred
PERRY Reactor
Perry Ohio
Alternate
Advanced Test Reactor,
Idaho Falls, Idaho
3875
120
Morton Salt/IMB mine (!)
New excavation
Painesville, Ohio
Idaho National Laboratory
13 km - the only reactor in the US at a
1 km
suitable distance from a deep mine
1430
~360
Morton Salt has approved
installation
INL has approved
excavation studies
Greater physics potential due to
greater depth
19
Antineutrino
signal and background
Backgrounds:
Signal in 1 kiloton of water
511 keV
511 keVe+
e
prompt
p
n
e+
m
Gd
1. Real antineutrinos
2. Random event pair coincidences
3. Muon induced high energy
neutrons
4. Long-lived radionuclide decays
 ~ 8 MeV
t ~ 30 ms
n
signal + n capture on Gd
n
9Li
b
(100-200 MeV
n
m
• Exactly two Cerenkov flashes
• within ~100 microseconds
• Within a cubic meter voxel
Very different from most backgrounds
20
Full Signal and Background Monte Carlo
at the PERRY reactor site
Depth Dependent
per day
• Fast Punch-through Neutrons
• Radionuclides  not well known
~1
~1-10
Depth-Independent
• PMT and Rock Gamma/Neutrons
~1
Other Reactors
<1
Geo-antineutrinos
negligible
___________________________________________
Total Background
~10
Perry Reactor Signal
8-12
21
Preliminary Design Task
• 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
78
feet
Drift layout at Morton Salt Mine
Close-up of Veto PMT Wall
22
Background Measurements at the
Kimballton Underground Research Facility
• Drive in access down to
1500 foot depth
• First-ever continuous
measurement as a
function of depth
Entering KURF
• Most important at
shallow depths
(300 feet, alternative
site)
• Final measurement
will be at the 1400 foot
depth of preferred site
Small version of WATCHMAN
(WATCHBOY)
to measure muogenic
radionuclide backgrounds
Multiplicity and Recoil Spectrometer
for fast neutron energy spectrum
23
Physics Synergy
WATCHMAN will provide:
• The U.S.’s only and one of the world’s largest
supernova detectors
•
A test facility for future large neutrino detectors
(advanced PMTs, water-based scintillator…)
WATCHMAN may also measure:
• the ordering of the neutrino masses
– a major question for 21rst century physics
• a proposed 4th neutrino flavor
(e, m, t ?)
• non-standard neutrino interactions
Requires
upgrade
to scint.
Requires
nearby
neutrino
beam
Science funding agency co-investment is critical to the project’s success
‘Positive dual-use’ aspect strengthens the case for long-range monitoring
24
Underground Detectors for Supernova Neutrinos
WATCHMAN
(400 events)
SNO+
(400)
LVD (400)
Borexino (100)
Baksan
(100)
Super-K (104)
KamLAND (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 pointing
capability to the supernova source in the sky
IceCube (106)
Georg Raffelt, MPI Physics, Munich
In brackets events
for a “fiducial SN”
at distance 10 kpc
ISOUPS, Asilomar, 24–27 May 2013
Isotope Decay at Rest (ISODAR) neutrino source at 16
meters could extend WATCHMAN physics
1. Sterile neutrino search
2. Non-standard interactions/Weinberg angle
arXiv:1205.4419v2
arXiv:1307.5081v1
ISODAR (green) improves
significantly
on previous constraints
from LSND (red)
and TEXONO (blue)
1
gL = sin 2 qW , gR = + sin 2 qW
2
ISODAR (solid) has outstanding sensitivity to sterile
neutrinos (not affected by the reactor)
• 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
gLand gR modifications seen
in anomalous n e + e- ® n e + e- rate
• Issues under study:
• Accelerator deployment feasiblity
and mine acceptance
• Oil or water-based scintillator may
be needed
• 2014 WATCHMAN decision will
precede accelerator availabilty
Sensitivity of WATCHMAN to sterile neutrino
oscillations using the ISODAR beam - examples
Predicted
Expected
measurement
Observed/Predicted
1.000
0.950
0.900
! m2 = 1.0 eV2
Pure Water
sin22² ee = 0.1
0.850
0
1
2
3
4
5
6
7
L/E (m/MeV)
Oscillation patterns for a sterile neutrino
ISODAR 6 MeV antineutrino source
16 meter standoff from detector center
Observed/Predicted
1.000
0.950
0.900
! m2 = 1.0 eV2
0.850
0
Plots courtesy of Mike Shaevitz, Columbia U.
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2
3
4
L/E (m/MeV)
5
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1.000
Observed/Predicted
Pure water, 1% scintillator and
pure scintillator options
Light Scintillator
sin22² ee = 0.1
total flux: 0.14
eff_det: 0.60 e
beta-decay endp
mass: 1000.0
nyrs_dat_array:
elimit_factor =
sinsq2th_limit d
Smearing box s
Using Kamland
norm error: 0.
Eend error: 0.
0.7861E-02 1
L/E Result for dm
ile
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0.950
0.900
! m2 = 1.0 eV2
Pure Scintillator
sin22² ee = 0.1
0.850
0
1
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Watchman dm
Conclusions
• 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
28