Prospects for the Use of Large Water-Based Anti-neutrino Detectors for Monitoring Fission Bomb Detonations

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Prospects for the Use of Large Water-Based
Anti-neutrino Detectors for Monitoring Fission
Bomb Detonations

• Eugene Guillian, Queens University
• John G. Learned, University of Hawaii

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Monitoring Rogue Nuclear Activity with
Anti-neutrino Detectors

• Two types rogue nuclear activities that have
  anti-neutrinos as a by-product

Objective Activity to Achieve Objective
Production of weapons-grade plutonium Operation of breeder-reactor
Fission bomb design tests Detonation of fission bomb

• Signatures of the above activities

Breeder Reactor Anti-neutrinos produced at a steady rate Reactor fuel is replaced prematurely to avoid poisoning with 240Pu
Fission Bomb Almost all anti-neutrinos produced in a burst of 10 seconds Accompanied by other signatures (CTBTO monitoring)
focus on fission bomb detection in this talk
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Motivation to Employ Neutrino Monitoring

• Neutrinos cannot be shielded, hidden or faked.
• Neutrino flux proportional to nuclear weapon
  energy.
• CTBT methods (seismic, infrasound, air sampling)
  while well established, signatures can be hidden
  and have large errors.
• Nuclear tests have been missed in the past, and
  also false accusations have been made.
• In recent times there have been strong
  suggestions that DPRK weapon test may have not
  been nuclear. Neutrinos could resolve questions.
• The long known problem of employing huge neutrino
  detectors is now within our science and
  technology horizon.

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Anti-neutrinos Produced by a Fission Bomb

• The bomb yield is typically quoted in
  TNT-equivalent units
• 1 kilo-tonne TNT 4.184 ? 1012 Joule
• The amount of thermal energy released by a single
  fission event
• ? 204 MeV ? 3.3 ? 10-11 Joule
• The number of fissions per kilo-tonne of yield

Fission Rate of a Nuclear Reactor Rfiss 3.1 ?
1019 fissions/sec/GWt

• Fission anti-neutrinos are produced in a burst of
  about 10 seconds

A. Bernstein, T. West, V. Gupta An assessment
of Antineutrino Detection as a Tool for
Monitoring Nuclear Explosions
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Anti-neutrino Detection Method

• The currently available mature technology is
  based on inverse beta decay on a free proton
  target

Prompt energy deposition

• Captured after a delay of 101 102 ms
• Gamma ray emission produces delayed energy
  deposition

• The delayed coincidence greatly reduces the
  background noise
• A feasible detector needs to have a mass of about
  1 Mega-ton or greater
• The only economically viable detector with
  current technology is H2O loaded with a neutron
  absorber (Gd or Cl)

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Anti-neutrino Detection Rate

• Factors that determine the detection rate

Factor Symbol Units
Bomb Yield E kilo-tonne TNT
Distance to Detonation Site R 100 km
Cross Section of Target s(En) cm2

• Inverse Beta Cross Section

• Anti-neutrino Fluence _at_ 100 km

i.e. number of anti-neutrinos per unit area
Most anti-neutrinos are detected in this energy
window
En Thresh. (MeV) Detector Fluence (cm-2 kton-1)
0 N/A 5?108
1.8 Liq. Scint. 2?108
3.4 Liq. Scint. 0.5?108
3.8 Gd-loaded H2O 0.3?108
Detection Threshold
Cross Section 10-42 cm2
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Anti-neutrino Detection Rate

• Detecting a 1 kton bomb at 100 km

0.3 ? 108 cm-2
10-42 cm2
?

10-35
Number of antineutrinos per cm2 from bomb above
detection threshold
Typical interaction cross section
Probability of interacting with a target proton

• In order to detect 1 anti-neutrino, the detector
  needs
• 1035 free protons

100 m
This is about 1 mega-ton of H2O
100 m
100 m
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Anti-neutrino Detection Rate

• More precisely

Symbol Units Description
E kton TNT Energy from bomb
N 1035 free protons Number of free protons in detector
R 100 km Distance between the bomb detonation site and the detector

• Other Factors

Neutrino Survival Probability 0.57
Event Selection Cut Efficiency 0.86
Combined Rate Reduction Factor 0.49
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Detector Mass Units

• 1035 free protons in H2O corresponds to 1.5
  Mega-ton H2O
• The anti-neutrino detection rate in terms of H2O
  mass becomes

Symbol Units Description
E kton TNT Energy from bomb
M Mega-ton H2O Mass of H2O
R 100 km Distance between the bomb detonation site and the detector
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Anti-neutrino Detector Mass versus Distance
10 yield estimate
30 yield estimate
Confirmatory evidence
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Background Noise
Background Source Measures Taken to Eliminate Background Assumed Background Level
Cosmic Ray Overburden gt 3000 m.w.e. 0
Internal Radioactivity Use existing purification techniques and require delayed coincidence 0
Geo-neutrinos Prompt event below detection threshold 0
Reactor Anti-neutrinos Irreducible See Below

• Use North Korea as a model case
• The plot to the left shows the number of reactor
  anti-neutrino detection events in a 10 second
  window from all registered nuclear reactors in
  the world (from ANLs INSCDB)
• Most of the anti-neutrinos come from South Korea
  and Japan
• For North Korea monitoring, the background rate
  is about 0.01 0.1 events per 10 sec. for a 1
  megaton detector

DPRK
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Test Scenario North Korea, October 9, 2006
Information Regarding the Alleged October 9, 2006 Bomb Detonation Information Regarding the Alleged October 9, 2006 Bomb Detonation
October 3 North Korea announces its intention to perform a test detonation
20 minutes before detonation China notified of imminent test. This information was immediately relayed to Washington D.C.
013527 UTC (103527 a.m. local time, UTC9), October 9, 2006 USGS records a seismic event (4.2 Richter scale) at 4117'38.4?N, 12908'2.4?E
Early seismic estimates by South Korea Earthquake magnitude 3.58 Richter scale ? 0.1 0.8 kton bomb
Revised seismic estimates from several independent sources 4.2 Richter scale ? 212 kton bomb
October 14 US government reports finding radioactive isotopes in the atmosphere, presumably from the detonation
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Detonation Site

• An underwater detector could have been as close
  as 110 km in international waters.

4117'38.4?N 12908'2.4?E
100 km
200 km
300 km
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Detecting the Bomb

• 6 days advance notice was given
• But the location was not known (in public press)
• Perhaps intelligence organizations had some idea?
• If the detector is a submarine-type, it may be
  moved around. But 6 days may not be enough time.
• Of course, in general, advance notice should not
  be expected

• Realistically, the detectors should be placed
  strategically along the land border or in
  international waters.

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Test Case 1 Got Lucky

• A 1 Mton detector happened to be located as close
  as possible
• A private report by Makai Ocean Engineering (Oct.
  11, 2006)
• The closest distance to a depth of 3000 m of
  ocean was about 110 km
• Location about 130.5º E, 41º N

99 detection probability and 30 yield estimate
for 10 kiloton weapon
Signal Rate 0.91 events/kton TNT
Background Rate 0.01 events/10 sec
60 chance of detecting a 1 kton bomb

• Background noise 1 event per 1000 sec.

Stand-alone mode Cannot tell event from background
Input from CTBTO-type monitoring 1 chance of background event occurring in 10 sec. window
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Test Case 2 One 1 Mt Detector along East Coast
of North Korea

• Typical distance 150 km

Signal Rate 0.49 events/kton TNT
Background Rate 0.01 events/10 sec
1 kiloton yield gt 38 detection probability
10 kiloton yield gt 99 detection probability
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Test Case 3 Require 99 Detection Probability
under Optimal Conditions

• Optimal Condition
• We got lucky, and the detector was 110 km from
  bomb detonation site
• 99 detection probability requires 4.6
  anti-neutrinos detected
• from 1 kton bomb,
• then we require a detector mass given by

1
MDet 5.1 Mega-ton
4.6
(1.1)2
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Test Case 4 99 Detection for Typical Distance

• Same as previous slide, but R 150 km requires

MDet 9.4 Mega-ton
And if yield were 10 kiloton, we would detect 49
events on average, for a 14 yield measurement.
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Test Case 5 Stand-alone Running

• Require lt 1 false positive events from nuclear
  reactors for 1 year of running
• 1 year ? 3.16 ? 106 10 second windows (trials)
• Background rate 0.01 events / 10 seconds

N Background Events/10 sec. Poisson Probability of N per 10 sec interval Number of occasions per 100 years
1 9.9 ? 10-3 3.13 x 106
2 5.0 ? 10-5 1.58 x 104
3 1.7 ? 10-7 53.7
4 4.1 ? 10-10 0.13
Typical Location Detector Mass
Optimal Location Detector Mass
1 kT
4.4 Mega-ton
8.2 Mega-ton
Hence require gt 4 events
10 kT
0.4 Mega-ton
0.8 Mega-ton
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Test Case 6 Complete Coverage

• So far, we have considered detector
  configurations that can detect detonations along
  the eastern coast of northern North Korea
• What would be required for complete coverage?

• Based on the map, it appears that about 6
  detectors placed strategically along the border
  will cover most of North Korea within a distance
  of 300 km

• Detector mass requirement

1 detector _at_ 300 km 8.1 Megaton per event
6 detectors 48 Megatons per event

• Multiply the above by the required number of
  detected events
• 4.6 events for 99 detection probability
• gt 4 events for 99 rejection of false positive
  for 1 year of running

An array of about 6 strategically placed
detectors of total mass 220 Mega-ton could cover
all of North Korea with 99 detection probability
and 99 false positive rejection per year
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Cost Scale

• Consider a 1 Megaton module to be a cube of sides
  100 m
• Photodetector costs set overall scale
• Require 40 present technology photo-cathode
  coverage
• 118k 20 PMTs / 453k 10 PMTs
• 2k per PMT ? 0.20.9 billion dollars
• Total cost on the order of 1 billion
  dollar/detector
• Typical cost of new large HEP experiments,
  telescopes, satellites
• Maximum stand alone coverage of PRK, array scale
  
• 220 Mega-ton ? 220 billion
  dollars
• New Photodetection technology can lower
  photodetector cost by factor of 10-100
• Need decade of development

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Test Case Conclusion

• With current technology and under optimal
  conditions, a 1 Mega-ton Gd/Cl-doped H2O detector
  had a 60 chance of confirming the Oct. 6, 2006
  alleged nuclear detonation, assuming a 1 kton TNT
  yield 99 if yield was 10 kT
• Given a 9.4 Megaton detector placed at a typical
  location along the north-east coast of North
  Korea, the detection probability would have been
  99. This size also rejects false-positive
  detection at the 99 level.
• The present cost per Megaton is estimated at 1
  Billion US
• Given tens of billions of dollars, one can
  monitor most of the east coast of North Korea
• Given hundreds of billions of dollars, one can
  stand-alone monitor most of North Korea

Summary Large water Cherenkov based
anti-neutrino detectors can play a critical role
in detection and measurements of clandestine
nuclear weapons testing. Technology
development, particularly of photodetection and
studies should proceed, as should development of
prototype detectors.