december 16, 2005eugene h. guillian / neutrino geophysics conference1 far-field monitoring of rogue...
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December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Far-field Monitoringof
Rogue Nuclear Activitywith an
Array of Large Antineutrino Detectors
Neutrino Geophysics Conference
University of Hawaii, Manoa
December 14-16, 2005
Eugene H. GuillianUniversity of Hawaii, Manoa
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Rogue Nuclear Activity
Two Types: Fission Reactor Fission Bomb
Purpose:Produce
weapons-grade material
Test to make sure bomb explodes
Size: < ≈ 100 MWth 1 kton TNT
Commercial Reactor≈ 2500 MWth
First Atomic Bombs10-20 kton
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Characteristics of Rogue Nuclear Activity
(1) Small compared to “normal” activities
(2) Operated by a “hostile” regime
Need large detector to compensate for small signal
Won’t be allowed to monitor nearby (≈100 km)
Signal decreases as 1 / distance2
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Detector Module Specifications
(1) Required target mass > ≈ 1 Megaton
(2) Required exposure time ≈ 1year (reactor)(10-second burst for bomb)
100 m
100
m
100 m
(3) Target material Water + 0.2% GdCl3
Cheap Enable Antineutrino
DetectionGADZOOKS!
Super-K with Gadolinium
J. F. Beacom & M. R. Vagins, Phys. Rev. Lett. 93, 171101 (2004)
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Detection Mechanism
€
ν e + p→ n + e+Inverse Beta Decay
Delayed Event
≈ 20µs
n + Gd Gd + cascade
Evis ≈ 3~8 MeV
Prompt Event
Cherenkov radiation
€
Ee+ ≈ Eν −1.3 MeV
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Neutrino Energy Spectrum
GADZOOKS! Threshold
• Eν > 3.8 MeVKamLAND Threshold
• Eν > 3.4 MeV
GADZOOKS! Efficiency58% of entire spectrum (Eν > 1.8 MeV)82% of KamLAND efficiency
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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A Very Basic Look at the Detector Hardware
100 m
100
m
100 m
Photo-Sensor Requirement≈ 120,000 units (10 Super-Kamiokande)
Gadolinium2000 metric tons
Water Purification200 Super-Kamiokande’s capacity
~$120 Million @ $1000 per unit
~$10 Million @ $3 / kg
Cost?
The cost of just one module looks to be easily about $500 Million!
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Is a Megaton Module Outlandish?
The linear dimensions are not that much larger than those of
Super-Kamiokande
Challenges• Deep-Ocean environment
• Remote operations• Mega-structure
engineering
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Shielding from Cosmic Rays
Super-Kamiokande
• Shielded by 1000 m of rock (equivalent to 2700 m of
water)• Mitsui Mining Co. property
Super-Kamoikande (SNOLAB, Gran Sasso, Baksan, Homestake, IMB, etc.)
would have cost too much if shielding had to be erected from scratch!
For the megaton module array, we assume that cost of shielding on land is prohibitive.
Ocean & Lake = Affordable Shielding
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Array Configurations
Global1. 5° 5°2. Equidistant3. Coast-
Hugging
RegionalNorth Korea
• ≈ 1000 modules• 10 Megatons per module• 1 year exposure
• Several modules• 1 Megaton per module• 1 year exposure
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Global Array 15º 5º Array Total of
1596 modules
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Global Array 2Equidistant Array
Total of 623 modules
Minimum nearest-neighbor
distance ≈ 600 km
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Global Array 3Coast-hugging Array Total of
1482 modulesMinimum
nearest-neighbor
distance ≈ 100 kmModules
removed from coast line by ≈
100 km
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Regional ArrayNorth Korea
€
log10 S / S + B
Choose locations based on sensitivity map
(red dots are candidate module positions)
• 250 MWth fission reactor deep inside
of North Korea• Background from commercial nuclear
reactors
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Rogue Activity Detection Strategy
Log-Likelihood Function
Input Output(1) Hypothesis
(2) Observation
Log-likelihood function
value
€
B1,B2,B3,{ L ,Bn}
“No rogue activity is taking place” Bi events expected in detector “i”
€
N1,N2,N3,{ L ,Nn}
Ni events observed in detector “i”
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Scenario 1: No Rogue Activity
Log-Likelihood Function
Input Output
(1) Hypothesis
(2) Observation
Large value
Hypothesisagrees with
Observation!
(most of the time…)
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Scenario 2: Small Rogue Activity
Log-Likelihood Function
Input Output
(1) Hypothesis
(2) Observation
Slightly biased
to lower values
(but can’t distinguish from null hypothesis)
Hypothesismaybe agrees with
Observation, but maybe not!
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Scenario 3: Large Rogue Activity
Log-Likelihood Function
Input Output
(1) Hypothesis
(2) Observation
Biased to lower values
Hypothesisdisagrees withObservation!
Confidently reject null hypothesis
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Likelihood Distribution for Scenario 1
• The value varies from measurement to measurement because of statistical variation• The distribution is known a priori
1% False Positive
If value < threshold, ALARM!
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Likelihood Distribution for Scenario 2
If the rogue power is small, the bias is too small
Large overlap with null distribution
False negative happens too often
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Likelihood Distribution for Scenario 3
Define a quantity called “P99”
P99 = the power above which the chance of false negative is < 1%
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Illustration of the Detection Strategy
If no rogue activity takes
place, module 1, 2, & 3 detects B1, B2, and B3 events
The size of the excess goes as:
Power / Distance2
With rogue activity, module 1, 2, and 3 sees an extra S1, S2, and S3 events
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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B = # background events
S = # signal events
Signal Strength
€
B= statistical uncertainty
Signal Strength
€
B
SS
€
B
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Map of Signal Strength
Rogue Activity
2000 MWth
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Equidistant Detector Array Configuration10 Megaton per module
1 year exposure
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Detectors with Signal Strength > 3
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Detectors with Signal Strength > 2
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Detectors with Signal Strength > 1
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Signatures of Rogue Activity
(1)Log-likelihood function is below threshold
(2)Cluster of near-by detectors with significant excess
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Global Array Performance
• For each array configuration, make a map of P99
• Procedure for making map:1. Vary the rogue reactor position2. At each location, determine P99
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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P99 Map for 5° 5° Array
MWth
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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P99 Map for Equidistant Array
Scaled to 1596 Modules MWth
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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P99 Map for Coast-hugging Array
Scaled to 1596 Modules MWth
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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5º 5º
Equidistant
Coast-Hugging
P99 Summary
Location
P99
In Water< 100 MWth
W/in several
100 km of coast
Several 100 MWth
Deep in continent
Up to 2000 MWth
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Regional Monitoring
Example:• A rogue reactor in North Korea
Signal
Background
Signal StrengthAbout the Plots
Signal
• Rogue power = 250 MWth
• Detector mass = 1 Megaton• Exposure = 1 year
Background
• Commercial nuclear reactors• 1 Megaton• 1 year
€
log10 S
€
log10 B
€
log10 S / S + B
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Detector Locations
€
log10 S / S + B
23 candidate locations based on map of sensitivity
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Performance of Various Array Configurations
Consider configurations with 2, 3, and 4 detector modules
For each configuration, determine:• P99
• Probable location of rogue reactor
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Two Modules
95% Confidence
99% Confidence
P99 = 250 MWth
• Confidence = probability that rogue activity is taking place inside of band• 2 saturates above 20 in the map
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Two Modules
95% Confidence
99% Confidence
P99 = 120 MWth
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Three Modules
95% Confidence
99% Confidence
P99 = 626 MWth
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Four Modules
95% Confidence
99% Confidence
P99 = 336 MWth
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Four Modules
95% Confidence
99% Confidence
P99 = 502 MWth
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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What if a Georeactor Exists?
The Georeactor Hypothesis:• Unorthodox, but surprising things can happen….• If it does exist, its power is likely to be 1-10 TWth
Total commercial nuclear activity ≈ 1 TWth
If a terawatt-level georeactor does exist, the background
level for rogue activity monitoring increases
significantly!
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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log10 BackgroundNo Georeactor
log10 Background3 TWth Georeactor
Ratio3 TWth / No Georeactor
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Fission Bomb Monitoring
Fission Bomb• Assume 100% detection efficiency for En > 1.8 MeV• Integrated over 10 sec. burst time
€
2.25 events ⋅V
106 m3
⎛
⎝ ⎜
⎞
⎠ ⎟⋅
100 km
D
⎛
⎝ ⎜
⎞
⎠ ⎟2
⋅Y
1 kiloton
⎛
⎝ ⎜
⎞
⎠ ⎟
The background from reactors is small (in most places) because of the 10-
second window
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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log10 (signal) from 1-kiloton bomb just north of Hawaii
log10(background) from commercial
reactors
log10(S/sqrt(S+B))
For all three plots:•10-Megaton modules•10-second exposure
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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log10(background) from commercial reactors + 3 TWth
georeactor
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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“Y99” for Bomb Monitoring
kton TNT
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Conclusions• Untargeted global monitoring requires a very large array
≈ 1000 modules 10-Megaton per module 1-year exposure time
• A targeted regional monitoring regime looks credible
Several modules 1-Megaton per module 1-year exposure time
P99 ≈ 100 MWth and localization within 100 km are attainable if:
1. At least one module is placed at about 100 km from the rogue activity
2. At least three modules are placed strategically at greater distances
• The existence of a terawatt-level georeactor increases the background level significantly
This must be established before-hand Experiments like Hano Hano are crucial
• Obstacles toward realizing far-field monitoring
Cost (several $100 million per module)Lack of experience with deep-ocean environment
• In Summary: Targeted regional monitoring can deter rogue activity at a realistic level at a cost of several billion dollars The detector technology is mostly well- established Uncertainty with deep-ocean environment New developments in photo-detector technology would help greatly
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Cosmic Ray Background
• Like bullets!• Occasionally they destroy atomic nuclei
Unstable nuclei
Sometimes indistinguishable from antineutrinos!
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Array ConfigurationsGlobal Monitoring
RegimeRegional Monitoring
RegimeWant sensitivity to anywhere on
EarthWant sensitivity to a well-defined
region
Can’t optimize module positioning
Module positions can be optimized because of prior
knowledge of likely locations
Larger Modules Required• 10 Megatons• 1 year exposure
Smaller Modules Will Do• 1 Megatons• 1 year exposure
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Rogue Activity Detection Strategy
(1) Assume that no rogue activity is taking place
(2) If this assumption is incorrect AND if the rogue activity is sufficiently large, there would be a discrepancy between observation & expectation(3) Use a statistical technique (minimum log-likelihood) to
estimate the position & power of the rogue activity
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Seeing the Rogue Activity Above Random Fluctuations
ObservedNumber
ofEvents
Backgroundonly
ObservedNumber
ofEvents
Small Signal + Background
RandomStatistical
Fluctuation
Large Signal + Background
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Antineutrino Detection Rate for H2O + GdCl3
Detector
€
3040 Events ⋅T
1 year
⎛
⎝ ⎜
⎞
⎠ ⎟⋅
V
106 m3
⎛
⎝ ⎜
⎞
⎠ ⎟⋅
100 km
D
⎛
⎝ ⎜
⎞
⎠ ⎟2
⋅P
100 MWth
⎛
⎝ ⎜
⎞
⎠ ⎟
€
2.25 events ⋅V
106 m3
⎛
⎝ ⎜
⎞
⎠ ⎟⋅
100 km
D
⎛
⎝ ⎜
⎞
⎠ ⎟2
⋅Y
1 kiloton
⎛
⎝ ⎜
⎞
⎠ ⎟
Reactor• Assume 100% detection efficiency for En > 1.8 MeV
Fission Bomb• Assume 100% detection efficiency for En > 1.8 MeV• Integrated over 10 sec. burst time
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Antineutrino Detection Rate for H2O + GdCl3
Detectors
€
832 Events ⋅T
1 day
⎛
⎝ ⎜
⎞
⎠ ⎟⋅
V
109 m3
⎛
⎝ ⎜
⎞
⎠ ⎟⋅
1000 km
D
⎛
⎝ ⎜
⎞
⎠ ⎟2
⋅P
1 GWth
⎛
⎝ ⎜
⎞
⎠ ⎟
€
22.5 events ⋅V
109 m3
⎛
⎝ ⎜
⎞
⎠ ⎟⋅
1000 km
D
⎛
⎝ ⎜
⎞
⎠ ⎟2
⋅Y
1 kiloton
⎛
⎝ ⎜
⎞
⎠ ⎟
Reactor• Assume 100% detection efficiency for En > 1.8 MeV
Fission Bomb• Assume 100% detection efficiency for En > 1.8 MeV• Integrated over 10 sec. burst time
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Background ProcessesAntineutrinos from
sources other than the rogue reactor
Non-antineutrino background mimicking
antineutrino events
• Commercial nuclear reactors• Geo-neutrinos• Georeactor (possibly)
• Cosmic rays• Radioactivity in the detector
• Require En > 3.4 MeV
• Place detector at > 3 km depth under water• Fiducial volume cut + radon free environment
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Antineutrino Detection with a H2O + GdCl3
DetectorInverse beta decay on target hydrogen nuclei
ne + p n + e+ Prompt Event
Delayed Event
En > 1.8 MeVEe ≈ En – 1.3 MeV
Detector Threshold: Ee > 2.5 MeV
En > 3.8 MeV
Physics Threshold:≈ 20 µs
n + Gd Gd*
Ecascade ≈ 3~8 MeV
Gd + g cascade
90% neutron captured by Gd @ 0.2% concentration
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Commercial Nuclear Reactors
• 433 reactors• Total thermal power ≈ 1 TW
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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The effect of commercial nuclear
reactors on the detection
sensitivity for a rogue nuclear
reactor Assume that a rogue reactor with P = 250 MWth is operating just north of Hawaii
Top:
Middle:
Bottom:
log10 S
log10 B
€
log10 S / S + B
# events from rogue
reactor# events
from commercial
reactors
3.5
7.0
1.5
• Detector target mass = 10 megatons• 1 year exposure• Detectors allowed only in oceans & large lakes• 100% detection efficiency
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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Possible Detector Locations
23 Locations based on S/sqrt(S+B)
log10(S)
log10(B)
€
log10 S / S + B
Map of S, B, and S/sqrt(S+B) for 1 megaton target
exposed for 1 year
December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference
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If a Geo-Reactor Exists…
• If it does exist, its power is expected to be 1 ~ 10 TWth, 3 TWth being the most favored value.
• The total power from all commercial reactors world-wide ≈ 1 TWthIn most locations around the world, antineutrinos
from a georeactor would outnumber those from commercial reactors
€
2.25 ×104 Events T
1 year
⎛
⎝ ⎜
⎞
⎠ ⎟⋅
M
1 Megaton
⎛
⎝ ⎜
⎞
⎠ ⎟ 3 TWth Georeactor