Far-field Monitoring of Rogue Nuclear Activity with an Array of Large Antineutrino Detectors Neutrino Geophysics Conference University of Hawaii, Manoa December 14-16, 2005 Eugene H. Guillian University of Hawaii, Manoa December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 1
Rogue Nuclear Activity Two Types: Fission Reactor Fission Bomb Purpose: Produce weaponsgrade material Test to make sure bomb explodes Size: < 100 MW th 1 kton TNT Commercial Reactor 2500 MW th First Atomic Bombs 10-20 kton December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 2
Characteristics of Rogue Nuclear Activity (1) Small compared to normal activities Need large detector to compensate for small signal (2) Operated by a hostile regime Won t be allowed to monitor nearby ( 100 km) Signal decreases as 1 / distance 2 December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 3
Detector Module Specifications (1) Required target mass > 1 Megaton (2) Required exposure time 1year (reactor) 100 m 100 m (10-second burst for bomb) 100 m (3) Target material Water + 0.2% GdCl 3 GADZOOKS! Super-K with Gadolinium Cheap Enable Antineutrino Detection J. F. Beacom & M. R. Vagins, Phys. Rev. Lett. 93, 171101 (2004) December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 4
Detection Mechanism Inverse Beta Decay ν e + p n + e + 20µs Prompt Event Cherenkov radiation E e + E ν 1.3 MeV Delayed Event n + Gd Gd + γ cascade E vis 3~8 MeV December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 5
Neutrino Energy Spectrum GADZOOKS! Threshold E ν > 3.8 MeV KamLAND Threshold E ν > 3.4 MeV GADZOOKS! Efficiency 58% of entire spectrum (E ν > 1.8 MeV) 82% of KamLAND efficiency December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 6
A Very Basic Look at the Detector Hardware 100 m 100 m 100 m Photo-Sensor Requirement ~$120 Million @ $1000 per unit 120,000 units (10 Super-Kamiokande) Gadolinium ~$10 Million @ $3 / kg 2000 metric tons Water Purification Cost? 200 Super-Kamiokande s capacity The cost of just one module looks to be easily about $500 Million! December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 7
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 8
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 9
Array Configurations Global 1. 5 5 2. Equidistant 3. Coast-Hugging 1000 modules 10 Megatons per module 1 year exposure Regional North Korea Several modules 1 Megaton per module 1 year exposure December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 10
Global Array 1 5º 5º Array Total of 1596 modules December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 11
Global Array 2 Equidistant Array Total of 623 modules Minimum nearestneighbor distance 600 km December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 12
Global Array 3 Coast-hugging Array Total of 1482 modules Minimum nearestneighbor distance 100 km Modules removed from coast line by 100 km December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 13
Regional Array North Korea log 10 S / S + B 250 MW th fission reactor deep inside of North Korea Background from commercial nuclear reactors Choose locations based on sensitivity map (red dots are candidate module positions) December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 14
Rogue Activity Detection Strategy Input Output (1) Hypothesis No rogue activity is taking place B i events expected in detector i { B 1,B 2,B 3, L,B n } (2) Observation N i events observed in detector i { N 1,N 2,N 3, L,N n } Log-Likelihood Function Log-likelihood function value December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 15
Scenario 1: No Rogue Activity Input Hypothesis agrees with Observation! Output (1) Hypothesis (2) Observation Log-Likelihood Function Large value (most of the time ) December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 16
Scenario 2: Small Rogue Activity Input Hypothesis maybe agrees with Observation, but maybe not! Output (1) Hypothesis (2) Observation Log-Likelihood Function Slightly biased to lower values (but can t distinguish from null hypothesis) December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 17
Scenario 3: Large Rogue Activity Input Hypothesis disagrees with Observation! Output (1) Hypothesis (2) Observation Log-Likelihood Function Biased to lower values Confidently reject null hypothesis December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 18
Likelihood Distribution for Scenario 1 The value varies from measurement to measurement because of statistical variation The distribution is known a priori If value < threshold, ALARM! 1% False Positive December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 19
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 20
Likelihood Distribution for Scenario 3 Define a quantity called P 99 P 99 = the power above which the chance of false negative is < 1% December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 21
Illustration of the Detection Strategy If no rogue activity takes place, module 1, 2, & 3 detects B 1, B 2, and B 3 events With rogue activity, module 1, 2, and 3 sees an extra S 1, S 2, and S 3 events The size of the excess goes as: Power / Distance 2 December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 22
Signal Strength S = # signal events Signal Strength B = statistical uncertainty B = # background events S B S B December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 23
Map of Signal Strength Rogue Activity 2000 MW th December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 24
Equidistant Detector Array Configuration 10 Megaton per module 1 year exposure December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 25
Detectors with Signal Strength > 3 December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 26
Detectors with Signal Strength > 2 December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 27
Detectors with Signal Strength > 1 December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 28
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 29
Global Array Performance For each array configuration, make a map of P 99 Procedure for making map: 1. Vary the rogue reactor position 2. At each location, determine P 99 December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 30
P 99 Map for 5 5 Array MW th December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 31
P 99 Map for Equidistant Array Scaled to 1596 Modules MW th December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 32
P 99 Map for Coast-hugging Array Scaled to 1596 Modules MW th December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 33
P 99 Summary 5º 5º Location P 99 In Water W/in several 100 km of coast Deep in continent < 100 MW th Several 100 MW th Up to 2000 MW th Equidistant Coast-Hugging December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 34
Regional Monitoring Signal log 10 S Example: A rogue reactor in North Korea Background log 10 B Signal About the Plots Rogue power = 250 MW th Detector mass = 1 Megaton Exposure = 1 year Signal Strength log 10 S / S + B Commercial nuclear reactors Background 1 Megaton 1 year December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 35
Detector Locations log 10 S / S + B 23 candidate locations based on map of sensitivity December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 36
Performance of Various Array Configurations Consider configurations with 2, 3, and 4 detector modules For each configuration, determine: P 99 Probable location of rogue reactor December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 37
Two Modules P 99 = 250 MW th 99% Confidence 95% Confidence Confidence = probability that rogue activity is taking place inside of band Δχ 2 saturates above 20 in the map December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 38
Two Modules P 99 = 120 MW th 99% Confidence 95% Confidence December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 39
Three Modules P 99 = 626 MW th 99% Confidence 95% Confidence December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 40
Four Modules P 99 = 336 MW th 99% Confidence 95% Confidence December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 41
Four Modules P 99 = 502 MW th 99% Confidence 95% Confidence December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 42
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 TW th Total commercial nuclear activity 1 TW th 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 43
log 10 Background No Georeactor Ratio 3 TW th / No Georeactor log 10 Background 3 TW th Georeactor December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 44
Fission Bomb Monitoring Fission Bomb Assume 100% detection efficiency for E n > 1.8 MeV Integrated over 10 sec. burst time V 100 km 2.25 events 10 6 m 3 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 45
log 10 (signal) from 1-kiloton bomb just north of Hawaii log 10 (background) from commercial reactors log 10 (S/sqrt(S+B)) December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 46 For all three plots: 10-Megaton modules 10-second exposure
log 10 (background) from commercial reactors + 3 TW th georeactor December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 47
Y99 for Bomb Monitoring kton TNT December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 48
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 P 99 100 MW th 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 wellestablished Uncertainty with deep-ocean environment New developments in photo-detector technology would help greatly December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 49
Appendix December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 50
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 51
Array Configurations Global Monitoring Regime Want sensitivity to anywhere on Earth Regional Monitoring Regime Want 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 52
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 53
Seeing the Rogue Activity Above Random Fluctuations Observed Number of Events Observed Number of Events Random Statistical Fluctuation Large Signal + Background Background only Small Signal + Background December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 54
Antineutrino Detection Rate for H 2 O + GdCl 3 Detector Reactor Assume 100% detection efficiency for E n > 1.8 MeV T V 100 km 3040 Events 1 year 10 6 m 3 D 2 P 100 MW th Fission Bomb Assume 100% detection efficiency for E n > 1.8 MeV Integrated over 10 sec. burst time V 100 km 2.25 events 10 6 m 3 D 2 Y 1 kiloton December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 55
Antineutrino Detection Rate for H 2 O + GdCl 3 Detectors Reactor Assume 100% detection efficiency for E n > 1.8 MeV T V 1000 km 832 Events 1 day 10 9 m 3 D 2 P 1 GW th Fission Bomb Assume 100% detection efficiency for E n > 1.8 MeV Integrated over 10 sec. burst time V 1000 km 22.5 events 10 9 m 3 D 2 Y 1 kiloton December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 56
Background Processes Antineutrinos from sources other than the rogue reactor Commercial nuclear reactors Geo-neutrinos Georeactor (possibly) Non-antineutrino background mimicking antineutrino events Cosmic rays Radioactivity in the detector Require E n > 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 57
Antineutrino Detection with a H 2 O + GdCl 3 Detector Inverse beta decay on target hydrogen nuclei n e + p n + e + Delayed Event n + Gd Gd* Gd + g cascade 20 μs E cascade 3~8 MeV Prompt Event Physics Threshold: E n > 1.8 MeV E e E n 1.3 MeV Detector Threshold: E e > 2.5 MeV E n > 3.8 MeV 90% neutron captured by Gd @ 0.2% concentration December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 58
Commercial Nuclear Reactors 433 reactors Total thermal power 1 TW December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 59
The effect of commercial nuclear reactors on the detection sensitivity for a rogue nuclear reactor 3.5 Assume that a rogue reactor with P = 250 MW th is operating just north of Hawaii 7.0 Top: log 10 S Middle: log 10 B # events from rogue reactor # events from commercial reactors 1.5 Bottom: log 10 S / S + B 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 60
log 10 (S) Possible Detector Locations log 10 (B) Map of S, B, and S/sqrt(S+B) for 1 megaton target exposed for 1 year log 10 S / S + B 23 Locations based on S/sqrt(S+B) December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 61
If a Geo-Reactor Exists If it does exist, its power is expected to be 1 ~ 10 TW th, 3 TW th being the most favored value. The total power from all commercial reactors world-wide 1 TW th In most locations around the world, antineutrinos from a georeactor would outnumber those from commercial reactors 2.25 10 4 Events T M 1 year 1 Megaton 3 TW th Georeactor December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference 62