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Far-field Monitoring of Rogue Nuclear Activity with an Array of Large Antineutrino Detectors

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. First Atomic Bombs 10-20 kton. Commercial Reactor ≈ 2500 MW th.

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Far-field Monitoring of Rogue Nuclear Activity with an Array of Large Antineutrino Detectors

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  1. Far-field MonitoringofRogue Nuclear Activitywith anArray of Large Antineutrino Detectors Neutrino Geophysics Conference University of Hawaii, Manoa December 14-16, 2005 Eugene H. Guillian University of Hawaii, Manoa Eugene H. Guillian / Neutrino GeophysicsConference

  2. First Atomic Bombs 10-20 kton Commercial Reactor ≈ 2500 MWth Rogue Nuclear Activity Fission Reactor Fission Bomb Two Types: Produce weapons-grade material Test to make sure bomb explodes Purpose: < ≈ 100 MWth 1 kton TNT Size: Eugene H. Guillian / Neutrino GeophysicsConference

  3. Need large detector to compensate for small signal Won’t be allowed to monitor nearby (≈100 km) Signal decreases as 1 / distance2 Characteristics of Rogue Nuclear Activity (1) Small compared to “normal” activities (2) Operated by a “hostile” regime Eugene H. Guillian / Neutrino GeophysicsConference

  4. (2) Required exposure time ≈ 1year (reactor) (10-second burst for bomb) 100 m 100 m 100 m Cheap Enable Antineutrino Detection GADZOOKS! Super-K with Gadolinium J. F. Beacom & M. R. Vagins, Phys. Rev. Lett. 93, 171101 (2004) Detector Module Specifications (1) Required target mass > ≈ 1 Megaton (3) Target material  Water + 0.2% GdCl3 Eugene H. Guillian / Neutrino GeophysicsConference

  5. Prompt Event Cherenkov radiation ≈ 20µs Delayed Event n + Gd  Gd + g cascade Evis ≈ 3~8 MeV Detection Mechanism Inverse Beta Decay Eugene H. Guillian / Neutrino GeophysicsConference

  6. Neutrino Energy Spectrum • GADZOOKS! Threshold • En > 3.8 MeV • KamLAND Threshold • En > 3.4 MeV GADZOOKS! Efficiency 58% of entire spectrum (En > 1.8 MeV) 82% of KamLAND efficiency Eugene H. Guillian / Neutrino GeophysicsConference

  7. ~$120 Million @ $1000 per unit ~$10 Million @ $3 / kg 100 m Cost? 100 m 100 m The cost of just one module looks to be easily about $500 Million! A Very Basic Look at the Detector Hardware Photo-Sensor Requirement ≈ 120,000 units (10  Super-Kamiokande) Gadolinium 2000 metric tons Water Purification 200  Super-Kamiokande’s capacity Eugene H. Guillian / Neutrino GeophysicsConference

  8. Is a Megaton Module Outlandish? • Challenges • Deep-Ocean environment • Remote operations • Mega-structure engineering The linear dimensions are not that much larger than those of Super-Kamiokande Eugene H. Guillian / Neutrino GeophysicsConference

  9. 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 Eugene H. Guillian / Neutrino GeophysicsConference

  10. Array Configurations • Several modules • 1 Megaton per module • 1 year exposure • ≈ 1000 modules • 10 Megatons per module • 1 year exposure Eugene H. Guillian / Neutrino GeophysicsConference

  11. Global Array 15º  5º Array Total of 1596 modules Eugene H. Guillian / Neutrino GeophysicsConference

  12. Global Array 2Equidistant Array Total of 623 modules Minimum nearest-neighbor distance ≈ 600 km Eugene H. Guillian / Neutrino GeophysicsConference

  13. Global Array 3Coast-hugging Array Total of 1482 modules Minimum nearest-neighbor distance ≈ 100 km Modules removed from coast line by ≈ 100 km Eugene H. Guillian / Neutrino GeophysicsConference

  14. Regional ArrayNorth Korea • 250 MWth fission reactor deep inside of North Korea • Background from commercial nuclear reactors Choose locations based on sensitivity map (red dots are candidate module positions) Eugene H. Guillian / Neutrino GeophysicsConference

  15. “No rogue activity is taking place”  Bi events expected in detector “i” Rogue Activity Detection Strategy Input Output Hypothesis Log-Likelihood Function Log-likelihood function value Observation Ni events observed in detector “i” Eugene H. Guillian / Neutrino GeophysicsConference

  16. Scenario 1: No Rogue Activity Hypothesis agrees with Observation! Input Output Log-Likelihood Function Hypothesis Large value Observation (most of the time…) Eugene H. Guillian / Neutrino GeophysicsConference

  17. Scenario 2: Small Rogue Activity Hypothesis maybe agrees with Observation, but maybe not! Input Output Log-Likelihood Function Slightly biased to lower values Hypothesis Observation (but can’t distinguish from null hypothesis) Eugene H. Guillian / Neutrino GeophysicsConference

  18. Scenario 3: Large Rogue Activity Hypothesis disagrees with Observation! Input Output Log-Likelihood Function Hypothesis Biased to lower values Observation Confidently reject null hypothesis Eugene H. Guillian / Neutrino GeophysicsConference

  19. If value < threshold, ALARM! 1% False Positive Likelihood Distribution for Scenario 1 • The value varies from measurement to measurement because of statistical variation • The distribution is known a priori Eugene H. Guillian / Neutrino GeophysicsConference

  20. 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 Eugene H. Guillian / Neutrino GeophysicsConference

  21. Likelihood Distribution for Scenario 3 Define a quantity called “P99” P99 = the power above which the chance of false negative is < 1% Eugene H. Guillian / Neutrino GeophysicsConference

  22. With rogue activity, module 1, 2, and 3 sees an extra S1, S2, and S3 events 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 Eugene H. Guillian / Neutrino GeophysicsConference

  23. S = # signal events Signal Strength = statistical uncertainty S S B = # background events Signal Strength Eugene H. Guillian / Neutrino GeophysicsConference

  24. Map of Signal Strength Rogue Activity 2000 MWth Eugene H. Guillian / Neutrino GeophysicsConference

  25. Equidistant Detector Array Configuration 10 Megaton per module 1 year exposure Eugene H. Guillian / Neutrino GeophysicsConference

  26. Detectors with Signal Strength > 3 Eugene H. Guillian / Neutrino GeophysicsConference

  27. Detectors with Signal Strength > 2 Eugene H. Guillian / Neutrino GeophysicsConference

  28. Detectors with Signal Strength > 1 Eugene H. Guillian / Neutrino GeophysicsConference

  29. Signatures of Rogue Activity Log-likelihood function is below threshold Cluster of near-by detectors with significant excess Eugene H. Guillian / Neutrino GeophysicsConference

  30. Global Array Performance • For each array configuration, make a map of P99 • Procedure for making map: • Vary the rogue reactor position • At each location, determine P99 Eugene H. Guillian / Neutrino GeophysicsConference

  31. P99 Map for 5°  5° Array MWth Eugene H. Guillian / Neutrino GeophysicsConference

  32. Scaled to 1596 Modules P99 Map for Equidistant Array MWth Eugene H. Guillian / Neutrino GeophysicsConference

  33. Scaled to 1596 Modules P99 Map for Coast-hugging Array MWth Eugene H. Guillian / Neutrino GeophysicsConference

  34. P99 Summary 5º  5º Equidistant Coast-Hugging Eugene H. Guillian / Neutrino GeophysicsConference

  35. Signal Regional Monitoring Example: • A rogue reactor in North Korea Background Signal Strength Eugene H. Guillian / Neutrino GeophysicsConference

  36. Detector Locations 23 candidate locations based on map of sensitivity Eugene H. Guillian / Neutrino GeophysicsConference

  37. Performance of Various Array Configurations Consider configurations with 2, 3, and 4 detector modules • For each configuration, determine: • P99 • Probable location of rogue reactor Eugene H. Guillian / Neutrino GeophysicsConference

  38. Two Modules P99 = 250 MWth 99% Confidence 95% Confidence • Confidence = probability • that rogue activity is taking • place inside of band • Dc2 saturates above 20 in • the map Eugene H. Guillian / Neutrino GeophysicsConference

  39. Two Modules P99 = 120 MWth 99% Confidence 95% Confidence Eugene H. Guillian / Neutrino GeophysicsConference

  40. Three Modules P99 = 626 MWth 99% Confidence 95% Confidence Eugene H. Guillian / Neutrino GeophysicsConference

  41. Four Modules P99 = 336 MWth 99% Confidence 95% Confidence Eugene H. Guillian / Neutrino GeophysicsConference

  42. Four Modules P99 = 502 MWth 99% Confidence 95% Confidence Eugene H. Guillian / Neutrino GeophysicsConference

  43. Total commercial nuclear activity ≈ 1 TWth 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 If a terawatt-level georeactor does exist, the background level for rogue activity monitoring increases significantly! Eugene H. Guillian / Neutrino GeophysicsConference

  44. log10 Background No Georeactor Ratio 3 TWth / No Georeactor log10 Background 3 TWth Georeactor Eugene H. Guillian / Neutrino GeophysicsConference

  45. Fission Bomb Monitoring • Fission Bomb • Assume 100% detection efficiency for En > 1.8 MeV • Integrated over 10 sec. burst time The background from reactors is small (in most places) because of the 10-second window Eugene H. Guillian / Neutrino GeophysicsConference

  46. 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 Eugene H. Guillian / Neutrino GeophysicsConference

  47. log10(background) from commercial reactors + 3 TWth georeactor Eugene H. Guillian / Neutrino GeophysicsConference

  48. “Y99” for Bomb Monitoring kton TNT Eugene H. Guillian / Neutrino GeophysicsConference

  49. 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: At least one module is placed at about 100 km from the rogue activity At least three modules are placed strategically at greater distances Conclusions • • Untargeted global monitoring requires a • very large array • ≈ 1000 modules • 10-Megaton per module • 1-year exposure time • • 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 Eugene H. Guillian / Neutrino GeophysicsConference

  50. Appendix Eugene H. Guillian / Neutrino GeophysicsConference

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