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Far-field Monitoring

Far-field Monitoring. of. Rogue Nuclear Activity. with. an Array of Antineutrino Detectors. Neutrino Sciences 2005. Neutrino Sciences 2005. University of Hawaii, Manoa. University of Hawaii, Manoa. December 14-16, 2005. December 14-16, 2005. Eugene H. Guillian

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Far-field Monitoring

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  1. Far-field Monitoring of Rogue Nuclear Activity with an Array of Antineutrino Detectors Neutrino Sciences 2005 Neutrino Sciences 2005 University of Hawaii, Manoa University of Hawaii, Manoa December 14-16, 2005 December 14-16, 2005 Eugene H. Guillian University of Hawaii, Manoa Eugene H. Guillian University of Hawaii, Manoa

  2. Small! Hard to Detect! Rogue Nuclear Activity Typical commercial reactor ≈ 2500 MWth Little Boy ≈ 15 kiloton Fat Man ≈ 23 kiloton

  3. These factors strongly constrain the detector & array specifications Far-Field Monitoring Uncooperative Regime Access within ~100 km not allowed Far Away Small event rate (1 / distance2) • Large Detector • Shielding from cosmic rays • Detector must be affordable

  4. Detector must be on the order of 106 m3 100 m 100 m 100 m Water is the only economically feasible target • H2O loaded with 0.2% GdCl3 • C.f. GADZOOKS! (Super-K with GdCl3) J. F. Beacom & M. R, Vagins, Phys. Rev. Lett. 93, 171101 (2004) Antineutrino Detector Module Specification • Far-field monitoring • Distance > ≈ 100 km

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

  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

  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 a Megaton Detector Module Photo-Sensor Requirement ≈ 120,000 units (10  Super-Kamiokande) Gadolinium 2000 metric tons Water Purification 200  Super-Kamiokande’s capacity

  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

  9. Unstable nuclei Sometimes indistinguishable from antineutrinos! Cosmic Ray Background • Like bullets! • Occasionally they destroy atomic nuclei

  10. Shielding from Cosmic Rays Super-Kamiokande • Shielded by 1000 m of rock (equivalent to 2700 m of water) • Mitsui Mining Co. property Super-Kamoikande (and similar experiments) 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

  11. Module positions can be optimized because of prior knowledge of likely locations Can’t optimize module positioning • Larger Modules Required • 10 Megatons • 1 year exposure • Smaller Modules Will Do • 1 Megatons • 1 year exposure Array Configurations

  12. Global Array 15º  5º Array Total of 1596 modules

  13. Global Array 2Equidistant Array Total of 623 modules Minimum nearest-neighbor distance ≈ 600 km

  14. Global Array 3Coast-hugging Array Total of 1482 modules Minimum nearest-neighbor distance ≈ 100 km Modules removed from coast line by ≈ 100 km

  15. 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)

  16. 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

  17. 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

  18. Observed Number of Events Observed Number of Events Random Statistical Fluctuation Large Signal + Background Background only Small Signal + Background Seeing the Rogue Activity Above Random Fluctuations

  19. S = # signal events Signal Strength = statistical uncertainty S S B = # background events Signal Strength

  20. Map of Signal Strength Rogue Activity 2000 MWth

  21. Equidistant Detector Array Configuration 10 Megaton per module 1 year exposure

  22. Detectors with Signal Strength > 3

  23. Detectors with Signal Strength > 2

  24. Detectors with Signal Strength > 1

  25. Cluster of nearby detector modules with significant excess Pin-Pointing Rogue activity location given roughly by the position of the cluster • Cutting on Signal Strength • Tight cut low background noise, but loss of signal • Loose cut  more signal, but more background noise Measuring Power Use log-likelihood to obtain the most likely power Remarks on Rogue Activity Detection Rogue Activity: Has sufficiently large power Is sufficiently close to detector modules

  26. P99: Benchmark for Array Performance • Log-likelihood Function • A statistical tool used for • hypothesis testing • Hypothesis • No rogue activity is taking place • Information Used in Log-likelihood Function • Expected number of background • events in each detector (from • commercial nuclear reactors) • Observed number of events in • eachdetector • The log-likelihood value is not defined • a priori because of random fluctuations in • the measurement • Its distribution, however, is defined a priori

  27. 99% of measurements give log-likelihood above the alarm threshold 1% of measurements sets off false alarm 1% False Positive

  28. Rogue Reactor Exists  Hypothesis Incorrect  Log-likelihood function is biased to lower values Rogue Reactor Power is Weak  Large overlap between observed vs. expected distributions  Can’t reliably detect rogue activity Unacceptably Large Frequency of False Negatives

  29. Definition of P99 P99 = Rogue reactor power which gives 1% chance of false negative

  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

  31. P99 Map: 5º  5º MWth

  32. Scaled to 1596 Modules P99 Map: Equidistant MWth

  33. Scaled to 1596 Modules P99 Map: Coast-hugging MWth

  34. P99 Summary 5º  5º Equidistant Coast-Hugging

  35. Signal Regional Monitoring Example: • A rogue reactor in North Korea Background Signal Strength

  36. Detector Locations 23 candidate locations based on map of sensitivity

  37. Performance of Various Array Configurations Consider configurations with 2, 3, and 4 detector modules • For each configuration, determine: • P99 • Estimated area that contains rogue reactor

  38. Two Modules P99 = 250 MWth 99% Confidence 95% Confidence

  39. Two Modules P99 = 120 MWth 99% Confidence 95% Confidence

  40. Three Modules P99 = 626 MWth 99% Confidence 95% Confidence

  41. Four Modules P99 = 336 MWth 99% Confidence 95% Confidence

  42. Four Modules P99 = 502 MWth 99% Confidence 95% Confidence

  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!

  44. log10 Background No Georeactor Ratio 3 TWth / No Georeactor log10 Background 3 TWth Georeactor

  45. Squeezing More Information from the Data

  46. Fission Bomb Monitoring

  47. Conclusion • One module costs several hundred million dollars • multiply this by number of modules in array • A terawatt-level georeactor increases the background level by a factor of several in most locations around the world • A regional monitoring regime seems not-too-outlandish

  48. Appendix

  49. Antineutrino Detection Rate for H2O + GdCl3 Detector • 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

  50. Antineutrino Detection Rate for H2O + GdCl3 Detectors • 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

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