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

1. Prospects for the Use of Large Water-Based Anti-neutrino Detectors for Monitoring Fission Bomb Detonations Eugene Guillian, Queen’s University John G. Learned, University of Hawaii

2. Monitoring Rogue Nuclear Activity with Anti-neutrino Detectors • Two types rogue nuclear activities that have anti-neutrinos as a by-product • Signatures of the above activities: focus on fission bomb detection in this talk Guillian & Learned at AAP 2007

3. 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. Guillian & Learned at AAP 2007

4. 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 Guillian & Learned at AAP 2007

5. 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 ~ 102ms • 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) Guillian & Learned at AAP 2007

6. Anti-neutrino Detection Rate • Factors that determine the detection rate: • Inverse Beta Cross Section • Anti-neutrino Fluence @ 100 km i.e. number of anti-neutrinos per unit area Most anti-neutrinos are detected in this energy window Detection Threshold Cross Section ~ 10-42 cm2 Guillian & Learned at AAP 2007

7. 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 Guillian & Learned at AAP 2007

8. Anti-neutrino Detection Rate • More precisely: • Other Factors: Guillian & Learned at AAP 2007

9. 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: Guillian & Learned at AAP 2007

10. Anti-neutrino Detector Mass versus Distance 10% yield estimate 30% yield estimate Confirmatory evidence Guillian & Learned at AAP 2007

11. Background Noise • 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 ANL’s 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 Guillian & Learned at AAP 2007

12. Test Scenario: North Korea, October 9, 2006 Guillian & Learned at AAP 2007

13. Detonation Site 41°17′38.4″N 129°08′2.4″E • An underwater detector could have been as close as 110 km in international waters. 100 km 200 km 300 km Guillian & Learned at AAP 2007

14. Detecting the Bomb • 6 day’s 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. Guillian & Learned at AAP 2007

15. 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 60% chance of detecting a 1 kton bomb • Background noise: 1 event per 1000 sec. Guillian & Learned at AAP 2007

16. Test Case 2: One 1 Mt Detector along East Coast of North Korea • Typical distance ~150 km 1 kiloton yield => 38% detection probability 10 kiloton yield => 99% detection probability Guillian & Learned at AAP 2007

17. 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 Guillian & Learned at AAP 2007

18. 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. Guillian & Learned at AAP 2007

19. Test Case 5: Stand-alone Running • Require < 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 Optimal Location Detector Mass Typical Location Detector Mass 1 kT 4.4 Mega-ton 8.2 Mega-ton Hence require >= 4 events 10 kT 0.4 Mega-ton 0.8 Mega-ton Guillian & Learned at AAP 2007

20. 100 km 200 km 300 km 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: • Multiply the above by the required number of detected events • 4.6 events for 99% detection probability • >= 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 Guillian & Learned at AAP 2007

21. 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  0.2~0.9 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 Guillian & Learned at AAP 2007

22. 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. Guillian & Learned at AAP 2007