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

2007-Dec-13Guillian & Learned at AAP Monitoring Rogue Nuclear Activity with Anti-neutrino Detectors Two types rogue nuclear activities that have anti-neutrinos as a by-product ObjectiveActivity to Achieve Objective Production of weapons-grade plutoniumOperation of breeder-reactor Fission bomb design testsDetonation of fission bomb Signatures of the above activities: Breeder Reactor Anti-neutrinos produced at a steady rate Reactor fuel is replaced prematurely to avoid poisoning with 240 Pu Fission Bomb Almost all anti-neutrinos produced in a burst of 10 seconds Accompanied by other signatures (CTBTO monitoring) focus on fission bomb detection in this talk

2007-Dec-13Guillian & Learned at AAP 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.

2007-Dec-13Guillian & Learned at AAP Anti-neutrinos Produced by a Fission Bomb The bomb yield is typically quoted in TNT-equivalent units: –1 kilo-tonne TNT =  Joule The amount of thermal energy released by a single fission event: –  204 MeV  3.3  Joule The number of fissions per kilo-tonne of yield: 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 Fission Rate of a Nuclear Reactor R fiss = 3.1  fissions/sec/GWt

2007-Dec-13Guillian & Learned at AAP 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 10 1 ~ 10 2  s 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 H 2 O loaded with a neutron absorber (Gd or Cl)

2007-Dec-13Guillian & Learned at AAP Anti-neutrino Detection Rate Factors that determine the detection rate: FactorSymbolUnits Bomb YieldEkilo-tonne TNT Distance to Detonation Site R100 km Cross Section of Target  (E ) cm 2 Anti-neutrino 100 km i.e. number of anti-neutrinos per unit area E Thresh. (MeV) Detector Fluence (cm -2 kton -1 ) 0N/A 5  Liq. Scint. 2   Gd-loaded H 2 O 0.3  10 8 Inverse Beta Cross Section Detection Threshold Most anti-neutrinos are detected in this energy window Cross Section ~ cm 2

2007-Dec-13Guillian & Learned at AAP Anti-neutrino Detection Rate Detecting a 1 kton bomb at 100 km 0.3  10 8 cm cm 2  Number of antineutrinos per cm 2 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 ~10 35 free protons This is about 1 mega-ton of H 2 O 100 m

2007-Dec-13Guillian & Learned at AAP Anti-neutrino Detection Rate More precisely: SymbolUnitsDescription Ekton TNTEnergy from bomb N10 35 free protonsNumber of free protons in detector R100 km Distance between the bomb detonation site and the detector Other Factors: Neutrino Survival Probability0.57 Event Selection Cut Efficiency0.86 Combined Rate Reduction Factor0.49

2007-Dec-13Guillian & Learned at AAP Detector Mass Units free protons in H 2 O corresponds to 1.5 Mega-ton H 2 O The anti-neutrino detection rate in terms of H 2 O mass becomes: SymbolUnitsDescription Ekton TNTEnergy from bomb MMega-ton H 2 OMass of H 2 O R100 km Distance between the bomb detonation site and the detector

2007-Dec-13Guillian & Learned at AAP Anti-neutrino Detector Mass versus Distance 10% yield estimate 30% yield estimate Confirmatory evidence

2007-Dec-13Guillian & Learned at AAP 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 Background Source Measures Taken to Eliminate Background Assumed Background Level Cosmic RayOverburden > 3000 m.w.e. 0 Internal Radioactivity Use existing purification techniques and require delayed coincidence Geo-neutrinos Prompt event below detection threshold Reactor Anti-neutrinosIrreducibleSee Below DPRK

2007-Dec-13Guillian & Learned at AAP Test Scenario: North Korea, October 9, 2006 Information Regarding the Alleged October 9, 2006 Bomb Detonation October 3 North Korea announces its intention to perform a test detonation 20 minutes before detonation China notified of imminent test. This information was immediately relayed to Washington D.C. 01:35:27 UTC (10:35:27 a.m. local time, UTC+9), October 9, 2006 USGS records a seismic event (4.2 Richter scale) at 41°17′38.4″N, 129°08′2.4″E Early seismic estimates by South Korea Earthquake magnitude 3.58 Richter scale  0.1 ~ 0.8 kton bomb Revised seismic estimates from several independent sources 4.2 Richter scale  2~12 kton bomb October 14 US government reports finding radioactive isotopes in the atmosphere, presumably from the detonation

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

2007-Dec-13Guillian & Learned at AAP 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.

2007-Dec-13Guillian & Learned at AAP 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 Signal Rate0.91 events/kton TNT Background Rate0.01 events/10 sec 60% chance of detecting a 1 kton bomb Background noise:1 event per 1000 sec. Stand-alone mode Cannot tell event from background Input from CTBTO- type monitoring 1% chance of background event occurring in 10 sec. window 99% detection probability and 30% yield estimate for 10 kiloton weapon

2007-Dec-13Guillian & Learned at AAP Test Case 2: One 1 Mt Detector along East Coast of North Korea Typical distance ~150 km Signal Rate0.49 events/kton TNT Background Rate0.01 events/10 sec 1 kiloton yield => 38% detection probability 10 kiloton yield => 99% detection probability

2007-Dec-13Guillian & Learned at AAP 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 Test Case 3: Require 99% Detection Probability under Optimal Conditions 4.6 (1.1) 2 1 M Det = 5.1 Mega-ton

2007-Dec-13Guillian & Learned at AAP Test Case 4: 99% Detection for Typical Distance Same as previous slide, but R = 150 km requires M Det = 9.4 Mega-ton And if yield were 10 kiloton, we would detect 49 events on average, for a 14% yield measurement.

2007-Dec-13Guillian & Learned at AAP Typical Location Detector Mass Optimal Location Detector Mass Test Case 5: Stand-alone Running Require < 1% false positive events from nuclear reactors for 1 year of running –1 year  3.16  second windows (trials) – Background rate: 0.01 events / 10 seconds N Background Events/10 sec. Poisson Probability of N per 10 sec interval Number of occasions per 100 years  x  x   Hence require >= 4 events 1 kT 4.4 Mega-ton8.2 Mega-ton 0.4 Mega-ton0.8 Mega-ton 10 kT

2007-Dec-13Guillian & Learned at AAP 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? 100 km 200 km 300 km 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: km8.1 Megaton per event 6 detectors48 Megatons per event 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

2007-Dec-13Guillian & Learned at AAP 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 –Need ~decade of development

2007-Dec-13Guillian & Learned at AAP Test Case Conclusion With current technology and under optimal conditions, a 1 Mega-ton Gd/Cl-doped H 2 O 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.