prospects for the use of large water- based anti-neutrino detectors for monitoring fission bomb...

Prospects for the Use of Large Prospects for the Use of Large Water-Based Anti-neutrino Water-Based Anti-neutrino

Detectors for Monitoring Fission Detectors for Monitoring Fission Bomb DetonationsBomb Detonations

Eugene Guillian, Queen’s UniversityJohn G. Learned, University of Hawaii

2007-Dec-13 Guillian & Learned at AAP 2007 2

Monitoring Rogue Nuclear Monitoring Rogue Nuclear Activity with Anti-neutrino Activity with Anti-neutrino

DetectorsDetectors• Two types rogue nuclear activities that have anti-

neutrinos as a by-product

Objective Activity to Achieve Objective

Production of weapons-grade plutonium

Operation of breeder-reactor

Fission bomb design tests Detonation 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 240Pu

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


Motivation to Employ Neutrino Motivation to Employ Neutrino MonitoringMonitoring

• 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.


Anti-neutrinos Produced by a Fission Anti-neutrinos Produced by a Fission BombBomb

• 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:

N fiss 1.31023 E(kilo - tonne TNT)

• Fission anti-neutrinos are produced in a burst of about 10 seconds

A. Bernstein, T. West, & V. GuptaAn assessment of Antineutrino Detection

as a Tool for Monitoring Nuclear Explosions

Fission Rate of a Nuclear Reactor

Rfiss = 3.1 1019 fissions/sec/GWt


Anti-neutrino Detection MethodAnti-neutrino Detection Method

• The currently available mature technology is based on inverse beta decay on a free proton target

e p n ePrompt energy deposition

• Captured after a delay of 101 ~ 102 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

H2O loaded with a neutron absorber (Gd or Cl)


Anti-neutrino Detection RateAnti-neutrino Detection Rate• Factors that determine the detection rate:

Factor Symbol Units

Bomb Yield E kilo-tonne TNT

Distance to Detonation Site

R 100 km

Cross Section of Target (E) cm2

• Anti-neutrino Fluence @ 100 km

i.e. number of anti-neutrinos per unit area

E Thresh.

(MeV)Detector

Fluence (cm-2 kton-

1)

0 N/A 5108

1.8Liq. Scint.

2108

3.4 0.5108

3.8 Gd-loaded H2O 0.3108

• Inverse Beta Cross Section

Det

ecti

on T

hres

hold

Most anti-neutrinos are detected in this

energy window

Cross Section ~ 10-42 cm2


Anti-neutrino Detection RateAnti-neutrino Detection Rate

• Detecting a 1 kton bomb at 100 km

0.3 108 cm-2 10-42 cm2Number of antineutrinos per

cm2 from bomb above detection threshold

Typical interaction cross section

~ 10-35

Probability of interacting with a target proton

• In order to detect ~1 anti-neutrino, the detector needs ~1035 free protons

This is about 1 mega-ton of H2O 100

m

100 m

100 m


Anti-neutrino Detection RateAnti-neutrino Detection Rate

• More precisely:

Ndet 3.5 Events E N

R2

Symbol

Units Description

E kton TNT Energy from bomb

N1035 free protons

Number of free protons in detector

R 100 kmDistance between the bomb

detonation site and the detector• Other Factors:

Neutrino Survival Probability 0.57

Event Selection Cut Efficiency 0.86

Combined Rate Reduction Factor

0.49

Ndet 1.7 Events E N

R2

Ndet 3.5 Events E N

R2


Detector Mass UnitsDetector 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:

Ndet 1.1 Events E M

R2

Symbol

Units Description

E kton TNT Energy from bomb

M Mega-ton H2O Mass of H2O

R 100 kmDistance between the bomb

detonation site and the detector


Anti-neutrino Detector Mass versus Anti-neutrino Detector Mass versus DistanceDistance

10% yield estimate

30% yield estimate

Confirmatory evidence


Background NoiseBackground 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 SourceMeasures Taken to

Eliminate BackgroundAssumed Background

Level

Cosmic Ray Overburden > 3000 m.w.e.

0Internal RadioactivityUse existing purification techniques and require

delayed coincidence

Geo-neutrinosPrompt event below detection threshold

Reactor Anti-neutrinos Irreducible See Below

DPRK


Test Scenario: Test Scenario: North Korea, October 9, 2006North Korea, October 9, 2006

Information Regarding the Alleged October 9, 2006 Bomb Detonation

October 3North Korea announces its intention

to perform a test detonation

20 minutes before detonationChina 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


• An underwater detector could have been as close as 110 km in international waters.

Detonation SiteDetonation Site

41°17′38.4″N129°08′2.4″E

100 km

200 km

300 km


Detecting the BombDetecting 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.


Test Case 1: Got LuckyTest 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 Rate 0.91 events/kton TNT

Background Rate 0.01 events/10 sec

60% chance of detecting a 1 kton bomb

• Background noise: 1 event per 1000 sec.

Stand-alone modeCannot 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


Test Case 2: One 1 Mt Detector Test Case 2: One 1 Mt Detector along East Coast of North Koreaalong East Coast of North Korea

• Typical distance ~150 km

Signal Rate 0.49 events/kton TNT

Background Rate 0.01 events/10 sec

1 kiloton yield => 38% detection

probability

10 kiloton yield =>99% detection probability


• 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% Test Case 3: Require 99% Detection Probability under Detection Probability under

Optimal ConditionsOptimal Conditions

Ndet 1.1 Events E M

R2

4.6 (1.1)2

1

MDet = 5.1 Mega-ton


Test Case 4: 99% Detection for Test Case 4: 99% Detection for Typical DistanceTypical 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 eventson average, for a 14% yield measurement.


Typical Location Detector Mass

Optimal Location Detector Mass

Test Case 5: Stand-alone Test Case 5: Stand-alone RunningRunning

• 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

N Background Events/10 sec.

Poisson Probability of N per 10 sec

interval

Number of occasions per 100 years

1 9.9 10-3 3.13 x 106

2 5.0 10-5 1.58 x 104

3 1.7 10-7 53.7

4 4.1 10-10 0.13

Hence require >= 4 events1 kT 4.4 Mega-ton 8.2 Mega-ton

0.4 Mega-ton 0.8 Mega-ton10 kT


Test Case 6: Complete CoverageTest 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:

1 detector @ 300 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 An array of about 6 strategically placed detectors of total mass 220 Mega-ton could cover all of North Korea with 99% 220 Mega-ton could cover all of North Korea with 99%

detection probability and 99% false positive rejection per year detection probability and 99% false positive rejection per year


Cost ScaleCost 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


Test Case ConclusionTest 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:Summary: Large water Cherenkov based anti-neutrino detectors Large water Cherenkov based anti-neutrino detectors can play a critical role in detection and measurements of can play a critical role in detection and measurements of clandestine nuclear weapons testing. Technology development,clandestine nuclear weapons testing. Technology development,particularly of photodetection and studies should proceed, as particularly of photodetection and studies should proceed, as should development of prototype detectors.should development of prototype detectors.

prospects for the use of large water- based anti-neutrino detectors for monitoring fission bomb...

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