December 16, 2005Eugene H. Guillian / Neutrino Geophysics Conference1 Far-field Monitoring of Rogue...

December 16, 2005 Eugene H. Guillian / Neutrino Geophysics Conference

1

Far-field Monitoringof

Rogue Nuclear Activitywith an

Array of Large Antineutrino Detectors

Neutrino Geophysics Conference

University of Hawaii, Manoa

December 14-16, 2005

Eugene H. GuillianUniversity of Hawaii, Manoa


2

Rogue Nuclear Activity

Two Types: Fission Reactor Fission Bomb

Purpose:Produce

weapons-grade material

Test to make sure bomb explodes

Size: < ≈ 100 MWth 1 kton TNT

Commercial Reactor≈ 2500 MWth

First Atomic Bombs10-20 kton


3

Characteristics of Rogue Nuclear Activity

(1) Small compared to “normal” activities

(2) Operated by a “hostile” regime

Need large detector to compensate for small signal

Won’t be allowed to monitor nearby (≈100 km)

Signal decreases as 1 / distance2


4

Detector Module Specifications

(1) Required target mass > ≈ 1 Megaton

(2) Required exposure time ≈ 1year (reactor)(10-second burst for bomb)

100 m

100

m

100 m

(3) Target material Water + 0.2% GdCl3

Cheap Enable Antineutrino

DetectionGADZOOKS!

Super-K with Gadolinium

J. F. Beacom & M. R. Vagins, Phys. Rev. Lett. 93, 171101 (2004)


5

Detection Mechanism

€

ν e + p→ n + e+Inverse Beta Decay

Delayed Event

≈ 20µs

n + Gd Gd + cascade

Evis ≈ 3~8 MeV

Prompt Event

Cherenkov radiation

€

Ee+ ≈ Eν −1.3 MeV


6

Neutrino Energy Spectrum

GADZOOKS! Threshold

• Eν > 3.8 MeVKamLAND Threshold

• Eν > 3.4 MeV

GADZOOKS! Efficiency58% of entire spectrum (Eν > 1.8 MeV)82% of KamLAND efficiency


7

A Very Basic Look at the Detector Hardware

100 m

100

m

100 m

Photo-Sensor Requirement≈ 120,000 units (10 Super-Kamiokande)

Gadolinium2000 metric tons

Water Purification200 Super-Kamiokande’s capacity

~$120 Million @ $1000 per unit

~$10 Million @ $3 / kg

Cost?

The cost of just one module looks to be easily about $500 Million!


8

Is a Megaton Module Outlandish?

The linear dimensions are not that much larger than those of

Super-Kamiokande

Challenges• Deep-Ocean environment

• Remote operations• Mega-structure

engineering


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


10

Array Configurations

Global1. 5° 5°2. Equidistant3. Coast-

Hugging

RegionalNorth Korea

• ≈ 1000 modules• 10 Megatons per module• 1 year exposure

• Several modules• 1 Megaton per module• 1 year exposure


11

Global Array 15º 5º Array Total of

1596 modules


12

Global Array 2Equidistant Array

Total of 623 modules

Minimum nearest-neighbor

distance ≈ 600 km


13

Global Array 3Coast-hugging Array Total of

1482 modulesMinimum

nearest-neighbor

distance ≈ 100 kmModules

removed from coast line by ≈

100 km


14

Regional ArrayNorth Korea

€

log10 S / S + B

Choose locations based on sensitivity map

(red dots are candidate module positions)

• 250 MWth fission reactor deep inside

of North Korea• Background from commercial nuclear

reactors


15

Rogue Activity Detection Strategy

Log-Likelihood Function

Input Output(1) Hypothesis

(2) Observation

Log-likelihood function

value

€

B1,B2,B3,{ L ,Bn}

“No rogue activity is taking place” Bi events expected in detector “i”

€

N1,N2,N3,{ L ,Nn}

Ni events observed in detector “i”


16

Scenario 1: No Rogue Activity


Input Output

(1) Hypothesis

(2) Observation

Large value

Hypothesisagrees with

Observation!

(most of the time…)


17

Scenario 2: Small Rogue Activity


Input Output

(1) Hypothesis

(2) Observation

Slightly biased

to lower values

(but can’t distinguish from null hypothesis)

Hypothesismaybe agrees with

Observation, but maybe not!


18

Scenario 3: Large Rogue Activity


Input Output

(1) Hypothesis

(2) Observation

Biased to lower values

Hypothesisdisagrees withObservation!

Confidently reject null hypothesis


19

Likelihood Distribution for Scenario 1

• The value varies from measurement to measurement because of statistical variation• The distribution is known a priori

1% False Positive

If value < threshold, ALARM!


20


If the rogue power is small, the bias is too small

Large overlap with null distribution

False negative happens too often


21


Define a quantity called “P99”

P99 = the power above which the chance of false negative is < 1%


22

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

With rogue activity, module 1, 2, and 3 sees an extra S1, S2, and S3 events


23

B = # background events

S = # signal events

Signal Strength

€

B= statistical uncertainty

Signal Strength

€

B

SS

€

B


24

Map of Signal Strength

Rogue Activity

2000 MWth


25

Equidistant Detector Array Configuration10 Megaton per module

1 year exposure


26

Detectors with Signal Strength > 3


27



28



29

Signatures of Rogue Activity

(1)Log-likelihood function is below threshold

(2)Cluster of near-by detectors with significant excess


30

Global Array Performance

• For each array configuration, make a map of P99

• Procedure for making map:1. Vary the rogue reactor position2. At each location, determine P99


31

P99 Map for 5° 5° Array

MWth


32

P99 Map for Equidistant Array

Scaled to 1596 Modules MWth


33

P99 Map for Coast-hugging Array

Scaled to 1596 Modules MWth


34

5º 5º

Equidistant

Coast-Hugging

P99 Summary

Location

P99

In Water< 100 MWth

W/in several

100 km of coast

Several 100 MWth

Deep in continent

Up to 2000 MWth


35

Regional Monitoring

Example:• A rogue reactor in North Korea

Signal

Background

Signal StrengthAbout the Plots

Signal

• Rogue power = 250 MWth

• Detector mass = 1 Megaton• Exposure = 1 year

Background

• Commercial nuclear reactors• 1 Megaton• 1 year

€

log10 S

€

log10 B

€

log10 S / S + B


36

Detector Locations

€

log10 S / S + B

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

• Probable location of rogue reactor


38

Two Modules

95% Confidence

99% Confidence

P99 = 250 MWth

• Confidence = probability that rogue activity is taking place inside of band• 2 saturates above 20 in the map


39

Two Modules

95% Confidence

99% Confidence

P99 = 120 MWth


40

Three Modules

95% Confidence

99% Confidence

P99 = 626 MWth


41

Four Modules

95% Confidence

99% Confidence

P99 = 336 MWth


42

Four Modules

95% Confidence

99% Confidence

P99 = 502 MWth


43

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

Total commercial nuclear activity ≈ 1 TWth

If a terawatt-level georeactor does exist, the background

level for rogue activity monitoring increases

significantly!


44

log10 BackgroundNo Georeactor

log10 Background3 TWth Georeactor

Ratio3 TWth / No Georeactor


45

Fission Bomb Monitoring

Fission Bomb• Assume 100% detection efficiency for En > 1.8 MeV• Integrated over 10 sec. burst time

€

2.25 events ⋅V

106 m3

⎛

⎝ ⎜

⎞

⎠ ⎟⋅

100 km

D

⎛

⎝ ⎜

⎞

⎠ ⎟2

⋅Y

1 kiloton

⎛

⎝ ⎜

⎞

⎠ ⎟

The background from reactors is small (in most places) because of the 10-

second window


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


47

log10(background) from commercial reactors + 3 TWth

georeactor


48

“Y99” for Bomb Monitoring

kton TNT


49

Conclusions• Untargeted global monitoring requires a very large array

≈ 1000 modules 10-Megaton per module 1-year exposure time

• 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:

1. At least one module is placed at about 100 km from the rogue activity

2. At least three modules are placed strategically at greater distances

• 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


50

Appendix


51

Cosmic Ray Background

• Like bullets!• Occasionally they destroy atomic nuclei

Unstable nuclei

Sometimes indistinguishable from antineutrinos!


52

Array ConfigurationsGlobal Monitoring

RegimeRegional Monitoring

RegimeWant sensitivity to anywhere on

EarthWant sensitivity to a well-defined

region

Can’t optimize module positioning

Module positions can be optimized because of prior

knowledge of likely locations

Larger Modules Required• 10 Megatons• 1 year exposure

Smaller Modules Will Do• 1 Megatons• 1 year exposure


53

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


54

Seeing the Rogue Activity Above Random Fluctuations

ObservedNumber

ofEvents

Backgroundonly

ObservedNumber

ofEvents

Small Signal + Background

RandomStatistical

Fluctuation

Large Signal + Background


55

Antineutrino Detection Rate for H2O + GdCl3

Detector

€

3040 Events ⋅T

1 year

⎛

⎝ ⎜

⎞

⎠ ⎟⋅

V

106 m3

⎛

⎝ ⎜

⎞

⎠ ⎟⋅

100 km

D

⎛

⎝ ⎜

⎞

⎠ ⎟2

⋅P

100 MWth

⎛

⎝ ⎜

⎞

⎠ ⎟

€

2.25 events ⋅V

106 m3

⎛

⎝ ⎜

⎞

⎠ ⎟⋅

100 km

D

⎛

⎝ ⎜

⎞

⎠ ⎟2

⋅Y

1 kiloton

⎛

⎝ ⎜

⎞

⎠ ⎟

Reactor• Assume 100% detection efficiency for En > 1.8 MeV



56

Antineutrino Detection Rate for H2O + GdCl3

Detectors

€

832 Events ⋅T

1 day

⎛

⎝ ⎜

⎞

⎠ ⎟⋅

V

109 m3

⎛

⎝ ⎜

⎞

⎠ ⎟⋅

1000 km

D

⎛

⎝ ⎜

⎞

⎠ ⎟2

⋅P

1 GWth

⎛

⎝ ⎜

⎞

⎠ ⎟

€

22.5 events ⋅V

109 m3

⎛

⎝ ⎜

⎞

⎠ ⎟⋅

1000 km

D

⎛

⎝ ⎜

⎞

⎠ ⎟2

⋅Y

1 kiloton

⎛

⎝ ⎜

⎞

⎠ ⎟

Reactor• Assume 100% detection efficiency for En > 1.8 MeV



57

Background ProcessesAntineutrinos from

sources other than the rogue reactor

Non-antineutrino background mimicking

antineutrino events

• Commercial nuclear reactors• Geo-neutrinos• Georeactor (possibly)

• Cosmic rays• Radioactivity in the detector

• Require En > 3.4 MeV

• Place detector at > 3 km depth under water• Fiducial volume cut + radon free environment


58

Antineutrino Detection with a H2O + GdCl3

DetectorInverse beta decay on target hydrogen nuclei

ne + p n + e+ Prompt Event

Delayed Event

En > 1.8 MeVEe ≈ En – 1.3 MeV

Detector Threshold: Ee > 2.5 MeV

En > 3.8 MeV

Physics Threshold:≈ 20 µs

n + Gd Gd*

Ecascade ≈ 3~8 MeV

Gd + g cascade

90% neutron captured by Gd @ 0.2% concentration


59

Commercial Nuclear Reactors

• 433 reactors• Total thermal power ≈ 1 TW


60

The effect of commercial nuclear

reactors on the detection

sensitivity for a rogue nuclear

reactor Assume that a rogue reactor with P = 250 MWth is operating just north of Hawaii

Top:

Middle:

Bottom:

log10 S

log10 B

€

log10 S / S + B

# events from rogue

reactor# events

from commercial

reactors

3.5

7.0

1.5

• Detector target mass = 10 megatons• 1 year exposure• Detectors allowed only in oceans & large lakes• 100% detection efficiency


61

Possible Detector Locations

23 Locations based on S/sqrt(S+B)

log10(S)

log10(B)

€

log10 S / S + B

Map of S, B, and S/sqrt(S+B) for 1 megaton target

exposed for 1 year


62

If a Geo-Reactor Exists…

• If it does exist, its power is expected to be 1 ~ 10 TWth, 3 TWth being the most favored value.

• The total power from all commercial reactors world-wide ≈ 1 TWthIn most locations around the world, antineutrinos

from a georeactor would outnumber those from commercial reactors

€

2.25 ×104 Events T

1 year

⎛

⎝ ⎜

⎞

⎠ ⎟⋅

M

1 Megaton

⎛

⎝ ⎜

⎞

⎠ ⎟ 3 TWth Georeactor

Date post:	21-Dec-2015
Category:	Documents
View:	214 times
Download:	2 times

December 16, 2005Eugene H. Guillian / Neutrino Geophysics Conference1 Far-field Monitoring of Rogue...

Documents