The Search for Special Nuclear Material Using Particle Physics Techniques

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The Search for Special Nuclear Material Using
Particle Physics Techniques
Professor David Koltick Director, Applied Physics
Laboratory Physics Department, Purdue University

• One of the most devastating attacks a terrorist
  group could mount would be to detonate an atomic
  bomb in a city. If exploded in Manhattan during
  working hours, for example, a bomb with a yield
  of only 1 kiloton could kill 200,000 people
  outright and flatten eleven city blocks. In
  theory, as little as 4 kilograms (9 pounds) of
  plutonium would be needed to make a bomb. As
  little as 16 to 20 kilograms of highly enriched
  uranium would be needed to make an efficient
  bomb a crude bomb could be made with 50 to 100
  kilograms of uranium. By contrast, the world's
  supply of highly enriched uranium is estimated to
  be 1,600,000 kilograms the supply of plutonium,
  450,000 kilograms.

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Higgs Production and Gluon Fusion Cross Sections
at LHC

• Large Hadron Collider (LHC)
• Search for Higgs is hard! Cost 6B

• Robert Harlander, Precise predictions for Higgs
  cross sections
• at the Large Hadron Collider Nuclear Physics B
  (Proc. Suppl.) 135 (2004)
• Journal of Physics G Nuclear and Particle
  Physics (2006 Vol. 33)

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Searching for 4 kg Plutonium-239

• 4 kg Pu-239
• 10 million cargo containers through U.S. ports
  per year
• Search for special nuclear materials is harder!

Nuclear car wash status report, August 2005
UCRL-TR-214636
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The Liquid Drop Model

• Forces within nucleus
• Competition between short-range attractive
  nuclear force versus repulsive electromagnetic
  force between protons
• When A 235, nuclear force gives way to Coulomb
  repulsion making spontaneous fission a
  possibility
• Binding energy of nucleus
• Binding energy of nucleus approximately
  proportional to A
• Coulomb repulsion energy grows faster as Z2
• Energetically favorable for a heavy nucleus to
  split than to remain whole because nuclei of
  intermediate mass have larger binding energy per
  nucleon than heavy nuclei
• Result of fission is a transition to tighter
  bound system release of energy

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28 November 2007
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Passive Special Nuclear Material Search

• Special Nuclear Materials U-235, U-233, Pu-239
  (NRC)
• Spontaneous fission neutron yields
• Low-energy signature gamma-ray lines
• U-235 (strongest) line 186 keV
• Pu-239 98 keV, 129 keV, 203 keV, 375 keV, 414
  keV
• Easily attenuated by high-Z shielding (e.g. lead)
• U-233
• Highly hazardous due to strong gamma ray emission
  
• Not commonly used in nuclear weapons

Passive Nondestructive Assay Nuclear Materials
US-NRC-1991
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Basic Nuclear Weapon Design

• From sub-critical mass to super-critical mass on
  ?s time scale
• Gun Assembly (simplest)
• Hollow fissile uranium bullet fired into
  fissile uranium target
• Plutonium spontaneous neutron yield too high for
  gun assembly
• Implosion (complex but more efficient)
• U-235, Pu-239, or combination surrounded by high
  explosives to compress and achieve critical mass

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Critical Mass

• Critical Mass
• Minimum mass of fissile material to sustain
  nuclear chain reaction
• Depends on density, shape, type of fissile
  material, effectiveness of reflector (tamper) at
  reflecting neutrons back into fissioning mass

DOE estimates 4 kg Plutonium needed for small
bomb.
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Nuclear Car Wash
Radiate Cargo Using Neutrons
60 seconds
Count Cargo in Scintillator 60 seconds
Pulsed neutron generator to induce fission Entire
contents of cargo container are irradiated Two
arrays of liquid scintillator detectors, detect
both delayed neutrons and delayed ?-rays Delayed
?-rays and neutrons are used as a signature of
SNM
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Delayed Neutrons
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Emission of Delayed Gamma-Rays
Delayed ?-rays are emitted at 5 different rates
For 60 second run
For E gt 3-MeV (strong natural radiation
background in cargo) 0.127
Delayed ?-rays 4.3 of prompt ?-rays
signal Delayed neutrons 1 of prompt neutron
signal
28 November 2007
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Secular Equation and Irradiation Time

Secular Equilibrium Shows Radiation Time ?
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Lawrence Livermore National Laboratory

• Disadvantages
• Delayed ?-rays weak signal
• Delayed neutrons weak signal
• To make up for weak signals, neutron flux
  1x1011 n/s
• Radiation issues become a problem

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28 November 2007
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Build detector Wall from Liquid Scintillator
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Nuclear Resonance Fluorescence
Bremsstrahlung Photon Spectrum from 30 MeV
Electron Beam
Density of Nuclear States
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Nuclear Resonance Fluorescence

• Nuclear Resonance Fluorescence (NRF) corresponds
  to
• Photon excitation of a nuclear state
• Energy spectrum of de-excitation photons contains
  elemental content
• Large cross-section nuclear interaction with
  resonant energy photon, even when doppler
  broadening effects are considered
• State energy is 2-8 MeV to penetrate through cargo

• Doppler recoil downshift 1 keV, eliminates
  self-absorption
• Natural Linewidth 0.1 eV
• Doppler broadening 10 eV

Graphic Courtesy Passport Systems, Inc.
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Nuclear Resonance Fluorescence

• Cargo sample is illuminated with beam of
  high-energy photons
• Electrons accelerated into bremsstrahlung target,
  producing broad energy spectrum of high energy
  photons
• Photon beam is collimated and used to interrogate
  a portion of the cargo
• Beam scans over the entire length of cargo to
  develop complete 3-D image of the cargo contents

Electron Accelerator
2-8 MeV Electron Beam
Bremsstrahlung Radiator
Cargo Container
Information Courtesy Passport Systems, Inc.
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Nuclear Resonance Fluorescence

• Photons excite nuclear states in cargo, resulting
  in emission of nuclear fluorescence gamma-ray
  photons
• Gamma-ray photons are captured by an array of
  collimated back-scatter radiation detectors
• Energy of nuclear states is used to determine the
  elemental content of each voxel of cargo
• Scanning photon beam along cargo gives 3-D
  information about elemental content of cargo

Back Scattered Radiation Detectors
Electron Accelerator
Voxels
2-8 MeV Electron Beam
Bremsstrahlung Radiator
Cargo Container
Information Courtesy Passport Systems, Inc.
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Nuclear Resonance Fluorescence

• Transmitted photon spectrum is analyzed for
  absorption lines
• After passing through cargo, beam scatters off of
  multiple reference materials
• Fluorescence photons from these materials are
  captured by collimated transmission radiation
  detectors
• Attenuation at energies where resonance states in
  the cargo exist will be dominated by absorption
• Decrease in the resonance signature for a
  reference scatterer is directly related to the
  amount of that material in the cargo

Transmission Detector
Electron Accelerator
2-8 MeV Electron Beam
Bremsstrahlung Radiator
Collimator
Cargo Container
Information Courtesy Passport Systems, Inc.
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Nuclear Resonance Fluorescence

• Schematic of a potential deployable scanner
• Passport Systems Inc. NRF Cargo Scanner

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Cosmic Ray Muons

• Flux of useful muons (at sea level)
  10,000/m2/min
• 40 muons/min incident on 4 kg block of Plutonium

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Cosmic Ray Muons

• Muons created in Cosmic Ray showers with mean
  energy 3 GeV

W-M Yao et al 2006 J. Phys. G Nucl. Part. Phys.
33 1
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Muon Radiography of Cargo

• Drift chambers placed above and below cargo
  record tracks of incident and scattered muons
• Intersection of tracks gives 3-dimensional
  location of imaged point
• Deflection angle (between tracks) gives Z imaged
  point

• Benefits of Technology
• No radiation hazard source is naturally
  occuring radiation
• Very penetrating 3 GeV muons penetrate 2.6
  meters of Fe
• 3-D imaging of cargo

www.lanl.gov/quarterly/q_spring03/muon_text.shtml
muon_deflect
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Z-Dependence of Muon Multiple-Scattering
Gaussian Angular Deviation of Multiple Coulomb
Scattering
Radiation Length
How much Fe looks like 6 cm of Pu?
Rutherford Scattering
1 GeV muons passing thru 10cm diameter sphere
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Cosmic Ray Test Stand

• Image of tungsten cylinder with steel support
  rails

Borozdin, K. N. et al. Nature 422, 277 (2003).
www.mu-vision.com/Composite20MU-Detector20Whitep
aper_08-03-04.pdf
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Applied Antineutrino Physics To Monitor
Production of Pu
Four Isotopes are the source of reactor power
U(235),U(238), Pu(239),Pu(240) Each Isotope
produces a unique neutrino spectrum. Pu breeding
results in a noticeable change in the neutrino
spectrum
6-Beta Decay /Fission
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Strong Signal for Neutrino Interactions
Signals (1)Flash of Ionization Caused by
positron (2)Two 511keV ?? (3) Neutron Capture ??
detector now deployed below ground
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Standard Applied Antineutrino Physics at
LLNL/SNL

• Measure thermal power to 3 in one week

Determine on/off status within 5 hours with
99.9 C.L.
Track Pu content to50 kg - with known power
and initial fuel content
burnup model with one free parameter
Time in hours
0
Detector is stable to 1 burnup is 10
130
Relative count rate
Continuous, non-intrusive, self-calibrated,
unattended, low cost and channel count, operable
for months to years with rare maintenance
1.5 tons 235U consumed 250 kg 239Pu produced
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Basic Principles of Coherent Scattering

• Neutrino-nucleus scatter coherent for
• En lt 50 MeV (in Argon)
• supernova, solar, reactor neutrinos

Recoil energies
among noble elements Argon (Z18) gives the
greatest number of detectable ionizations per
unit mass
Atomic Number
Cross-section
Neutron Number
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1-10 primaryscintillationphotons in liquid
very difficult to see these 1-10
primaryionization electrons(after quenching
gt25 photoelectronsper primary electron Herein
lies the signal This signal strength has already
been measured in existing ten kg noble
detectors
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A Range of Applications
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Detection and Imaging of Special Nuclear
Materials (SNM) in Containers using an Associated
Particle Neutron Generator
Reported November 29 2007 481 g Uranium (98.6
enriched) seized by Slovakian police http//www.ti
mesonline.co.uk/tol/news/world/europe/article29685
35.ece
17 December 2007
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Associated Particle Neutron Generator

• Deuterium and tritium ion mix accelerated to
  100 keV onto tritiated target
• 14.1 MeV neutrons and 3.5 MeV alpha particles
  produced through deuterium-tritium fusion
  reaction
• Neutron and correlated alpha particles travel in
  opposite directions to conserve momentum
• Maximum yield 109 n/s in 4p steradians
• Pixelization of alpha detector and the use of
  alpha-gamma ray coincidences suppresses background

APLs Associated Particle Neutron Generator
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ZnOGa Alpha Detector

• 1.5 ?m grain of ZnOGa powder (W. Lehmann)
  deposited on fiber optics faceplate by
  gravitational settling using potassium silicate
  as binder and strontium acetate as electrolyte
• Fast ( 1 ns) decay time compared to 20-30 ns for
  YAPCe scintillator detectors
• Time resolution of alpha detector lt 0.7 ns
• Measured 88 alpha detection efficiency
• Large solid-angle with 8 acceptance

Alpha spectrum with (red) without (blue) neutron
coincidence
(a) ZnOGa alpha detector with 2.6 inch active
diameter (b) Schematic depiction of alpha
detector
Time distribution between alpha and neutron
signals using TDS 3032B 300 MHz Tektronix
oscilloscope
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Associated Particle Neutron Generator
Pinhole Camera
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Neutron Interaction with Uranium

• 14 MeV Neutrons
• ?n 8.5 cm
• ?fission 18.7 cm
• ?2n 23.9 cm
• ?3n 46.2 cm
• ?elastic 7.5 cm
• ?n,n 104 cm

• 2 MeV Neutrons
• ?elastic 5.1 cm
• ?fission 39 cm

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Gamma Rays from Fission
5 kg Sphere of U235
High Density and High Z Cause Jet Structure in
the Emitted Gamma Rays from Fission Events
Fission Jet
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Neutron-Induced Fission of SNM

• Fission signature of SNM U-235, U-233, Pu-239
• Prompt signals 1 to 2 orders of magnitude
  stronger than delayed signals
• Delayed neutron emission reduced by 2 orders of
  magnitude within 100 sec
• Prompt ?-ray coincidences from fissions induced
  by 14.1-MeV neutrons used as SNM signature
• U-235 fission cross-sections
• Thermal 584 b
• 14.1-MeV 2 b

APLs A-920 Neutron Generator
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Liquid Krypton (LKr) Scintillation Detectors

• LKr ?-ray scintillation detectors
• 600 ps resolution per channel
• 94 efficiency for 1 MeV ?-rays for 30 cm cell
  depth

Concept design of a multichannel multicell LKr
scintillation detector in the cryostat
A MCNP simulation of 1 MeV ?-rays interacting
in LKr. The division lines are spaced at 10
cm. B Detection efficiency for ?-rays having
energy deposition greater than 0.5 MeV in LKr
scintillator for 1 MeV, 3 MeV, and 5 MeV source
?-rays.
Concept design of an individual 10 kg cell of LKr
scintillation detector
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Scintillating Calorimeter LIDER
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Concept for APLs SNM Cargo Scanner

• Demand coincidences in 3 adjacent detector panels
  with alpha detector
• ?-rays escape SNM in narrow jets
• Example of angular distribution of observed
  prompt ?-rays for 1-kg U-235 using MCNP-Polimi

standard 8 ft x 8 ft x 10 ft cargo
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Concept for Coincidence Circuitry

• Alpha signal strength indicates both presence of
  SNM and spatial location in the appropriate
  voxel

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API Search for Special Nuclear Materials
A Fast neutron fission event 14.1 MeV neutron
initiates fission in SNM to produce a multi-gamma
jet producing coincidences in panels P1, P2, and
P3, and with the alpha particle within a specific
time gate. B Slow neutron fission event gamma
rays in coincidence in panels P1, P2, P3, and P4
indicate SNM. Location determined from LKr
subnanosecond timing of gamma rays. C MCNP
simulation of a 4-fold coincident multi-gamma
fission event as a function of angle.
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Expected Coincidence Rates using MCNP Simulations

• Simulation Set Up
• 5kg U-235, U-238
• centered in 8 ft x 8 ft x 10 ft cargo container
• flux 109 n/s
• demand coincidences in adjacent detector panels
• lead or plastic (C10H11) shielding material

Using R 1.0 MHz, ? 15 ns
U-235 Data
U-238 Data
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Particle Beams
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Search for Special Nuclear Materials Conclusion
High Energy Physics Techniques are Applicable to
the Search for SNM
Particle Probes Include Muons Neutrinos Neutrons
Gamma Rays
Hardware Includes Proton Accelerators Electron
Accelerators Radiation Sources Many types of
Detector Technology
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14.1 MeV Neutron Interactions in the SNM

• Dominant interactions are elastic scattering and
  neutron producing
• Elastic scattering
• Mean free path lelastic 7.5 cm
• Strongly forward diffracted
• Nuclear reactions producing neutrons
• Fission sFission 1.14 b
• (n, 2n) s(n,2n) 0.87 b
• (n, 3n) s(n,3n) 0.45 b
• Mean free path lneutron 8.5 cm
• Governs the penetration depth
• Secondary neutrons are capable of inducing
  fission

Angular distribution of elastically scattered,
outgoing neutrons from a U-238 deflector
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Enhanced Signal-to-Noise and Imaging

• Enhanced signal-to-noise (S/N) ratio due to alpha
  particle coincidence
• Coincidence circuit triggers when ?-rays detected
  in coincidence with associated alpha particle
• Enhanced S/N due to segmentation of alpha
  detector
• Noise distributed evenly throughout alpha
  detectors pixels without affecting signal
• For 10-pixel alpha detector, noise in each
  channel drops by factor of 10
• Total expected S/N enhancement 100x
• Imaging capability using pixilated alpha detector
• Tagged-neutrons path known
• Neutron time of flight is time difference between
  observation of ?-rays and associated alpha
  particle
• 15 ns coincidence gate depth of 75 cm

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The Random Coincidence Rate
Number of requested coincidences m 3

• S singles rate, ? coincidence time, m detector
  channels fire coincidentally out of n detectors
• Select gate 15 ns
• ?-ray flight time 10 ns
• Not neutron flight time 1 ?s too long

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Fast Neutron/Gamma-ray Radiography Scanner for
Air Cargo Containers

• For high Z Materials
• Gamma attenuation high
• Neutrons are forward diffracted with little
  attenuation
• For low Z Materials
• Gamma attenuation low
• Neutron scattering high

Angular distribution of elastically scattered,
outgoing neutrons from a U-238 deflector
Elastic scattering in High Z Material Mean free
path lelastic 7.5 cm Strongly forward
diffracted
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Fast Neutron/Gamma-ray Radiography Scanner for
Air Cargo Containers
Inside the Container
Scanning a Cargo Container
Scanning Image
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Comparison of Systems
Ancore PFNA
COUNTER
Ancore NaI(Tl) Spectrum
Counter HPGe Spectrum
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El Paso PFNA
PFNA inspection tunnel
PFNA building
AGV (Automatic ground vehicle to pull trucks for
inspection)
PFNA 3.2MV tandem electrostatic accelerator
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Voxel Size and Fast Decision Making

• Information Content of a Voxel is to First Order
  Independent of Volume
• Optimal Search and Most Rapid Search When
• Voxel Size Object Searched For

• Ancore ACI/PFNA
• Voxel 6cm x 6cm x 6cm
• COUNTER
• Voxel 30cm x 30cm x 45cm

ACI Voxel mismatch - 100X smaller than searched
for object
COUNTER matched to object search size

• When Voxel Size ltlt Object Searched For
• IMPACTS
• Overly Complex gt Effects System Reliability
• gt Man Power
• gt System Costs
• gt Logistics
• gt Specialized
  Manpower
• Overly Large gt System Mobility
• gt Perimeter
  Protection (Man Power)
• gt Ownership Costs

• When Voxel Size Object Searched For
• IMPACTS
• Optimal Search gt Minimal System
• gt Most
  Reliability for Task
• gt Minimal Man Power
• gt Minimized Costs
• gt Best
  Logistics
• gt Least
  Specialized Manpower
• Optimal Size gt Maximum System Mobility
• gt Least Perimeter
  Protection
• gt Lowest Ownership
  Costs

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COUNTER and ACI