Post on 24-Dec-2015
Lawrence Livermore National Laboratory
Noble liquid and gas detectors for nuclear security
Adam BernsteinAdvanced Detector Group Leader
Lawrence Livermore National LaboratoryLBL-LLNL xenon workshop
Nov 17 2009
Dennis Carr, Darrell Carter, Mike Heffner, Kareem Kazkaz, Peter Sorensen - LLNL Tenzing Joshi, Rick Norman UCB Nuclear Engineering
Michael Foxe, Igor Jovanovic, Purdue University Nucl Eng.
2J1153-02
Talk outline
The Nuclear Materials Problem And its Connection With Dark Matter and Neutrino Science
Current Detectors and Detection Needs High Pressure Xenon for Spectroscopy and Imaging in
the Field Applied Antineutrino Physics and Coherent Scatter
Detection Improvements in sub-MeV neutron Detection with Liquid
Argon Detectors Conclusions
3J1153-02
The world is awash in civil and military plutonium and highly enriched uranium
Estimate from http://www.isis-online.org Separated plutonium: • 340 tons civil stocks (includes military surplus)• 150 tons military stocks• 490 tons total separated plutonium
In units of Hiroshima style fission weapons …From HEU ~75,000From separated Plutonium ~ 60,000From all plutonium ~ 230,000
Category Plutonium (tonnes)
HEU (tonnes)
Civil 1675 175
Military 155 1725
Total 1830 1900
4J1153-02
What is being done to monitor and reduce global stockpiles of nuclear materials and weapons ?
Civil nuclear fuel cycle monitoring:IAEA safeguards regime, Euratom, ABACC..
Weapons dismantlement verification: START I and II, SORT..
Military nuclear materials control and monitoring – Nunn-Lugar, Fissile Material Cutoff Treaty, HEU Purchase
Domestic nuclear security in individual states – DHS etc.
‘National Technical Means’
5J1153-02
Lawrence Livermore National Laboratory
Detection and monitoring of plutonium and HEU is central to all of these efforts
Quiescent nuclear material: Plutonium and HEU emit penetrating gamma rays and neutrons that can be passively detected out to many tens of meters
Critical systems: Reactors emit huge fluxes of antineutrinos, which can be detected at stand-off distances of tens of meters to hundreds of kilometers
6J1153-02
Neutrino Physics: oscillations and neutrino mass
~1-10 MeV antineutrinos~1-10 MeV antineutrinos
~1 keV to 10 MeV Neutrons and Gamma-rays~1 keV to 10 MeV Neutrons and Gamma-rays
Rare neutral particle detection underlies nuclear security and fundamental nuclear science
Dark Matter and Neutrino Physics are top priorities in 21rst century physics
Fissile Material Search and Monitoring are top priorities for global nuclear security
Rare Event DetectionRare Event Detection
Reactor antineutrino signature
SNM gamma/neutron signatures Dark Matter signatures: Axions and WIMPS
Both areas require improved keV to MeV-scale neutral particle rare event detectors
7J1153-02
Talk Outline
The Nuclear Materials Problem And its Connection With Dark Matter and Neutrino Science
Current Detectors and Detection Needs High Pressure Xenon for Spectroscopy and Imaging in
the Field Applied Antineutrino Physics and Coherent Scatter
Detection Improvements in HEU/PU Characterization with Liquid
Argon Detectors Conclusions
8J1153-02
Nuclear security needs impose unique constraints on detectors
Excellent background rejection through:•Energy resolution •Particle tracking •Particle identification•Active/passive shielding
Excellent background rejection through:•Energy resolution •Particle tracking •Particle identification•Active/passive shielding
Dark Matter and Neutrino Physics Fissile Material Search /Monitoring
High efficiency for the signal of interestHigh efficiency for the signal of interest
• Robust, easy to operate and to interpret
• non-cryogenic usually preferred.. but not always
• Little or no overburden
• Simplicity a secondary consideration
• Cryogenic detectorsoften used
• 100-5000 m.w.e.overburden
Unique to applications Common Needs Unique to fundamental scienceUnique to applications Common Needs Unique to fundamental science
9J1153-02
Current detectors and possible improvements from noble liquid/gas detectors
Particle Current detectors
Example Detector Noble Liquid candidate
Benefit of noble liquid detector
Gamma-ray HPGeNaI(Tl) plastic scintillator Mechanically cooled
handheld HPGe
HPXe Non-cryogenic high resolution Imaging and spectroscopy
Antineutrino Liquid scintillator
Dual phase Argon
Higher rate/smaller footprint
Neutron 3He (thermal) liquid scintillator (fast)
Liquid Argon with PSD
50 keV 1 MeV neutron identification
10J1153-02
Talk outline
The Nuclear Materials Problem And its Connection With Dark Matter and Neutrino Science
Current Detectors and Detection Needs High Pressure Xenon for Spectroscopy and Imaging in
the Field Applied Antineutrino Physics and Coherent Scatter
Detection Improvements in HEU/PU Characterization with Liquid
Argon Detectors Conclusions
11J1153-02
Location and monitoring of nuclear material with gamma-rays
Current spectroscopic systems• Cryogenic detectors (e.g. Ge) have the
best resolution but are hard to field - though this is getting easier
• 3-6% resolution (662 keV FWHM) is far more common in fieldable devices
Current imaging devices
• Few gamma-ray imaging devices used in nuclear security applications –mostly demonstrations or lab devices
• low resolution and/or restricted field of view
A handheld Ge detector
Imaging a MIRved warhead with a CsI coded aperture device
12J1153-02
Possible advantages of xenon gamma-ray spectrometers and imagers for nuclear security applications
Xenon for spectroscopy• High Z (good photo-absorption
capability)• 0.56% FWHM resolution @ 662 keV
(within 3-4x of HPGe)• Non-cryogenic/room temperature
operation• Stable against temperature variations• Highly linear, no nonproportional
response as in for example NaI(Tl)
Xenon for imaging• Spectroscopy advantages, plus..• nearly 4p field of view• Potential for 10-20x improvement in
imaging efficiency using Compton camera approach (relative to segmented Ge)
Performance range of current xenon gas detectors – 2-4% FWHM for 662 keV
Theoretical limit in resolution0.6% FWHM
A. Bolotnikov, B. Ramsey /NIM. A 396 (1997) 360-370
13J1153-02
A recent industrial effort at HPXe spectroscopy
"Field-Deployable, High-Resolution, High Pressure Xenon Gamma Ray Detector” www.proportionaltech.com
DTRA funded project ca 2001-2005:a) No fragile Frisch grid as in prior high resolution designsb) Correct event energy based on event radius derived from
primary and secondary scintillation on wire
Result – ~2% resolution
Fundamental limitations – electronics noise, statistical fluctuations, loss of electrons to impurities
14J1153-02
Can we build a better gas spectrometer ?
These numbers can’t be improvedN = number of liberated electrons F = fano factor in HPXe ~0.15
But these might be.. L= 1-ε = loss factor/inefficiency for electronsG= fluctuations in gain on wires or other
readout mechanism n = rms electronics noise (m = gain factor)
€
δEE
⎛
⎝ ⎜
⎞
⎠ ⎟= 2.35
F
N(E)
⎛
⎝ ⎜
⎞
⎠ ⎟= 2.35
0.15
26480
⎛
⎝ ⎜
⎞
⎠ ⎟= 0.56% @ 662keV
0.56% FWHM resolution @ 662 keV may be possible in a fieldable spectrometer (G=L=δE(electronics) << Fano factor
15J1153-02
Negative Ion Drift to achieve the theoretical limit in gamma-ray energy resolution
Benefits – ideal resolution-. No e- losses, no gain fluctuations, lower purity requirements
Xenon gas with electronegative dopant E
2) Electronegative ions capture electrons and drift (slowly)
1) Xenon ion recoils, inducing ionization
e-
e-
e-
e-
0) Incoming gamma
3) Electron released to Large Electron Multiplier or other gain device
4) LEM amplifies individual electronby 500-10000 well above electronics noise floor (200 e-)
Principle: electronegative dopants capture ionization electrons, slowly drift them to a readout plane, and release them one at a time
Catch (for nonproliferation) – slow drift implies low rate ~1-10 kHz (modest sizedetectors/drift lengths, not for imaging)
But low rate not an issue for zero-rate experiments – see Mike Heffner talk on DOE-OS funded DUSEL R&D project for neutrinoless double beta decay
16J1153-02
Compton imaging in HPXe using electron drift
Segmented Compton camera HPXe Compton camera
Scatter and absorption plane thicknesses must be optimizedImaging efficiency is ~2%
Scatter and absorption ‘planes’throughout the detectorImaging efficiencies >10%
cosq = E = E1 + Eabsorption
17J1153-02
GEANT simulation of efficiencies for Compton scatter + absorption in 1 cubic meter of HPXe
8-12% efficiency from 0.4-0.9 MeV at 10 atm (simulation by Steve Dazeley)
Photon energy (MeV)
Pressure (atm)
Imagingefficiency(Compton+p.e.)
18J1153-02
Talk outline
The Nuclear Materials Problem And its Connection With Dark Matter and Neutrino Science
Current Detectors and Detection Needs High Pressure Xenon for Spectroscopy and Imaging in
the Field Applied Antineutrino Physics and Coherent Scatter
Detection Improvements in HEU/PU Characterization with Liquid
Argon Detectors Conclusions
19J1153-02
The history of Applied Antineutrino Physics
Our group, 2007: Demonstrated practical, self-calibrating, low channel count, non-intrusive, automated antineutrino detectors
Reines and Cowan, 1960: Detect antineutrinos using a reactor source
Mikelyan Group, 1975-1984: First to suggest/demonstrate reactor monitoring with an antineutrino detector
W. Pauli, 1930: “I have done a terrible thing, I have postulated a particle that cannot be detected.”
IAEA Spokesperson, …. “The American group has done the first practical demonstration, and its detector is promising, because it is not much bigger than other systems the IAEA currently deploys at reactors.”
IEEE Spectrum, April 2008
20J1153-02
Reduction of the detector footprint is an important consideration for the end user, the IAEA
Current useful prototypes are ~ 3 meter on a side Smaller detectors would be more attractive
A. Increase efficiency of inverse beta detectors — Shrink footprint to 1.5 m x 1.5 m
B. Discover and exploit coherent neutrino nucleus scattering — Shrink footprint to 1 m x 1 m ? — Slight problem – no one has ever measured this process after 3
decades of trying
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Neutral current
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21J1153-02
The basic principles of coherent scattering in argon – signature is very similar to the higher energy WIMP recoil
22244
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elastic
MeVcm100.4
4π
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ENG
=σ
ν
νF
Neutron Number
A
)(E=>E ν MeV
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recoil
Atomic Number
Cross-section
Recoil energies among the nobles Argon (Z=18) gives the greatest number of detectable
ionizations per unit mass
44.81.85010Supernova υ
4.00.07152Solar υ
1.150.01881Reactor υ
<Erecoil> (keV)Eυ(MeV)Energies
q << 1/(nucleus radius) ~ tens of MeV(condition of coherence)
Quenching detectable ionization energy only a fraction of the recoil energy
Q(Germanium) 0.2Q(Argon) ?=0.2
Detection of few hundreds of eV
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q
Neutral current
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Neutral current
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22J1153-02
A limiting background: solar neutrinos also scatter coherently
The solar neutrino background is comparable with the reactor neutrino signal at distances >1.5 km from the reactor core.
The solar background prevents using coherent scatter detectors to monitor reactors beyond a few kilometers
Detector typefrom
reactor , R_core=20m
from solar
Distance where solar and
reactor counts are equal (Km)
Argon 52.3 6.3e-4 5.8
Estimated counts/day kg
Detector
23J1153-02
Estimates of antineutrino signal & backgrounds @ 10 mwe overburden
10 kg Ar, 25 m standoff, 3.4 GWtSignal: estimated after quenching: 1-10 free e-
Signal Rate ~200 per day (1 or more liquid e-)
Background Rates
counts/ dy/10 kg
Dominant: 39Ar(sim.; depleted Ar reduces
20x)
1000
External U/Th/K :(sim., after 2 cm Pb
shield)
~ 100
External neutrons: (sim. after 10 cm borated
poly shield,)
~ 20
Internal gammas:(as measured in
XENON10):
~ 50 per day @ 3 keVee; but ~1 Hz of single liquid electrons
Shield: Inner: 2cm LeadOuter: 10cm borated polyethylene
Monte Carlo Simulation of signal and backgrounds in 10 kg Ar, per day
Rates in plot and table simulated@ 20 mwe
24J1153-02
Detection concept for coherent scatter – dual phase, S2 only
current test-bed: gas-phase ~1 liter drift volumeOnly look for liquid electrons via
secondary scintilationPrimary signal is too small
25J1153-02
Lawrence Livermore National Laboratory
Attempted neutron-nuclear recoil measurement with gas phase detector
Neutron beam
Argon detector 7Li (p,n) 7Be, 10-100 keV neutrons2-MeV LINAC Li-target neutron generator
100 Hz rep. rate, ~105 neutrons / spill
Gamma Background
478 keV from 7Li(p,p’)
lead or borated poly shielding
Nuclear collisions produce fewer ionizations than electronic collisions. We want to measure this quenching factor.
12”
26J1153-02
Predicted nuclear recoil spectrum – very low energy recoils generated by10-100 keV source overlap with the antineutrino (and WIMP) recoil region
Nuclear recoil spectrum (keVr)Quenched spectrum (keVee) (assume q = 0.25)Simulated detected spectrum (keVee) (geometric losses, quenching)
Incident neutron spectrum Predicted nuclear recoil spectrum(With an assumed quenching factor)
Energy (keVr) or (keVee)
Am
plitu
de
Incident neutrons within this 80keV resonance will contribute to the bulk of measured n-Ar recoils
27J1153-02
First attempt in 2008 - nuclear recoil data analysis using neutrons
Lead data:
neutrons & residual gammas
Poly data:
Mostly residual gammas
Result 8 keVr, 1.8 keVee recoil
Momenta comparable to what is needed for coherent scatter
But detector calibration was an issue…
preliminary
28J1153-02
Improvements on the gas detector test bed
Understand optical collection v. position with movable55Fe source
demonstrate purification with getter plot show 55Fe peak stability versus time in days
Purifier off
replace single PMT with 4 PMT array
Next step: directly measure low energyquench factors in gas, then liquid
29J1153-02
Design of the dual-phase detector is underway now
• 1 kg liquid target• 60 keV neutron source• Fiducialization
with 4 1” square PMTs• May consider LEM
readout
• 5mm x-y resolution would keep multiple scatters to < 8% of total
30J1153-02
Talk outline
The Nuclear Materials Problem And its Connection With Dark Matter and Neutrino Science
Current Detectors and Detection Needs High Pressure Xenon for Spectroscopy and Imaging in
the Field Applied Antineutrino Physics and Coherent Scatter
Detection Improvements in HEU/PU Characterization with Liquid
Argon Detectors Conclusions
31Option:UCRL# J1153-02
21rst century multiplicity counters:Exploiting the theory of the fission chain in quiescent material
Problem: Neutrons and gammas from HEU and Pu, downscattered by shielding, are hard to detect
Timing at the scale of tens of nanoseconds helps select this rare signal from backgrounds
Particle ID is essential Good energy spectroscopy
desirable Current methods work either
at > 0.5 MeV with fast timing or at 0.025 eV (thermal energy) with slow (hundred microsecond interevent times)
32Option:UCRL# J1153-02
Lawrence Livermore National Laboratory
A recent success: detection of shielded HEU in minutes through 6" lead and 2" polyethylene using 200 kg liquid scintillator array
[Analysis and plot by Ron Wurtz/Neal Snyderman]
No HEU HEU present
33Option:UCRL# J1153-02
Cosmic background neutrons
Pu sphere
Implosion weapon with 1” steel shielding(contains some hydrogenous material)
Liqu
id s
cint
illat
ir
Fast timing information 1/1000 PSD degradesbelow ~0.5 MeV
MeV
LAr could improve PSD and preserve timing in this important region
LAr
dete
ctor
E*Dphi/DE
Emission spectra and sensitivity bands compared to neutron background – energy weighted flux
34Option:UCRL# J1153-02
Lawrence Livermore National Laboratory
An operating 7-kg detector— SNOLAB design
Gamma/neutron discrimination in Ar
Liquid argon compared to liquid scintillator
Liquid scintillator woes: • Part-per-thousand gamma/neutron
discrimination • Discrimination does not work
below 500 keV• 35% energy resolution
Pure liquid argon • Part-per-100-million
gamma/neutron discrimination • Works down to 50-60 keV• ~5% energy resolution • Can be mechanically cooled• 10 kg scale detectors demonstrated
35Option:UCRL# J1153-02
Lawrence Livermore National Laboratory
Conclusions
• Significant and useful overlap between nuclear security and dark matter/neutrino applications
• HPXe for imaging and spectrometry relevant for double beta detection
• Dual phase Ar for coherent scattering closely analogous to DM detectors
and an interesting discovery anyway
• Liquid Ar for multiplicity measurements closely analogous to DM detectors