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 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 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

Dark Matter and Neutrino Physics Fissile Material Search /Monitoring

High 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 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 tryingq

,k

,k’

q

Neutral current

+

++

+

q,k

,k’

q

Neutral current

+

++

+ +

++

+

21J1153-02

The basic principles of coherent scattering in argon – signature is very similar to the higher energy WIMP recoil

22244

222

elastic

MeVcm100.44π

)(EN

ENG=σ

ν

νF

Neutron Number

A)(E=>E ν MeVeV716

2

recoil

Atomic NumberCross-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

q,k

,k’

q

Neutral current

+

++

+

q,k

,k’

q

Neutral current

+

++

+ +

++

+

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 gammasPoly 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 d

etec

tor

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

36Option:UCRL# J1153-02

Lawrence Livermore National Laboratory

Backups

37Option:UCRL# J1153-02

Ways in which nuclear security is not like nuclear science..S1/S2, PSD, shielding are not the main issues

LLNL Physicist and IAEAinspector George Anzelon being kicked out of North KoreaFollowing a recent nuclear inspection- April 15 2009

November 13 2009