Adam Bernstein Advanced Detector Group Leader Lawrence Livermore
Adam Bernstein Advanced Detector Group Leader Lawrence Livermore National Laboratory LBL-LLNL xenon workshop Nov 17 2009 Noble liquid and gas detectors for nuclear security 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. Lawrence Livermore National Laboratory
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-Me. V neutron Detection with Liquid Argon Detectors § Conclusions J 1153 -02 2
The world is awash in civil and military plutonium and highly enriched uranium Separated plutonium: • 340 tons civil stocks (includes military surplus) • 150 tons military stocks • 490 tons total separated plutonium Category Plutonium (tonnes) HEU (tonnes) Civil 1675 175 Military 155 1725 Total 1830 1900 Estimate from http: //www. isis-online. org In units of Hiroshima style fission weapons … From HEU ~75, 000 From separated Plutonium ~ 60, 000 From all plutonium ~ 230, 000 J 1153 -02 3
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’ J 1153 -02 4
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 Lawrence Livermore National Laboratory J 1153 -02 5
Rare neutral particle detection underlies nuclear security and fundamental nuclear science Fissile Material Search and Monitoring are top priorities for global nuclear security Rare Event Detection Reactor antineutrino signature Dark Matter and Neutrino Physics are top priorities in 21 rst century physics Neutrino Physics: oscillations and neutrino mass ~1 -10 Me. V antineutrinos SNM gamma/neutron signatures ~1 ke. V to 10 Me. V Neutrons and Gamma-rays Dark Matter signatures: Axions and WIMPS Both areas require improved ke. V to Me. V-scale neutral particle rare event detectors J 1153 -02 6
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 J 1153 -02 7
Nuclear security needs impose unique constraints on detectors Fissile Material Search /Monitoring Dark Matter and Neutrino Physics High efficiency for the signal of interest • Robust, easy to operate and to interpret Excellent background rejection through: • non-cryogenic usually preferred. . but not always • Energy resolution • Particle tracking • Particle identification • Active/passive shielding • Little or no overburden • Simplicity a secondary consideration • Cryogenic detectors often used • 100 -5000 m. w. e. overburden Unique to applications Common Needs Unique to fundamental science J 1153 -02 8
Current detectors and possible improvements from noble liquid/gas detectors Particle Current detectors Gamma-ray HPGe Na. I(Tl) plastic scintillator Example Detector Noble Liquid candidate Benefit of noble liquid detector HPXe Non-cryogenic high resolution Imaging and spectroscopy Mechanically cooled handheld HPGe Antineutrino Liquid scintillator Dual phase Argon Higher rate/smaller footprint Neutron 3 He (thermal) liquid scintillator (fast) Liquid Argon with PSD 50 ke. V 1 Me. V neutron identification J 1153 -02 9
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 J 1153 -02 10
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 ke. V 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 Cs. I coded aperture device J 1153 -02 11
Possible advantages of xenon gamma-ray spectrometers and imagers for nuclear security applications § Xenon for spectroscopy Performance range of current xenon gas detectors – 2 -4% FWHM for 662 ke. V • High Z (good photo-absorption capability) • 0. 56% FWHM resolution @ 662 ke. V (within 3 -4 x of HPGe) • Non-cryogenic/room temperature operation • Stable against temperature variations • Highly linear, no nonproportional response as in for example Na. I(Tl) Theoretical limit in resolution 0. 6% FWHM A. Bolotnikov, B. Ramsey /NIM. A 396 (1997) 360 -370 § Xenon for imaging • Spectroscopy advantages, plus. . • nearly 4 p field of view • Potential for 10 -20 x improvement in imaging efficiency using Compton camera approach (relative to segmented Ge) J 1153 -02 12
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 designs b) 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 J 1153 -02 13
Can we build a better gas spectrometer ? These numbers can’t be improved N = number of liberated electrons F = fano factor in HPXe ~0. 15 But these might be. . L= 1 -ε = loss factor/inefficiency for electrons G= fluctuations in gain on wires or other readout mechanism n = rms electronics noise (m = gain factor) 0. 56% FWHM resolution @ 662 ke. V may be possible in a fieldable spectrometer (G=L=δE(electronics) << Fano factor J 1153 -02 14
Negative Ion Drift to achieve theoretical limit in gamma-ray energy resolution Principle: electronegative dopants capture ionization electrons, slowly drift them to a readout plane, and release them one at a time 0) Incoming gamma eee- 2) Electronegative ions capture electrons and drift (slowly) e- 3) Electron released to Large Electron Multiplier or other gain device 4) LEM amplifies individual electron by 500 -10000 well above electronics noise floor (200 e-) Catch (for nonproliferation) – slow drift implies low rate ~1 -10 k. Hz (modest sizedetectors/drift lengths, not for imaging) 1) Xenon ion recoils, inducing ionization Xenon gas with electronegative dopant Benefits – ideal resolution-. No e- losses, no gain fluctuations, lower purity requirements E 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 J 1153 -02 15
Compton imaging in HPXe using electron drift cosq = Segmented Compton camera Scatter and absorption plane thicknesses must be optimized Imaging efficiency is ~2% E = E 1 + Eabsorption HPXe Compton camera Scatter and absorption ‘planes’ throughout the detector Imaging efficiencies >10% J 1153 -02 16
GEANT simulation of efficiencies for Compton scatter + absorption in 1 cubic meter of HPXe Imaging efficiency (Compton+p. e. ) Photon energy (Me. V) Pressure (atm) 8 -12% efficiency from 0. 4 -0. 9 Me. V at 10 atm (simulation by Steve Dazeley) J 1153 -02 17
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 J 1153 -02 18
The history of Applied Antineutrino Physics W. Pauli, 1930: “I have done a terrible thing, I have postulated a particle that cannot be detected. ” Reines and Cowan, 1960: Detect antineutrinos using a reactor source Mikelyan Group, 1975 -1984: First to suggest/demonstrate reactor monitoring with an antineutrino detector Our group, 2007: Demonstrated practical, selfcalibrating, low channel count, non-intrusive, automated antineutrino detectors 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 J 1153 -02 19
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 J 1153 -02 20
The basic principles of coherent scattering in argon – signature is very similar to the higher energy WIMP recoil Energies Eυ(Me. V) <Erecoil> (ke. V) Reactor υ 1 8 0. 018 1. 15 Solar υ 2 15 0. 07 4. 0 10 50 1. 8 44. 8 Supernova υ q << 1/(nucleus radius) ~ tens of Me. V (condition of coherence) among the nobles Argon (Z=18) gives the greatest number of detectable ionizations per unit mass Recoil energies Atomic Number Cross-section Neutron Number § Quenching detectable ionization energy only a fraction of the recoil energy Q(Germanium) 0. 2 Q(Argon) ? =0. 2 Detection of few hundreds of e. V J 1153 -02 21
A limiting background: solar neutrinos also scatter coherently Estimated counts/day kg Detector type from reactor , R_core=20 m Argon 52. 3 from solar Distance where solar and reactor counts are equal (Km) 6. 3 e-4 5. 8 § The solar neutrino background is comparable with the reactor neutrino signal at distances >1. 5 km from the reactor core. Detector § The solar background prevents using coherent scatter detectors to monitor reactors beyond a few kilometers J 1153 -02 22
Estimates of antineutrino signal & backgrounds @ 10 mwe overburden 10 kg Ar, 25 m standoff, 3. 4 GWt Signal: estimated after quenching: 1 -10 free e. Signal Rate ~200 per day (1 or more liquid e-) Background Rates counts/ dy/10 kg Monte Carlo Simulation of signal and backgrounds in 10 kg Ar, per day Dominant: 39 Ar 1000 (sim. ; depleted Ar reduces 20 x) 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 XENON 10): ~ 50 per day @ 3 ke. Vee; but ~1 Hz of single liquid electrons Shield: Inner: 2 cm Lead Outer: 10 cm borated polyethylene Rates in plot and table simulated@ 20 mwe J 1153 -02 23
Detection concept for coherent scatter – dual phase, S 2 only Only look for liquid electrons via secondary scintilation Primary signal is too small current test-bed: gas-phase ~1 liter drift volume J 1153 -02 24
Attempted neutron-nuclear recoil measurement with gas phase detector Nuclear collisions produce fewer ionizations than electronic collisions. We want to measure this quenching factor. lead or borated poly shielding Neutron beam Gamma Background 12” Argon detector 478 ke. V from 7 Li(p, p’ ) 7 Li (p, n) 7 Be, 10 -100 ke. V neutrons 2 -Me. V LINAC Li-target neutron generator 100 Hz rep. rate, ~105 neutrons / spill Lawrence Livermore National Laboratory J 1153 -02 25
Predicted nuclear recoil spectrum – very low energy recoils generated by 10 -100 ke. V source overlap with the antineutrino (and WIMP) recoil region Incident neutron spectrum Amplitude Predicted nuclear recoil spectrum (With an assumed quenching factor) Incident neutrons within this 80 ke. V resonance will contribute to the bulk of measured n-Ar recoils Nuclear recoil spectrum (ke. Vr) Quenched spectrum (ke. Vee) (assume q = 0. 25) Simulated detected spectrum (ke. Vee) (geometric losses, quenching) Energy (ke. Vr) or (ke. Vee) J 1153 -02 26
First attempt in 2008 - nuclear recoil data analysis using neutrons preliminary Lead data: neutrons & residual gammas Poly data: Mostly residual gammas Result 8 ke. Vr, 1. 8 ke. Vee recoil Momenta comparable to what is needed for coherent scatter But detector calibration was an issue… J 1153 -02 27
Improvements on the gas detector test bed Understand optical collection v. position with movable 55 Fe source replace single PMT with 4 PMT array Purifier off demonstrate purification with getter plot show 55 Fe peak stability versus time in days Next step: directly measure low energy quench factors in gas, then liquid J 1153 -02 28
Design of the dual-phase detector is underway now • 1 kg liquid target • 5 mm x-y resolution would • 60 ke. V neutron source keep multiple scatters to < • Fiducialization 8% of total with 4 1” square PMTs • May consider LEM readout J 1153 -02 29
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 J 1153 -02 30
21 rst century multiplicity counters: Exploiting 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 Me. V with fast timing or at 0. 025 e. V (thermal energy) with slow (hundred microsecond interevent times) Option: UCRL# J 1153 -02 31
A recent success: detection of shielded HEU in minutes through 6" lead and 2" polyethylene using 200 kg liquid scintillator array No HEU present [Analysis and plot by Ron Wurtz/Neal Snyderman] Lawrence Livermore National Laboratory Option: UCRL# J 1153 -02 32
Emission spectra and sensitivity bands compared to neutron background – energy weighted flux Implosion weapon with 1” steel shielding (contains some hydrogenous material) LAr could improve PSD and preserve timing in this important region Liquid scintillatir Pu sphere LAr detector E*Dphi/DE Cosmic background neutrons Fast timing information 1/1000 PSD degrades below ~0. 5 Me. V Option: UCRL# J 1153 -02 33
Liquid argon compared to liquid scintillator § Liquid scintillator woes: • Part-per-thousand gamma/neutron discrimination • Discrimination does not work below 500 ke. V • 35% energy resolution § Pure liquid argon • Part-per-100 -million gamma/neutron discrimination • Works down to 50 -60 ke. V • ~5% energy resolution • Can be mechanically cooled • 10 kg scale detectors demonstrated An operating 7 -kg detector — SNOLAB design Gamma/neutron discrimination in Ar Lawrence Livermore National Laboratory Option: UCRL# J 1153 -02 34
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 Lawrence Livermore National Laboratory Option: UCRL# J 1153 -02 35
Backups Lawrence Livermore National Laboratory Option: UCRL# J 1153 -02 36
Ways in which nuclear security is not like nuclear science. . S 1/S 2, PSD, shielding are not the main issues LLNL Physicist and IAEA inspector George Anzelon being kicked out of North Korea Following a recent nuclear inspection - April 15 2009 November 13 2009 Option: UCRL# J 1153 -02 37
- Slides: 37