Next Steps In Applied Antineutrino Physics at LLNL

Adam Bernstein, Group Leader,

Advanced Detectors Group,

Lawrence Livermore National LaboratoryDec 14 2007

neutrinos.llnl.gov

nuclear.llnl.gov

LLNL

Outline

• LLNL/SNL Work to Date

• Thoughts about Practical Near-Field Monitoring

• Next Steps at LLNL

1 Range Extension: Studies of Argon Coherent Scatter Detection

2 Understanding Backgrounds and Operating at the Surface of the Earth

• White Paper Status

LLNL

“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 to~50 kg - with known power and initial fuel content

Relative count rate

Time in hours0 130

Continuous, non-intrusive, self-calibrated, unattended, low cost and channel count, operable for months to years with rare maintenance

An

tin

eutr

ino

s

det

ecte

d/d

ay

300

320

340

360

380

400

Days at Full Power0 100 200 300 400 500 600

Det

ecto

r

Sta

bil

ity

(%)

-1

0

1

burnup model with one free parameter

Detector is stable to ~ 1%; burnup is ~ 10%

1.5 tons 235U consumed 250 kg 239Pu produced

NIM A 572 (2007)

J. App. Phys.publication pending

LLNL

What is Needed for Near-Field Cooperative Monitoring and Safeguards ?

– 3x3x3 meter deployment at SONGS is already demonstrably non-intrusive for reactor operators

– Acceptance depends on ability to meet diversion detection goals, cost, ease of use and operator/IAEA acceptance - not primarily on the physical footprint

– there is plenty of physical space with overburden in many safeguarded reactors worldwide

– New designs will be non-toxic, have negligible flammability, no cryogenics, be self-calibrated and easy to deploy

• For Near-Field Monitoring at 10-100 meters, Inverse Beta Detectors May Suffice

• What is the Use of Coherent Scatter Detectors ?

• Above-Ground Detection Would Expand Deployment Opportunities

LLNL

Basic Principles of Coherent Scattering

Neutrino-nucleus scatter coherent for

E < 50 MeV (in Argon)supernova, solar, reactor neutrinos

Antineutrino

ν + Ar → ν + Ar

22244

222

elastic

)MeV(cm104.0

4

EN

ENGF

Neutron Number

A

EE

)MeV(eV716

2

recoil

Atomic Number

Cross-section

Recoil energiesamong noble elements Argon (Z=18)

gives the greatest number of detectable ionizations per unit mass

Energies  E(MeV) <Erecoil> (keV)

Reactor 1 8 0.04 2.5

Solar 2 15 0.16 9.0

Supernova 10 50 4 100

LLNL

Beyond Cross-Section: Detectable Coherent Scatter Rates For Reactor Monitoring

1. Discovery - Ge and Ar both have potential

2. Exploitation – Argon enjoys scalability and (possibly) cost advantages

1. Full CNS detection efficiency required for any significant reduction in footprint

2. Near-field deployment needs already well met with well engineeredinverse beta detectors

3. There may be promise in scaling to 0.1-10 kilometer ranges

Element A N Events Per Kg/Day/3GWt – 25 m standoff

Assumptions

Ar 40 22 4

20

>2 primary electrons

>1 primary electron

Germanium 72 41 2

28

330 eV threshold

100 eV threshold

Charged Current for comparison

- - 0.6

1.5

10% efficiency (SONGS)

25% efficiency (Palo Verde)

LLNL

1-10 primaryscintillationphotons in liquid –very difficult to see these

1-10 primaryionization electrons(after quenching

>~25 photoelectronsper primary electronHerein lies the signalThis signal strength has already been measured in existing ten kg noble detectors

LLNL

Predicted Signal and Background in a 10 kg detector

Ar-39 the dominantbackground: what canbe done about it ?

The neutrino signal including nuclear quenching

Modest (few cm) passive shieldssuffice to screenexternal backgrounds

In this simulation: external neutrons and gammas, internal Ar-39Not yet in this simulation: PMTs ~10000 emitted gammas per day (20 mBq/tube)

LLNL

Are PMT Backgrounds Manageable ?

• ~10,000 decays per day total from PMTs - must incorporate in model

Simulated internalbackgrounds In 100 kg xenon detector (5 keV threshold)104 suppression

Real backgrounds10 kg xenon detector (4.5 keV threshold)59 days livetime

Fiducial and energy cuts shouldsuppress these: most PMT gammaswill be above energy thresholdor multiply scatter

LLNL

The Ar-39 beta background

• 565 keV endpoint – 0.9 Bq/kg in Natural Argon– An important background for coherent scatter

• Gram quantities of depleted Ar created by recovery from underground natural gas reserves (Princeton, Calaprice, Galbiati et. al.)

• Kilogram quantities manufactured by Russian group

Activity limit : at least a factor of 20 lower than natural Argon

This would eliminate Ar-39 as a concern for coherent scatter in Ar

- cost could be an issue- discovery can be done even with Natural Ar

LLNL

Is The Signal Within Reach of Existing Dual-Phase Detectors ?

Lossless drift of electrons over 10 cm distances amply demonstrated in many LAr/LXe experiments – Argon purification techniques are well understood

Sensitivity to single primary electrons –

accomplished in 10 kg Xe detectors (ZEPLIN, XENON10)

Quench factor:

gas-phase quench measurement, consistent with predictions, has been measured at LLNL – this must be repeated in liquid

recoil neticelectromag– energy via deposited ofunit per pairsion

recoil-n– energy via deposited ofunit per pairsion

LLNL

Gas Phase Studies of Very Low Energy Nuclear Recoils

Field cage mounted inside Argon-filled chamber

12 in.

By studying nuclear recoils in the gas phase, we learn about: ionization, gas phase quenching, light collection, scintillation properties

Calibration 55Fe5.9 keV X-rays

Single- photoelectronresponse of PMT

Calibration & Noise-floor estimation

Noise wall

Energy (integral units)

• Only 1 PMT in this detector• ~20 in full scale detector• 1% Ni for wavelngth shifting

LLNL

60 keV Neutron Source: Neutrons Recoils at 8 keV and below

Neutron beam

Argon detectorLLNL LINAC Li-target ~60 keV neutron generator

Gamma

Background

478 keV from 7Li(p,p’)

LeadGamma shield

Borated plasticNeutron shield

7Li (p,n) 7Be100 Hz rep. rate~105 neutrons / spill

LLNL

The Predicted Recoil Spectrum

1) Incident neutrons selectedby resonance

2-4) Neutron kinematics, quenching optical collection efficiency

Deposited energy(before quenching)

Predicted effect of quenching

Actual detector response including PMT coll. eff.

keV

LLNL

A Menagerie of Raw Events

Gate width

Single p.e.~20 ns

X-ray or neutron~2 s

Extended event~6 s

200-μsec time trace during neutron beam measurement -

←Neutron beam on→

LLNL

Extraction of a Quench Factor –the Lowest Ever Measured in Ar ?

Energy threshold for neutron recoils

Gamma signal only above neutron recoil threshold

8 keV neutron recoilgenerates 1.8 keV electronequivalent energy deposition

Derived Quench factor:(preliminary)0.22

Predicted: 0.2

Residual signalattributed to neutrons

LLNL

For comparison: Liquid n-recoil Results from McKinsey Group, Yale

LLNL

A 10 kg Liquid Argon Coherent Neutrino Detector

Design by W. Stoeffl

Coherent ScatterGroup:Chris HagmannCeleste WinantKareem KazkazIgor JovanovicMichael FoxeWolfgang Stoeffl

Pulse tube fridge

PMTs

Turbo-pump

Insulation Vacuum

Valves

Super Insulation

Liquid Nitrogen transport reservoir

Gain region

Drift region

Level gauge

BellowsSupport

HV

Liquid Argon 87K

LLNL

Background Considerations for Antineutrino Detectors at the Surface of the Earth

1. Veto trigger rates increase by 5-10 relative to ‘SONGS1’ - what about deadtime ?

2. Correlated backgrounds gammas neutrons, pions, protons - are an additional concern, beyond the usual problem of time-correlated events from muons

http://abyss.uoregon.edu/~js/glossary/cosmic_rays.html

We are justbeginning to studythis problem

LLNL

First Consideration: Shrink Deadtime By Shrinking Detector

SONGS (3 meter)3 veto - ~30% dead at sea level (~5% at 10 m.w.e.)

(1.5 meter)3 detector/veto – ~5% dead time at sea level - but more elaborate vetoing strategies may be needed* “Standard” veto (100 microsecond following any cosmic)

Current (3 m)3Target (1.5 m)3

Example: (water detector nowdeployed at SONGS, below ground)

LLNL

Second Consideration: Studying Above Ground Time Correlated Backgrounds

1. Characterize with Monte Carlo

2. Measure in meter2 detector arrays (Muon, Liquid Scint., Plastic, 3He)

3. Deploy existing prototypes at SONGS and measure signal and background empirically in antineutrino detectors

4. Explore alternative means to reject backgrounds1. Water Cerenkov detectors2. Segmentation (Jim’s talk)3. Others..

LLNL

Monte Carlo Generation and Detection of Sea Level Backgrounds

A) Public Code package CRY: nuclear.llnl.gov

Due to strong natl. lab interest in surface detection of plutonium and uranium, codes exist to study time correlated backgrounds at sea level – like antineutrinos, fission chains are highly time correlated

All secondaries propagated through 42 layers of atmospheretime correlated energy spectra recorded with up to 300 m horiz separation

B) GEANT and MCNP models of detectors

LLNL

Benchmark examples from sea-level flux (CRY) code

- Muon, Pion, Neutron energy spectra match h.e. data

A First Comparison (For Us) Of Sea Level Showers In Meter2 Detector Arrays

Data

Cumulative number of counts

Time until Next count

2 seconds

Cumulative number of counts

Time until Next count

2 minutes

Simulation

Mixed Array of 3He, NaI, PSD and plastic– 100 detectors, here near 1 ton of lead

LLNL

B) Initial Background Modeling For Water Cerenkov Detectors

– Fast neutrons should not be problem since they are below the Cerenkov threshold up to high energies

– But: energy scale is smeared by low light collection

250 kg detectorNow deployedbelow-groundAt San Onofre

above-ground test in ’08-09

LLNL

Conclusions

• Dual Phase Detectors appear to have the sensitivity needed forcoherent scatter discovery

• Significant Infrastructure for background measurement and modeling at the Earth’s surface will help guide and small surface antineutrino detector designs

LLNL

A Range of Applications

Near Field Mid-Field Far-Field

Use Power, Pu content, operational status

Exclude presence of an operating reactor

Exclude presence of an operating reactor

Example Application: (no interest or disinterest imputed to any USG entity! )

Material Accountancy for Current IAEA Safeguards

Installation at Yong Byon in North Korea to exclude operational reactors

Installation in P.G to detect/exclude reactors in Gulf States of interest

Reactor Power 100-3000 GWt 10 MWt<~1 bomb/year

10 MWt <~1 bomb/year

Standoff/Sensitive Radius

5-50 m 6 km 250 km

Detector Size 1-100 ton with shielding

600 tons (KamLAND fiducial)

1,000,000 tons

Rate 100-1000 events per day (eff~0.1-0.5)

16 events per year (25% power measurement)

16 events per year (25% power measurement)

LLNL

White Paper: A Review of the State of the Art in Antineutrino Detection as Applied to Nonproliferation of Nuclear Weapons

1 Introduction 12 Current Safeguards and Cooperative Monitoring Practice for Light Water

Reactors 33 Current Nuclear Explosion Detection Technology 104 Production and Detection of Antineutrinos From Nuclear Reactors and

Nuclear Explosions 115 Near-Field Detection 136 Mid-Field Detection 137 Far-Field Detection 148 Overview of Fundamental Physics Using Reactor Antineutrinos

179 Research and Development Needs for Basic and Applied Antineutrino

Detection 25

Inputs received for all but two chaptersediting in progress..

Summary for policy and physics community to understand state of the art and R&D program