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Use of Cosmic-Ray Neutron Data in Nuclear Threat Detection Use of Cosmic-Ray Neutron Data in Nuclear Threat Detection

Use of Cosmic-Ray Neutron Data in Nuclear Threat Detection - PowerPoint Presentation

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Use of Cosmic-Ray Neutron Data in Nuclear Threat Detection - PPT Presentation

and Other Applications Neutron Monitor Community WorkshopHonolulu Hawaii October 2425 2015 Physicist National Urban Security Technology Laboratory Science and Technology Directorate ID: 465657

cosmic neutron ray neutrons neutron cosmic neutrons ray background energy detection radiation nuclear monitor rate rays data pressure solar

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Slide1

Use of Cosmic-Ray Neutron Data in Nuclear Threat Detection and Other Applications

Neutron Monitor Community Workshop—Honolulu, Hawaii

October 24-25, 2015

PhysicistNational Urban Security Technology Laboratory Science and Technology Directorate

Paul GoldhagenSlide2

National Urban Security Technology Laboratory

(formerly, Environmental Measurements Laboratory)

2

~30 people

Established 1947, AEC- DOE - DHS

HASL - EML -

NUSTL

Support to emergency responders

Long history of fallout and radiation measurements35 years of neutron spectrometry

DHS

Government lab in New York City Science

and Technology Directorate Slide3

Cosmic rays and cosmic-ray-induced (cosmogenic) neutronsVariation of cosmic particle intensity in the atmosphereCosmic rays and cosmogenic neutrons on Earth affect:

Nuclear threat detection for homeland/national securityMeasurements for nuclear treaty verificationMicroelectronics reliability (single-event upsets)

Radiation dose to airplane crews/passengers (and everyone)Hydrology measurements

Production of cosmogenic radionuclides – atmospheric tracers, geological dating, background for neutron activationCalculations and measurements of cosmic-ray neutron spectraImportance of neutron monitor data

Overview

3Slide4

Cosmic rays in Earth’s atmosphere

4

electrons/positrons

photons

neutrons

protons

mesons

muons Slide5

Cosmic rays: energetic atomic nuclei from spaceProtons (90%), He ions (9%), heavier ions (1%); No neutronsCollision with atmosphere

 cascades of all kinds of particles, including neutrons (and protons, mesons, muons, photons, electrons)Two kinds / sources

Galactic (GCR) – continual, high energy, dominate effectsSolar – sporadic (~1 GLE/y), high rates for hours, lower energy, affect GCRGCR-induced neutrons dominate radiation effects in the atmosphere from airplane altitudes to the ground

Rates depend on air pressure, magnetic latitude, solar activity, and nearby materialsMaterials can scatter, absorb, moderate, regenerate neutrons

Effects depend on neutron energy distribution

Cosmic-ray-induced neutrons in the atmosphere5Slide6

Altitude or air pressure - Shielding by airBig effect, but calculable, measured, well known

Neutron rate at 10,000 ft. = 11  rate at sea levelBarometric pressure changes can change rate >50% at sea level

Latitude - Shielding by geomagnetic field Calculable, measured

Effect increases with altitudeRate at poles / equator  8 at 20 km, 3.3 at 9 km, 2 at sea levelSolar activity - magnetic field of solar wind

Not

calculable, measured by neutron monitors~11-year sunspot cycle: Radiation min at sunspot maxEffect increases with geomagnetic latitude & altitudeSolar modulation >2 (polar) at 20 km, <30% at sea levelGCR neutron rates in the atmosphere depend on6Slide7

Neutron monitor count rate and barometric pressure during super-storm Sandy

7

Neutron count rate (counts/sec)

Pressure (mm-Hg)

712

760

Newark neutron monitor12 days in 2012

PressureRaw count rate

Pressure-correctedrateSlide8

Effect of air pressure (elevation)

8

Log scale

(6,250 ft)

Neutron flux decreases

exponentially

with increasing air pressure

(11,300 ft)Slide9

Effect of geomagnetic field (latitude)

9

Measured

CalculatedSlide10

Solar activity changes

10Slide11

Sunspot number

and GCR flux

11

11Slide12

Solar modulation of cosmic-ray neutron fluxDaily

neutron monitor rate in Delaware

12Slide13

Uses of cosmic-ray neutron dataSlide14

DHS, DOE, and DoD fund programs to improve detection of hidden nuclear devices and fissile materials Primary method is radiation detection

Passive detection – detect gamma rays emitted by uranium and gammas and neutrons emitted by plutoniumActive interrogation: use pulsed incident radiation; detect neutrons and

 rays from induced fission of HEU as well as PuTo find hidden materials, detectors must be sensitive enough to detect / measure

background radiationPassive gamma detection: Low-E  rays easily shielded; variable background from common radioactive materials

;

nuisance alarms from medical treatments, commercial sourcesRadiation detection to find nuclear threats14Slide15

Neutrons are a signature of fissile materials Plutonium emits neutrons – spontaneous fission of 240Pu

Common radioactive materials don’tPassive neutron detectionFar fewer nuisance alarms for neutrons than for gamma raysNeutrons are harder to shield than gamma rays

Active interrogation: use pulsed incident radiation; detect neutrons and  rays from induced fission of HEU as well as Pu

To find hidden materials, detectors must be sensitive enough to detect / measure backgroundThe background for neutron detection is neutrons produced by cosmic rays

Neutron detection for homeland/national security

15Slide16

Background rate in deployed detectors can and must be measured, but need to understand background in advance to: Design new, better detection systems

Improve signal/background; reduce nuisance alarmsTest and compare developmental detection systemsDeal with rapidly varying position-dependent background

Mobile standoff detection in cities – varying shielding from buildings Searching shipsFor some applications, can’t measure background, must calculate it

For some applications, cosmogenic neutrons are the signal Need to understand background neutrons

16Slide17

DHS DNDO TAR funded LANL, NUSTL, UD to calculate the cosmic-ray neutron background everywhere on Earth.UD: Primary CR spectrum, directional geomagnetic cutoffs, atmosphere

LANL: coding, normalization, transport, solar modulationNUSTL: Benchmark measurements of cosmogenic neutron energy spectra in airplane and on ground at various locations

MCNP6 calculations: cosmic source, method, results, version 2.0 n, p,

,  spectra on 2054 point global grid at ground and 10 altitudesDirectional n,

spectra on ground; altitude scaling to location of interestAgreement with NUSTL measurementsDate (corresponding to NM data) is an input. To be valid in future, calculations require ongoing neutron monitor dataBackground radiation algorithm development17Supported by the US Department of Homeland Security, Domestic

Nuclear Detection Office, under competitively awarded

contract/IAA HSHQDC-12-X-00251.Slide18

MCNP6

cosmic source option

Built-in spectra

Historic (

PRL / Lal

, 1980)Modern (UoD / Clem, 2006)SDEF cardPAR keyword enhancedNew keyword

DAT

New keyword LOC (Clem)BenchmarkingNASA ER-2 flights

NUSTL Long Dwell / Goldhagen 18Description of SDEF keywords.KeywordValues

Description

PAR

[-]

cr

[-]

ch

[-]

ca

[-]c7014

[-]c14028

[-]c26056

All cosmic particles

Cosmic

protons only

Cosmic

alphas only

Cosmic

nitrogen only

Cosmic silicon only

Cosmic iron only

DAT

M

D

Y

Month (1-12)

Day (1-31)

Year (4 digit)

LOC

LAT

LNG

ALT

Latitude (-90 to 90; S to N)

Longitude (-180 to 180; W to E)

Altitude (km)

Garrett McMath and

Gregg McKinney

LANL, Nuclear Engineering & Nonproliferation DivisionSlide19

Cosmic-ray neutron spectrum on the groundLivermore, CA - Nov 2006

19

with geomagnetic field

in the atmosphereSlide20

20

2 Ways to plot neutron spectra

Same data

Differential Flux,

d

F

/dE

(m

-2

s

-1

MeV

-1

)

.

E

·

d

F

/dE

(m

-2

s

-1

)

.

Flux

proportional

to area

under curveSlide21

Cosmic-ray neutron spectrum

21

Thermal

High energy

Slowing-down region ~1/E

EvaporationSlide22

NUSTL has measured the energy spectrum of cosmic-ray neutrons on:Airplanes

GroundShipsNUSTL measurements

22

Components of NUSTL’s new neutron spectrometerSlide23

Measurement on the groundLivermore, CA - Nov 2006

23Slide24

24

2 Ways to plot neutron spectra

Same data

Differential Flux,

d

F

/dE

(m

-2

s

-1

MeV

-1

)

.

E

·

d

F

/dE

(m

-2

s

-1

)

.

Flux

proportional

to area

under curveSlide25

Measurements on these container ships

25

SS Lurline

826 ft

22,221 Tons

MV Mahimahi and MV Manoa

860 ft

30,167

TonsSlide26

Neutron spectra from cosmic rays on shipsand from simulated threat

26Slide27

Paths of AIR ER-2 flights Altitude profiles of 3 flights

Have analyzed data

from boxed portions

of flights

NASA ER-2

Paul Goldhagen Atmospheric Neutrons

27

June 1997Slide28

High-altitude cosmic-ray neutron spectra

28

(preliminary)

(preliminary)

(preliminary)

(preliminary)Slide29

Multisphere neutron spectrometer (Bonner spheres)Set of spherical moderators of different sizes surrounding detectors (

3He counters) that respond to slow (thermal-energy) neutronsBig moderators slow down higher-energy neutrons than small moderators (up to ~30 MeV)To detect high-energy neutrons, add heavy-metal

shells (Pb, Fe) to some spheres High-energy neutron hits large nucleus 

hadron spray with readily detectable fission-energy “evaporation” neutrons Covers whole energy range of cosmic-ray neutrons: 10-8 - 10

4

MeVCalculate energy response of detector assemblies using MCNPX/6Low resolution; need spectral unfolding: MAXED codeExtended-range multisphere neutron spectrometers29Slide30

NUSTL multisphere neutron spectrometer

30Slide31

High-energy neutron detector

31

15-inch diameter

polyethylene ball

Steel shell

3

He gas proportional counterSlide32

NUSTL multisphere neutron spectrometer

32

“Ship effect”Slide33

Multisphere neutron spectrometer in container33Slide34

Measurements on the ground in Hawaii elevations from sea level to 12,800 feet

34Slide35

Other applications – national securitySlide36

For INF and START treaties, radiation detection equipment (RDE) used to verify number of missile warheadsRDE

: array of moderated 3He counters used to measure fission neutron rate (subtracting cosmogenic background neutrons)Proper operation verified in field using Am-Li neutron source

Russia proposed using background neutrons instead of transporting neutron source – less hassle

Can we trust that proper operation of RDE is verified using just background neutrons?Need calculated cosmic-ray neutron count rate at each site / timeReal-time neutron rate needs real-time neutron monitor data

Nuclear arms treaty verification

36Slide37

Argon-37 (T½ = 35 days) is produced by nuclear explosionsProposed for use in CTBT inspections to detect underground nuclear tests

Cosmic-ray neutrons produce background 37Ar in the ground DTRA-funded

researchers at Univ. of Texas use MCNP6 to calculate cosmic-ray neutron spectrum / intensity

incident on the ground and 37Ar background production rateRate depends on soil composition, location, solar modulationRequires neutron monitor data for most recent 2 months

Test ban treaty nuclear forensics

37Slide38

Single-event upsets in microelectronics

(Mike Gordon, IBM)

38

A few

nucleons cause

Most

nucleons

pass

 particles, heavy ions Neutrons & protons (ionization by each particle) (via recoils from nuclear reaction)

Flip bits, corrupt data (JEDEC Standard JESD89A)

Occur if enough charge is deposited in the sensitive volume.Slide39

Aircrews occupationally exposed to radiation from cosmic raysHigh-energy mixed radiation fieldEffective dose can’t be measured using personal dosimeters

40% - 60% of biologically effective dose from neutronsContinual exposure of large group~160,000 civilian aircrew members in U.S. Civil aircrew working hours aloft ~ 500-1000 h / year

Annual effective dose 1 to 6 mSv (U.S. radiation workers average 2.2)Air crews are one of the most exposed groups of radiation workers

Radiation protection for airplane crews(Kyle Copeland, FAA)

39Slide40

Measure soil water, snow, biomass using cosmogenic neutronsPreviously elusive scale, tens of hectares, 10

– 60 cm deep Same principal as Am-Be soil moisture gauges: water moderates / thermalizes evaporation (MeV) neutrons

Use moderated (and bare) neutron detectors to measure rates of 1 – 1000 eV slowing-down neutrons (and thermals)Over 200 probes in use

COSMOS network in U.S. (NSF); networks in other countriesThermal-neutron rate depends on soil composition

Normalize using neutron monitor rate;

best if nearby (U.S.)HydrologyZreda, Desilets, et al., Univ. of Arizona, Sandia Natl. Lab.40Slide41

Cosmic-ray neutrons create cosmogenic radionuclides in the air and ground

Atmospheric tracers (7Be)Geological dating (10

Be,14C, 36Cl, …)Background for neutron activation measurements

Source terms require knowledge of cosmic-ray neutron spectrum and intensity For shorter half-life nuclides, intensity requires neutron monitor data

DS2002 resolution of Hiroshima neutron dosimetry discrepancy

Measurements of neutron activation nuclides in Hiroshima samples (36Cl, 60Co, 63Ni, 152Eu) seemed high at large distances. Actually caused by cosmic-ray neutron background. Production of cosmogenic radionuclides41Slide42

Cosmic particle intensity in the atmosphere varies withAltitude/pressure – big, but calculable, measured, well known

Geomagnetic latitude / cutoff rigidity – calculable, measuredSolar activity – measured by neutron monitors, not predictableCosmic rays and cosmogenic neutrons

on Earth affect:Nuclear threat detection for homeland securityMeasurements for nuclear treaty verification, nuclear forensics

Radiation dose to airplane crews/passengers and everyoneMicroelectronics reliability (single-event upsets)Hydrology measurements

Production of cosmogenic radionuclides – atmospheric tracers, geological dating, background for neutron

activationThese applications need ongoing neutron monitor dataSummary42Slide43

43Slide44

Additional / background information44

Slides following this one contain

additional and background information

that is not part of the planned oral presentation.

These slides may be useful for answering questions.

paul.goldhagen@hq.dhs.govSlide45

Neutron flux on a logarithmic energy scale45Slide46

Cosmic rays during high solar activity46

A:

First coronal mass ejection (CME) at Sun. B:

First CME arrives at Earth. GCR decrease suddenly — a “Forbush decrease.” C: 2nd

CME at Sun. This one accelerates

high-energy particles that reach Earth minutes later. The sudden increase recorded by the neutron monitors is a “ground level enhancement.” D: 2nd CME arrives at Earth. GCR decrease again. This CME produces largest geomagnetic storm in 10 years. Cosmic ray variations recorded at 7 different neutron monitor stations

On average, solar activity

reduces

cosmic ray intensity on Earth Slide47

Largest solar particle event ground level enhancement in 50 years

47

07:00

Time

08:00

Neutron Rate (counts/second)Jan 20, 2005

US

East coast

2.5

South Pole

50 Slide48

Cosmic-ray neutron spectrum on the

ground

Livermore, CA, Nov 2006

48

(preliminary)

without

geomagnetic field

in the atmosphereSlide49

Radiation exposure of U.S. population NCRP 160

49

Percent of all sources

(6.2 mSv)

Percent of background

(3.2 mSv)

Space 5%

Space 11%Slide50

Neutrons, unlike charged particles, pass through the electron clouds of atoms without slowing downWhen neutrons hit atomic nuclei, they usually bounce off (scatter), though sometimes they get absorbedIf the target nucleus is heavy, the neutrons barely slow, like a golf ball bouncing off a bowling ball

If the target nucleus is light, it recoils, and the neutron slows down a lot, like a golf ball bouncing off another golf ballHydrogen is the element with the lightest nucleus, so materials with a lot of hydrogen (plastic, oil, water) slow neutrons best

After a few tens of scatters, neutrons get as slow as the thermal motion of the hydrogen atoms and don’t slow moreThese thermal neutrons are the easiest to detect or absorb

Neutron moderation (slowing) & thermalization50Slide51

“Ship effect”: increase in the neutron background generated by cosmic rays near large masses of metal, such as shipsHigh-energy cosmic-ray neutrons

hit iron nuclei and excite them, releasing many fission-energy neutrons (spallation/evaporation)Cold war study of standoff ship effect – classifiedOn ships, increased neutron background can cause nuisance alarms that interfere with detection and identification of hidden nuclear materials.

Background neutrons at fission energies are increased on ships by up to a factor of 2 to 4. Varies with size/type of ship, location on ship, cargoNeutron energy spectrum similar to shielded fission

The neutron “ship effect”51Slide52

If terrorists hide a nuclear device or material in cargo on a container ship to U.S., how can we detect it before it arrives? For a nuclear device, detection after arrival is too late

>10 million containers per year arrive in U.S.Difficult to screen all containers in all foreign portsProposed solution: radiation detection in transit – detectors on every container or every container ship

Days or weeks for detection (

long dwell) instead of seconds Very difficult and expensive in practice

Can it work – even theoretically? (No.)

If not, don’t fund pilot deployment; save tens of $millionsLong-Dwell In-Transit (LDIT) study, mostly for gamma detection; NUSTL did neutron background measurementsDNDO Long-Dwell In-Transit Study52Slide53

Cosmic-ray background neutron spectrameasured on container ships and land

53Slide54

Neutron spectra from cosmic rays on shipsand from simulated threat

54Slide55

Ground measurements outdoors, 2002-2003

55Slide56

Cosmic-ray neutron spectra measured on the ground at 5 locations with different elevations

56Slide57

Effect of air pressure (elevation)

57

Log scale

(6,250 ft)

Neutron flux decreases

exponentially

with increasing air pressure

(11,300 ft)Slide58

Measured cosmic-ray neutron spectra scaled to sea level, NYC, mean solar activity

58Slide59

Analytic model of neutron flux cutoff dependence

59

From: Belov, A., A. Struminsky, and V. Yanke, "Neutron Monitor Response Functions for Galactic and Solar Cosmic Rays", 1999 ISSI Workshop on Cosmic Rays and Earth, poster presentation.

Described in: Clem, J. and L. Dorman, "Neutron monitor response functions,"

Space Sci. Rev

.,

93

: 335-363 (2000).Slide60

Results used to define terrestrial neutron flux in Annex A,

“Determination of terrestrial neutron flux” in

JESD89A Measurement and Reporting of Alpha Particle and Terrestrial Cosmic Ray-Induced Soft Errors in Semiconductor Devices

http://www.jedec.org

“Standard” neutron spectrum from NUSTL-IBM measurementScaling factor for any altitude/pressure, geographic location, solar activity from BSYD model Also at http://www.seutest.com/cgi-bin/FluxCalculator.cgi Must manually enter solar modulation from neutron monitor dataUncertainty ~20%; thermals may vary by factor of 2Systematically high towards equatorMeasured ground-level cosmic-ray neutron spectrum and

scaling factor60Slide61

GCR-induced particles in the atmosphere

Effective dose rate vs. altitude

61Slide62

Radiation doses to aircrews are calculatedFAA: Air crews are occupationally exposed

No regulations, recommendation to inform, training materialsCivil Aerospace Medical Institute Radiobiology Research Team – Copeland

CARI-6 route-dose computer code – requires neutron monitor data European Community: Air crews true radiation workers

Doses assessed, records to be keptFunded program to calculate and measure dosesSeveral route-dose computer

codes (all require

neutron monitor data)Some airlines ground pregnant aircrew ISO standard under development to validate air route-dose codesWhat has been done - commercial aviation62Slide63

High-altitude cosmic-ray neutron spectra

63

(preliminary)

(preliminary

)

(preliminary: before

atmospheric B field

and heavy ions

)

(preliminary

)

(preliminary

)