use of cosmic-ray neutron data in nuclear threat detection and other applications neutron monitor...

Use of Cosmic-Ray Neutron Data in Nuclear Threat Detection and Other ApplicationsNeutron Monitor Community Workshop—Honolulu, Hawaii

October 24-25, 2015

PhysicistNational Urban Security Technology Laboratory Science and Technology Directorate

Paul Goldhagen

Paul Goldhagen Uses of cosmic-ray neutron data

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 measurements

35 years of neutron spectrometry

DHS Government lab in New York City Science and Technology Directorate

Paul Goldhagen Uses of cosmic-ray neutron data 3

Cosmic rays and cosmic-ray-induced (cosmogenic) neutrons

Variation of cosmic particle intensity in the atmosphere

Cosmic rays and cosmogenic neutrons on Earth affect: Nuclear threat detection for homeland/national security Measurements for nuclear treaty verification Microelectronics 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 activation

Calculations and measurements of cosmic-ray neutron spectra

Importance of neutron monitor data

Overview


Cosmic rays in Earth’s atmosphere

electrons/positrons

photonsneutronsprotonsmesonsmuons


Cosmic rays: energetic atomic nuclei from space Protons (90%), He ions (9%), heavier ions (1%); No neutrons Collision 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 effects Solar – sporadic (~1 GLE/y), high rates for hours, lower energy, affect GCR

GCR-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 materials Materials can scatter, absorb, moderate, regenerate neutrons

Effects depend on neutron energy distribution

Cosmic-ray-induced neutrons in the atmosphere


Altitude or air pressure - Shielding by air Big effect, but calculable, measured, well known Neutron rate at 10,000 ft. = 11 rate at sea level Barometric pressure changes can change rate >50% at sea level

Latitude - Shielding by geomagnetic field Calculable, measured Effect increases with altitude Rate at poles / equator 8 at 20 km, 3.3 at 9 km, 2 at sea level

Solar activity - magnetic field of solar wind Not calculable, measured by neutron monitors ~11-year sunspot cycle: Radiation min at sunspot max Effect increases with geomagnetic latitude & altitude Solar modulation >2 (polar) at 20 km, <30% at sea level

GCR neutron rates in the atmosphere depend on


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

Neu

tron

cou

nt r

ate

(co

unts

/sec

)

Pre

ssur

e (

mm

-Hg)

712

760

Newark neutron monitor12 days in 2012

Pressure

Raw count rate

Pressure-correctedrate


Effect of air pressure (elevation)

Atmospheric Depth (g cm-2)700 800 900 1000

Ne

utr

on

Flu

x, E

> 1

0 M

eV (m

-2 s

-1) Fremont Pass, CO

Leadville, CO (10,300 ft)

Mt. Washington, NH

Yorktown Heights, NY

Houston, TX

500

50

100

200

300

30

Log scale

(6,250 ft)Neutron flux decreases exponentially with increasing air pressure

(11,300 ft)


Effect of geomagnetic field (latitude)

Cou

nt R

ate

(10

4 /h)

Measured

Calculated


Solar activity changes

10


Sunspot number and GCR flux

1111


Solar modulation of cosmic-ray neutron fluxDaily neutron monitor rate in Delaware


Uses of cosmic-ray neutron data


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 plutonium

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 background radiation

Passive gamma detection: Low-E rays easily shielded; variable background from common radioactive materials; nuisance alarms from medical treatments, commercial sources

Radiation detection to find nuclear threats


Neutrons are a signature of fissile materials Plutonium emits neutrons – spontaneous fission of 240Pu Common radioactive materials don’t

Passive neutron detection Far fewer nuisance alarms for neutrons than for gamma rays Neutrons 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 background

The background for neutron detection is neutrons produced by cosmic rays

Neutron detection for homeland/national security


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 alarms

Test and compare developmental detection systems

Deal with rapidly varying position-dependent background Mobile standoff detection in cities – varying shielding from buildings Searching ships

For some applications, can’t measure background, must calculate it

For some applications, cosmogenic neutrons are the signal

Need to understand background neutrons


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 modulation

NUSTL: 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 altitudes

Directional n, spectra on ground; altitude scaling to location of interest

Agreement with NUSTL measurements

Date (corresponding to NM data) is an input. To be valid in future, calculations require ongoing neutron monitor data

Background radiation algorithm development

Supported by the US Department of Homeland Security, Domestic Nuclear Detection Office, under competitively awarded contract/IAA HSHQDC-12-X-00251.


MCNP6 cosmic source option

Built-in spectra Historic (PRL / Lal, 1980) Modern (UoD / Clem, 2006)

SDEF card PAR keyword enhanced New keyword DAT New keyword LOC (Clem)

Benchmarking NASA ER-2 flights NUSTL Long Dwell / Goldhagen

18

Description of SDEF keywords.

Keyword Values Description

PAR

[-]cr[-]ch[-]ca

[-]c7014[-]c14028[-]c26056

All cosmic particlesCosmic protons onlyCosmic alphas onlyCosmic nitrogen onlyCosmic silicon onlyCosmic iron only

DATMDY

Month (1-12)Day (1-31)Year (4 digit)

LOCLATLNGALT

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 Division


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

Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104

0

10

20

E d

/dE

(m

-2 s

ec-1

)

Calculated

Measured

with geomagnetic fieldin the atmosphere



0

10

20

30


10-8

10-6

10-4

10-2

100

102

104

2 Ways to plot neutron spectra E/dE Φd vs E/dE ΦdE vsSame data

Diff

eren

tial F

lux,

dF/

dE

(m

-2 s

-1 M

eV-1)

.

E ·

dF/

dE

(m

-2 s

-1).

Flux proportional

to areaunder curve


Cosmic-ray neutron spectrum


0

10

20

E d

/dE

(m

-2 s

ec-1

)

Calculated

Measured

Thermal

High energy

Slowing-down region ~1/E

Evaporation


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

Airplanes

Ground

Ships

NUSTL measurements

Components of NUSTL’s new neutron spectrometer


Measurement on the groundLivermore, CA - Nov 2006



0

10

20

30


10-8

10-6

10-4

10-2

100

102

104

2 Ways to plot neutron spectra E/dE Φd vs E/dE ΦdE vsSame data

Diff

eren

tial F

lux,

dF/

dE

(m

-2 s

-1 M

eV-1)

.

E ·

dF/

dE

(m

-2 s

-1).

Flux proportional

to areaunder curve


Measurements on these container ships

SS Lurline826 ft22,221 Tons

MV Mahimahi and MV Manoa860 ft30,167 Tons


Neutron spectra from cosmic rays on shipsand from simulated threat

26


0

10

20

30

.E

d

/dE

(m

-2 s

ec-1

)

Paul GoldhagenDHS National Urban Security Technology Laboratory 12 Apr 2011

Container ship – above top tier

Container ship – on deck

Cosmic-ray background neutrons

Simulated threat

Shielded WGPu at 2.5 m

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

Have analyzed datafrom boxed portions

of flights

Time after Takeoff (hours) 0 1 2 3 4 5 6

Alti

tude

(k

m)

0

5

10

15

20

East

South 1

North 2

NASA ER-2

Paul Goldhagen Atmospheric Neutrons 27

June 1997


BRAD CR n spectra, 2015Oct.JNB


0.00

0.05

0.10

0.15

E d

/dE

(c

m-2

sec

-1)

Measured and CalculatedHigh-Altitude Cosmic-Ray Neutron Spectra

Calculated

Measured

11.6 GV vert. cutoff54 g/cm2 20.3 km



0.0

0.1

0.2

0.3

0.4

0.5

E d

/dE

(c

m-2

sec

-1)


Calculated

Measured

4.3 GV vert. cutoff201 g/cm2 12 km, 39 kft



0.0

0.5

1.0

E d

/dE

(c

m-2

sec

-1)


Calculated

Measured

0.7 GV vert. cutoff101 g/cm2 16 km, 53,300 ft



0.0

0.5

1.0

E d

/dE

(c

m-2

sec

-1)



Calculated

Measured

High-altitude cosmic-ray neutron spectra

(preliminary) (preliminary)



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

(3He counters) that respond to slow (thermal-energy) neutrons Big 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 - 104 MeV

Calculate energy response of detector assemblies using MCNPX/6

Low resolution; need spectral unfolding: MAXED code

Extended-range multisphere neutron spectrometers


NUSTL multisphere neutron spectrometer

30


0

5

10

15

987

6

1

Res

po

nse

(C

oun

ts c

m2 n

eutr

on-1

)

13

14

Calculated using MCNPX

12

11

4

10

2

14

5

89

10

11

12

3


High-energy neutron detector

31

15-inch diameterpolyethylene ball

Steel shell

3He gas proportional counter


NUSTL multisphere neutron spectrometer

32


0

5

10

15

987

6

1

Res

po

nse

(C

oun

ts c

m2 n

eutr

on-1

)

13

14

Calculated using MCNPX

12

11

4

10

2

14

5

89

10

11

12

3

“Ship effect”


Multisphere neutron spectrometer in container


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


Other applications – national security


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

RDE: 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 / time

Real-time neutron rate needs real-time neutron monitor data

Nuclear arms treaty verification


Argon-37 (T½ = 35 days) is produced by nuclear explosions

Proposed 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 rate

Rate depends on soil composition, location, solar modulation

Requires neutron monitor data for most recent 2 months

Test ban treaty nuclear forensics


Single-event upsets in microelectronics(Mike Gordon, IBM)

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.


Aircrews occupationally exposed to radiation from cosmic rays High-energy mixed radiation field Effective dose can’t be measured using personal dosimeters 40% - 60% of biologically effective dose from neutrons

Continual 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)


Measure soil water, snow, biomass using cosmogenic neutrons

Previously 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 countries

Thermal-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.


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

Atmospheric tracers (7Be)

Geological dating (10Be,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 radionuclides


Cosmic particle intensity in the atmosphere varies with Altitude/pressure – big, but calculable, measured, well known Geomagnetic latitude / cutoff rigidity – calculable, measured Solar activity – measured by neutron monitors, not predictable

Cosmic rays and cosmogenic neutrons on Earth affect: Nuclear threat detection for homeland security Measurements for nuclear treaty verification, nuclear forensics Radiation dose to airplane crews/passengers and everyone Microelectronics reliability (single-event upsets) Hydrology measurements Production of cosmogenic radionuclides – atmospheric tracers, geological

dating, background for neutron activation

These applications need ongoing neutron monitor data

Summary


Additional / background information

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.

[email protected]


Neutron flux on a logarithmic energy scale

2log

1log

2

1

)(log

1

E

E

E

E

EddE

dE

dEEdE

dE


Cosmic rays during high solar activity

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


Largest solar particle event ground level enhancement in 50 years

07:00 Time 08:00

Ne

utr

on

Ra

te (

coun

ts/s

econ

d)Jan 20, 2005

USEast coast 2.5 South Pole 50


BRAD CR n spectra, 2012Jan.JNB


0

10

20

E d

/dE

(

m-2

sec

-1)

Calculated

Measured

Measured and calculated cosmic-ray neutron spectrain High-bay building at Sandia Labs, Livermore, CA

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

(preliminary)without geomagnetic fieldin the atmosphere


Radiation exposure of U.S. population NCRP 160

Percent of all sources (6.2 mSv)

Percent of background (3.2 mSv)

Space 5%

Space 11%


Neutrons, unlike charged particles, pass through the electron clouds of atoms without slowing down

When neutrons hit atomic nuclei, they usually bounce off (scatter), though sometimes they get absorbed If 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 ball

Hydrogen 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 more

These thermal neutrons are the easiest to detect or absorb

Neutron moderation (slowing) & thermalization


“Ship effect”: increase in the neutron background generated by cosmic rays near large masses of metal, such as ships

High-energy cosmic-ray neutrons hit iron nuclei and excite them, releasing many fission-energy neutrons (spallation/evaporation)

Cold war study of standoff ship effect – classified

On 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, cargo

Neutron energy spectrum similar to shielded fission

The neutron “ship effect”


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 ports

Proposed 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 $millions

Long-Dwell In-Transit (LDIT) study, mostly for gamma detection; NUSTL did neutron background measurements

DNDO Long-Dwell In-Transit Study


Cosmic-ray background neutron spectrameasured on container ships and land


0

10

20

30Scaled to samemagnetic latitude

& air pressure

.E

d

/dE

(m

-2 s

ec-1

)

Land, Livermore CA

Container shipabove top tier

Container ship – on deckunder ~3 layers of empties


Neutron spectra from cosmic rays on shipsand from simulated threat

54


0

10

20

30

.E

d

/dE

(m

-2 s

ec-1

)

Paul GoldhagenDHS National Urban Security Technology Laboratory 12 Apr 2011

Container ship – above top tier

Container ship – on deck

Cosmic-ray background neutrons

Simulated threat

Shielded WGPu at 2.5 m


Ground measurements outdoors, 2002-2003

55


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

56


0

20

40

60

80

100

120

140

160

180

.E

d

/dE

(m

-2 s

ec-1

)

HoustonYorktown Hts.

Mt. Washington

LeadvilleFremont Pass


Effect of air pressure (elevation)

Atmospheric Depth (g cm-2)700 800 900 1000

Ne

utr

on

Flu

x, E

> 1

0 M

eV (m

-2 s

-1) Fremont Pass, CO

Leadville, CO (10,300 ft)

Mt. Washington, NH

Yorktown Heights, NY

Houston, TX

500

50

100

200

300

30

Log scale

(6,250 ft)Neutron flux decreases exponentially with increasing air pressure

(11,300 ft)


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

58


0

5

10

15

.E

d

/dE

(m

-2 s

ec-1

)

HoustonYorktown Hts.

Mt. Washington

LeadvilleFremont Pass


Analytic model of neutron flux cutoff dependence

,,,cBA0 dIRFdFdE

Ed

dE

Ed

1c1cquietB, exp1098.1, kRhRF (A.6)

and

,50exp150exp1exp1098.1, 21221c2cactiveB,

kkkRhRF (A.7)

where the parameters and k are given by

,11exp09.0094.084.1exp1 hh (A.8)

,8.8exp24.056.04.11 hhk (A.9)

,10exp18.015.093.1exp2 hh (A.10)

and .5.9exp18.049.032.12 hhk (A.11)

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).


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 measurement

Scaling 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 data

Uncertainty ~20%; thermals may vary by factor of 2

Systematically high towards equator

Measured ground-level cosmic-ray neutron spectrum and scaling factor

http://www.jedec.org/

http://www.jedec.org/

http://www.seutest.com/cgi-bin/FluxCalculator.cgi


GCR-induced particles in the atmosphere

Effective dose rate vs. altitudeEffective Dose vs. Altitude

for Galactic Cosmic Ray Components

Altitude (km)0 5 10 15 20 25

Effe

ctiv

e D

ose

Ra

te

(S

v h-1

)

0.001

0.01

0.1

1

10

(1000 ft)

10 20 30 40 50 60 70 80

Totalneutrons

photons +electrons

protons (wR = 2)

muons

pions

Data from O'Brien LUIN-98Fcalculation at 55.4° N, 120° W


Radiation doses to aircrews are calculated

FAA: Air crews are occupationally exposed No regulations, recommendation to inform, training materials

Civil 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 kept

Funded program to calculate and measure doses

Several route-dose computer codes (all require neutron monitor data)

Some airlines ground pregnant aircrew

ISO standard under development to validate air route-dose codes

What has been done - commercial aviation


High-altitude cosmic-ray neutron spectra



0.00

0.05

0.10

0.15

E d

/dE

(

cm-2

sec

-1)


Calculated

Measured

11.6 GV vert. cutoff54 g/cm2 20.3 km



0.0

0.1

0.2

0.3

0.4

0.5

E d

/dE

(

cm-2

sec

-1)


Calculated

Measured




0.0

0.5

1.0

E d

/dE

(

cm-2

sec

-1)


Calculated

Measured

0.7 GV vert. cutoff101 g/cm2 16 km, 53,300 ft




0.0

0.5

1.0

E d

/dE

(

cm-2

sec

-1)



Calculated

Measured

(preliminary: before atmospheric B field and heavy ions)

(preliminary)

(preliminary)

use of cosmic-ray neutron data in nuclear threat detection and other applications neutron monitor...

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