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