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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 CityScience and Technology Directorate
Paul Goldhagen Uses of cosmic-ray neutron data
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
3
Paul Goldhagen Uses of cosmic-ray neutron data
Cosmic rays in Earth’s atmosphere
4
electrons/positrons photonsneutronsprotonsmesonsmuons
Paul Goldhagen Uses of cosmic-ray neutron data
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
5
Paul Goldhagen Uses of cosmic-ray neutron data
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
6
Paul Goldhagen Uses of cosmic-ray neutron data
Neutron monitor count rate and barometric pressure during super-storm Sandy
7
Neu
tron
coun
t rat
e (c
ount
s/se
c)
Pre
ssur
e (m
m-H
g)
712
760
Newark neutron monitor12 days in 2012
Pressure
Raw count rate
Pressure-correctedrate
Paul Goldhagen Uses of cosmic-ray neutron data
Effect of air pressure (elevation)
8
Atmospheric Depth (g cm-2)700 800 900 1000
Neu
tron
Flux
, E >
10
MeV
(m
-2 s
-1) Fremont Pass, CO
Leadville, CO (10,300 ft)
Mt. Washington, NH
Yorktown Heights, NYHouston, TX
500
50
100
200
300
30
Log scale
(6,250 ft)Neutron flux decreases exponentially with increasing air pressure
(11,300 ft)
Paul Goldhagen Uses of cosmic-ray neutron data
Effect of geomagnetic field (latitude)
9
Cou
nt R
ate
(104 /h
)
Measured
Calculated
Paul Goldhagen Uses of cosmic-ray neutron data
Solar activity changes
10
Paul Goldhagen Uses of cosmic-ray neutron data
Sunspot number and GCR flux
1111
Paul Goldhagen Uses of cosmic-ray neutron data
Solar modulation of cosmic-ray neutron fluxDaily neutron monitor rate in Delaware
12
Paul Goldhagen Uses of cosmic-ray neutron data
Uses of cosmic-ray neutron data
Paul Goldhagen 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
14
Paul Goldhagen Uses of cosmic-ray neutron data
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
15
Paul Goldhagen Uses of cosmic-ray neutron data
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
16
Paul Goldhagen Uses of cosmic-ray neutron data
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
17
Supported by the US Department of Homeland Security, Domestic Nuclear Detection Office, under competitively awarded contract/IAA HSHQDC-12-X-00251.
Paul Goldhagen Uses of cosmic-ray neutron data
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 McKinneyLANL, Nuclear Engineering & Nonproliferation Division
Paul Goldhagen Uses of cosmic-ray neutron data
Cosmic-ray neutron spectrum on the groundLivermore, CA - Nov 2006
19
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
0
10
20
E d /
dE
(m-2
sec
-1)
Calculated
Measured
with geomagnetic fieldin the atmosphere
Paul Goldhagen Uses of cosmic-ray neutron data 20
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
0
10
20
30
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
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,
d
/dE
(m-2
s-1
MeV
-1)
.
E·d
/dE
(m-2
s-1 )
.
Flux proportional
to areaunder curve
Paul Goldhagen Uses of cosmic-ray neutron data
Cosmic-ray neutron spectrum
21
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
0
10
20E
d/d
E
(m-2
sec
-1)
Calculated
Measured
Thermal
High energy
Slowing-down region ~1/E
Evaporation
Paul Goldhagen Uses of cosmic-ray neutron data
NUSTL has measured the energy spectrum of cosmic-ray neutrons on: Airplanes Ground Ships
NUSTL measurements
22
Components of NUSTL’s new neutron spectrometer
Paul Goldhagen Uses of cosmic-ray neutron data
Measurement on the groundLivermore, CA - Nov 2006
23
Paul Goldhagen Uses of cosmic-ray neutron data 24
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
0
10
20
30
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
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,
d
/dE
(m-2
s-1
MeV
-1)
.
E·d
/dE
(m-2
s-1 )
.
Flux proportional
to areaunder curve
Paul Goldhagen Uses of cosmic-ray neutron data
Measurements on these container ships
25
SS Lurline826 ft22,221 Tons
MV Mahimahi and MV Manoa860 ft30,167 Tons
Paul Goldhagen Uses of cosmic-ray neutron data
Neutron spectra from cosmic rays on shipsand from simulated threat
26
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
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 tierContainer ship – on deck
Cosmic-ray background neutrons
Simulated threatShielded 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
(km
)
0
5
10
15
20
EastSouth 1North 2
NASA ER-2
Paul Goldhagen Atmospheric Neutrons 27
June 1997
Paul Goldhagen Uses of cosmic-ray neutron data
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
0.00
0.05
0.10
0.15
E d /
dE
(cm
-2 s
ec-1
)
Calculated
Measured
11.6 GV vert. cutoff54 g/cm2 20.3 km
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
0.0
0.1
0.2
0.3
0.4
0.5
E d /
dE
(cm
-2 s
ec-1
)
Calculated
Measured
4.3 GV vert. cutoff201 g/cm2 12 km, 39 kft
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
0.0
0.5
1.0
E d /
dE
(cm
-2 s
ec-1
)
Calculated
Measured
0.7 GV vert. cutoff101 g/cm2 16 km, 53,300 ft
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
0.0
0.5
1.0
E d /
dE
(cm
-2 s
ec-1
) 0.8 GV vert. cutoff56 g/cm2 20 km, 66 kft
Calculated
Measured
High-altitude cosmic-ray neutron spectra
28
(preliminary) (preliminary)
(preliminary) (preliminary)
Paul Goldhagen Uses of cosmic-ray neutron data
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
29
Paul Goldhagen Uses of cosmic-ray neutron data
NUSTL multisphere neutron spectrometer
30
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
0
5
10
15
9876
1
Res
pons
e (C
ount
s cm
2 neu
tron-1
)
13
14
Calculated using MCNPX
12
11
4
10
2
14
5
89
10
1112
3
Paul Goldhagen Uses of cosmic-ray neutron data
High-energy neutron detector
31
15-inch diameterpolyethylene ball
Steel shell
3He gas proportional counter
Paul Goldhagen Uses of cosmic-ray neutron data
NUSTL multisphere neutron spectrometer
32
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
0
5
10
15
9876
1
Res
pons
e (C
ount
s cm
2 neu
tron-1
)
13
14
Calculated using MCNPX
12
11
4
10
2
14
5
89
10
1112
3
“Ship effect”
Paul Goldhagen Uses of cosmic-ray neutron data
Multisphere neutron spectrometer in container
33
Paul Goldhagen Uses of cosmic-ray neutron data
Measurements on the ground in Hawaii elevations from sea level to 12,800 feet
34
Paul Goldhagen Uses of cosmic-ray neutron data
Other applications – national security
Paul Goldhagen Uses of cosmic-ray neutron data
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
36
Paul Goldhagen Uses of cosmic-ray neutron data
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
37
Paul Goldhagen Uses of cosmic-ray neutron data
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.
Paul Goldhagen Uses of cosmic-ray neutron data
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)
39
Paul Goldhagen Uses of cosmic-ray neutron data
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.
40
Paul Goldhagen Uses of cosmic-ray neutron data
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
41
Paul Goldhagen Uses of cosmic-ray neutron data
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
42
43
Paul Goldhagen Uses of cosmic-ray neutron data
Additional / background information
44
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.gov
Paul Goldhagen Uses of cosmic-ray neutron data
Neutron flux on a logarithmic energy scale
45
2log
1log
2
1
)(log
1
E
E
E
E
EddEdE
dEEdE
dE
Paul Goldhagen Uses of cosmic-ray neutron data
Cosmic rays during high solar activity
46
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
Paul Goldhagen Uses of cosmic-ray neutron data
Largest solar particle event ground level enhancement in 50 years
47
07:00 Time 08:00
Neu
tron
Rat
e(c
ount
s/se
cond
)Jan 20, 2005
USEast coast 2.5 South Pole 50
Paul Goldhagen Uses of cosmic-ray neutron data
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
0
10
20
E d /
dE
(m-2
sec
-1)
Calculated
Measured
Cosmic-ray neutron spectrum on the groundLivermore, CA, Nov 2006
48
(preliminary)without geomagnetic fieldin the atmosphere
Paul Goldhagen Uses of cosmic-ray neutron data
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%
Paul Goldhagen Uses of cosmic-ray neutron data
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
50
Paul Goldhagen Uses of cosmic-ray neutron data
“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”
51
Paul Goldhagen Uses of cosmic-ray neutron data
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
52
Paul Goldhagen Uses of cosmic-ray neutron data
Cosmic-ray background neutron spectrameasured on container ships and land
53
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
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
Paul Goldhagen Uses of cosmic-ray neutron data
Neutron spectra from cosmic rays on shipsand from simulated threat
54
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
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 tierContainer ship – on deck
Cosmic-ray background neutrons
Simulated threatShielded WGPu at 2.5 m
Paul Goldhagen Uses of cosmic-ray neutron data
Ground measurements outdoors, 2002-2003
55
Paul Goldhagen Uses of cosmic-ray neutron data
Cosmic-ray neutron spectra measured on the ground at 5 locations with different elevations
56
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
0
20
40
60
80
100
120
140
160
180
.E
d
/dE
(m
-2 s
ec-1
)
HoustonYorktown Hts.Mt. WashingtonLeadvilleFremont Pass
Paul Goldhagen Uses of cosmic-ray neutron data
Effect of air pressure (elevation)
57
Atmospheric Depth (g cm-2)700 800 900 1000
Neu
tron
Flux
, E >
10
MeV
(m
-2 s
-1) Fremont Pass, CO
Leadville, CO (10,300 ft)
Mt. Washington, NH
Yorktown Heights, NYHouston, TX
500
50
100
200
300
30
Log scale
(6,250 ft)Neutron flux decreases exponentially with increasing air pressure
(11,300 ft)
Paul Goldhagen Uses of cosmic-ray neutron data
Measured cosmic-ray neutron spectra scaled to sea level, NYC, mean solar activity
58
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
0
5
10
15
.E
d
/dE
(m
-2 s
ec-1
)
HoustonYorktown Hts.Mt. WashingtonLeadvilleFremont Pass
Paul Goldhagen Uses of cosmic-ray neutron data
Analytic model of neutron flux cutoff dependence
59
,,,cBA0 dIRFdFdE
EddE
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).
Paul Goldhagen Uses of cosmic-ray neutron data
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 Deviceshttp://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
60
Paul Goldhagen Uses of cosmic-ray neutron data
GCR-induced particles in the atmosphere Effective dose rate vs. altitude
61
Altitude (km)0 5 10 15 20 25
Effe
ctiv
e D
ose
Rat
e (
Sv 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
Paul Goldhagen Uses of cosmic-ray neutron data
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
62
Paul Goldhagen Uses of cosmic-ray neutron data
High-altitude cosmic-ray neutron spectra
63
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
0.00
0.05
0.10
0.15
E d /
dE
(cm
-2 s
ec-1
)
Calculated
Measured
11.6 GV vert. cutoff54 g/cm2 20.3 km
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
0.0
0.1
0.2
0.3
0.4
0.5
E d /
dE
(cm
-2 s
ec-1
)
Calculated
Measured
4.3 GV vert. cutoff201 g/cm2 12 km, 39 kft
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
0.0
0.5
1.0
E d /
dE
(cm
-2 s
ec-1
)
Calculated
Measured
0.7 GV vert. cutoff101 g/cm2 16 km, 53,300 ft
(preliminary) (preliminary)
Neutron Energy (MeV)10-8 10-6 10-4 10-2 100 102 104
0.0
0.5
1.0
E d /
dE
(cm
-2 s
ec-1
) 0.8 GV vert. cutoff56 g/cm2 20 km, 66 kft
Calculated
Measured
(preliminary: before atmospheric B field and heavy ions)
(preliminary)
(preliminary)
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