Use of Cosmic-Ray Neutron Data in Nuclear Threat Detection and Other Applications Neutron Monitor Community Workshop—Honolulu, Hawaii
October 24-25, 2015
Paul Goldhagen Physicist National Urban Security Technology Laboratory Science and Technology Directorate National Urban Security Technology Laboratory (formerly, Environmental Measurements Laboratory) . DHS Government lab in New York City Science and Technology Directorate . ~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
Paul Goldhagen Uses of cosmic-ray neutron data 2 Overview
. 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
Paul Goldhagen Uses of cosmic-ray neutron data 3 Cosmic rays in Earth’s atmosphere
electrons/positrons photons neutrons protons mesons muons
Paul Goldhagen Uses of cosmic-ray neutron data 4 Cosmic-ray-induced neutrons in the atmosphere . 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
Paul Goldhagen Uses of cosmic-ray neutron data 5 GCR neutron rates in the atmosphere depend on . 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
Paul Goldhagen Uses of cosmic-ray neutron data 6 Neutron monitor Raw count rate count rate and barometric pressure during super-storm Sandy 760
Newark neutron monitor 12 days in 2012 Pressure-corrected rate
Neutron count rate (counts/sec) Pressure Pressure (mm-Hg)
712
Paul Goldhagen Uses of cosmic-ray neutron data 7 Effect of air pressure (elevation)
Log scale ) 500 Fremont Pass, CO -1 (11,300 ft)
s Leadville, CO (10,300 ft) -2 300 (m
200 Mt. Washington, NH
> 10 MeV > 10 (6,250 ft)
E 100 Neutron flux decreases exponentially with increasing 50 air pressure Yorktown Heights, NY
Neutron Flux, Houston, TX 30
700 800 900 1000 Atmospheric Depth (g cm -2)
Paul Goldhagen Uses of cosmic-ray neutron data 8 Effect of geomagnetic field (latitude) /h) 4
Calculated
Count Rate (10 Measured
Paul Goldhagen Uses of cosmic-ray neutron data 9 Solar activity changes
Paul Goldhagen Uses of cosmic-ray neutron data 10 Sunspot number and GCR flux
Paul Goldhagen Uses of cosmic-ray neutron data 11 Solar modulation of cosmic-ray neutron flux Daily neutron monitor rate in Delaware
Paul Goldhagen Uses of cosmic-ray neutron data 12 Uses of cosmic-ray neutron data
Paul Goldhagen Uses of cosmic-ray neutron data Radiation detection to find nuclear threats
. 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
Paul Goldhagen Uses of cosmic-ray neutron data 14 Neutron detection for homeland/national security
. 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
Paul Goldhagen Uses of cosmic-ray neutron data 15 Need to understand background neutrons
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
Paul Goldhagen Uses of cosmic-ray neutron data 16 Background radiation algorithm development
. 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
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 17 MCNP6 cosmic source option
. Built-in spectra Description of SDEF keywords. Keyword Values Description . Historic (PRL / Lal, 1980) . Modern (UoD / Clem, 2006) [-]cr All cosmic particles [-]ch Cosmic protons only [-]ca Cosmic alphas only PAR . SDEF card [-]c7014 Cosmic nitrogen only . PAR keyword enhanced [-]c14028 Cosmic silicon only [-]c26056 Cosmic iron only . New keyword DAT . New keyword LOC (Clem) M Month (1-12) DAT D Day (1-31) Y Year (4 digit) . Benchmarking LAT Latitude (-90 to 90; S to N) . NASA ER-2 flights LOC LNG Longitude (-180 to 180; W to E) ALT Altitude (km) . NUSTL Long Dwell / Goldhagen
Garrett McMath and Gregg McKinney LANL, Nuclear Engineering & Nonproliferation Division
Paul Goldhagen Uses of cosmic-ray neutron data 18 Cosmic-ray neutron spectrum on the ground Livermore, CA - Nov 2006
20
) Measured -1 Calculated
sec with geomagnetic field -2 in the atmosphere m
10 /dE ( /dE E d
0 10-8 10-6 10-4 10-2 100 102 104 Neutron Energy (MeV)
Paul Goldhagen Uses of cosmic-ray neutron data 19 2 Ways to plot neutron spectra dΦ/dE vs E Same data EdΦ/dE vs E )
-1 104 30
MeV Flux -1 2 ) s 10
-1 proportional -2 s
-2 to area (m 0 20 10 (m under curve /dE . /dE
-2 . d 10
10-4 E·d 10
10-6
Differential Flux, Differential 10-8 0 10-8 10-6 10-4 10-2 100 102 104 10-8 10-6 10-4 10-2 100 102 104 Neutron Energy (MeV) Neutron Energy (MeV)
Paul Goldhagen Uses of cosmic-ray neutron data 20 Cosmic-ray neutron spectrum
20 Evaporation
) Measured
-1 High energy Calculated sec
-2 Thermal m
10 /dE (
E d Slowing-down region ~1/E
0 10-8 10-6 10-4 10-2 100 102 104 Neutron Energy (MeV)
Paul Goldhagen Uses of cosmic-ray neutron data 21 NUSTL measurements
. NUSTL has measured the energy spectrum of cosmic-ray neutrons on: . Airplanes . Ground . Ships
Components of NUSTL’s new neutron spectrometer
Paul Goldhagen Uses of cosmic-ray neutron data 22 Measurement on the ground Livermore, CA - Nov 2006
Paul Goldhagen Uses of cosmic-ray neutron data 23 2 Ways to plot neutron spectra dΦ/dE vs E Same data EdΦ/dE vs E )
-1 104 30
MeV Flux -1 2 ) s 10
-1 proportional -2 s
-2 to area (m 0 20 10 (m under curve /dE . /dE
-2 . d 10
10-4 E·d 10
10-6
Differential Flux, Differential 10-8 0 10-8 10-6 10-4 10-2 100 102 104 10-8 10-6 10-4 10-2 100 102 104 Neutron Energy (MeV) Neutron Energy (MeV)
Paul Goldhagen Uses of cosmic-ray neutron data 24 Measurements on these container ships
SS Lurline 826 ft 22,221 Tons
MV Mahimahi and MV Manoa 860 ft 30,167 Tons
Paul Goldhagen Uses of cosmic-ray neutron data 25 Neutron spectra from cosmic rays on ships and from simulated threat 30
Cosmic-ray background neutrons
) Container ship – on deck -1 Container ship – above top tier
sec 20 -2 Simulated threat
(m Shielded WGPu at 2.5 m /dE .
10 E d
0 10-8 10-6 10-4 10-2 100 102 104 Paul Goldhagen DHS National Urban Security Technology Laboratory Neutron Energy (MeV) 12 Apr 2011
Paul Goldhagen Uses of cosmic-ray neutron data 26 Paths of AIR ER-2 flights Altitude profiles of 3 flights
20
15
10 East South 1
Altitude (km) Altitude North 2 5
June 1997 0 0 1 2 3 4 5 6 Time after Takeoff (hours)
NASA ER-2
Have analyzed data from boxed portions of flights
Paul Goldhagen Atmospheric Neutrons 27 High-altitude cosmic-ray neutron spectra ) ) 0.8 GV vert. cutoff 0.7 GV vert. cutoff -1 -1 2 2 56 g/cm 20 km, 66 kft 101 g/cm 16 km, 53,300 ft 1.0 1.0 sec sec
-2 Measured -2 Measured Calculated Calculated (preliminary) (preliminary)
/dE (cm 0.5 /dE (cm 0.5 E d E d
0.0 0.0 10-8 10-6 10-4 10-2 100 102 104 10-8 10-6 10-4 10-2 100 102 104 Neutron Energy (MeV) Neutron Energy (MeV)
0.5 0.15 ) ) 4.3 GV vert. cutoff 11.6 GV vert. cutoff -1 -1 2 2 201 g/cm 12 km, 39 kft 54 g/cm 20.3 km 0.4 sec sec -2 -2 Measured Measured 0.10 0.3 Calculated Calculated (preliminary) (preliminary) /dE (cm /dE (cm 0.2 0.05 E d E d 0.1
0.0 0.00 10-8 10-6 10-4 10-2 100 102 104 10-8 10-6 10-4 10-2 100 102 104 Neutron Energy (MeV) Neutron Energy (MeV)
Paul Goldhagen Uses of cosmic-ray neutron data 28 Extended-range multisphere neutron spectrometers
. 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
Paul Goldhagen Uses of cosmic-ray neutron data 29 NUSTL multisphere neutron spectrometer
15 )
-1 Calculated using MCNPX
1 14 neutron 2 10 13 cm 5 8 4 7 9 3 6 10
(Counts 11
5 14
2 12 12 11
Response 10 9 8 0 10-8 10-6 10-4 10-2 100 102 104 Neutron Energy (MeV)
Paul Goldhagen Uses of cosmic-ray neutron data 30 High-energy neutron detector
15-inch diameter polyethylene ball
Steel shell
3He gas proportional counter
Paul Goldhagen Uses of cosmic-ray neutron data 31 NUSTL multisphere neutron spectrometer
15 )
-1 Calculated using MCNPX
1 14 neutron 2 10 13 cm 5 8 4 7 9 3 6 10
(Counts 11
5 14 “Ship effect” 2 12 12 11
Response 10 9 8 0 10-8 10-6 10-4 10-2 100 102 104 Neutron Energy (MeV)
Paul Goldhagen Uses of cosmic-ray neutron data 32 Multisphere neutron spectrometer in container
Paul Goldhagen Uses of cosmic-ray neutron data 33 Measurements on the ground in Hawaii elevations from sea level to 12,800 feet
Paul Goldhagen Uses of cosmic-ray neutron data 34 Other applications – national security
Paul Goldhagen Uses of cosmic-ray neutron data Nuclear arms treaty verification
. 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
Paul Goldhagen Uses of cosmic-ray neutron data 36 Test ban treaty nuclear forensics
. 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
Paul Goldhagen Uses of cosmic-ray neutron data 37 Single-event upsets in microelectronics (Mike Gordon, IBM) . Flip bits, corrupt data (JEDEC Standard JESD89A) . Occur if enough charge is deposited in the sensitive volume. particles, heavy ions Neutrons & protons (ionization by each particle) (via recoils from nuclear reaction) Most nucleons pass
A few nucleons cause
Paul Goldhagen Uses of cosmic-ray neutron data 38 Radiation protection for airplane crews (Kyle Copeland, FAA)
. 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
Paul Goldhagen Uses of cosmic-ray neutron data 39 Hydrology Zreda, Desilets, et al., Univ. of Arizona, Sandia Natl. Lab.
. 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.)
Paul Goldhagen Uses of cosmic-ray neutron data 40 Production of cosmogenic radionuclides
. 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.
Paul Goldhagen Uses of cosmic-ray neutron data 41 Summary
. 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
Paul Goldhagen Uses of cosmic-ray neutron data 42 43 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.
Paul Goldhagen Uses of cosmic-ray neutron data 44 Neutron flux on a logarithmic energy scale E 2 d 1 E dE E1 dE E log E 2 d E d(log E) log E1 dE
Paul Goldhagen Uses of cosmic-ray neutron data 45 Cosmic rays during high solar activity On average, solar activity reduces cosmic ray intensity on Earth
Cosmic ray variations recorded at A: First coronal mass ejection 7 different neutron monitor stations (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.
Paul Goldhagen Uses of cosmic-ray neutron data 46 Largest solar particle event ground level enhancement in 50 years
Jan 20, 2005
US East coast 2.5 South Pole
(counts/second) 50 Neutron Rate
07:00 Time 08:00
Paul Goldhagen Uses of cosmic-ray neutron data 47 Cosmic-ray neutron spectrum on the ground Livermore, CA, Nov 2006
) Measured -1 20 Calculated
sec (preliminary) -2 without geomagnetic field m in the atmosphere
/dE ( 10 E d
0 10-8 10-6 10-4 10-2 100 102 104 Neutron Energy (MeV)
Paul Goldhagen Uses of cosmic-ray neutron data 48 Radiation exposure of U.S. population NCRP 160 Percent of all sources Percent of background (6.2 mSv) (3.2 mSv) Space 5%
Space 11%
Paul Goldhagen Uses of cosmic-ray neutron data 49 Neutron moderation (slowing) & thermalization
. 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
Paul Goldhagen Uses of cosmic-ray neutron data 50 The neutron “ship effect”
. “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
Paul Goldhagen Uses of cosmic-ray neutron data 51 DNDO Long-Dwell In-Transit Study . 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
Paul Goldhagen Uses of cosmic-ray neutron data 52 Cosmic-ray background neutron spectra measured on container ships and land 30 Container ship – on deck Scaled to same under ~3 layers of empties magnetic latitude
) & air pressure -1 Container ship above top tier
sec 20 -2 Land, Livermore CA (m /dE .
10 E d
0 10-8 10-6 10-4 10-2 100 102 104 Neutron Energy (MeV)
Paul Goldhagen Uses of cosmic-ray neutron data 53 Neutron spectra from cosmic rays on ships and from simulated threat 30
Cosmic-ray background neutrons
) Container ship – on deck -1 Container ship – above top tier
sec 20 -2 Simulated threat
(m Shielded WGPu at 2.5 m /dE .
10 E d
0 10-8 10-6 10-4 10-2 100 102 104 Paul Goldhagen DHS National Urban Security Technology Laboratory Neutron Energy (MeV) 12 Apr 2011
Paul Goldhagen Uses of cosmic-ray neutron data 54 Ground measurements outdoors, 2002-2003
Paul Goldhagen Uses of cosmic-ray neutron data 55 Cosmic-ray neutron spectra measured on the ground at 5 locations with different elevations 180
160 Fremont Pass Leadville )
-1 140 Mt. Washington 120 Yorktown Hts. sec
-2 Houston 100 (m 80 /dE .
60
E d 40 20 0 10-8 10-6 10-4 10-2 100 102 104 Neutron Energy (MeV)
Paul Goldhagen Uses of cosmic-ray neutron data 56 Effect of air pressure (elevation)
Log scale ) 500 Fremont Pass, CO -1 (11,300 ft)
s Leadville, CO (10,300 ft) -2 300 (m
200 Mt. Washington, NH
> 10 MeV > 10 (6,250 ft)
E 100 Neutron flux decreases exponentially with increasing 50 air pressure Yorktown Heights, NY
Neutron Flux, Houston, TX 30
700 800 900 1000 Atmospheric Depth (g cm -2)
Paul Goldhagen Uses of cosmic-ray neutron data 57 Measured cosmic-ray neutron spectra scaled to sea level, NYC, mean solar activity 15
Fremont Pass Leadville )
-1 Mt. Washington Yorktown Hts.
sec 10
-2 Houston (m /dE .
5 E d
0 10-8 10-6 10-4 10-2 100 102 104 Neutron Energy (MeV)
Paul Goldhagen Uses of cosmic-ray neutron data 58 Analytic model of neutron flux cutoff dependence
d E d0 E FA d FB Rc , I, d , dE dE
k F R ,h 1.0981 exp R 1 (A.6) B,quiet c 1 c and k k k 2 1 2 FB,active Rc,h 1.0981 exp 2 Rc 1 exp 1 50 1 exp2 50 , (A.7)
where the parameters and k are given by
1 exp1.84 0.094h 0.09exp11h , (A.8)
k1 1.4 0.56h 0.24exp 8.8h, (A.9)
2 exp1.93 0.15h 0.18exp10h , (A.10)
and k2 1.32 0.49h 0.18exp 9.5h. (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 59 Measured ground-level cosmic-ray neutron spectrum and scaling factor . 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
Paul Goldhagen Uses of cosmic-ray neutron data 60 GCR-induced particles in the atmosphere Effective dose rate vs. altitude
Total 10 neutrons ) -1
photons + Sv h electrons 1 protons
(wR = 2)
muons 0.1 pions
Effective( Dose Rate 0.01 Data from O'Brien LUIN-98F calculation at 55.4° N, 120° W
(1000 ft) 0.001 10 20 30 40 50 60 70 80
0 5 10 15 20 25 Altitude (km)
Paul Goldhagen Uses of cosmic-ray neutron data 61 What has been done - commercial aviation
. 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
Paul Goldhagen Uses of cosmic-ray neutron data 62 High-altitude cosmic-ray neutron spectra ) ) 0.8 GV vert. cutoff 0.7 GV vert. cutoff
-1 2 -1 2 56 g/cm 20 km, 66 kft 101 g/cm 16 km, 53,300 ft 1.0 1.0 sec sec
-2 Measured -2 Measured Calculated Calculated (preliminary(preliminary)) (preliminary)
/dE (cm /dE 0.5 (cm /dE 0.5 E d E d
0.0 0.0 10-8 10-6 10-4 10-2 100 102 104 10-8 10-6 10-4 10-2 100 102 104 Neutron Energy (MeV) Neutron Energy (MeV)
0.5 0.15
) 4.3 GV vert. cutoff ) 11.6 GV vert. cutoff
-1 2 -1 2 201 g/cm 12 km, 39 kft 54 g/cm 20.3 km 0.4 sec sec
-2 Measured -2 Measured 0.10 0.3 Calculated Calculated (preliminary: before (preliminary)
/dE (cm /dE 0.2 atmospheric B field (cm /dE and heavy ions) 0.05 E d E d 0.1
0.0 0.00 10-8 10-6 10-4 10-2 100 102 104 10-8 10-6 10-4 10-2 100 102 104 Neutron Energy (MeV) Neutron Energy (MeV)
Paul Goldhagen Uses of cosmic-ray neutron data 63