Upload
vudiep
View
215
Download
2
Embed Size (px)
Citation preview
Paul Goldhagen
The Atmospheric Ionizing Radiation (AIR) Project –
Preliminary Results for
Neutron Spectra and Ionization Rate
Paul Goldhagen, M. Reginatto, W. Van SteveninckU.S. Department of Energy Environmental Measurements Laboratory
R.C. Singleterry Jr., J.W. Wilson, H. Tai, I.W. Jones, J. L. ShinnNASA Langley Research Center
10th Annual Space Radiation Health Investigators’ WorkshopJune 13-16, 1999
Brookhaven National Laboratory, Upton, NY
Paul Goldhagen
Radiation Protection for Air Crews
• High-energy mixed radiation from cosmic raysRoughly half of effective dose from neutronsLarge uncertainties in neutron spectrum and H
• Continual exposure of large group167,000 air crew members in U.S.Civil aircrew working hours aloft ~ 500-1000 h / yearAir crews are one of the most exposed groups of
radiation workers
• Radiation protection limits going down
• New high-altitude civil aircraft designs (?)
Paul Goldhagen
Paul Goldhagen
Dose Rates from Galactic Cosmic Raysin the Atmosphere Depend on
• Altitude - Shielding by air1030 g/cm2 at sea level, 55 g/cm2 at 20 km (66,000 ft)Dose equivalent rate, H, at 20 km ~500 × H at sea level
• Latitude - Shielding by geomagnetic fieldBends slower particles back into spaceEffect on H increases with altitudeH at poles >6 × H at equator at 20 km
• Time in Solar Cycle - magnetic field of solar wind11-year sunspot cycle: Radiation max at sunspot minEffect on H increases with geomagnetic latitude & altitudeSolar modulation >2 in polar regions at 20 km
Paul Goldhagen
Effective Dose vs. Altitudefor Galactic Cosmic Ray Components
Altitude (km)0 5 10 15 20 25
Effective D
ose Rat
µ 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 55.4Į N, 120Į W
Corresponds to
Mars
Paul Goldhagen
Paul Goldhagen
0vse.jnb
Neutron Ambient Dose Equivalent & Effective DoseConversion Factors
Neutron Energy (MeV)10 -8 10 -7 10 -6 10 -5 10 -4 10 -3 10-2 10-1 100 101 102 103 104 105
H*(10) or
E / fluence (pS
v . cm
2)
10
100
1000
10000
Siebert & Schumacher, '95Sanikov & Savitskaya, '96
H* (10), using ICRP 60 Q(LET)
Effective Dose, E , (ICRP 60 W R)Ferrari, Pellicioni & Pillon '97(isotropic irradiation)
file h10vse.jnb Paul Goldhagen
Paul Goldhagen
Jet Altitude Cosmic Ray Neutron Spectra -Previous Measurements
Neutron Energy (MeV)10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101 102 103 104
0.0
0.5
1.0
1.5Hess '59200 g ?cm -2 (11.75 km), 4.0 GV cutoff
Korff '7970 g ?cm-2 (18.6 km), polar
Hewitt '78190 g ?cm -2 (12.3 km), 2.4 GV cutoff
Nakamura '87 ( ↔ 3)220 g ?cm-2 (11.3 km), 10 GV cutoff
Neutron
E
dM
/dE = d
M/d ln(E
(MeV
)) (cm
-2 sec
-1)
Pau l Goldhagen
Paul Goldhagen
Existing_CR_n_spec-Hessetc.jnb
Existing Jet-Altitude Cosmic Ray Neutron Spectra
Neutron Energy (MeV)10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 10 0 101 102 103 104 105
0.0
0.5
1.0
1.5
Neutron Flu
E
dM
/dE = d
M/d ln(E
(MeV
)) (cm
-2 sec
-1)
Hess 1959, 220 g/cm2 (11.4 km)
Merker '73 , 90 g/cm 2 (17 km)
Hewett '78, 190 g/cm 2 (12.3 km)
Calculated
Measured
Paul Goldhagen
Armstrong '73 , 100 g/cm 2 (16.3 km)
Korff '79, 70 g/cm 2 (18.6 km)
file Existing_CR_n_spec-Hessetc.jnb
Paul Goldhagen
The Atmospheric Ionizing Radiation(AIR) Measurements Project
• Collaboration of ~12 laboratories, 6 countriesStarted by NASA LaRC and EML
• Suite of 14 radiation measuring instruments
• Dedicated flights of NASA ER-2 aircraftAltitudes: 16 - 21 km (53,000 - 70,000 ft) 110 - 50 g/cm2
Latitudes: 18- 60 N over western U.S., Canada, PacificEach flight 6.5 to 8 hoursMultiple flight series over several years of solar cycle ?
• First flight series successfully completed June 1997• Measurements benchmark/validate AIR model code
Funded by NASA High Speed Research Program as part of HSCT Environmental Impact studies and by collaborating laboratories
Paul Goldhagen
Paul Goldhagen
Paul Goldhagen
Paul Goldhagen
Altitude Profiles for 3 AIR Flights
Time after Takeoff (hours) 0 1 2 3 4 5 6
Altitude (km
)
0
5
10
15
20
EastSouth 1North 2
Paul Goldhagen
Paul Goldhagen
Ionization Chamber ReadingAll Four 6.5-Hour Flights
Time After Takeoff (minutes) 0 60 120 180 240 300 360
Raw
Ion
(10
3 C
ounts per Minute)
0
10
20
30
40
South 1
North 2
South 2
East
file Ion chamber figs.jnb
Paul Goldhagen
Paul Goldhagen
Predicted and Measured Ionization Rate
Time after Takeoff (minutes)0 60 120 180 240 300 360
Ionization
-1 s
-1)
0
100
200
300
400
North 2 Flight EML ion chamber
measurement
AIR Modelprediction
Paul Goldhagen
file Ion chamber figs.jnb
Paul Goldhagen
Multisphere Neutron Spectrometer(Bonner Spheres)
Set of spherical moderators of different sizes surrounding slow-neutron detectors
Big moderators slow down higher-energy neutrons than small moderators.
Paul Goldhagen
Multisphere SpectrometerAdvantagesWide energy range (9 - >11 decades)Highly sensitive to neutrons, but not gamma
raysIsotropic response TransportableStable response, tried and true
DisadvantagesLow resolutionUseful only for uniform, stable or monitored field
To use, need:Response functionsUnfolding
Paul Goldhagen
RFcans.jnb6/8/99 Response Functions of EML
High-Energy Multisphere Neutron Spectrometer
Neutron Energy (MeV)10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101 102 103 104 105
0
5
10
15
9876
5
1
Response
(Counts
cm2
neutron-1
)
1314
protonresponse
14
Paul Goldhagen
12 11
4
10
without containers
MCNP / LAHET
2
13
Paul Goldhagen
Paul Goldhagen
Accomplishments• 5 science flights successfully completedJune 1997, solar minimum (radiation maximum)
• Full energy range neutron spectrometer developedResponse functions - calculations, verification experimentMAXED unfolding code
• Good data, preliminary results for:
• Relative ionization rate vs. latitude and altitude
• Full-range neutron spectra measured in an aircraftHigh-altitude (50-110 g/cm2): wide range of latitudesCommercial altitudes: one latitude
Paul Goldhagen
Conclusions• Current AIR Model fits relative ionization rate well
for all latitudes and altitudes• AIR neutron measurements will reduce uncertainties in
neutron spectrum and effective dose rateneutron measurements must include correction for protons
• High-energy neutrons are significantabout half of neutron dose equivalent
• AIR measurements can be used to validate cosmicradiation transport codes for Mars
• CR dose calculations for Mars residents should consider Surface composition - hadron cascades from ironLow-Z shielding below as well as above/around habitats
• 2nd series of AIR flights would be worthwhile
Paul Goldhagen
Thanks
NASA Langley Research Center: J. W. Wilson, D. Maiden, I. W. Jones and crew of engineers & technicians, J. L. Shinn, H. Tai, R. Singleterry, High Speed Project Office
EML: M. Reginatto, W. Van Steveninck, F. Hajnal, F. Raccah
University of Akron: T. Kniss
NASA Ames (Dryden ) Research Center: ER-2 liaison staff, scientists, engineers, ground crew, pilots
All the AIR investigators, their collaborators & support people
W. Friedberg, K. Copeland, K. O’Brien, V. Mares, S. Roesler and others
Paul Goldhagen
file AIR_luin-jun13_rfh.jnb unfolded 3/15/98 High-Altitude Cosmic Ray Neutron Spectra
Effect of Default Spectrum
Neutron Energy (MeV)10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101 102 103 104 105
0.0
0.5
1.0
1.5
Armstrong '73, HETC-ANISN50 g/cm
2, solar min, 42Į NGM
Paul Goldhagen
Roesler et al. '98, FLUKA200 g/cm 2 , 47Į N, 11Į E, 5/95
EML measurement (preliminary unfoldings)56 g/cm 2 (20 km, 66,000 ft), solar minimum, near polar plateauAIR ER-2 flight 97-108, 6/13/97, 54Į N, 117 Į Wcorrected for protons
Using as default spectrum for unfolding:
file AIR_luin-jun13_rfh.jnb unfolded 3/15/98
Neutron F
lu
E d
N/dE
= d
N/d ln(E
(MeV
)) (cm
-2 sec
-1)
Paul Goldhagen
file AIR_luin-jun13_rfh.jnb unfolded 3/15/98 High-Altitude Cosmic Ray Neutron Spectra
Effects of Protons and Energy Limit
Neutron Energy (MeV)10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101 102 103 104 105
0.0
0.5
1.0
1.5
2.0EML measured neutron spectrum, ( preliminary unfoldings)56 g/cm
2 (20 km, 66 kft), so lar minimum, near polar plateau
NSMED unfolding
default spectrum: Armstrong '73, HETC-ANISN,50 g/cm 2, 42Į NGM, solar minx2.34 for best fit to data
with correction for protonswithout correction for protons
Paul Goldhagen
Same data ( without correction for proton effects )
SANDII unfolding cut off at 1 GeV
Neutron F
E
dN
/dE = d
N/d ln(E
(MeV
)) (cm
-2 sec
-1)
file AIR_luin-jun13_rfh.jnb unfolded 3/15/98
Paul Goldhagen
IntroductionAIR Model
• Dose rate empirical formulationsair ionization, charged particle stars, 1 to 10 MeV
neutrons• Dose rate equivalent from ICRU 40• Data set from solar cycle 20 and scaled to the
Deep River neutron monitor with the geomagnetic cutoff
Paul Goldhagen
Current AIR Model
• Set of scaling and interpolation subroutines• Data set from solar cycle 20• Use of the geomagnetic cutoff• Scaled to the Deep River neutron monitor• Solar variation with latitude, longitude, altitude,
and pressure
Paul Goldhagen
Current AIR Model
• Dose rate empirical formulationsAir ionizationCharged particle stars1 to 10 MeV neutrons
• Dose rate equivalentICRU 40
Paul Goldhagen
Ultimate AIR Model Purpose
• Accurate prediction of dose and dose equivalent anywhere in the Earth’s atmosphere
• Enable assessment of health risks to flight crew and passengers for airline industry
• Validation model of space radiation transport codes
Paul Goldhagen
R_luin-jun13_rfh.jnb ded 3/15/98 Calculated High-Altitude Cosmic Ray Neutron Spectra
Neutron Energy (MeV)10-8 10 -7 10-6 10-5 10-4 10-3 10-2 10-1 100 101 102 103 104 105
0.0
0.5
1.0
1.5
2.0
2.5
Armstrong '73, HETC-ANISN50 g/cm 2, solar min, 42Į NGMx 2.34 for best fit to EML dataat above coordinates
Paul Goldhagen
Roesler et al. '98, FLUKA200 g/cm 2, 47Į N, 11Į E, 5/95x 4.0 for best fit to EML data
O'Brien, LUIN-97 (FAA, CARI)56 g/cm 2 (20 km, 66,000 ft),solar minimum, near polar plateau6/13/97, 54Į N, 117Į W
file AIR_luin-jun13_rfh.jnb unfolded 3/15/98
Neutron Flu
E
dN
/dE = d
N/d ln(E(M
eV)) (cm
-2 sec
-1)
Paul Goldhagen
RFcans.jnb6/8/99 Response Functions of EML
High-Energy Multisphere Neutron Spectrometer
Neutron Energy (MeV)10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 100 101 102 103 104 105
0
5
10
15
9876
5
1
Response
(Counts
cm2 neutron
-1) 13
14
det 13 proton responsedet 14 proton response
Paul Goldhagen
12 11
4
10
without containers
MCNP / LAHET
2