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