DOT/FAA/AM-16/8

Office of Aerospace Medicine

Washington, DC 20591

Data for Rapid Evaluation of 

Vehicle Structure Related 

Radiation Shielding of 

Occupants of ExtremeAltitude Aircraft and 

Spacecraft

Kyle Copeland

Civil Aerospace Medical Institute 

Federal Aviation Administration 

Oklahoma City, OK 73125

November 2016

Final Report
NOTICE

This document is disseminated under the sponsorship of 

the U.S. Department of Transportation in the interest of 

information exchange. The United States Government 

assumes no liability for the contents thereof.

___________

This publication and all Office of Aerospace Medicine 

technical reports are available in full-text from the 

Civil Aerospace Medical Institute’s publications website: 

http://www.faa.gov/go/oamtechreports
i

Technical Report Documentation Page

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.

DOT/FAA/AM-16/8

4. Title and Subtitle 5. Report Date

Data for Rapid Evaluation of Vehicle Structure Related Radiation 

Shielding of Occupants of Extreme-Altitude Aircraft and Spacecraft

November 2016

6. Performing Organization Code

7. Author(s) 8. Performing Organization Report No.

Copeland K

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)

FAA Civil Aerospace Medical Institute

P.O. Box 25082

Oklahoma City, OK 73125

11. Contract or Grant No.

12. Sponsoring Agency name and Address 13. Type of Report and Period Covered

Office of Aerospace Medicine

Federal Aviation Administration

800 Independence Ave., S.W.

Washington, DC 20591 14. Sponsoring Agency Code

15. Supplemental Notes

16. Abstract

For aircraft and spacecraft, mass must be kept as low as possible; every kilogram of radiation shielding is 

one less kilogram of payload or fuel. The dominant source of ionizing radiation in the aerospace 

environment is galactic cosmic radiation (GCR). Unshielded effective dose rates from GCR are calculated to 

be as high as several tens of microsieverts per hour. Typical aircraft skin affords occupants less than 1 g/cm2 

of Al as shielding. Added shielding of persons is a secondary concern because of limits on vehicle mass. 

Electronics are typically lightly shielded and redundant so as to avert critical failures or prolonged loss of 

use. Currently, in-flight dose rate calculations, such as those done by CARI-6 and CARI-7, ignore effects of 

vehicle structure and contents, as inclusion of such has been shown to increase accuracy by less than 10%, 

even at SST altitudes, while adding greatly to the calculation complexity by forcing each calculation to be ad 

hoc (i.e., such calculations typically add considerable complexity to the overall calculations for almost no 

benefit). However, in suborbital and extreme high-altitude flight, where atmospheric shielding is thin or 

absent, vehicle shielding can be considerably more important. 

This report describes the construction of a database of secondary particle spectra resulting from irradiation of 

common aerospace materials of varying thicknesses with typical cosmic rays of varying energy. Examples 

are given for secondary particle spectra resulting from irradiation of aluminum (Al) and polyethylene (PE). 

These materials are commonly used as structural (Al) and/or shielding (Al and PE) materials for occupants 

of aircraft and spacecraft. The secondary spectra are calculated using Monte Carlo radiation transport 

program MCNPX 2.7.0 inside shells with of up to 100 cm thicknesses. The database of materials response 

matrices will enable programs like CARI and ESRAS to incorporate vehicle shielding of occupants in dose 

calculations, extending their usefulness to the space environment, where primary shielding of occupants 

comes from the vehicle.

17. Key Words 18. Distribution Statement

Ionizing Radiation, Shielding Data, Spacecraft, Aircraft, 

Aluminum

Document is available to the public through 

the Internet:

http://www.faa.gov/go/oamtechreports/

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price

Unclassified Unclassified 6

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
ii

Contents

DATA FOR RAPID EVALUATION OF VEHICLE STRUCTURE RELATED RADIATION SHIELDING 

OF OCCUPANTS OF EXTREME-ALTITUDE AIRCRAFT AND SPACECRAFT

1. INTRODUCTION.......................................................................................................................................................................1

2. METHODS ....................................................................................................................................................................................1

3. RESULTS........................................................................................................................................................................................1

4. DISCUSSION................................................................................................................................................................................2

4. REFERENCES..............................................................................................................................................................................3
1

DATA FOR RAPID EVALUATION OF VEHICLE STRUCTURE 

RELATED RADIATION SHIELDING OF OCCUPANTS OF 

EXTREME-ALTITUDE AIRCRAFT AND SPACECRAFT

1. INTRODUCTION

In the U.S., protection of commercial passengers 

and crew from ionizing radiation is the responsibility of 

the company operating the aircraft or spacecraft. Ionizing radiation is a threat to both vehicle systems and vehicle occupants. However, because vehicle weight is 

limited by available thrust, radiation shielding in aircraft 

and spacecraft must be as light as possible. While important, long-term biological radiation effects such as 

carcinoma, leukemia, and heart disease do not result in 

immediate risk to crew or passengers, thus are not considered of primary importance. Radiation protection is 

focused on the more immediate risk, in-flight device 

failure, which could lead to the vehicle and its occupants 

being in immediate mortal danger. Protective strategies 

for devices include device design, device shielding, and 

redundancy, all with the goal of minimal added vehicle 

mass. Protection of persons is usually by means of adopting exposure limits and tracking total career exposure. 

During flight under all but the most unusual circumstances, only a conceptus in early pregnancy is in 

immediate mortal danger from direct effects of ionizing 

radiation. Once the cell population is sufficiently high, 

the danger to the unborn and to adult and child vehicle 

occupants from ionizing radiation arises mostly from 

stochastic effects. Because the primary exposure source 

is galactic cosmic radiation (GCR) and dose rates are typically below threshold for deterministic effects (e.g., radiation sickness), long term health effects are the primary 

concern for crew and any passengers, and the most 

common strategy used by companies to control radiation 

exposure of crewmembers is to limit exposure time. For 

more extensive background information on in-flight radiation exposure and the biologic effect of low doses of 

ionizing radiation, see Friedberg and Copeland [2011].

For space missions, calculations of dose rate inside 

the vehicle are traditionally performed on an ad hoc basis for the specific vehicle using a specific expected radiation environment for the mission under consideration. 

A set of tools for this sort of calculation for space missions called OLTARIS is available from a NASA website [Sandridge, 2014]. For aircraft flights, software such 

as the FAA CARI-6 program is used to calculate inflight doses, but it and similar programs neglect vehicle 

structure because it has been shown to have minimal 

effect on doses at commercial cruise altitudes [O’Brien 

et al, 2003]. This report describes the calculation of a 

database of materials response functions that can be 

used to extend CARI-7 flight dose calculations more 

accurately into regions where vehicle shielding of occupants is an important consideration.

2. METHODS

Monte Carlo radiation transport program MCNPX 

2.7.0 (Monte Carlo N-Particle eXtreme) developed at 

Los Alamos National Laboratory and distributed by the 

Radiation Safety and Information Computing Center 

(RSICC) was used to generate secondary particle spectra 

(Tallied particles were neutrons, pions, protons, photons, muons, electrons, deuterons, tritons, helions, alphas, and heavier atomic fragments up to iron.) inside 

spherical shells of polyethylene and aluminum resulting 

from isotropic irradiation of mono-energetic particles 

[Pelowitz, 2011; RSICC, 2011]. Thickness of shielding 

ranged from 0.1 cm to 100 cm. Ion kinetic energy 

ranged from 1 MeV to 100 GeV. 

Secondary particle fluence spectra can be converted 

to various endpoints by the user: effective dose, effective dose equivalent, ambient dose equivalent, absorbed 

dose in silicon, etc., by means of fluence-to-dose conversion factors such as those published by Pelliccioni 

[2000] and Sato et al. [2009,2010]. 

Figure 1 shows the irradiation geometry. Primary 

particles leave the outer surface, radius 501 cm, directed 

inward isotropically. They then interact with the shield 

producing secondary radiation. Secondary radiation that 

exits the shield in the inner sphere can interact again as 

it tries to leave the sphere. Tallies of the flux are made at 

the center of the sphere (neutrons and photons only, 

due to limitations in MCNPX), just inside the sphere, 

and just outside the sphere.

3. RESULTS

Figures 2 and 3 show calculated spectra for selected 

secondary particles under various conditions. Data in 

each figure are normalized such that the spectra are per 

incident proton leaving the source surface. Error bars, 

where visible, represent one standard deviation. Figure 2 

shows neutron and photon spectra inside a 10 cm thick 

polyethylene (specific gravity 0.93) spherical shell irradiated isotropically with 10 GeV protons. Figure 3 shows 

neutron flux spectra inside 0.1 cm, 0.4 cm, and 5 cm 

thick Aluminum (specific gravity 2.2) spherical shells 

irradiated isotropically with 1 GeV protons. The wellknown phenomenon of increasing neutron flux with 

increasing shell thickness for thin layers, leading to increasing dose per incident proton as shielding is added, 

is evident.
2

Figure 1. Irradiation and tally geometry. Radiation leaves the 

source sphere headed isotropically inward, interacts with the 

shield, and is tallied inside and outside the shield.

4. DISCUSSION

The database described here is being calculated to 

enable a multi-step dose evaluation process. As an example, for calculations inside the atmosphere, the data 

can be used to approximate effects of spacecraft shielding since they provide the information needed to convert the secondary cosmic ray spectrum outside the vehicle to a spectrum inside the vehicle, without the need 

for repeating the Monte Carlo radiation transport calculations. If no atmosphere is present, the data may be 

used directly for simple shielding effects estimates or in 

combination for more estimates of the effects of more 

complex shielding configurations. 

The advantage of this database is that unlike previous published data of this sort, which provide the dose 

behind various depths of monolithic shielding for a given named input spectrum (e.g. GCR at solar min or missions to Mars cumulative dose), these data can be used 

to rapidly calculate the approximate dose behind arbitrary shielding, if certain approximations are acceptable, 

for any input spectrum within the bounds of the database. As the number of primary particles, shielding maFigure 2. Neutron and photon spectra inside a 10 cm thick polyethylene sphere irradiated isotropically with 10 GeV protons. Data 

are normalized such that the spectra are per incident proton leaving the source surface (see Figure 1). Error bars represent one 

standard deviation.
3

terials, and depths thereof expands, this database will be 

an increasingly powerful tool that can be integrated into 

existing dose calculators such as CARI-7, the FAA’s 

GCR dose calculation software, enabling more accurate 

estimates of doses on extreme-altitude and space flights, 

where the dominant source of occupant shielding is 

from the vehicle rather than Earth’s atmosphere.

As time and computing resources permit, future activities may expand the target materials to include carbon, hydrogen, water, and other frequently used aerospace materials. The source particles will eventually include all common GCR secondary radiations and atomic 

nuclei up to iron. As each subset is completed, it will be 

made available from the author.

5. REFERENCES

Foelsche, T.; Mendell, R.B.; Wilson, J.W.; Adams, R.R. 

Measured and Calculated Neutron Spectra and Dose 

Equivalent Rates at High Altitudes; Relevance to SST 

Operations and Space Research. Report No. NASA TN 

D-7715. Washington, DC: National Aeronautics and 

Space Administration; 1974.

Oak Ridge National Laboratory (ORNL). Monte Carlo 

N-Particle Transport Code System for Multiparticle and 

High Energy Applications (MCNPX 2.7.0), RSICC code 

package C740, developed at Los Alamos National Laboratory, released 2011 (available from the Radiation 

Safety Information Computational Center at ORNL, 

Oak Ridge, TN).

O'Brien, K., Smart, D.F.; Shea, M.A.; Felsberger, E.; 

Schrewe, U.; Friedberg, W.; Copeland, K. World-wide 

radiation dosage calculations for air crew members. Advan Space Res, 2003, 31(4), 835-840.

Pelliccioni, M. Overview of fluence-to-effective dose 

and fluence-to-ambient dose equivalent conversion coefficients for high energy radiation calculated using 

FLUKA code. Radiat Prot Dosim, 2000, 88(4), 279–297.

Figure 3. Neutron spectra inside 0.1 cm, 0.4 cm, and 5 cm thick aluminum spherical shells. The shells are irradiated isotropically with 1 GeV protons. Data are normalized such that the spectra are per incident proton leaving the source surface (see 

Figure 1). Error bars represent one standard deviation.
4

Sato, T.; Endo, A.; Zankl, M.; Petoussi-Henss, N.; Niita, 

K. Fluence-to-dose conversion coefficients for neutrons 

and protons calculated using the PHITS code and 

ICRU/ICRP adult reference computational phantoms. 

Phys Med Biol, 2009, 54, 1997-2014, doi:10.1088/0031-

9155/54/7/009.

Sandridge, C. OLTARIS-An overview and recent updates (3056.pdf). Presented at the 2014 NASA Human 

Research Program Investigators Workshop. Available at: 

www.hou.usra.edu/meetings/hrp2014/pdf/3056.pdf, 

accessed 14, Jan 2016.

Sato, T.; Endo, A.; Niita, K. Fluence-to-dose conversion 

coefficients for heavy ions calculated using the PHITS 

code and the ICRP/ICRU adult reference computational phantoms. Phys Med Biol, 2010, 55, 2235 

doi:10.1088/0031-9155/55/8/008.

Wilson, J.W.; Townsend, L.W.; Schimmerling, W.; 

Khandelwal, G.S.; Khan, F.; et al. Transport methods 

and interactions for space radiation. NASA RP-1257, 

1991.

Wilson, J.W.; Badavi, F.F.; Cucinotta, F.A.; Shinn, J.L.; 

Badhwar, G.D.; et al. HZETRN:Description of a freespace ion and nucleon transport and shielding computer 

program. NASA Technical Paper 3495. Hampton, VA: 

National Aeronautics and Space Administration, Langley Research Center; 1995.