Federal Aviation Administration DOT/FAA/AM-11/9 Office of Aerospace Medicine Washington, DC 20591 Ionizing Radiation in Earth’s Atmosphere and in Space Near Earth Wallace Friedberg Kyle Copeland Civil Aerospace Medical Institute Federal Aviation Administration Oklahoma City, OK 73125 May 2011 Final Report OK-11-0024-JAH 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 Web site: www.faa.gov/library/reports/medical/oamtechreports Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. DOT/FAA/AM-11/9 4. Title and Subtitle 5. Report Date Ionizing Radiation in Earth's Atmosphere and in Space Near Earth May 2011 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. Friedberg W, Copeland K 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) FAA Civil Aerospace Medical Institute P.O. Box 25082 11. Contract or Grant No. Oklahoma City, OK 73125 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 The Civil Aerospace Medical Institute of the FAA is charged with identifying health hazards in air travel and in commercial human space travel. This report addresses one of these hazards – ionizing radiation. Ionizing radiation is a subatomic particle of matter or packet of energy (photon) with sufficient energy to eject an orbital electron from an atom. Charged subatomic particles from exploding stars (supernovae) are a constant source of ionizing radiation in the atmosphere and in space. In space another constant source of ionizing radiation is the solar wind from the Sun. The solar wind consists mostly of electrons and protons with energies between 10 and 100 keV. The Sun undergoes an approximately 11-year cycle of rise and decline in activity and during its active phase there is an increased emission of the solar wind and occasional eruptions of high-energy particles (coronal mass ejections). Other sources of ionizing radiation during air travel include radioactive cargo, radioactive substances released into the atmosphere as a result of a nuclear reactor accident or terrorist activity, lightning, and terrestrial gamma-ray flashes. A health effect following exposure to ionizing radiation for which the severity is radiation dose related is called a deterministic effect (non-stochastic effect, tissue reaction). Deterministic effects may occur soon after radiation exposure. For example, nausea and vomiting might be experienced by a space traveler a few hours after receiving a large dose of ionizing radiation while outside a space vehicle during a coronal mass ejection. If the probability (risk) of a health effect after exposure to ionizing radiation is dose related, it is called a stochastic effect. Such effects seldom occur until years after the radiation exposure. Examples of stochastic effects are cancer and genetic disorders. If one or both parents are irradiated prior to conceiving a child, there is a risk of genetic disorders in the child and in its progeny. The report can be used as a source book for instruction on ionizing radiation exposure of air and space travelers. 17. Key Words 18. Distribution Statement Ionizing Radiation, Cosmic Radiation, Radioactive Document is available to the public through the Contamination, Space Weather, Geoomagnetism, Defense Technical Information Center, Ft. Belvoir, VA 22060; and the National Technical Information Radiation Exposure Limits, Flight Doses, Radiation Health Risks Service, Springfield, VA 22161 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 28 Form DOT F 1700.7 (8-72) Reproduction of completed page authorized i ACKNOWLEDGMENTS For help in preparing this report we thank: Katherine Wade, Roni G. Anderson, Michael E. Wayda, Dr. William S. Irving Jr., and Frances E. Duke of the Civil Aerospace Medical Institute; Herbert H. Sauer of the National Geophysical Data Center, National Oceanic and Atmospheric Administration; Dr. Donald E. Parker (Professor Emeritus) of the University of Oklahoma Health Sciences Center; Dr. Edgar B. Darden Jr. (retired) of the Oak Ridge Associated Universities; Daniel Friedberg, Jacqueline Bist, and Anielia M. Bist. iii Contents INTRODUCTION. 1 IONIZING RADIATION DOSE TERMINOLOGY. 2 Linear Energy Transfer. 2 Relative Biological Effectiveness. 3 Gray . 3 Gray Equivalent . 3 Organ Equivalent Dose (Equivalent Dose). 3 Dose Equivalent . 3 Effective Dose. 4 Effective Dose Equivalent. 4 Sievert . 4 EARTH’S ATMOSPHERE. 5 Atmospheric Layers . 5 EARTH’S MAGNETIC FIELD. 5 GALACTIC COSMIC RADIATION. 7 Composition and Sources. 7 Galactic Cosmic Radiation in Earth’s Atmosphere . 8 THE SUN AND ITS EMISSIONS. 10 Layers of the Sun’s Atmosphere. 10 Sunspots. 10 Solar Wind . 10 Coronal Mass Ejection and Solar Flare . 10 Solar Proton Event. 10 RECOMMENDED IONIZING RADIATION DOSE LIMITS. 10 U.S. Federal Aviation Administration. 10 International Commission on Radiological Protection . 11 National Council on Radiation Protection and Measurements . 11 European Union. 11 IONIZING RADIATION EXPOSURE DURING AIR AND SPACE TRAVEL. 12 Radiation Doses Received During Air Travel . 12 Radiation Doses Received During Space Travel. 15 HEALTH EFFECTS OF IONIZING RADIATION. 15 Deterministic Effects (Non-Stochastic Effects, Tissue Reactions) . 15 Stochastic Effects . 17 Prenatal Irradiation. 17 RADIOACTIVE CONTAMINATION IN EARTH’S ATMOSPHERE . 17 LIGHTNING AND TERRESTRIAL GAMMA-Ray Flashes. 21 CONCLUDING REMARKS. 21 REFERENCES. 21 v IonIzIng RadIatIon In EaRth’s atmosphERE and In spacE nEaR EaRth INTRODUCTION an atom before decaying. Neutrinos and antineutrinos pass through matter with almost no effect, and usually they are The U.S. Federal Aviation Administration’s (FAA’s) not considered in dose calculations. Civil Aerospace Medical Institute (CAMI) is charged Wilhelm Conrad Roentgen in 1895 discovered ionizing with identifying health hazards in air travel and in com- radiation while experimenting with a Crookes tube (a primi- mercial human space travel. This report addresses one of tive vacuum tube) (2). Working in a dark room with the tube these hazards – ionizing radiation. in a carton, Roentgen found that a paper plate coated with Air and space travelers are constantly exposed to galactic barium platinocyanide (a chemical that fluoresces when ex- cosmic radiation (GCR), which is ionizing radiation from posed to UV light from the Sun), which was outside the carton exploding stars (supernovae). They are also exposed to and 9 feet away from the tube, emitted a fluorescent light solar cosmic radiation (SCR), which is ionizing radiation when the tube was supplied with electric current. Roentgen from the Sun. Other sources of ionizing radiation include: concluded that an invisible radiation from the tube, which radioactive air cargo, radioactive substances released into he called X-rays, penetrated the wall of the carton and trav- the atmosphere from a detonated nuclear weapon or from eled to the barium platinocyanide. He could not deflect the a nuclear reactor as the result of an accident or terrorist radiation with a magnetic field, and he found that objects in attack, lightning, and terrestrial gamma-ray flashes (TGFs). the path of the radiation showed variable transparency. With Radiation is energy in transit. The energy travels as (a) a photographic plate, Roentgen used the device to make a subatomic particles of matter (e.g., electrons, neutrons, picture of the skeleton of his wife’s hand (3). protons, alpha particles, pions, muons), and (b) photons, Antoine-Henri Becquerel in 1896 discovered a natural which are packets of electromagnetic energy (e.g., visible source of ionizing radiation while investigating phospho- light, ultraviolet [UV] light, radio waves, microwaves, rescence (4). He observed that a photographic plate covered gamma radiation, X-radiation). with an opaque paper was fogged when placed near uranyl Ionizing radiation is a subatomic particle or photon suf- potassium sulfate (a uranium salt). Becquerel demonstrated ficiently energetic to directly or indirectly eject an orbital that unlike X-rays, the radiation from uranium could be electron from an atom. Photons and electrically-charged deflected by a magnetic field and therefore consisted of particles ionize directly by means of electromagnetism. charged particles. Neutrons cannot ionize directly, but they can ionize Theodore Wulf measured ionizing radiation levels with indirectly. On impacting the nucleus of an atom (e.g., an electroscope at the bottom and at the top of the Eiffel atmospheric nitrogen or oxygen), a neutron can (a) in- Tower (300 m high) and found that radiation levels at the duce emission of a gamma-radiation photon by nuclear top of the tower were higher than at ground level (5). In excitation, or (b) break apart the nucleus and release 1912, Victor F. Hess measured ionization rates with an protons (which can ionize directly), neutrons (which can electroscope during balloon flights (6). He found that at decay