NCRP Report No. 142 Operational Radiation Safety Program for Astronauts in Low- Earth Orbit: A Basic Framework Recommendations of the NATIONAL COUNCIL ON RADIATION PROTECTION AND MEASUREMENTS Issued November 30, 2002 NationalCouncilonRadiationProtectionandMeasurements 7910 Woodmont Avenue, Suite 400 / Bethesda, Maryland 20814 LEGAL NOTICE ThisReportwaspreparedbytheNationalCouncilonRadiationProtectionand Measurements(NCRP).TheCouncilstrivestoprovideaccurate,completeanduseful informationinitsdocuments.However,neithertheNCRP,themembersofNCRP, other persons contributing to or assisting in the preparation of this Report, nor anypersonactingonthebehalfofanyoftheseparties:(a)makesanywarrantyor representation, express or implied, with respect to the accuracy, completeness or usefulnessoftheinformationcontainedinthisReport,orthattheuseofanyinforma- tion,methodorprocessdisclosedinthisReportmaynotinfringeonprivatelyowned rights;or(b)assumesanyliabilitywithrespecttotheuseof,orfordamagesresulting fromtheuseofanyinformation,methodorprocessdisclosedinthisReport,under theCivilRightsActof1964,Section701etseq.asamended42U.S.C.Section2000e etseq.(TitleVII)oranyotherstatutoryorcommonlawtheorygoverningliability. LibraryofCongressCataloging-in-PublicationData NationalCouncilonRadiationProtectionandMeasurements. Operationalradiationsafetyprogramforastronautsinlow-earthorbit:abasic framework:recommendationsoftheNationalCouncilonRadiationProtection andMeasurements. p.cm.—(NCRPreport;no.142) ‘‘IssuedNovember2002.’’ Includesbibliographicalreferencesandindex. ISBN0-929600-75-4 1. Extraterrestrialradiation—Safetymeasures.2.Astronauts—Healthand hygiene.3.Spacemedicine.I.Title.II.Series RA1151.R33N382002 616.9(cid:1)80214—dc21 2002037861 Copyright©NationalCouncilonRadiation ProtectionandMeasurements2002 Allrightsreserved.Thispublicationisprotectedbycopyright.Nopartofthispublica- tion may be reproduced in any form or by any means, including photocopying, or utilizedbyanyinformationstorageandretrievalsystemwithoutwrittenpermission fromthecopyrightowner,exceptforbriefquotationincriticalarticlesorreviews. [FordetailedinformationontheavailabilityofNCRPpublicationsseepage150.] Preface This Report was developed under the auspices of Scientific Com- mittee 46, the National Council on Radiation Protection and Measurements (NCRP) program area committee concerned with operational safety.This Report addresses theoperational radiation safetyprogramforastronautsworkinginlow-Earthorbit,withpar- ticular attention to the radiation dosimetry needed, the radiation exposure information that should be recorded, and ways to imple- ment the radiation protection principle of ‘‘as low as reasonably achievable’’foractivitiesinvolvingtheSpaceShuttleandtheInter- nationalSpaceStation.ItisacompaniondocumenttoNCRPReport No. 132, Radiation Protection Guidance for Activities in Low-Earth Orbit, published in December 2000, and provides advice on imple- mentation of NCRP Report No. 132 guidance. ThisworkwasperformedattherequestoftheNationalAeronau- tics and Space Administration (NASA) and NCRP gratefully acknowledges NASA’s support. The Scientific Committee that pre- paredthisReportalsobenefitedfromaseriesofbriefingsfromNASA staffattheCommittee’sfirstmeetinginDecember1999inHouston. ThisReportwaspreparedbyScientificCommittee46-15onOpera- tional Radiation Safety Program for Astronauts. Serving on Scien- tific Committee 46-15 were: Richard J. Vetter, Chairman Mayo Clinic Rochester, Minnesota Members Ellen S. Baker David T. Bartlett National Aeronautics and National Radiological SpaceAdministration ProtectionBoard Lyndon B. Johnson Space Chilton, Oxon, United Center Kingdom Houston, Texas Thomas B. Borak Susan M. Langhorst Colorado State University Washington University in Fort Collins, Colorado St. Louis School of Medicine St. Louis, Missouri iii iv / PREFACE Stephen W.S. McKeever Jack Miller Oklahoma State University Lawrence Berkeley National Stillwater, Oklahoma Laboratory Berkeley, California R. Julian Preston John W. Wilson U.S. Environmental Protection National Aeronautics and Agency Space Administration Research Triangle Park, Langley Research Center NorthCarolina Hampton, Virginia Advisor Charles B. Meinhold National Council on Radiation Protection and Measurements Bethesda, Maryland NCRP Secretariat Marvin Rosenstein, Consultant Cindy L. O’Brien, Managing Editor The Council wishes to express its appreciation to the Committee members for the time and effort devoted to the preparation of this Report. Thomas S. Tenforde President Contents Preface ........................................................................................ iii 1. Summary and Recommendations ................................... 1 1.1 Components of an Operational Radiation Safety Program ......................................................................... 1 1.2 Team Management in the Radiation Safety Program 2 1.3 Sources of Radiation in Space ...................................... 3 1.4 Dose Limits for Astronauts ........................................... 3 1.5 Sources of Exposure Included in the Dose Limits forAstronauts ................................................................ 4 1.6 Types of Radiation to be Assessed ............................... 5 1.7 Approach to Dose Assessment for Astronauts ........... 6 1.8 Operational Radiation Monitoring ............................... 7 1.8.1 Area Monitoring .................................................. 7 1.8.2 Personal Dosimetry ............................................. 8 1.8.3 Calibration ........................................................... 10 1.9 Biodosimetry .................................................................. 11 1.10 Immediate Dose Management and ‘‘As Low As Reasonably Achievable’’ ................................................ 11 1.11 Radiation Safety Training ............................................ 12 1.12 Dosimetry Record .......................................................... 13 2. Objectives of the Operational Radiation Safety Program for Astronauts .................................................... 15 2.1 The Low-Earth Orbit Program ...................................... 15 2.2 Dose Limits for Astronauts ........................................... 17 2.2.1 Deterministic Limits............................................. 18 2.2.2 Stochastic Limits .................................................. 18 2.3 Operational Radiation Protection Considerations ........ 22 3. Current Management of Astronaut Radiation Safety Program ................................................................................. 24 3.1 Flight Rules for Management of Dose ........................... 24 3.2 Biomedical Research ....................................................... 26 3.3 Individuals Involved in Management of Dose ............... 26 3.3.1 Astronaut ............................................................. 26 3.3.2 Flight Director ...................................................... 26 3.3.3 Flight Surgeon ...................................................... 27 3.3.4 Radiation Health Officer ..................................... 27 3.3.5 Space Radiation Analysis Group ......................... 28 v vi / CONTENTS 4. Radiation Environment in Low-Earth Orbit ............... 29 4.1 Trapped Electrons (0.5 to 6 MeV; (cid:1)0.2 keV (cid:2)m(cid:1)1) ...... 30 4.2 Reentrant and Splash Albedo Electrons (1 MeV to (cid:3)1 GeV; 0.2 to (cid:3)3 keV (cid:2)m(cid:1)1) ........................................ 31 4.3 Trapped Protons ((cid:4)10 MeV; (cid:3)5 keV (cid:2)m(cid:1)1) .................. 31 4.4 Trapped and Solar Protons and Light Nuclear Particles(10to400MeV;0.3to5keV(cid:2)m(cid:1)1) .................. 31 4.5 Galactic Cosmic Radiation Ions and High-Energy Secondary Fragments ((cid:3)50 MeV n(cid:1)1; Z(cid:3) 1; 1 to 1,000 keV (cid:2)m(cid:1)1) .............................................................. 32 4.6 Charged Target Fragments ((cid:4)10 MeV n(cid:1)1; 2 to 1,200 keV (cid:2)m(cid:1)1) .............................................................. 32 4.7 Neutrons (0.1 to 500 MeV) ............................................. 33 4.8 Summary for Particle Types ........................................... 33 5. Approach to Dose Assessment for Astronauts ............. 35 5.1 Exterior Exposure Field ................................................. 38 5.1.1 Radiation Environment Models ........................... 38 5.1.2 Spacecraft External Measurements .................... 39 5.2 Interior Exposure Field................................................... 39 5.2.1 Shielding Models for the Space Shuttle, International Space Station, and Space Suits .... 39 5.2.2 Spacecraft Internal Measurements ..................... 40 5.3 Tissue Exposure Fields ................................................... 41 5.3.1 Human Shielding Models ..................................... 41 5.3.2 Occupancy Factors ................................................ 41 6. Data Collection and Interpretation for Dose Assessment ........................................................................... 42 6.1 Introduction .................................................................... 42 6.2 Dose Quantities to be Determined ................................ 43 6.3 Proposed Measurement Package .................................... 44 6.3.1 General Discussion ............................................... 44 6.3.2 Proposed Measurement Package: Active Devices ................................................................... 46 6.3.2.1 Tissue Equivalent Proportional Counters ................................................... 47 6.3.2.2 Solid-State Detectors............................... 47 6.3.2.3 Active Electronic Personal Dosimeters .... 48 6.3.2.4 Active Detectors for Electrons ................ 48 6.3.3 Proposed Measurement Package: Passive Devices .................................................................. 49 6.3.3.1 Low Linear Energy Transfer Dosimetry: Thermoluminescent Dosimeters ............................................... 50 6.3.3.2 Direct Ion Storage Dosimeters ............... 51 CONTENTS / vii 6.3.3.3 Neutron and High Atomic Number, High-Energy Particle Dosimetry: Plastic Nuclear Track Detectors ............ 51 6.3.3.4 Use of Thermoluminescent Dosimeters and Plastic Nuclear Track Detectors to Estimate Effective Dose .......................... 52 6.3.3.5 Superheated Drop/Bubble Dosimeters ..... 52 6.3.4 Recommendations for Measurement Packages .. 53 6.3.4.1 Recommendations for Area Monitoring ... 53 6.3.4.2 Recommendations for Personal Dosimetry ................................................ 54 6.4 Accuracy, Performance Testing, and Calibration ........ 55 6.4.1 Operational Radiation Protection Requirements on Accuracy of Dose Measurements .................... 55 6.4.1.1 Recommendations of ICRP and ICRU ... 55 6.4.1.2 General Requirements ........................... 56 6.4.2 Tests of Instrument and Dosimeter Performance .......................................................... 56 6.4.3 Calibration ............................................................ 57 7. Role of Biodosimetry in Dose Assessment .................. 59 7.1 Electron Spin Resonance ................................................ 59 7.2 Biochemical Indicators ................................................... 60 7.3 Erythrocytes with Transferrin Receptors ...................... 60 7.4 Gene Mutation Assays ................................................... 60 7.5 Cytogenetic Alterations ................................................... 61 7.5.1 Micronuclei ............................................................ 61 7.5.2 Acentric Fragments in Prematurely Condensed Chromosomes ........................................................ 62 7.5.3 Chromosomal Aberrations .................................. 62 7.6 Summary for Methods .................................................... 63 7.7 Current NASA (Lyndon B. Johnson Space Center) Methods ........................................................................... 63 7.8 Recommendations and Future Considerations ............. 64 8. Recommended Management of Astronaut Radiation Safety Program .................................................................... 66 8.1 Components of a Low-Earth Orbit Operational Radiation Safety Program ............................................. 66 8.2 Radiation Protection Principles Applied to Low-Earth Orbit Missions ................................................................ 67 8.3 Sources of Exposure Included in NCRP Dose Limits for Astronauts ................................................................. 68 viii / CONTENTS 8.4 Immediate Dose Management and Basic ‘‘As Low As Reasonably Achievable’’ Concepts .................................. 69 8.4.1 Immediate Dose Management Issues ................. 70 8.4.2 Basic ‘‘As Low As Reasonably Achievable’’ Concepts ................................................................ 70 8.4.3 Considerations for Spacecraft and Space Suit Design .................................................................... 70 8.4.4 Considerations for Preflight Planning ................ 71 8.4.5 Considerations for Continuous In-Flight Review ................................................................... 71 8.4.6 Considerations for Postflight Review .................. 72 8.5 Radiation Safety Training for NASA Personnel ........... 72 8.5.1 Astronauts ............................................................. 73 8.5.2 Flight Directors ..................................................... 74 8.5.3 Flight Surgeons ..................................................... 75 8.5.4 Radiation Health Officer and Radiation Safety Support Groups .................................................... 75 8.5.5 Other Supporting Specialists ............................... 76 9. Radiation Safety Records ................................................. 77 9.1 Content of Records .......................................................... 78 9.1.1 Records of Career Doses ....................................... 80 9.1.2 Records of Prospective and Retrospective Studies .................................................................. 81 9.2 Continuity of Records Over Time ................................... 82 9.2.1 Existing Records and Unanalyzed Data Files .... 82 9.2.2 Future Adjustment of Records ............................. 82 9.3 Retention of Records ....................................................... 83 Appendix A. Time-Dependent Variations in the Space Radiation Environment and the Need for Active Real-Time Monitoring ........................................................ 84 A.1 Background ..................................................................... 84 A.2 Types of Active Detectors Used in Space ...................... 86 A.2.1 Tissue Equivalent Proportional Counters .......... 86 A.2.2 Semiconductor Detectors ..................................... 91 A.2.3 Cerenkov Counters ............................................. 93 A.2.4 Ionization Chambers ........................................... 93 Appendix B. Computational Methods ................................ 95 Appendix C. Thermoluminescence Dosimetry Materials ............................................................................... 99 CONTENTS / ix C.1 Lithium Fluoride, Doped with Magnesium and Titanium........................................................................ 99 C.2 Calcium Fluoride, Doped with Thulium ..................... 105 C.3 Lithium Fluoride, Doped with Magnesium, Copper and Phosphorus ............................................................ 107 C.4 Aluminum Oxide, Doped with Carbon ........................ 108 C.5 Evaluation of Absorbed Dose and Dose Equivalent ..... 110 C.5.1 Equivalent Gamma-Ray Dose ........................... 110 C.5.2 Mean, or Effective, Linear Energy Transfer .... 111 C.5.3 Dose Equivalent ................................................. 112 Appendix D. Plastic Nuclear Track Detectors ................. 115 D.1 Description of Method .................................................. 115 D.2 Neutron Dosimetry ..................................................... 116 D.3 Dosimetry of Cosmic Radiation Fields ....................... 117 Glossary .................................................................................... 122 Acronyms, Abbreviations, and Main Symbols .................. 126 References ................................................................................ 128 The NCRP .................................................................................. 141 NCRP Publications .................................................................. 150 Index ........................................................................................... 160 1. Summary and Recommendations Astronauts are living and working for extended periods in low- Earthorbit (LEO)during SpaceShuttle missionsand construction, maintenanceandoperationoftheInternationalSpaceStation(ISS). Theradiationenvironmenttheyencounterinspaceiscomplex,with unique high-LET (linear energy transfer) and high-energy compo- nents, as distinct from the predominately low-LET and low-energy radiation environments encountered by most radiation workers on Earth. The primary purpose of an operational radiation safety pro- gram for astronauts working in LEO is to assess and control the radiationexposureofindividualastronautscommensuratewithmis- sion tasks and the prevailing radiation conditions in LEO. 1.1 Components of an Operational Radiation SafetyProgram Themaincomponentsofanoperationalradiationsafetyprogram designedtoimplementtheprinciplesofdoselimitationandALARA (aslowasreasonablyachievable)forastronautsworkinginLEOare: ● to facilitate actions, both in advance of a mission and in-flight, that respond to space radiation conditions or mission decisions that significantly affect the level of radiation exposure to the astronauts,andradiationprotectiondecisionsthatsignificantly influence the conduct of the mission; ● tocollectandrecorddatatoassessastronautdosesforindividual mission and cumulative career records; and ● toidentify,planandcarryoutpracticalALARAactionstoavoid unnecessary levels of radiation exposure. Recommendation1: NationalAeronautics andSpace Admin- istration (NASA) management should implement and main- tainaneffectiveradiationsafetyprogramwiththefollowing features: clear definition of the goals of the program, state- ment of the organization’s commitment to the application 1