Operational Radiation Safety Program for Astronauts in Low-Earth Orbit: A Basic Framework (Ncrp Report)

190 Pages·2002·2.491 MB·English

by  National Council on Radiation Protection and Measurements

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