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(2. National Council on Radiation Protection and Measurements \(NCRP\). 1\
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(BERRIEN MOORE III, University of New Hampshire )Tj
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(KENNETH H. NEALSON, University of Wisconsin )Tj
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(SIMON OSTRACH, Case Western Reserve University )Tj
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(MORTON B. PANISH, AT&T Bell Laboratories \(retired\) )Tj
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(ROBERT E. WILLIAMS, Space Telescope Science Institute )Tj
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( )Tj
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(MARC S. ALLEN, Director )Tj
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(MARSHA I. LESTER, University of Pennsylvania )Tj
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(THOMAS A. PRINCE, California Institute of Technology )Tj
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(CHARLES A. ZRAKET, MITRE Corporation \(retired\) )Tj
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(NORMAN METZGER, Executive Director )Tj
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( )Tj
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(Foreword)Tj
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( )Tj
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( )Tj
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( )Tj
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( )Tj
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( Astronauts who venture beyond the protection of Earth's atmosphere and\
magnetosphere risk exposure )Tj
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(to levels of radiation far exceeding those on Earth. Of all the risks th\
ey face, this one is probably the )Tj
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(most straightforward to control-by providing adequate shielding. However\
, because shielding adds )Tj
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(weight, cost, and complexity to space vehicles, it is very important for\
designers to have a good, )Tj
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(quantitative understanding of the true risk and its degree of certainty.\
)Tj
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( This report assesses our understanding of radiation hazards in space. \
It also considers the additional )Tj
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(research needed to reduce the areas of uncertainty, research that must b\
e completed prior to undertaking )Tj
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(the detailed design of a vehicle carrying crew members into space for pe\
riods of extended exposure. The )Tj
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(report finds that it will take more than a decade of research to answer \
even the narrowest set of key )Tj
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(questions, although happily the needed studies can all be conducted on t\
he ground rather than in space. )Tj
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( The nation has backed away from a specific timetable for human explora\
tion of the moon and Mars. )Tj
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(Yet it seems plausible that such expeditions will be mounted sometime in\
the first quarter of the 21st )Tj
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(century, especially given the recent resurgence of interest in possible \
life on Mars from the study of )Tj
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(meteorites. It becomes clear, when the lengthy time scale of the researc\
h is also taken into account, that )Tj
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(the present report is indeed timely and should receive prompt considerat\
ion by NASA planners. )Tj
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(Claude R. Canizares, )Tj
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( )Tj
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(Preface)Tj
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( )Tj
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( )Tj
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( The study that is the subject of this report was initiated as a result\
of a series of discussions between the )Tj
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(leaders of NASA's Office of Life and Microgravity Sciences and Applicati\
ons \(OLMSA\), NASA's Life )Tj
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s Committee on Space )Tj
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(Biology and Medicine \(CSBM\). In order to address concerns within NASA \
and CSBM regarding the )Tj
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(many uncertainties in the understanding of radiation hazards to the crew\
of long-duration missions in )Tj
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(space, CSBM formed an expert task group on radiation biology and physics\
whose members had no )Tj
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(direct involvement with NASA's radiation programs. A CSBM member with th\
e appropriate expertise )Tj
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(was appointed to lead the group. )Tj
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( The Task Group on the Biological Effects of Space Radiation \(TGBESR\)\
was asked to review current )Tj
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(knowledge on the effects of long-term exposure to radiation in a space e\
nvironment and to consider )Tj
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(NASA radiation shielding requirements for orbital and interplanetary spa\
cecraft. The task group was )Tj
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(charged with assessing the adequacy of NASA planning for the protection \
of humans from radiation in )Tj
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(those environments and with making recommendations regarding needed rese\
arch and/or new shielding )Tj
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(requirements. Where feasible, the task group would also provide NASA wit\
h radiation safety guidelines. )Tj
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( Early in the study the task group was informed by NASA that plans for \
the international space station )Tj
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(were at such an advanced stage that any recommendations affecting shield\
ing of orbital craft could not )Tj
T*
(be implemented by the agency. The task group therefore decided to concen\
trate on the radiation hazards )Tj
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(of interplanetary missions. Further, at the urging of NASA, the task gro\
up has attempted to provide )Tj
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(reasonable estimates of time lines for completing the radiation research\
it has recommended. )Tj
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( Although the recommendations of the task group are published here as a\
separate and independent )Tj
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(report of TGBESR, it is the intent of CSBM that this report will also fo\
rm the basis of a section in a )Tj
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(space life sciences strategy report being prepared by CSBM for publicati\
on at a later date. )Tj
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( During the course of this study the task group was briefed extensively\
by representatives of OLMSA )Tj
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(and LBSAD regarding NASA's planning for deep-space missions and projecti\
ons for radiation shielding. )Tj
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(The task group also received in-depth technical briefings on the status \
of NASA's radiation research and )Tj
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(the agency's current understanding of radiation hazards, and it consulte\
d a wide range of technical )Tj
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(documentation . When verification or additional details of prior researc\
h were needed, task group )Tj
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(members made direct queries to the pertinent investigators in the radiat\
ion research community. )Tj
T*
( A number of individuals who assisted the task group by supplying infor\
mation deserve special thanks )Tj
T*
(for their contributions: Harry Holloway, Frank Sulzman, and Walter Schim\
merling of NASA )Tj
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(headquarters; John Wilson of NASA Langley Research Center; Amy Kronenber\
g of Lawrence Berkeley )Tj
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(National Laboratory; and Gregory Nelson of the Jet Propulsion Laboratory\
. )Tj
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(EXECUTIVE SUMMARY 1)Tj
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(1 INTRODUCTION 5 )Tj
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(Statement of Problem, 5 )Tj
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(Contributions and Use of Past Radiation Research, 7 )Tj
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(Current Understanding of Biological Effects of Radiation, 8 )Tj
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(Types of Effects, 8 )Tj
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(Effects Induced by Protons, 8 )Tj
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(Effects Induced by Heavy Ions, 9 )Tj
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( )Tj
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(References, 11 )Tj
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(2 ISSUES OF CONCERN TO NASA: DISCUSSION AND CONCLUSIONS 13 )Tj
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(Types of Particles and Their Energies, 14 )Tj
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(Galactic Cosmic Rays, 14 )Tj
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(Solar Particles, 15 )Tj
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(Secondary Particles, 18 )Tj
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(Estimates of Uncertainty in Radiation Risk Factors, 18 )Tj
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(Conclusions, 18 )Tj
-3.095 -1.2 Td
(Biological Effects of Radiation, 19 )Tj
3.095 -1.2 Td
(Early Effects, 19 )Tj
3.095 -1.2 Td
(General Considerations, 19 )Tj
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(Early Systemic Effects, 20 )Tj
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(Skin, 20 )Tj
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(Fertility, 21 )Tj
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(Other Organ Systems, 21 )Tj
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(Conclusions, 21 )Tj
-3.095 -1.2 Td
(Late Effects, 21 )Tj
3.095 -1.2 Td
(General Considerations, 21 )Tj
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(Cancer and Uncertainty in Estimates of Its Induction, 22 )Tj
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(Central Nervous System, 24 )Tj
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(Cataracts, 27 )Tj
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(Heritable Effects, 28 )Tj
-3.095 -1.2 Td
(Variation in Susceptibility to Radiation Across Subject Types, 28 )Tj
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(DNA Repair, 29 )Tj
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(Repair of Oxidative Damage and Double-Strand Breaks, 29 )Tj
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(Other Studies, 30 )Tj
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(Conclusion, 31 )Tj
-3.095 -1.2 Td
(Loss of Research Programs, 31 )Tj
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(References, 32 )Tj
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(3 HOW TO REDUCE RISK AND THE UNCERTAINTY IN RISK ESTIMATES 35 )Tj
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(Shielding, 35 )Tj
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(Recommendations for Research to Better Determine Shielding Requirements,\
35 )Tj
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(Knowledge Base Development, 35 )Tj
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(Shielding Approaches, 36 )Tj
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(Cost of Research vs. Cost of Excess Shielding, 38 )Tj
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(Radioprotective and Chemoprotective Drugs and Diet, 38 )Tj
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(Crew Selection, 39 )Tj
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(Optimal Time for Flight, 39 )Tj
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(Solar Particle Event Warning System, 40 )Tj
3.095 -1.2 Td
(Flares, 40 )Tj
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(Coronal Mass Ejections/lnterplanetary Shocks, 40 )Tj
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(Conclusions, 40 )Tj
-3.095 -1.2 Td
(References, 40 )Tj
-3.095 -2.67 Td
(4 PRIORITY RESEARCH QUESTIONS AND STRATEGIES 42 )Tj
3.095 -2.67 Td
(Higher-Priority Research Questions, 42 )Tj
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(Lower-Priority Research Questions, 47 )Tj
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(Time Scale of Research, 50 )Tj
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(What Will Still Remain Unknown, and What Risk Does This Represent?, 54 )Tj
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(References, 54 )Tj
-3.095 -2.67 Td
(5 OTHER ISSUES 55 )Tj
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(Need for Animal Use, 55 )Tj
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(Experimental Techniques and New Data Required, 56 )Tj
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(Ground- vs. Space-based Research, 56 )Tj
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(Plants and Food Supply, 57 )Tj
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(References, 57 )Tj
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( )Tj
-3.095 -1.57 Td
(APPENDIXES )Tj
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( )Tj
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(A Acronyms and Abbreviations, 61 )Tj
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(B Glossary, 63 )Tj
T*
(C Beam Sources, 69 )Tj
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(D Previous Advice of the National Research Council )Tj
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( Regarding the BEVALAC Facility, 72 )Tj
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( )Tj
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( )Tj
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(NASA's long-range plans include possible human exploratory missions to t\
he moon and Mars within the )Tj
0 -1.2 TD
(next quarter century. Such missions beyond low Earth orbit will expose c\
rews to transient radiation from )Tj
0 -1.2 TD
(solar particle events as well as continuous high-energy galactic cosmic \
rays ranging from energetic )Tj
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(protons with low mean linear energy transfer \(LET\) to nuclei with high\
atomic numbers, high energies, )Tj
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(and high LET. Because the radiation levels in space are high and the mis\
sions long, adequate shielding )Tj
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(is needed to mini mize the deleterious health effects of exposure to rad\
iation.)Tj
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(The knowledge base needed to design shielding involves two sets of facto\
rs, each with quantitative )Tj
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(uncertainty-the radiation spectra and doses present behind different typ\
es of shielding, and the effects of )Tj
T*
(the doses on relevant biological systems. It is only prudent to design s\
hielding that will protect the crew )Tj
T*
(of spacecraft exposed to predicted high, but uncertain, levels of radiat\
ion and biological effects. Because )Tj
T*
(of the uncertainties regarding the degree and type of radiation protecti\
on needed, a requirement for )Tj
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(shielding to protect against large deleterious, but uncertain, biologica\
l effects may be imposed, which in )Tj
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(turn could result in an unacceptable cost to a mission. It therefore is \
of interest to reduce these )Tj
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(uncertainties in biological effects and shielding requirements for reaso\
ns of mission feasibility, safety, )Tj
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(and cost.)Tj
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(This report of the Task Group on the Biological Effects of Space Radiati\
on summarizes current )Tj
0 -1.2 TD
(knowledge of the types and levels of radiation to which crews will be ex\
posed in space and discusses the )Tj
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(range of possible human health effects that need to be protected against\
\(Chapters 1 and 2\). It points out )Tj
T*
(that recent reductions in facilities for radiation research raise concer\
ns about how best to acquire needed )Tj
T*
(new knowledge. The report goes on to suggest other steps to be taken and\
the types of experiments )Tj
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(needed to reduce significantly the level of uncertainty regarding health\
risks to human crews in space )Tj
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(\(Chapter 3\). In Chapter 4 the task group recommends priorities for res\
earch from which NASA can )Tj
T*
(obtain the information needed to evaluate the biological risks faced by \
humans exposed to radiation in )Tj
T*
(space and to mitigate such risks. It outlines, in general terms, the com\
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(should make to carrying out these experiments in order to design effecti\
ve shielding in time for a )Tj
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(possible mission launch to Mars by 2018, which would allow for energetic\
ally favorable flight )Tj
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(trajectories. Chapter 5 addresses additional issues pertinent to carryin\
g out studies on the effects of )Tj
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(radiation, and the appendixes provide additional details and clarificati\
on as appropriate.)Tj
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(Summarized below are the task group's conclusions, its recommendations f\
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(12. Major radiation facilities-including both specialized radiation sour\
ces and animal colonies-have been )Tj
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(shut down in recent years. At present, there are severe limits on the av\
ailability of radiation particle )Tj
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(types and particle energies for HZE particle research. NASA can no longe\
r rely on the Department of )Tj
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(Energy and the Department of Defense for expertise, research, and facili\
ties. If the necessary facilities, )Tj
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(expertise, and funding were available now, it would take approximately 1\
0 years to provide data that )Tj
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(NASA needs to assess the best way to provide appropriate safeguards for \
its spaceflight crews.)Tj
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( )Tj
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(13. Unless NASA obtains access to a reliable source of HZE particles wit\
h an appropriate support staff )Tj
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(for a significant fraction of each year, it will take well over 10 years\
, perhaps over 20 years, depending )Tj
0 -1.2 TD
(on the level of effort, to reduce the present large uncertainties in par\
ticle transport behavior and in the )Tj
T*
(biological response functions for cancer induction. Such a delay will po\
stpone the design of necessary )Tj
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(shielding or may result in the use of excess shielding \(at a higher cos\
t\) and possibly delay any planned )Tj
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(Mars mission beyond the next quarter century.)Tj
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(14. In Chapter 4, the task group outlines its recommendations for resear\
ch priorities that NASA should )Tj
0 -1.2 TD
(follow to obtain the information needed to evaluate the biological risks\
faced by humans exposed to )Tj
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(radiation in space and to mitigate such risks. The research priorities r\
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(include extensive physical and biological experiments, including animal \
studies using light and heavy )Tj
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(nuclei up to 1 GeV/ nucleon. Such experiments could take more than 20 ye\
ars at NASA's present )Tj
T*
(utilization rate of approximately 100 hr/yr of accelerator time at Brook\
haven National Laboratory's )Tj
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(Alternating Gradient Synchrotron \(AGS\), the only source for HZE partic\
les supported by NASA.)Tj
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( )Tj
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(15. To carry out needed research expeditiously, NASA should explore a nu\
mber of possibilities, )Tj
0 -1.2 TD
(including international collaborations, so as to increase the research t\
ime available for experiments with )Tj
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(HZE particles and protons at energies over 250 MeV. Such possibilities i\
nclude a combination of more )Tj
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(running time at the AGS and at lower-energy accelerators, expansion of e\
xisting facilities \(see Appendix )Tj
T*
(C\), the commissioning of new beam lines at existing facilities, and the\
construction of a new facility. A )Tj
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NRC-1997