Nuclear Physics The Core of Matter, The Fuel of Stars Committee on Nuclear Physics Board on Physics and Astronomy Commission on Physical Sciences, Mathematics, and Applications National Research Council NATIONAL ACADEMY PRESS Washington, D.C. 1999 Notice Committee Preface Acknowledgment of Reviewers Contents Summary and Recommendations NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. William A. Wulf is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an advisor to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine. The National Research Council was established by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce Alberts and Dr.William A. Wulf are chairman and vice chairman, respectively, of the National Research Council. This project was supported by the Department of Energy under Contract No. DE-FG02-96ER40957 and the National Science Foundation under Grant No. PHY-9515524. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the agencies that provided support for this project. Library of Congress Card Catalog Number 98-89539 International Standard Book Number 0-309-06276-4 Additional copies of this report are available from: National Academy Press (http://www.nap.edu)   Board on Physics and Astronomy 2101 Constitution Ave., NW, Box 285   National Research Council, HA 562 Washington, D.C. 20055   2101 Constitution Avenue, N.W. 800-624-6242   Washington, DC 20418 202-334-3313 (in the Washington metropolitan area)     Copyright 1999 by the National Academy of Sciences. All rights reserved. Printed in the United States of America COMMITTEE ON NUCLEAR PHYSICS John P. Schiffer, Argonne National Laboratory and University of Chicago, Chair Sam M. Austin, Michigan State University Gordon A. Baym, University of Illinois at Urbana-Champaign Thomas W. Donnelly, Massachusetts Institute of Technology Bradley Filippone, California Institute of Technology Stuart Freedman, University of California at Berkeley Wick C. Haxton, University of Washington Walter F. Henning, Argonne National Laboratory Nathan Isgur, Thomas Jefferson National Accelerator Facility Barbara Jacak, State University of New York at Stony Brook Witold Nazarewicz, University of Tennessee at Knoxville Vijay R. Pandharipande, University of Illinois at Urbana-Champaign Peter Paul,* State University of New York at Stony Brook Steven E. Vigdor, Indiana University Donald C. Shapero, Director Robert L. Riemer, Senior Program Officer * Currently at Brookhaven National Laboratory. BOARD ON PHYSICS AND ASTRONOMY ROBERT C. DYNES, University of California at San Diego, Chair ROBERT C. RICHARDSON, Cornell University, Vice Chair STEVEN CHU, Stanford University VAL FITCH, Princeton University IVAR GIAEVER, Rensselaer Polytechnic Institute RICHARD HAZELTINE, University of Texas at Austin JOHN P. HUCHRA, Harvard-Smithsonian Center for Astrophysics JOHN C. MATHER, NASA Goddard Space Flight Center R.G. HAMISH ROBERTSON, University of Washington JOSEPH H. TAYLOR, JR., Princeton University KATHLEEN C. TAYLOR, General Motors Research and Development Center J. ANTHONY TYSON, Lucent Technologies GEORGE WHITESIDES, Harvard University DONALD C. SHAPERO, Director ROBERT L. RIEMER, Associate Director KEVIN D. AYLESWORTH, Program Officer NATASHA CASEY, Senior Administrative Associate GRACE WANG, Project Assistant COMMISSION ON PHYSICAL SCIENCES, MATHEMATICS, AND APPLICATIONS PETER M. BANKS, ERIM International, Inc., Co-chair W. CARL LINEBERGER, University of Colorado, Co-chair WILLIAM BROWDER, Princeton University LAWRENCE D. BROWN, University of Pennsylvania MARSHALL H. COHEN, California Institute of Technology RONALD G. DOUGLAS, Texas A&M University JOHN E. ESTES, University of California at Santa Barbara JERRY P. GOLLUB, Haverford College MARTHA P. HAYNES, Cornell University JOHN L. HENNESSY, Stanford University CAROL M. JANTZEN, Westinghouse Savannah River Company PAUL KAMINSKI, Technovation, Inc. KENNETH H. KELLER, University of Minnesota MARGARET G. KIVELSON, University of California at Los Angeles DANIEL KLEPPNER, Massachusetts Institute of Technology JOHN R. KREICK, Sanders, a Lockheed Martin Company MARSHA I. LESTER, University of Pennsylvania M. ELISABETH PATÉ-CORNELL, Stanford University NICHOLAS P. SAMIOS, Brookhaven National Laboratory CHANG-LIN TIEN, University of California at Berkeley NORMAN METZGER, Executive Director Preface The Committee on Nuclear Physics was established by the Board on Physics and Astronomy as part of its decadal survey series, Physics in a New Era. The committee met four times over the course of a year. It heard from program managers at the U.S. Department of Energy (DOE) and the National Science Foundation (NSF) and solicited input from the nuclear physics community through the American Physical Society's Division of Nuclear Physics. A set of peer readers who were asked by the committee to read the draft report (J. Friar, G. Garvey, K. Gelbke, E. Henley, B. Holstein, and R. Holt) provided valuable perspectives, and their comments had an influence on the report. The comments of the reviewers of the report (see page ix) also provided useful input. The committee would like to thank both groups for their time and help. In addition, the list of individuals who helped with material for the report in a variety of ways is too long to enumerate, and the committee wishes to express its gratitude for this assistance. As part of the physics survey, the overall objective of the study was to help the general public, the government agencies concerned with the support of science, Congress, and the physics community to envision the future of this field within the nation's overall physics effort. The report of the committee is in the context of previous planning for the field and follows the reports of the 1972 Physics Survey's Nuclear Physics Panel, chaired by J. Weneser, and the 1986 Physics Survey's Nuclear Physics Panel, chaired by J. Cerny, as well as the planning of the Nuclear Science Advisory Committee (NSAC), a joint advisory committee of the NSF and DOE. In particular, the committee drew on the 1996 report Nuclear Science: A Long Range Plan, prepared by NSAC (available from the Division of Nuclear Physics, Office of Science, DOE, or the Nuclear Science Section, Physics Division, NSF). The NSAC Long Range Plans represent a wide community involvement in shaping the field. The committee would like to acknowledge the assistance of Donald C. Shapero, director, Board on Physics and Astronomy, and Robert L. Riemer, senior program officer. The committee would especially like to acknowledge the late David Schramm, who started the present review and discussed the com-mittee's task at its first meeting. His unique enthusiasm for physics and profound interest and many contributions to the nuclear physics of astrophysical phenomena are missed in nuclear physics as indeed in all of physics. The committee would like to acknowledge the support provided by grants from NSF's Physics Division and DOE's Office of Science. John P. Schiffer, Chair Committee on Nuclear Physics Acknowledgment of Reviewers This report has been reviewed by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the National Research Council's (NRC's) Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the authors and the NRC in making the published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The contents of the review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their participation in the review of this report: Gary Adams, Rensselaer Polytechnic University, Felix Boehm, California Institute of Technology, Stanley J. Brodsky, Stanford Linear Accelerator Center, Richard Casten, Yale University, Ernest M. Henley, University of Washington, Jerry Garrett, Oak Ridge National Laboratory, J. Ross Macdonald, University of North Carolina, Peter Parker, Yale University, R.G. Hamish Robertson, University of Washington, and James P. Vary, Iowa State University. Although the individuals listed above have provided many constructive comments and suggestions, responsibility for the final content of this report rests solely with the authoring committee and the NRC. Contents Summary and Recommendations 1 1   Introduction 8   Origins and Fundamentals 8   Scope of the Field 9   Recent Accomplishments 11   Intellectual Horizons 14   International Aspects 17   Educational Aspects 17   Societal Applications 18 2   The Structure of the Nuclear Building Blocks 19   Introduction 19   The Internal Structure of Protons and Neutrons 21     First Steps 22     Technological Advances 22     Experimental Opportunities 28   Accounting for Confinement: From QCD to Nuclear Theory 35     Working with Quarks and Gluons 36     Working with Nucleons and Mesons 37   Hadrons in Nuclear Matter 42   Outlook 45 3   The Structure of Nuclei 47   Introduction 47   Nuclear Forces and Simple Nuclei 49   Advances and Challenges in Understanding Light Nuclei 51   Nuclear Forces and Complex Nuclei 58     The Shell Model of Nuclei 58     Mean Field Methods 60     Limits of Nuclear Stability 61     The Quest for Superheavy Elements 61     Toward the Limits in Neutron-to-Proton Ratio 64     Limits of Angular Momentum 67   Nuclear Matter 77   Outlook 78 4   Matter at Extreme Densities 80   Introduction 80   Ultrarelativistic Heavy-Ion Collisions 83   Stopping 86   Evolution of Collisions 87     Hot Dense Initial State 91   Hadronic Rescattering and Freezeout 92   Thermal Description of the Final State 93   Signatures of Quark-Gluon Plasma Formation 94   Chiral Symmetry 99   Relativistic Heavy-Ion Collider 99     Experiments at RHIC 100   Outlook 102 5   The Nuclear Physics of the Universe 104   Introduction: Challenges for the Field 104   The Solar Neutrino Problem 105   The Big Bang, the Quark-Gluon Plasma, and the Origin of the Elements 112   The Supernova Mechanism 115   Measuring Stellar Nuclear Reactions in the Laboratory 118   Neutron Stars 122   Particle Properties from Nuclear Astrophysics 126   Outlook 127 6   Symmetry Tests in Nuclear Physics 128   Introduction: Priorities and Challenges 128   The Standard Model 129   Testing Symmetries 132     Spatial Reflection Symmetry 134     Time-Reversal Symmetry 136   Precision Measurements of Standard Model Parameters 138   The Search for Neutrino Mass 141   The Weak Interaction Within the Nuclear Environment 146   Exotic Particle Searches, Rare Decays, and Nuclear Physics 147   Outlook 148 7   The Tools of Nuclear Physics 150   Introduction 150   Accelerators 151     Historical Perspective 151     Accelerator Research and Development 155   Instrumentation 158     Examples of New Detector Systems 158       Ion and Atom Traps 158       Exploring the Structure of Exotic Nuclei 159       Detectors for the Quark Structure of Matter 163       Detectors for the Frontier of High-Energy Density 164       Detection Schemes for Fundamental Symmetries and Underground Laboratories 166     Computers in Nuclear Physics 169     Relativistic Heavy-Ion Data Storage and Retrieval 169     Quantum Monte Carlo Simulations of Nuclei 170     Computer Simulations of Supernovae 170     Lattice Quantum Chromodynamics 170   Outlook 171 8   Nuclear Physics and Society 172   Introduction 172   Human Health 174     Radiation Therapy for Cancer 174       Cancer Therapy with Protons 174       Cancer Therapy with Neutrons and Heavy Ions 175     Diagnostic Imaging 175       SPECT and PET Imaging 176       Nuclear Magnetic Resonance Imaging 176     Trace-Isotope Analysis 179     Accelerator Mass Spectrometry 179   Environmental Applications 180   Impact on Industry 183     Nuclear Analysis and Testing 183       Testing with Particle Beams 183       Testing with Neutron Beams 184     Materials Modification 185     U.S. Nuclear Data Program 185   Energy 186     Burning of Long-Lived Waste and Accelerator-Driven Reactors 187     Inertial Confinement Fusion Reactors 188   National Security 188     Stockpile Stewardship 188     Nonproliferation of Nuclear Weapons 189   Education of the Nation's Technical Workforce 191     Graduate Education in Nuclear Physics 191     Graduate Student and Faculty Demographics 193     Undergraduate Education 193     Earlier Education, Outreach, and Scientific Literacy 194       K-8 Education in Elementary and Middle Schools 194       Contact with Teachers and Students in High Schools 195       Activities Addressing Underrepresentation of Women and Minorities 195   Outlook 195 Appendix: Accelerator Facilities for Nuclear Physics in the United States 197 Summary and Recommendations Nuclear physics addresses the nature of matter making up 99.9 percent of the mass of our everyday world. It explores the nuclear reactions that fuel the stars, including our Sun, which provides the energy for all life on Earth. The field of nuclear physics encompasses some 3,000 experimental and theoretical researchers who work at universities and national laboratories across the United States, as well as the experimental facilities and infrastructure that allow these researchers to address the outstanding scientific questions facing us. This report provides an overview of the frontiers of nuclear physics as we enter the next millennium, with special attention to the state of the science in the United States. The current frontiers of nuclear physics involve fundamental and rapidly evolving issues. One is understanding the structure and behavior of strongly interacting matter in terms of its basic constituents, quarks and gluons, over a wide range of conditionsfrom normal nuclear matter to the dense cores of neutron stars, and to the Big Bang that was the birth of the universe. Another is to describe quantitatively the properties of nuclei, which are at the centers of all atoms in our world, in terms of models derived from the properties of the strong interaction. These properties include the nuclear processes that fuel the stars and produce the chemical elements. A third active frontier addresses fundamental symmetries of nature that manifest themselves in the nuclear processes in the cosmos, such as the behavior of neutrinos from the Sun and cosmic rays, and in low-energy laboratory tests of these symmetries. With recent developments on the rapidly changing frontiers of nuclear physics the Committee on Nuclear Physics is greatly optimistic about the next ten years. Important steps have been taken in a program to understand the structure of matter in terms of quarks and gluons. The United States has made two major and farsighted investments in this program. The Continuous Electron Beam Accelerator Facility (CEBAF) has recently come into operation and is now delivering beams of unprecedented quality. It will serve as the field's primary "microscope" for probing the building blocks of matter such as the nucleons (protons, neutrons) and the nuclei of atoms, at the small length scales where new physics phenomena involving quarks and gluons should first appear. It will provide new insights into the structure of both isolated nucleons and nucleons imbedded in the nuclear medium. The Relativistic Heavy Ion Collider (RHIC), whose construction is now nearing completion, will produce the world's most energetic collisions of heavy nuclei. This will allow nuclear physicists to probe the properties of matter at energies and densities similar to those characterizing the cores of neutron stars and the Big Bang. RHIC experiments should teach us about the expected transition to a new phase of nuclear matter in which the quarks and gluons are no longer confined within nucleons and mesons. The theory supporting these new efforts has produced new bridges between quantum chromodynamics (QCD)the theory of quarks and gluonsand the field's more traditional models of nuclear structure, which involve nucleons and mesons. Nuclear theorists have begun to construct "effective theories" that are equivalent to QCD at low energies, yet share many of the properties of traditional models that view nuclei as quantum fluids of protons and neutrons. This work is providing the field with new tools for more critically addressing the structure of nuclei and the properties of bulk nuclear matter. An area that at present is generating intense interest is related to nuclear processes in the cosmos. Experiments measuring neutrinos from the Sun and from cosmic-ray interactions in Earth's atmosphere strongly suggest that neutrinos are massive, a result that would imply new physics beyond the current "Standard Model" of particle physics. U.S. nuclear physicists, who have worked in the field since initiating the first experiment more than 30 years ago, are currently partners in the Sudbury Neutrino Observatory, the first detector that will distinguish solar neutrinos of different types, or "flavors." Such experiments are part of a larger effort to carefully test the Standard Model at low energies. The nucleus is a powerful laboratory for probing many of the fundamental symmetries of nature, because it can magnify subtle effects that may hide beyond the direct reach of the world's most energetic accelerators. Another frontier area is the study of how the nucleus changes when subjected to extreme conditions, such as very rapid rotation or severe imbalances between the numbers of neutrons versus protons. Exotic nuclei play essential roles in the evolution of our galaxy: the "parents" of about half of the heavy elements are very neutron-rich nuclei, believed to have been created within the spectacular stellar explosions known as supernovae, at temperatures in excess of a billion degrees. Remarkable advances in accelerator technology have now provided the tools needed to produce such unusual nuclei in the laboratory, opening the door to new experiments on the properties of nuclear matter near the limits of binding. The recommendations by this committee should be considered in the context of the careful planning in the nuclear physics community summarized by the Long Range Plans developed by the Nuclear Science Advisory Committee (NSAC). NSAC advises the two principal funding agencies for this field, the Department of Energy and the National Science Foundation. The Division of Nuclear Physics of the American Physical Society also played an important role, joining with NSAC to organize various town meetings for the purpose of gathering input from the community. The NSAC Long Range Plans have been prepared at about 6-year intervals (1979, 1983, 1989, and 1996). They have been influential in expressing new priorities of the field and in justifying new initiatives.1 The 1979 and 1983 Long Range Plans, for example, identified CEBAF and RHIC as the most promising new initiatives for decisively advancing the scientific frontiers of the field. The recent adoption of a similar planning process by the European nuclear physics community is an indication of the perceived effectiveness of the Long Range Plans. In parallel with CEBAF and the construction of RHIC, the NSAC Long Range Plans have also identified and recommended several smaller targets of opportunity. Among those currently being implemented with agency funding are an upgrade to the capabilities for producing energetic beams of short-lived nuclei at Michigan State University, the construction of new detectors for studying solar neutrinos, and the adaptation of RHIC to the investigation of previously inaccessible aspects of the proton's structure. Both the Department of Energy and the National Science Foundation support user facilities of world-class capability and both have strong university programs. DOE supports the largest user facilities and university groups, while NSF supports user facilities at universities and many university user groups. The committee believes that the continuing programs in the two agencies are essential to the field, with the DOE emphasis on national laboratory facilities and the NSF emphasis at the universities providing complementary strengths and opportunities. Because there exists a tradition of successful deliberation and planning within the nuclear physics community, the Committee on Nuclear Physics chose to emphasize the science rather than the process in the recommendations presented below. However, it would be remiss if it failed to bring into focus the funding stresses that now severely threaten the field. At present it seems to be generally agreed by policymakers on all sides that the support of basic research is in the public interest, and there is considerable talk of increasing the corresponding budgets. However, the reality in nuclear physics, as in many other fields of research, is quite different. In 1996 the budget guidance provided by the DOE and NSF to help formulate the most recent Long Range Plan2 for nuclear physics was for roughly constant manpower budgets. This goal has been undercut by the budgets of recent years. The cumulative result of a dollar-flat budget in the case of the DOE is that it now is 3 to 10 percent below the range of the guidance. In the case of NSF, there has been a larger decline, to about 15 percent below the 1996 guidance. These decreases will curtail the utilization of new facilities and instrumentation and will jeopardize our nation's world-leading role in the field. This situation has arisen even as the efficient commissioning of CEBAF, the approaching completion of RHIC, new technical advances in the exploration of nuclei near the limits of binding, and discoveries in low-energy neutrino physics have made execution of the 1996 Long Range Plan all the more urgent, requiring the level of funding given in the guidance by the agencies. Recommendation I: Discoveries in nuclear physicsnew phenomena connected with the role of quarks and gluons in the nucleus, the structure and dynamics of nuclei, the nuclear physics of the cosmos, and the limits of the Standard Modelare within reach due to our recent investments in new facilities and instrumentation. With CEBAF having started on its research program of the quark-gluon structure of matter, RHIC about to embark on the study of matter at the limits of energy density, and with other recent advances in technical capabilities, a rich scientific harvest is limited by severely constrained budgets. The committee recommends the near-term allocation of resources needed to realize these unique experimental and theoretical opportunities. Careful laboratory measurements of nuclear reactions that take place in stars have provided the foundation for some of the field's most important achievements in understanding the nuclear bases of the cosmos, including the solar neutrino problem and the origin of the light chemical elements in the Big Bang. Beams of exotic short-lived nuclei are opening up new opportunities for measuring nuclear properties and reactions in the poorly understood regions near the limits of stability. The properties of these barely stable nuclei have direct quantitative connections to the processes that fuel the stars and create the chemical 2Nuclear Science: A Long Range Plan, Nuclear Science Advisory Committee, 1996, available from the Division of Nuclear Physics, Office of Science, DOE, and the Nuclear Science Section, Division of Physics, NSF. elements of our world. Beams of exotic nuclei hold great promise as tools for probing new nuclear properties and for testing fundamental symmetries at low energies. These considerations provide a compelling argument for constructing a next-generation facility that will use isotope separator online (ISOL) techniques to produce high-intensity, high-resolution beams of short-lived nuclei over a broad mass range. Recommendation II: The committee recommends the construction of a dedicated, high-intensity accelerator facility to produce beams of short-lived nuclei. Such a facility will open up a new frontier in nuclear structure near the limits of nuclear binding and will strengthen our understanding of nuclear properties relevant to explosive nucleosynthesis and other aspects of the physics governing the cosmos. Frontier research in nuclear physics relies on both large accelerators, such as CEBAF and RHIC, and smaller facilities, where specialized low-energy measurements can be made. These smaller facilities include several university and national laboratory accelerators where weak interaction, nuclear structure, and nuclear astrophysics studies are done. Both small and large accelerators rely critically on innovative instrumentation to make new discoveries. In the case of CEBAF and RHIC, the quality of the physics programs depends on specialized detectors. The development of much of this equipment is on a scale that is suitable for university laboratories, where graduate students can participate in the construction and gain experience with cutting-edge technology. Many of the equipment needs at the smaller facilities are equally specialized. Examples include atom and ion traps designed for precision studies of weak interactions and sensitive detector arrays for measuring nuclear reactions at the very low energies characteristic of stars like our Sun. Recommendation III: The committee recommends continued investment in instrumentation for research. As new discoveries come to light and new ideas for experiments emerge, upgrades of detector systems at CEBAF and RHIC and instrumentation needs at smaller laboratories should be considered in accordance with their potential for new discoveries. NSAC is well positioned to provide DOE and NSF appropriate advice on relative priorities and specific major upgrades. To foretell the course of a science beyond the near term is always difficult, as it depends both on the discoveries of the next few years and the doors that new advances in technology will open. The following represents some of the future options, among a number of attractive possibilities that can be perceived at the present time, for possible implementation in the early part of the next century. CEBAF probes nuclei at length scales where the quark and gluon substructure of nuclei should first become apparent. It thus represents a first step in probing the relationship between standard nuclear physics based on protons, neutrons, and mesons, and the underlying fundamental degrees of freedomquarks and gluons. To understand the transition between these regimes, it may be necessary to extend the measurements to even finer resolution, such as that offered by a 15- to 30-GeV electron accelerator. The construction of a 25-GeV machine is now under discussion in Europe, and future upgrades of CEBAF are being considered in the United States. RHIC is about to open a new door to ultrahigh energy densities in nuclear matter. The potential discovery there of a new phase of mattera plasma of quarks and gluonscould point the way to issues requiring still higher beam intensities or energies. Construction of the Large Hadron Collider (LHC) at CERN in Europe has recently begun, with U.S. participation. Early in the next century, this facility will allow collisions of nuclei at 40 times the beam energy of RHIC. Future discoveries at RHIC will guide upgrades of RHIC and the participation of U.S. nuclear physicists in the LHC effort. The impact of the discovery that neutrinos may have mass will be felt throughout physics. Thus, following the Sudbury Neutrino Observatory, there may be an urgent need to develop and deploy detectors capable of exploring the spectrum of lower-energy solar neutrinos, or of greatly improving the sensitivity to neutrinos from the next supernova neutrino burst. Terrestrial neutrino experiments have put important constraints on neutrino properties; a compelling case may arise for new terrestrial experiments. Studies of fundamental symmetries in nuclei can isolate and enhance new phenomena beyond the Standard Model. In particular, new experimental searches for a neutron electric-dipole moment and precision measurements of beta-decay correlation coefficients can become the most stringent constraints on our understanding of fundamental symmetries. Promising possibilities exist for developing sources of cold and ultracold neutrons of unprecedented intensity. Recommendation IV: Within the ten-year time frame envisioned for this report, new discoveries will provide strong arguments for one or more major new endeavors. Possible candidates include a higher-energy electron machine, capability for the study of heavy-ion collisions with increased energy densities, new detectors to explore mass effects on the solar and supernova neutrino fluxes, and an ultracold neutron facility providing an order-of-magnitude increase in the neutron densities for studies of fundamental symmetries. The committee recommends the continuation of frequent NSAC Long Range Plan efforts, to help retain the responsiveness of the field to the most promising new opportunities. Nuclear physics not only advances the frontiers of knowledge but also makes remarkable contributions to the needs of society. The generation of nuclear energy, both for civilian power consumption and for nuclear weapons, has had a profound impact on our society in the last 50 years. Equally far-reaching has been the impact of nuclear physics in medicine; results of nuclear physics and nuclear physics techniques, from magnetic resonance to detector technologies to the use of isotopes, have led to remarkable advances in diagnostic and therapeutic power. Nuclear diagnostic techniques have a growing and pervasive role in industry, national security, nonproliferation, geophysics, global climate research, and paleontology. Nuclear physics is the basis of important technologies in the design and preparation of materials. Through such applications, through the technical and intellectual intersections of nuclear physics with other fields of science, and through its intrinsic intellectual challenges, nuclear physics stands as one of the core sciences in the continuing advancement of knowledge. Facilities and instrumentation are essential for progress, but science ultimately depends on the people who carry it outon their individual creativity, drive, and enterprise. The scientists who conduct experiments and develop the theoretical framework for interpreting the results are the most essential components of the field. The continued intellectual vitality of nuclear physics as a science, and the continuation of the field's more direct contributions to societal needs, depend critically on the capacity to educate the next generation of physicists. Past performance has demonstrated that students trained in solving the enormously challenging problems of forefront physics research develop the array of skills needed to lead the nation in harnessing the rapidly advancing technology that often emerges from the research itself. The remainder of this report summarizes the current status of the science of nuclear physics. Several items of more general interest are highlighted in boxes throughout the scientific chapters. Note 1 It is important to recognize that support for funding of these new opportunities was achieved through often painful priority decisions made by the community of nuclear physicists during the past decade. Other facilities, some unique and most still world-class, had to be sacrificed to pursue the scientific endeavors that were judged to be of highest priority. Major programs, such as the Bevalac relativistic heavy-ion accelerator at Berkeley and nuclear physics support for the Los Alamos Meson Physics Facility (LAMPF) were phased out, and a number of small university accelerators have been closed since 1980.