Recent strides have brought nuclear science to the threshold of major advances in understanding the atomic nucleus and the possible applications of nuclear techniques. This progress is largely due to technological breakthroughs that allow for a deeper understanding of nuclei, their constituents, and the role of nuclei in the cosmos and to the development of many practical applications.
To remain vital, nuclear science must attract and retain top talent by providing a dynamic environment where innovation can flourish. This is possible only with the strong support of research and a diverse portfolio of wisely selected and efficiently operated facilities needed to carry out the program. Nuclear science research is diverse in scale, involving small and large groups of scientists and students from universities and research laboratories. The integration of research and teaching at universities is the natural environment for the incubation of new ideas and the education and training of the scientific workforce. Small university-based facilities support important research in nuclear structure, nuclear astrophysics, and fundamental symmetries. The infrastructure at such universities—a local accelerator, the technologies for advanced detectors, and instrumentation—enables university scientists and students to lead and to make important contributions to significant initiatives in nuclear science. Support for smaller-scale operations at the universities along with the operations of the major user facilities are indispensable components of the U.S. nuclear science program. In recent years the resources that go to the major facilities have made up an increasing fraction of the total budget, especially that devoted to the Department of Energy (DOE) portion. Continuing
to increase the share reserved for facilities operations at the expense of the research budget is not sustainable.
Recently the DOE nuclear physics program took over the stewardship of the National Isotopes Program. This program continues to grow in importance as the uses of nuclear techniques in medical imaging and therapeutic procedures accelerate. The isotopes program and nuclear physics have been ideal partners and the impact has been positive on both sides. The overall costs of the isotope program have not impacted the budget in other areas of nuclear physics, but the synergy between the two programs has resulted in more efficient operations on the isotope production side and more opportunities for research and development on the nuclear physics side, including opportunities for accelerator physicists to develop new techniques in isotope production. Another example of mutual benefit is the inclusion of the isotopes program in the Small Businesses Innovation Research program and the Early Career and Graduate Fellowship program in nuclear physics, while isotopes produced for research do not incur additional costs for nuclear physics. The continued health of the isotopes program, in particular, reinforces the need for a workforce trained in nuclear science and the need for strong university programs to provide that training.
The Department of Energy Office of Nuclear Physics operates three user facilities for nuclear physics research in the United States: the Argonne Tandem Linear Accelerator System (ATLAS), the Continuous Electron Beam Accelerator Facility (CEBAF) at the Thomas Jefferson National Accelerator Facility (JLAB), and the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL). The National Science Foundation (NSF) operates one nuclear physics user facility, the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University (MSU). The Spallation Neutron Source (operated by the Department of Energy Office of Basic Energy Research) hosts the Fundamental Neutron Physics Beam line at Oak Ridge, which provides cold neutron beams for nuclear physics research. A number of NSF- or DOE-supported smaller facilities at universities make unique contributions to the field. Two large centers—the Institute for Nuclear Theory and the Joint Institute for Nuclear Astrophysics—serve the nuclear physics community and facilitate strong connections to other fields of science.
As a consequence of a systematic long-range planning process and strategic investments by funding agencies, nuclear physicists have access to U.S. facilities with world-class physics programs. CEBAF is undergoing major upgrades of its accelerator and detectors, opening up a new frontier in nuclear electroweak physics. The upgrade of the CEBAF electron accelerator and detector systems will enable the measurements required to search for exotic mesons, a fundamental prediction
of quantum chromodynamics (QCD). It will also further our understanding of how quarks and gluons form nucleons and nuclei, the most fundamental building blocks of visible matter, and enable a precision test of the Standard Model. The luminosity at RHIC has been increased and the detectors have been upgraded, providing the opportunity to conduct experiments that can make more incisive measurements of the contributions of quarks and gluons to the spin of the proton and capitalizing on RHIC’s recent discovery of a liquid phase for quarks and gluons. U.S.-sponsored scientists participate in experiments at the Large Hadron Collider (LHC) that should bring new ways of exploring this new phase of matter. Neutrino experiment discoveries at underground laboratories already required the first revision to the Standard Model in four decades, and new experiments to answer important questions about neutrinos are under way or planned in the United States and around the world. The low-energy nuclear physics user facilities, ATLAS and NSCL, are developing new paradigms of nuclear structure. These facilities, together with low-energy stable beam and neutron beam facilities, provide an array of beams and equipment required for the understanding of nuclear structure and nuclear reactions responsible for element production in stars and stellar explosions. These are also the tools needed for giving society innovative applications of nuclear science. The Facility for Rare Isotope Beams (FRIB), now under construction at MSU, will provide unique capabilities within an expanding worldwide arsenal of rare isotope facilities. The Fundamental Neutron Beam line is poised to begin its research program, which includes experiments with enormous discovery potential by making unprecedented tests of the fundamental symmetries of nature. Nuclear theorists, computer scientists, and applied mathematicians are taking advantage of state-of-the art supercomputers to carry out calculations of previously intractable complexity, leading to new understanding of nuclear structure and reaction dynamics, supernova explosions, nucleon structure, and quark-gluon plasma properties. With all these new tools, the U.S. nuclear physics community is poised to make important discoveries in the coming decade.
Finding: By capitalizing on strategic investments, including the ongoing upgrade of the continuous electron beam accelerator facility (CEBAF) at the Thomas Jefferson National Accelerator Facility and the recently completed upgrade of the relativistic heavy ion collider (RHIC) at Brookhaven National Laboratory, as well as other upgrades to the research infrastructure, nuclear physicists will confront new opportunities to make fundamental discoveries and lay the groundwork for new applications.
Conclusion: Exploiting strategic investments should be an essential component of the U.S. nuclear science program in the coming decade.
As an outcome of careful long-range planning by the community and funding agencies, two large construction projects for nuclear science research facilities are now on their way in the United States. For the coming decades, these projects will enable the U.S. nuclear science community to continue to make discoveries that push the boundaries of knowledge and benefit society. One of the projects is the upgrade to CEBAF. The other is a new facility, FRIB, which will be the world’s most powerful device for studying the properties of exotic unstable atomic nuclei and their reactions, providing unique research opportunities for the United States and the international community. Data to date on exotic nuclei are already beginning to revolutionize our understanding of the structure of atomic nuclei. FRIB will enable experiments in uncharted territory at the limits of nuclear stability. FRIB will provide new isotopes for research related to societal applications as it addresses long-standing questions about the astrophysical origin of the elements and the fundamental symmetries of nature.
Finding: The Facility for Rare Isotope Beams is a major new strategic investment in nuclear science. It will have unique capabilities and will offer opportunities to answer fundamental questions about the inner workings of the atomic nucleus, the formation of the elements in our universe, and the evolution of the cosmos.
Recommendation: The Department of Energy’s Office of Science, in conjunction with the state of Michigan and Michigan State University, should work toward the timely completion of the Facility for Rare Isotope Beams and the initiation of its physics program.
Nuclear scientists have a long and impressive record of scientific contributions with low background experiments at underground sites. In the most recent decade this work contributed to revolutionary discoveries about the neutrino. Further crucial experiments, including delicate experiments attempting to discover neutrinoless double-beta decay, are being mounted. Nuclear scientists are participating in experimentation that could lead to the discovery of rare nuclear interactions. This work could disclose the origin of dark matter, which may account for five times as much mass as that of all identified matter in the universe. An underground nuclear physics accelerator is being designed to study the nuclear reactions that are important to astrophysical processes associated with late stellar evolution. The nuclear physics community has participated in the exercise to make the scientific case for a deep underground laboratory in the United States. With private, state, and DOE funding, the Sanford Underground Research Facility (SURF), at moderate depth, will provide a home for experiments in dark matter and neutrinoless
double-beta decay at the Homestake site in South Dakota. The scientific case for a deep underground laboratory in the United States remains compelling.
Recommendation: The Department of Energy, the National Science Foundation, and, where appropriate, other funding agencies should develop and implement a targeted program of underground science, including important experiments on whether neutrinos differ from antineutrinos, on the nature of dark matter, and on nuclear reactions of astrophysical importance. Such a program would be substantially enabled by the realization of a deep underground laboratory in the United States.
Universities are crucibles in which new ideas in nuclear science emerge, scientific advances attract the brightest young minds to the field, and future nuclear scientists make their first research contributions. In nuclear science as well as more generally, American universities are unparalleled engines of scientific innovation. University laboratories and research programs play leading roles in advancing all the frontiers of nuclear science that have been described as well as in developing its applications.
Finding: The dual role of universities—education and research—is important in all aspects of nuclear physics, including the operation of small, medium, and large facilities, as well as the design and execution of large experiments at the national research laboratories. The vitality and sustainability of the U.S. nuclear physics program depend in an essential way on the intellectual environment and the workforce provided symbiotically by universities and the national laboratories. The fraction of the nuclear science budget reserved for facilities operations cannot continue to grow at the expense of the resources available to support research without serious damage to the overall nuclear science program.
Conclusion: In order to ensure the long-term health of the field, it is critical to establish and maintain a balance between funding of operations at facilities and the needs of university-based programs.
With a strong, broad university program and large-scale, versatile facilities, nuclear science will build upon its track record of discovery and innovation and will help to build the skilled workforce needed for a healthy economy and to meet the energy, medical, and national security challenges that are faced today. However, the symbiotic relationship between universities and facilities needs strengthening
across a variety of fronts in order to ensure a robust pipeline. In Chapter 5 we provide a selection of actions that would work toward the desired goals. Included among them are steps to encourage those entering graduate school to consider nuclear physics as an area of study. Graduate students play a key role in all aspects of the research programs of their advisors and help to fill the nation’s need for nuclear scientists, not only in basic research but in the many areas described in Chapter 3 to which nuclear physics contributes. Here the committee recommends one such step:
Recommendation: The Department of Energy and the National Science Foundation should create and fund two national competitions: one a fellowship program for graduate students that would help recruit the best among the next generation into nuclear science and the other a fellowship program for postdoctoral researchers to provide the best young nuclear scientists with support, independence, and visibility.
The rapid escalation in the power of computers is having an impact in all areas of human activity. The coming generation of extreme-scale computing resources will be required to make desired breakthroughs in key areas of nuclear physics. Nuclear physicists, computer scientists, and applied mathematicians are presently taking advantage of state-of-the art supercomputers to carry out very complex calculations, leading to new understanding of, and predictive capabilities for, nuclear forces, nuclear structure and reaction dynamics, hadronic structure, matter under extreme conditions, stellar evolution and explosions, and accelerator science. It is essential for the future health of nuclear physics that the theoretical nuclear science community have a clear strategy for exploiting the rapidly increasing power of modern computing for the benefit of their science.
Recommendation: A plan should be developed within the theoretical community and enabled by the appropriate sponsors that permits forefront computing resources to be exploited by nuclear science researchers and establishes the infrastructure and collaborations needed to take advantage of exascale capabilities as they become available.
Nuclear science is an international effort involving cooperation and competition between scientists from different institutions and different nations and utilizing a broad range of large- and smaller-scale research facilities. In order to maintain their scientific leadership and continue to come up with innovations, U.S. nuclear scientists must operate in an environment that enables them to seize new opportunities that might arise in the United States or abroad in a timely manner so that they are fully engaged in the discoveries that result. As discussed in more
detail in the section “The Need for Nimbleness” in Chapter 5, streamlining the sponsoring agencies’ procedures for initiating and managing projects, especially smaller-scale projects whose risks are more easily manageable and whose potential for discovery and/or applications is large, is essential for a program that can keep up with, and indeed lead, the global community.
Finding: The range of projects in nuclear physics is broad, and sophisticated new tools and protocols have been developed for successful management of the largest of them. At the other end of the scale, nimbleness is essential if the United States is to remain competitive and innovative on the rapidly expanding international nuclear physics scene.
Recommendation: The sponsoring agencies should develop streamlined and flexible procedures that are tailored for initiating and managing smaller scale nuclear science projects.
Without gluons, there would be no neutrons or protons and no atomic nuclei. Gluon properties in matter remain largely unexplored and mysterious. An electron ion collider facility would provide unprecedented capability for studies that are essential for understanding the fundamental structure of visible matter, including (1) precision imaging of quarks and gluons to determine the spin, flavor, and spatial structure of the nucleon and (2) definitive measurements of the gluon fields in nuclei in a regime in which they are expected to be both strong and universal.
Finding: An upgrade to an existing accelerator facility that enables the colliding of nuclei and electrons at forefront energies would be unique for studying new aspects of quantum chromodynamics. In particular, such an upgrade would yield new information on the role of gluons in protons and nuclei. An electron-ion collider is currently under scrutiny as a possible future facility.
Recommendation: Investment in accelerator and detector research and development for an electron-ion collider should continue. The science opportunities and the requirements for such a facility should be carefully evaluated in the next Nuclear Science Long Range Plan.