Report to the 1999 General Assembly for 1996-99
Chairman: E.W. Vogt, Canada
D. Ashery, Israel
K. Parlinski, Poland (C10)
Council Liaison Member:
Y. Yamaguchi, Japan
The General Aims of the Commission are to:
The work of the Commission is carried out at meetings and by correspondence. The annual meetings are scheduled during conferences sponsored by the C.12 Commission. Williamsburg (1996), Seattle (1997), Paris (1998). Participation by members remains at high level.
Conferences Sponsored by the Commission
1996 Conference on Particles and Nuclei (PANIC XIV) Williamsburg, Virginia.
1996 Sakharov Conference, Moscow, Russia
1996 Electromagnetic Isotope Separators. Bad Duerkheim, Germany.
1996 Nuclear Physics at Storage Rings. Bernkastel-Kues, Germany.
1997 Nuclear Data for Science and Technology, Trieste, Italy.
1997 Symmetry in Subatomic Physics, Seattle, Washington, U.S.A.
1997 Few Body Problems in Physics, Groningen, Netherlands.
1998 International Conference on Nuclear Physics (INPC'98), Paris, France.
1998 Cyclotrons and Their Applications, Caen, France.
1998 Exotic Atoms, Molecules and Muon-Catalysed Fusion, Ascona, Switzerland
The proposal to hold the next International Conference on Nuclear Physics (2001) in Berkeley (USA) has been approved by the C12 Commission.
FUNDAMENTAL SCIENTIFIC ISSUES IN NUCLEAR PHYSICS
The goal of nuclear physics is to understand the properties of nuclear matter, atomic nuclei and how nuclei are built up from elementary constituents. Nuclear physics involves the study of diverse phenomena at vastly different scales, from the interaction of elementary entities (quarks and gluons) inside nucleons or nuclei, to the formation of elements via nuclear synthesis in stars and supernovae, or the characteristics of hot, dense nuclear matter as it occurred in the early Universe.
The fundamental challenges of nuclear physics are the following:
The fundamental issues of Nuclear Physics have evolved in the past few years, especially because of the large new facilities, which have been completed or are now being planned. The continuous beam electron facility (CEBAF) providing electron beams up to 6 GeV, at the Jefferson Laboratory in Newport News, Virginia, was completed two years ago and now supports a large international users group. The relativistic heavy ion facility (RHIC) at Brookhaven will begin operation in 1999 and promises to provide much interesting new physics. These and the other planned facilities discussed below clearly define the current scientific priorities of Nuclear Physics. We also discuss below some of the large number of applications of nuclear physics, which continue to make the field of great benefit for society.
FUTURE FACILITIES FOR NUCLEAR PHYSICS
Radioactive Nuclear Beams (RNB)
To understand nuclear matter, one needs to study the properties of a wide variety of nuclei, not just those that exist in stable form in our surroundings (these "ordinary" nuclei constitute only about 10 per cent of all possible nuclei). Exotic nuclei (those with a very large number of nucleons, or an unusual ratio of protons to neutrons) can be created through collisions of energetic beams of ordinary, stable nuclei with other nuclei in a stationary target. The resulting exotic species that are emitted from the target (and which are then studied with a wide range of instruments) are typically unstable and very short-lived (radioactive). In addition to being a tool for the investigation of fundamental nuclear interactions, Radioactive Nuclear Beams (RNBs) provide a way to investigate advanced topics in astrophysics.
First generation RNB facilities are operating or under construction in the three regions of the world where nuclear physics is most actively pursued, Europe, North America and Asia/Pacific. These facilities produce important results, and ambitious experiments are planned with them in the next few years. However, several studies of the projected needs of nuclear physics carried out all around the world have made it quite clear that major breakthroughs towards the ultimate scientific goals will only be achieved by the next generation of RNB facilities. These will produce beams with several orders of magnitude higher intensity, making possible qualitatively new research with a wide range of nuclear species much further from the region of stable nuclei.
The construction of regional centers is discussed in Europe, North America and Asia/Pacific, major decisions concerning these new facilities are likely to be in the near future, and the corresponding next generation RNB facilities should be operational in 5 to 10 years.
High-energy electron facilities
High-energy electron beams provide a unique probe of nuclear structure and the interactions between nuclear constituents. By studying nuclear matter at high resolution and at different levels of aggregation, electron scattering explores the interface between particle and nuclear physics. The description of nuclear matter in terms of quarks and gluons is successful at very short distances and very high energies, but its application to nucleons and nuclei is a fundamental problem.
A highly active community is currently performing electron-nucleus scattering experiments at facilities around the world (CERN, SLAC, DESY, CEBAF, Bonn, GRAAL, Mainz, NIKHEF). The project for a high intensity continuous beam accelerator operating in the 20 to 30 GeV range is under active study in Europe at the DESY laboratory in Hamburg and at CERN, using the LEP superconducting cavities. In the United States, an evolutionary upgrade to 12 GeV by 2005 of the CEBAF accelerator is being considered.
Multi-Purpose Hadron Facilities
A rich and varied part of the nuclear physics scientific program is best carried out with particle beams at multi-purpose hadron accelerator facilities that produce high-quality, high-intensity secondary beams of kaons, pions, muons, neutrinos, neutrons and antiprotons. A broad range of topics can be addressed at these facilities, including fundamental symmetries, nuclear and particle spectroscopy, quantum chromodynamic (QCD) studies in the perturbative and non-perturbative regimes, as well as studies of the role of confinement and that of chiral symmetries. The availability of this large variety of secondary beams also provides unique opportunities for the development of applications such as materials science and energy research.
At this time, major hadron beam programs are under way at Brookhaven, Fermilab, CERN, KEK, PSI, TRIUMF, and, on a smaller scale, at several other laboratories. As existing programs are completed and phased out, the world-wide scientific community will shift its activities to a major new facility: the Japan Hadron Facility (JHF) which is planned to be built jointly by the KEK laboratory in Tsukuba and the JAERI laboratory in Mito, producing intense high-quality beams based on a new high-intensity 50 GeV proton synchrotron.
High-energy heavy ion collisions
A very powerful technique in nuclear physics involves generating head-on collisions of nuclei that have been accelerated to very high energies. Detailed analysis of the products of the collisions provides unique insights into the behavior of strongly interacting matter (that is, nucleons and mesons and, eventually, their constituent quarks and gluons) at extreme energy densities. Of particular interest is the prediction of quantum chromodynamics (QCD) that, under these conditions, nuclear matter should undergo a phase transition to an entirely new state, the "quark-gluon plasma", in which the recognizable components are not the familiar nucleons and mesons, but the elementary quarks and gluons themselves. Most physicists believe that all of the matter in the entire Universe existed in a similar high-temperature, high-density state a few microseconds after the Big Bang. The Universe's subsequent transition to a cooler, less-dense state is thought to be the last of a sequence of fundamental transitions involving the most elementary natural forces, creating the matter that we observe today. Thus, the study of the behavior of quarks and gluons under these primordial conditions is sure to provide exciting new insights into the structure and history of the Universe.
The next round of experiments will be carried out at two facilities. In 1999, the experimental program at the new RHIC accelerator at Brookhaven will begin, dedicated entirely to heavy ion collisions using four detectors. Beginning in 2005, part of the experimental program of the CERN Large Hadron Collider (LHC) will be devoted to the study of nuclear collisions in the special-purpose ALICE detector, at energies some thirty times higher than RHIC. (Most of LHC operations will involve proton/proton collisions.)
APPLICATIONS OF NUCLEAR PHYSICS
Nuclear science continues to make important contributions to society via the development of important applications and spin-offs.
Accelerator-driven systems for nuclear waste transmutation
In recent years, the accelerator-driven transmutation of nuclear wastes has emerged as a potentially complementary technology for radioactive waste handling, by transmuting the longest-lived radioactive isotopes into short-lived or stable ones. This technology could have a significant synergy with other megascience-scale projects like neutron sources and high-intensity accelerators. Around the world, there is considerable agreement on the short- and medium-term goals of the research. This is in itself remarkable, since the study of ADS is inherently multidisciplinary, involving for the nuclear physics community elements of basic and applied research in the following areas:
Cancer therapy with nuclear beams
The goal of radiation therapy is to maximise the tumour dose without harming surrounding healthy tissues. The use of heavy particles in radiotherapy is motivated by a superior accuracy in the spacial dose distribution in the human body for deep seated tumours compared to photons and electrons, and an inverse dose profile depositing the highest dose at the end of the particle range in the tumour volume. At present, proton therapy centres are located in the United States, Russia, Europe, Japan and South Africa.
Most of the clinical experience has been obtained at nuclear physics institutions that have devoted part of the accelerator time - mainly cyclotrons - to medical use. In the next ten years, more hospital-based facilities are needed, as exemplified by the creation of Loma Linda (USA), Chiba (Japan), NPTC (USA) centres and the new projects in Austria, France, Germany, Italy, Japan. For proton therapy, the needed accelerators are, at present, industrial products, while optimised medical synchrotrons for light ion therapy have recently been designed by CERN and GSI. Because all therapy facilities in operation use passive beam shaping methods (with both absorbers and apertures) the optimal dose profiles are not transferred into clinical routine. To improve these systems, active beam delivery systems using magnetic beam deflection and energy variation by the accelerator have recently been developed, and have been put into operation at PSI (Switzerland) for protons, and at GSI (Germany) for carbon beams.
Fast position monitors developed in the course of basic nuclear research, are now routinely used as control systems in hadron therapy. Finally, using positron emission tomography (PET), the small amounts of positron-emitting isotopes created by the carbon beam can be used to determine the exact beam location inside the patient's body.
The new techniques of more accurate beam delivery and precise control permit the treatment of tumours in critical locations such as the brain, or the vicinity of the spinal cord.
Significant progress can be expected in the next few years in the domain of medical imaging in terms of spatial resolution and sensitivity. Novel detection techniques involving new crystal scintillators and photodetectors and new solid-state sensors, originally developed for applications in nuclear and particle physics experiments, can now be adapted to medical imaging. Compact and powerful dedicated digital dual-modality imagers can be envisaged, directly combining (co-registering) structural information (such as is offered by digital mammography) with metabolic functional information (such as obtained from scintimammography or Positron Emission Mammography - PEM) to provide a unique diagnostic tool to the radiologist.
International cooperation in nuclear physics has become and will continue to be extremely lively and productive at the scientist-to-scientist level. Current examples include, among many others, the important detector contributions by European and Japanese scientists to CEBAF and RHIC in the US, and US participation in the Sudbury Neutrino Observatory (SNO) in Canada, US collaboration in CERN programs with muons (SMC), antiprotons and heavy ions, US and Canada participation in the HERMES program at the DESY/HERA facility in Germany. In Europe, several countries have joined their efforts to build a powerful 4p gamma ray spectrometer, EUROBALL and TAPS, a two arm photon spectrometer. In Europe, Japan has recently become an observer at CERN and will participate in the LHC. In the United States Japan will participate to the heavy ion program at RHIC with the PHENIX collaboration and the RHIC Spin collaboration.
Three years ago, C12 adopted international collaboration in nuclear physics as a major mission and established a new committee for that purpose. For the last two years, that work has been superseded by the Working Group on Nuclear Physics established for similar purposes by the OECD Megascience Forum. That workshop is now being completed and C12 plans then to carry on with the new mission. It appears that the outcome of the Nuclear Physics Working Group of the Megascience Forum will be very helpful to our field.
Nuclear Theory Centers
Three vigorous nuclear theory centers, at the University of Washington in Seattle (USA) , at Trento (Italy) in Europe and at Adelaide (Australia), have each year an extensive program of workshops with a large international participation from all over the world. Specific programs are devoted to interdisciplinary topics.
Research Center for the Subatomic Structure of Matter
This new center was formed by Professor A. Thomas and his colleagues at the University of Adelaide (Australia) in January 1, 1997. The central mission of the Center is to carry out research activities in the forefront of the fields of theoretical nuclear and particle physics with special emphasis on the strong interactions and their importance in determining the nature of matter.
The Nuclear Physics European Coordination Committee (NuPECC) of the European Science Foundation now coordinate nuclear physics activities in Europe. The Committee consists of 21 members from 14 European member states including Austria, Belgium, Denmark, Finland, France, Germany, Italy, The Netherlands, Norway, Portugal, Spain. Sweden, Switzerland and United Kingdom.
The journal edited by NuPECC, "Nuclear Physics News International" regularly provides information on the status, new directions and opportunities of nuclear science all over the world.
B. Frois and E. Vogt