A report from EXON 2009 on a rapidly developing area of nuclear physics.
Image credit: JINR.
The most sophisticated physics experiments today take place at large facilities – accelerators – which in turn need large financial investments that cannot be provided by a single country, even if it is highly developed. Such investigations can be carried out only by collaborations between scientific centres in several countries, each bringing financial and intellectual contributions to the development of the cutting-edge facilities that make it possible to penetrate deeper into the secrets of matter. The LHC at CERN, for example, is the result of contributions from 20 member states and many other countries worldwide. Similarly, the Joint Institute for Nuclear Research (JINR) in Dubna, with 18 member states, is home to several accelerators. This internationally based research leads to new information not only about physics but also other fields, such as astronomy, condensed-matter physics and modern technology. The methods used are also of great importance for interdisciplinary fields, such as nanotechnology, medicine and microelectronics.
The physics of nuclei in exotic states is one of the most important and rapidly developing areas in nuclear physics. Researchers can now produce nuclei in extreme states – such as nuclei with high angular momentum (rapidly rotating nuclei), high excitation energy (“hot” nuclei), highly deformed nuclei (nuclei with unusual, super- and hyper-deformed shapes), nuclei with extremely large numbers of neutrons or protons (neutron-rich and proton-rich nuclei) and superheavy nuclei with a proton number, Z, above 110. The investigations of nuclear matter in such extreme states provide important information about the properties of the microcosm and make possible the modelling of a variety of processes taking place in the universe.
These studies, which rely on collaborative effort between countries, were the subject of the international symposium EXON 2009 held in the Black Sea resort of Sochi, Russia, on 28 September – 2 October. The symposium was organized by the four largest centres involved in the investigation of exotic nuclear states: JINR in Russia; the Grand Accélérateur National d’Ions Lourds (GANIL) in France; the GSI Helmholtzzentrum für Schwerionenforschung in Germany; and the research centre RIKEN in Japan. Some 140 scientists from institutes in 24 countries as well as from JINR attended the conference, with the largest number of participants from outside Russia coming from Germany (20 participants), France (16), Japan (12) and the US (8), with about 40 participants from JINR and 16 from institutes across Russia.
EXON 2009 was the fifth in this series of symposia on exotic nuclei, all of which have been held in Russia, the first one in 1991. All have been of interest not only for the organizers, but also for participants from other research centres. In addition to the discussions of scientific problems and the collaboration necessary to address them, participants have the opportunity to become acquainted with some of the most remarkable places in Russia, while the local research authorities and universities find out about the latest results in nuclear physics and the possibilities of applications in interdisciplinary fields of science and technology.
The scientific programme included invited talks about pressing problems in the physics of exotic nuclei as well as about new projects for large accelerator complexes and experimental facilities. The main discussions about the properties of nuclei at the limits of nucleon stability took place on the first day, with reports on the newly observed unusual states at high values of the ratios of the proton to neutron numbers. The topics included: the change of the “accepted” magic numbers when approaching the limit of neutron stability; the coexistence in the same nucleus of two or more types of deformation; and the increase of nuclear stability resulting from deformation, which is important for understanding the stability of pure neutron matter. As UNESCO had declared 2009 the International Year of Astronomy, one talk was dedicated to investigations in this field. Shigeru Kubono from the University of Tokyo discussed the possibilities of studying important astrophysical problems with the use of radioactive secondary beams.
Superheavy elements
In addition to the talks on light exotic nuclei, other reports covered the results of the latest experiments on the synthesis and properties of superheavy elements. Joint experiments by JINR’s Flerov Laboratory of Nuclear Reactions (FLNR), GSI and the Paul Scherrer Institute have found interesting results on the chemical identification of elements 112 and 114 at the FLNR U400 cyclotron, as Heinz Gäggeler of PSI described. Speakers from different countries reported on a range of investigations of the properties of the superheavy elements using different methods. These reports underlined the importance of the investigations of superheavy elements that are carried out in Dubna by existing collaborations. One striking example is the experiment aimed at the synthesis of element 117 that is currently being performed at the U400 cyclotron by a large group of physicists and chemists under the guidance of Yuri Oganessian and Sergei Dmitriev, in collaboration with scientists from different laboratories in the US, who provided the target material of 249Bk. In addition, theoretical presentations included predictions of possible reactions for synthesizing superheavy elements and of their chemical properties.
A second day was dedicated to reports on the current and future heavy-ion and radioactive beam accelerator complexes in different scientific centres. The four laboratories that co-organized the symposium are currently creating a new generation of accelerators that will make it possible to improve considerably the work on the synthesis and studies of the properties of new exotic nuclei. There were detailed talks on the SPIRAL project at GANIL, the RI Beam Factory at RIKEN, the Facility for Antiproton and Ion Research (FAIR) at GSI and the DRIBs project at JINR. In his talk, Mikhail Itkis, JINR’s vice-director, presented plans for the development of the institute’s accelerator facilities, including the new complex, NICA. Georg Bollen of Michigan State University reported on the project for the Facility for Rare Isotope Beams (FRIB), now funded and to be built at the university. In this way, more centres are joining the group of institutes that are developing a new generation of accelerator complexes.
There were also presentations about other facilities for the production of radioactive beams, including ALTO in Orsay, EXCYT in Catania, RIBRAS at the University of Sao Paulo and the radioactive beams project at the Cyclotron Institute of Texas A&M University. The discussions around these talks showed that beams of radioactive nuclei are fundamental to investigations of the properties of nuclear matter in extreme states.
Round-table discussions also took place during the symposium to consider the results obtained in joint work and possible future collaborations. Bollen, a leader of the FRIB project, suggested including Michigan State University as a co-organizer of the next symposium, EXON 2012, which could take place in the city of Vladivostok in the Russian Federation.
• For full details about the scientific programme and speakers, see http://exon2009.jinr.ru/. There were about 80 talks in total and some 40 posters shown, all of which will be published in conference proceedings by the American Institute of Physics.
