LIBRA: The Nuclear Structure Program

The INP's Nuclear Structure research activities up to 2005

    The first nuclear structure experiments carried out in Demokritos using light-ion projectiles took place in 1973, following the commissioning of the Tandem accelerator. These lasted for almost a decade, after which the demand for accelerating heavy-ions at high-energies could not fulfilled by the in-house Tandem accelerator. As a result, the nuclear spectroscopy team joined multi-group collaborations at a European level and performed experiments abroad. In the mid-eighties, the group established itself in the international scientific community by participating in the first experiments aiming at the discovery and, further, at the study of the phenomenon of superdeformation. These experiments were carried out using the first European multi-detector array TESSA3 installed at SERC Daresbury, UK, and later its upgraded successor known as ESSA30. In the following years, the group has continued its nuclear structure activities by using the EUROGAM and later on the EUROBALL multi-detector arrays that were installed in various large-scale European accelerator facilities (LNL-Legnaro, Italy, and IReS-Strasbourg, France). The aim of these activities was the study of nuclear structure under extreme conditions of excitation energy and angular momentum, revealing new concepts such as nuclear deformation, shape coexistence and magnetic rotations (high-spin physics). Hereby, the group was intensively collaborating with the Nuclear Structure Group of the National Technical University of Athens. Besides a significant number of publications in refereed journals, 2 Ph.D. theses have been produced (N. Fotiades, 1995, and M. Serris, 1999). In the last few years the group participated in EUROBALL and GASP experiments at LNL Legnaro, for the study of neutron deficient f7/2 shell nuclei (52Mn, 52Fe: M. Axiotis, Ph.D. thesis).

    During 2000-2004, the group has carried out experimental work at the UNILAC facility of GSI-Darmstadt, Germany, as well as at the Laboratori Nazionali di Legnaro (LNL), Italy, in collaboration with the local groups as well as with that of the Institute of Nuclear Physics of the University of Cologne, Germany, and colleagues from the University of Sofia, Bulgaria. Measurements performed at GSI aimed at studying the beta decay of N»Z (exotic) nuclei around 100Sn. N=Z nuclei, like 100Sn and its neighbors, provide the best conditions for the study of the residual proton-neutron interaction in identical orbits (πν-pairing) and the role of core excitations. The study of these phenomena that give rise to, e.g., b-decaying high-spin isomers often referred as to spin-gap isomers, is of key importance for testing shell-model predictions. Unfortunately, these activities have now been interrupted due to the dismantling of the GSI On-line separator and the dispersing of the local group. In parallel to the latter activities, the nuclear structure group has carried out and participated in a number of lifetime measurements using the Cologne plunger apparatus and the GASP multi-detector array installed at LNL-Legnaro, Italy. The main goal of this program was the search for empirical signals of the so-called critical-point symmetries in nuclear structure. The first symmetries of this kind, known as E(5) and X(5) dynamical symmetries, were introduced by F. Iachello in 2000-2001. They describe nuclei that undergo shape-phase transitions between stable structural limits. As an example, X(5) one describes spectra of nuclei at the transition point from a prolate-shaped rotating nucleus to that of a vibrator. As phase transitions between stable structural limits serve as benchmarks for nuclear structure, their empirical proof is an important and challenging task. Transition probabilities obtained from lifetime measurements in the sub-nanosecond regime provide the most sensitive check of nuclei with structural features resembling those of a critical-point symmetry. The group concentrated its efforts in searching for E(5) candidates. So far, we have been able to confirm the best known E(5) nucleus, i.e. 102Pd.   [top] [relevant publications] [theses]


 Recent Nuclear Structure research activities (2006-today)

The research program described above continued with lifetime measurements of mainly E(5) candidates as well as of nuclei resembling the so-called Z(5) critical-point symmetry, which was recently introduced by the nuclear theory group of INP and is thought to describe the prolate-to-oblate shape phase transition. In this direction, lifetime measurements were carried out in the period 2006 to 2008 at the Cyclotron Laboratory of the University of Jyväskylä, using the JUROGAM multi-detector array and the Cologne Plunger. [top] [relevant publications] [theses]

LIBRA activities in Nuclear Structure

    On top of the activities aiming at searching for empirical proofs of critical-point symmetries, the LIBRA group is very much interested in pursuing a wider research programme which will be based on lifetime measurements employing the plunger method. This is because lifetime measurements of excited nuclear states are of key importance for nuclear structure studies. The reduced transition probabilities that are derived from such measurements are model independent. As such, they can be used for a very sensitive test of the predictions of various nuclear structure models. Up to date, the plunger method has been applied to measurements with stable ion-beams. As a consequence our knowledge on reduced transition probabilities comprises nuclei than can be accessed only with stable ion-beams. These are only a very small fraction of the nuclides existing in nature, the vast majority of which require radioactive ion-beams to be accessed. It is therefore of paramount importance to develop tools and techniques for lifetime measurements using radioactive beams at various energies. The feasibility of such an ambitious research program was recently demonstrated by the group of the University of Cologne group through a number of experiments at the National Superconducting Cyclotron Laboratory (NSCL) of the Michigan State University (MSU), in the United States. Yet, such measurements are not possible for several energy regimes of radioactive beams, e.g. post-accelerated ISOL beams, available at REX-ISOLDE, CERN, and relativistic beams, available at GSI. In view of this very challenging enterprise in nuclear physics, the LIBRA group aims at constructing a plunger device in collaboration with the Cologne Group to be installed at ISOLDE, CERN as part of a novel experimental setup comprising the MINIBALL array as well.   [top]

Upcoming LIBRA scientific events in Nuclear Structure

    Nuclear Structure will be the major topic to be addressed during the 3rd International Conference on “Frontiers in Nuclear Structure, Astrophysics, and Reactions – FINUSTAR 3”. FINUSTAR is a conference series holding a leading place among international scientific events. It is organized by the INP group together with the Department of Physics of the University of Jyväskylä, Finland. FINUSTAR 1 and 2 were organized in Sept. 2005 in the Isle of Kos, Greece, and in Sept. 2007 in Crete, Greece, respectively. Both conferences have been attended by more than 150 participants. FINUSTAR-3 is planned to be organized either in June or September 2010, most probably on the Isle of Rhodes or the Isle of Santorini, Greece. Its duration will be 5 days, starting on Monday. At least 150 participants are expected to attend. The scientific program will be based on the recommendations of an International Advisory Committee consisting of approx. 30 members that will ensure excellent scientific contributions. As in the case of FINUSTAR 1 and 2, there will be approximately 80 oral contributions and more than 40 poster presentations. FINUSTAR 3 will have an interdisciplinary character (nuclear structure-nuclear astrophysics-nuclear reactions) to give the opportunity to many participants not only to be updated in scientific activities in other nuclear physics topics but also establish new collaborations. Two prices are foreseen for the best 2 posters, one in theory – one in experiment, to be awarded during the conference by the international advisory committee and the participants. In addition, peer-reviewed proceedings will be published by a worldwide known publisher.   [top] [FINUSTAR 3 website]

Past scientific events in Nuclear Structure organized by the INP Group


LIBRA Seminars in Nuclear Structure

A series of seminars will be organized during the course of LIBRA. A list will be given here soon.


Other Worksops and Conferences of relevance to LIBRA research 


Nuclear Structure


Dr. Sotirios V. Harissopulos
Tandem Accelerator Laboratory,
Institute of Nuclear Physics,
NCSR "Demokritos",
POB 60228, 153.10 Aghia Paraskevi,
Athens, Greece