Synthesis and Fission of Superheavy Nuclei
The Experimental Study of Regularities of the Formation and Decay of the New Superheavy Elements Nuclei in Heavy Ion Reactions
Tech Area / Field
- PHY-ANU/Atomic and Nuclear Physics/Physics
3 Approved without Funding
Joint Institute of Nuclear Research, Russia, Moscow reg., Dubna
- National Nuclear Center of the Republic of Kazakstan / Institute of Nuclear Physics, Kazakstan, Almaty
- CNRS / IN2P3, France, Paris\nGSI, Germany, Darmstadt\nInstitute of Physical and Chemical Research (RIKEN) / RIKEN Accelerator Research Facility, Japan, Saitama, Wako\nLaboratoire de Physique Corpusculaire/ISMRA, France, Caen\nLawrence Livermore National Laboratory, USA, CA, Livermore
Project summaryDuring last three decades a synthesis and study of properties of new superheavy elements formed in reactions with heavy ions were one of the most intensely developed directions of nuclear physics. The huge interest to these work is stimulated both by aspiration to extend the Periodic table of chemical elements and unique opportunities for studying the fundamental properties of nuclear matter such as, for example, the ability of nucleons to form spherical or deformed shell closures bringing strong stabilizing influence on heavy nuclei and preventing their spontaneous fission. According to modern theoretical notions, this influence can appear so significant as to provide an existence of so called "island of stability" of long-lived superheavy elements.
Thus one should note that the theoretical predictions about the nucleon composition and properties of superheavy nuclei formed this "island of stability" strongly depend on a type of theoretical models and a set of model parameters used. So, the experimental works on synthesizing the new superheavy elements and studying their properties have the special importance.
The synthesis of superheavy nuclei with atomic number Z > 100 is accomplished on basis of complete fusion of target-nuclei with accelerated heavy ions. The exited compound nucleus formed as a result of the fusion can either come to a ground state after emission of several neutrons and g-quanta or go fission that is much more probable. In this region of nuclei the fission cross section exceeds that of evaporation channels of the de-excitation as a factor of 105-109. So, the fission cross section value gives almost complete information on a value of the complete fusion cross section that can be used both for testing the fusion probability model calculations and directly for planning rather expensive experiments on synthesis of new elements, as well.
In heavy ion reactions the fusion-fission process competes strongly against the reactions of deep inelastic scattering and "quasi-fission", which do not go through the stage of the compound nucleus formation, that in same cases makes it significantly difficult to extract events of "true" fusion-fission from the background of the other reactions products, especially quasi-fission ones.
Under this circumstances, Laboratory of Nuclear Reactions of Joint Institute for Nuclear Research (Dubna, Russia) and Institute of Nuclear Physics (Almaty, Kazakhstan) propose to carry out a series of experiments devoted to studying the fusion-fission cross section behavior in the reactions of target-nuclei 232Th, 238U, 244Pu, and 248Cm with heavy ions 48Ca, 58Fe, and 64Ni accelerated to energies close to Coulomb fusion barrier, to use the obtained data for determining the ion-target combinations, which are optimal from the complete fusion view point, and on the basis of the chosen reactions to synthesize the superheavy nuclei with 112 < Z < 124 in their ground states.
The scientific and technical personnel involved in realization of the Project has got a high qualification in the field of accelerator physics and engineering, modern methods of the automated nuclear physical experiments fulfillment, the synthesis and nuclear fission of superheavy elements in the heavy ion reactions. The Doctors of Science – 3, PhD – 9.
Thus, the aims of the Project are:
– study of new static and dynamic regularities determining the formation and de-excitation of superheavy compound nuclei with atomic numbers 112 < Z < 124;
– synthesis and study of properties of nuclei mentioned above in their ground states.
–· new systematic experimental data on the fusion-fission cross sections for superheavy nuclei with atomic numbers 112-124, which could be used for testing the modern theoretical models for describing the fusion and fission processes;
– extension of the Periodic table of chemical elements;
– new experimental data on properties and cross sections of formation of nuclei with 112 < Z < 124 in their ground states, which could be used for the further development of theoretical notions about the mechanism of the shell closure formation in superheavy nuclei;
– under lucky circumstances, the synthesis of long-lived superheavy elements with the proton and neutron shell closures.
Scope of activities.
The work includes the next stages:
– improvement of the 48Ca, 58Fe and 64Ni ion acceleration modes on cyclotron U-400 with the purpose to obtain stable beams of required intensity;
– test of an improved technique of the isolation of a superheavy compound nucleus formed in the complete fusion reactions of ions 48Ca with transactinide target-nuclei and the determination of the compound nucleus mass;
– creation of an incorporated database and computing center for experimental data processing within correlation algorithms;
– measurements and analysis of mass and energy yields of pair fragments of deep inelastic scattering, fission and quasi-fission with the purpose to determine the fusion-fission cross sections in their dependence both on ion-target combinations and incident ion energies, and the choice of optimum entrance parameters of the synthesis reactions, as well;
– fulfillment of experiments on synthesis of new superheavy nuclei;
– experimental data processing, development of new directions and techniques for synthesis, identification and study of superheavy nuclei.
The Project is in full accord with the ISTC objectives:
– this is an experimental physical research directed on the extension of the Periodic system of chemical elements modern borders and the deepening of scientific notions about fundamental properties of nuclear matter in an area that is certainly useless for military purposes;
– the Project results meet civil needs in the perfection of basic knowledge about the environmental world;
– the project encourages involving the Kazakhstan's weapon scientists and engineers into the international scientific community.