Relativistic many-body problems for heavy and superheavy nuclei

Date :From 2009-06-08 To 2009-06-27
Advisory committee :
Local coordinators :Zhong-Zhou Ren, Chang Xu, Hu-Shan Xu, Fu-Rong Xu, Shan-Gui Zhou
International coordinators :Nguyen Van Giai, Bao-An Li, Zhong-Zhou Ren, Peter Ring, Hiroshi Toki, Guo-Qing Xiao, Nu Xu, Yan-Lin Ye, En-Guang Zhao

Since the prediction of the existence of superheavy islands in 1950s and 1960s, the synthesis of superheavy elements has been one of the important topics both in nuclear physics and nuclear chemistry. During the period from 1995 to 1996 physicists at GSI in Germany produced the elements Z = 110, 111, and 112 successively by using heavy-ion collisions. Experimental studies on superheavy elements have received another major breakthrough with the most recent discoveries at Dubna, GSI, Berkeley, and RIKEN. In January 1999, it was reported that the new element Z = 114 was found at Dubna. This was followed by the production of another isotope of the Z = 114 element in April 1999 again at Dubna in collaboration with the physicists from Europe and Japan. The physicists at Dubna synthesized the new elements with Z = 115, 116 and 118 in the period 2000-2005. In RIKEN, the element with Z = 113 was produced in 2004. It is worthwhile to mention that nuclear physicists in China have started theirs efforts to explore new superheavy isotopes and successfully produced two new isotopes 259Db (Z = 105) and 265Bh (Z = 107) at Lanzhou. With the new facility developed at Lanzhou, Chinese physicists are trying to synthesize new elements.

After the first prediction of the superheavy island around Z = 114 based on the non-relativistic phenomenological models in 1950s and 1960s, many new progresses have been made based on the modern nuclear models, e.g., the non-relativistic and relativistic many-body models during 1970s-1990s. In recent years, these models are further developed and applied to heavy and superheavy nuclei. However, different predictions are made by the modern nuclear models. For example, the relativistic many-body models predict new magic numbers in the superheavy region which are different from the old predictions. It is also revealed from these models that in superheavy nuclei, new physics appears, such as strong deformation effects and long-lived isomeric states. This will certainly bring new impacts on current research of superheavy nuclei. It becomes more and more difficult to synthesize new elements with increasing proton number due to the tiny cross section in heavy-ion fusion. Theoretical investigation on the reaction cross section and exploration of new reaction mechanism will be helpful for experiments.

The relativistic many-body models has been successfully applied to study heavy and superheavy nuclei. One simple version of the relativistic many-body models, i.e. the relativistic mean-field (RMF) model, is widely used in researches of nuclear structure and nuclear collisions. The main merit of this model is that the spin-orbit splitting, which plays an important role for nuclear shell effect, can be given naturally due to the inclusion of the Lorentz covariance. The RMF calculations can reliably predict the nuclear deformation of heavy and superheavy nuclei. The calculated binding energies and alpha-decay energies are in good agreement with the recent data of superheavy nuclei and the new elements with Z = 110-116 and 118. The possible variation of nuclear magic numbers in unstable nuclei is predicted by the RMF model. The RMF model, combined with the effective scattering theory, has been generalized to the study of electron scattering with unstable nuclei, which is an interesting topic in nuclear physics as new machine of electron scattering with unstable nuclei is being built at RIKEN in Japan and at GSI in Germany.

It is interesting to go beyond current mean field models. By including the hyperon, the relativistic many-body models have been extended to the study of hyper nuclei where one or more nucleons are replaced by hyperons like the lambda. One also tries to include quark degree of freedom instead of nucleons and develops the quark meson coupling (QMC) model, though the application of this model to superheavy nuclei is still an open problem. In order to deal with the exotic nuclei where the neutron number is much more than the proton number (for very neutron rich nuclei), the isospin degree of freedom in relativistic many-body models must be treated suitably. It is interesting to investigate these problems.

This program will consist of the following topics: (1) synthesis and decay of superheavy nuclei; (2) structure of exotic nuclei; (3) nucleus-nucleus collisions at intermediate and high energies; (4) developments and applications of relativistic many-body models.