Study of light exotic and stable nuclei with heavy ion reactions

Abstract

Nuclear reactions with light and heavy ion beams are one of the most important methods for the investigation of nuclear structure, main features of the nuclear forces and mechanisms of the nuclear processes. At present the most information in these fields is available for the nuclei close to the stability region. The structure and interactions of the nuclei out of this region (exotic nuclei) are insufficiently studied yet. There are two experimental methods to perform such investigations: the first one employs experiments with the radioactive (secondary) beams (direct method) and the second one is based on experiments with the stable ion beams producing multi-nucleon-transfer reactions. Both methods are used at present and successfully complement one another. The direct-secondary-beam methods use equipments which produce and form the secondary beams, sometimes with the secondary beam accelerators and storage rings. These equipments are sophisticated and rather expensive. At present, the obtained experimental data are very important but rather poor. The secondary beams have rather small intensities and therefore only elastic and inelastic scattering are studied using this method. The potential parameters of the unstable exotic nuclei interaction and their deformation parameters can be obtained in these experiments. The deformation parameters can only be obtained from the inelastic scattering data from experiments with radioactive nuclei. The next limitation of the exotic nuclei study using the direct method is the fact, that they are possible only for the radioactive ions living longer than several microseconds. More information about the study of exotic nuclei with the method of direct experiments are placed in Section 1.2. The development of the nuclear reaction theory and of the computational methods give possibilities of wide use of the second method - the stable ion beam experiments with the nucleon-transfer and cluster-transfer reactions. It should be noticed, that investigation of the exotic nuclei interactions, presented in this work, needs of simultaneous investigation of stable nuclei, taking part in the same reactions. Theoretical analysis of the data, concerning the study of exotic nuclei with heavyion reactions is more complex than the investigations using the direct method. The data of elastic and inelastic scattering of radioactive ions are analyzed with the optical model (OM) and coupled-reaction-channels method (CRC) using the nucleus-nucleus potentials of the same systems both in entrance and exit channels On the other hand, the incoming and outgoing reaction systems are different for the transfer reactions. Before the CRCcalculation of the reaction cross section, the potential parameters for the entrance-reaction channel must be deduced from the analysis of the elastic and inelastic scattering data. Moreover, because the parameters of the nucleus-nucleus potentials are energy dependent, studies of the energy dependence of these parameters play important role in investigation of the nuclear reaction of exotic nuclei. For this reason, studies of the elastic and inelastic scattering, based on optical potential parameters and their energy dependence are included in the present work in Chapter 4. The next problem concerning the transfer reaction studies is connected with the calculations of the nucleon and cluster spectroscopic amplitudes (SA). These calculations for nucleons and clusters can be performed in the frame of Translationary Invariant Shell Model (TISM) using the method described in [91] for the 1s-1p-shell nuclei which includes the light stable and exotic nuclei only. Therefore, the reactions investigated in the present work include only the nuclear processes for the interactions of 1p-shell nuclei. The large base of the TISM cluster SA was calculated and successfully applied in the present reaction studies. Due to their importance for nuclear structure and reaction mechanism studies, the tables of calculated SA are presented in the Appendix. The present work includes the results obtained by the author and collaborators, presented in Refs. [1-20]. In the CRC-method all possible reaction channels: elastic and inelastic scattering as well as one-step and multi-step transfers of nucleons and clusters are strongly coupled. Then, calculation of optical potential parameters requires determination of contribution of all possible processes to considered reaction. For this reason every investigated reactions are described as separate Sections of Chapters 4 and 5. This work is devoted to the investigation of the exotic nuclei by nuclear reactions using stable ion beams. This is a traditional method for study of structure of nuclei. These experiments can be performed by many nuclear groups which use the standard experimental equipments. Moreover, a large experimental database, obtained from these experiments already exists. Next, properties of the short living exotic nuclei as well as mechanism of their production can also be studied with nuclear reactions. The study of the reaction mechanism are very important for deduction of the structure properties of exotic nuclei and of the potential parameters of their interactions. When dominant mechanism of the reaction is found, these parameters are fitted in order to describe the reaction data by the CRC-cross-section. The results of the reaction studies are presented in Chapter 5. Summary and conclusions are presented at the end of the work.