Special features of nuclear reactions induced by loosely bound 6 He and 6,7 Li nuclei in the vicinity of the Coulomb bar
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CLEI Experiment
Special Features of Nuclear Reactions Induced by Loosely Bound 6 He and 6,7 Li Nuclei in the Vicinity of the Coulomb Barrier Height Yu. E. Penionzhkevich* Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia Received December 25, 2008
Abstract—Excitation functions are measured for complete-fusion and transfer reactions induced by the interaction of 6 He and 6 Li with 206 Pb, 209 Bi, and Pt. Data obtained for fusion reactions induced by 6 He ions deviate from the predictions of the statistical model of compound-nucleus decay at projectile energies in the vicinity of the Coulomb barrier height. A strong enhancement of cross sections for fusion reactions induced by the interaction of 6 He with target nuclei is observed. The cross sections for reactions of cluster transfer, neutron transfer from 6 He, and deuteron transfer from 6 Li at deep-subbarrier energies are also found to be enhanced. These results are discussed from the point of view of the effect of the cluster structure of nuclei on the interaction probability at energies in the vicinity of the Coulomb barrier height. PACS numbers: 25.40.-h, 25.60.-t, 25.60.Pj, 25.60.Je DOI: 10.1134/S1063778809100020
1. INTRODUCTION Reactions involving loosely bound nuclei and occurring at energies in the vicinity of the Coulomb barrier height have many special features that have vigorously been discussed in recent years in a number of studies (see, for example, [1, 2]). These features include the the enhancement of interaction cross sections in the subbarrier energy region. This effect is especially pronounced for clustering nuclei (for example, 6,7 Li) [3], as well as neutron-halo nuclei (for example, 6 He) [4]. Transfer, breakup, and completefusion reactions are dominant interaction channels for such nuclei. Processes in which the breakup of loosely bound nuclei in the field of a heavy nucleus is followed by the fusion of the residual nucleus with the target nucleus have been the subject of numerous theoretical and experimental investigations. In accordance with classical concepts, the fusion of interacting nuclei occurs after they overcome the barrier determined by long-range Coulomb forces and a component of the short-range nuclear potential. But in the case of the interaction of loosely bound nuclei, the fusion process has a more intricate character because of a high probability of their breakup followed by residualnucleus capture (incomplete fusion). This complicates substantially the description of the interaction of such systems and leads to new, unexpected, effects at energies in the vicinity of the Coulomb barrier *
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height, such as deep-subbarrier fusion and reactions of cluster transfer from loosely bound nuclei, which, as a rule, have a cluster structure (see Fig. 1). At the present time, there are several theoretical approaches within which one attempts to describe the interaction of loosely bound nuclei [5, 6]. Difficulties in describing such processes stem from the need for employing a theory that woul
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