Dynamic polarization potentials for 6 He + 209 Bi and 11 Li + 208 Pb systems at near-barrier energies
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NUCLEI Theory
Dynamic Polarization Potentials for 6 He + 209 Bi and at Near-Barrier Energies*
11
Li +
208
Pb Systems
S. S. Duhan1) , M. Singh1) , R. Kharab1)** , and H. C. Sharma2) Received May 11, 2010
Abstract—The Coulomb dipole induced dynamic polarization potentials for 6 He + 209 Bi and 11 Li + 208 Pb systems within the framework of Feshbach’s formalism with a motive to ascertain the presence or absence of threshold anomaly have been studied. As a result of this study, the threshold anomaly has been found to be present for both systems. It has also been found that at deep sub-barrier energies the imaginary part either starts increasing or at least remains unchanged which indicates the presence of the breakup threshold anomaly. In addition, the Coulomb breakup transmission factors for both systems have been found to have maximum value below and near-barrier energies, but at very high energies due to closure of the breakup channel the breakup transmission coefficients quickly becomes zero. DOI: 10.1134/S1063778811010066
1. INTRODUCTION
resonance, the so-called pygmy resonance and the relative ease with which halo nuclei undergo breakup are the two main aspects which are of particular relevance to sub-barrier fusion.
Exploration of the region in the proximity of driplines in the nuclear landscape is one of the major aim of the contemporary nuclear physics. The experiments performed with the Radioactive Ion Beams (RIBs) of loosely bound nuclei have confirmed the existence of halo structure among some of isotopes lying in the close vicinity of driplines. Because of the small binding energy of last nucleon(s) the breakup is an important reaction channel for these nuclei and represents a prolific tool to understand their structure [1–4]. On the other hand, the fusion of RIB’s on stable targets have great ramifications both for the production of super heavy elements (SHE) and for the reactions of astrophysical interest. Various unique features like small binding energies (0.1–2.5 MeV), large values of isospin, extended wave function of the valence nucleon(s), a Borromean structure (a three-body bound system, where any of its two-body subsystems are unbound), existence of soft dipole (or pygmy) resonances and large breakup probabilities of halo nuclei are expected to strongly affect the fusion reactions especially at energies around the Coulomb barrier [5–12]. Controversial results regarding the effects of these unique features have been reported in the literature [13–19]. The existence of a soft dipole
Theoretically, the role of breakup channel in the fusion of halo nuclei is studied either by a coupledchannel (CC) approach or by an approach based on the dynamic polarization potential (DPP). However, the CC method becomes extremely complicated when more and more numbers of channels are to be included in the calculation. On the other hand, in the DPP approach the coupling between different excited states does not pose any problem as it can be considered as additive, so that the polarization potential induced by the co
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