Unusual near-threshold potential behavior for the weakly bound nucleus9Bein elastic scattering from209

Abstract

The cross sections for elastic scattering of the weakly bound 9 Be on 209 Bi around the Coulomb barrier have been measured with ϳ5% absolute accuracy from 40 to 48 MeV. The potential obtained from an optical model analysis has an unusual behavior. At the strong absorption radius the imaginary ͑absorptive͒ potential is increasing ͑rather than decreasing͒ with decreasing energy, as would be consistent with a long range polarization potential arising mainly from couplings to breakup channels. The real part, on the other hand, displays a strong attractive polarization contribution with the maximum at the barrier, as would be normally expected from a polarization contribution arising from strong couplings. The inelastic multiplet in 209 Bi of collective nature around 2.6 MeV, originating from the coupling ͓ 208 Pb(3 Ϫ ) h 9/2 Ϫ ͔ J , was seen only at 48 MeV. The total multiplet cross section is well reproduced by coupled channel calculations with the potential obtained from the optical analysis and the experimental B(E3) strengths of the 209 Bi multiplet levels.

Recent developments in fusion and direct reactions with weakly bound nuclei

“…For 9 Be the situation is even less clear than for 7 Li, since in some cases the real and imaginary potentials which fit the elastic scattering data do not obey the dispersion relation [121,122,60]. For this projectile there are not too many systems investigated: 12 209 Bi [122].…”

Cd110,116(α,α)Kiss1, Mohr2, Fülöp3 et al. 2011Phys. Rev. C

“…So it must be noted that the angular distributions at 16 MeV are not sufficiently sensitive to the width parameter w of the potential. Instead, the fits provide a so-called one-point potential [18,26,41,42]. The smaller (larger) width parameter w is compensated by a larger (smaller) strength parameter λ leading to a fixed potential depth at a large radius (e.g., a value R 0.2 where the real potential depth is 0.2 MeV is derived in [26] from the analysis of elastic scattering excitation functions).…”

Extended optical model analyses of elastic scattering and fusion cross sections for theLi6+Pb208system at near-Coulom

“…As a consequence, the resulting total polarization potential dominated by the DR potential becomes rather smooth as a function of the incident energy. This has explained the reason why the threshold anomaly is not seen in the optical potentials determined for systems involving loosely bound projectiles such as 6 He, 6 Li, and 9 Be [2,10,15].…”

“…In order to test this idea, we have thus carried out [8,9] simultaneous χ 2 analyses of elastic scattering and fusion cross section data for the 6 He+ 209 Bi [10,11,12], 6 Li+ 208 Pb [2,13,14], and 9 Be+ 209 Bi [15,16] systems at near-Coulomb-barrier energies in the framework of the extended optical model [17,18,19] that introduces two types of complex polarization potentials, the DR and fusion potentials. In such analyses, in addition to the elastic scattering cross sections dσ exp E /dΩ, the measured fusion cross section σ exp F , was taken into account together with the total experimental DR cross section, σ exp D , if available, or the semi-experimental DR cross section, σ semi−exp D , if σ exp D was not available.…”