Abnormal behavior of the optical potential for the halo nuclear system He6+Bi209

Abstract

In a recent transfer reaction measurement of 208 Pb(7 Li, 6 He) 209 Bi at energies around and below the Coulomb barrier, the optical model potentials of the halo nuclear system 6 He + 209 Bi were extracted by fitting the experimental data with the theoretical frameworks of the distorted-wave Born approximation and coupled reaction channels, respectively. With the high-precision result, a complete picture of the behavior of the optical potential for this halo system is clearly derived for the first time. The real potential presents a bell-like shape around the barrier as a normal threshold anomaly. However, for the imaginary part, it first increases with the energy decreasing below the barrier and then falls quickly to 0, hence the threshold energy can be determined by fitting the variation trend. Moreover, the result also provides some evidence that the dispersion relation does not hold for this halo nuclear system, which calls for further investigation of the underlying physics.

Reaction Mechanisms of Exotic Nuclear Systems at Low Energies

“…The detail of the transfer reaction method can be found in Refs. [9,10], where the sensitivity test and the comparison with the traditional elastic scattering method were also introduced.…”

Reactions with Exotic Nuclei at Near and Sub-barrier Energies

“…The detail of the transfer reaction method can be found in Refs. [10,11], where the sensitivity test and the comparison with the traditional elastic scattering method were also introduced.…”

“…We have applied the transfer reaction method to study the OMPs of neutron-halo 6 He systems, by measuring the one-proton transfer reactions induced by 7 Li beam accelerated by the HI-13 tandem accelerator at CIAE. Three systems have been measured at energies around the Coulomb barrier, i.e., 11 B( 7 Li, 6 He) 12 C, 63 Cu( 7 Li, 6 He) 64 Zn [12] and 208 Pb( 7 Li, 6 He) 209 Bi [11,13,14], to study the OMPs of the light system 6 He+ 12 C, the medium-mass system 6 He+ 64 Zn and the heavy system 6 He+ 209 Bi. Because the lowest terminal high voltage of the tandem accelerator is limited to 3 MV, corresponding to about 12 MeV of 7 Li beam energy.…”

“…It can be seen clearly the prediction of the dispersion relation cannot reproduce the experimental results. The possible reasons for the abnormal behavior are listed as follows [11,14]: (a) the dispersion relation is deduced from the Kramers-Kronig relation, which is derived from Cauchy residue theorem. One prerequisite of the theorem is that there should be a finite list of isolated singularities, corresponding to the discrete states of the interacting nuclear system [6].…”

“…Therefore, we performed a series of experiments to study the reactions induced by the protondrip line nucleus 17 F at energies around the Coulomb bar- Figure 2. Energy dependence of the depths of real (a) and imaginary (b) potentials at the sensitivity radius of 13.5 fm for the 6 He + 209 Bi system [11,13,14]. Curves in (b) represent the linear segment fitting for the imaginary potential.…”