Precise measurement of near-barrier He8+Pb208 elastic scattering: Comparison with He

Abstract

Dramatic differences in the elastic scattering of the neutron rich nuclei 6 He and 8 He are found when new high quality data for the 8 He + 208 Pb system are compared with previously published 6 He + 208 Pb data at the same laboratory frame incident energy. The new 8 He data are of the same level of detail as for stable beams. When comparing them with those previously obtained for 6 He + 208 Pb at the same energy, it is possible to determine from the data alone that 6 He has a much longer range absorption than 8 He. However, both nuclei show significant absorption beyond their strong absorption radii. While it has been known for a long time that elastic scattering at energies around the barrier only determines the optical potential over a small distance in radial space, typically ±0.5 fm or so, both the 6 He and the 8 He imaginary potentials obtained from various optical model fits to these data are the same over a much wider range of ±1.5 fm.

Interaction of He8 with Pb208 at near-barrier energies: HeMarquínez-Durán1, Martel2, Sánchez-Benítez3 et al. 2018Phys. Rev. CSelf Cite11020View full textAdd to dashboardCite

“…The experiment was carried out at the SPIRAL facility of the GANIL laboratory in Caen, France, and a detailed description of the experimental setup was given in Refs. [1,5]. As shown in these works, the double-sided silicon strip detector E-E telescopes of the GLORIA array [5] provided clear separation between the He isotopes produced in the interaction between the beam and target so that the 8 He, 6 He, and 4 He yields were unambiguously extracted.…”

“…In Fig. 3, we present the elastic scattering data for an incident 8 He energy of 16 MeV, together with the previously published data at 22 MeV [1]. The solid curves represent optical model fits to the data.…”

“…In addition to the previously reported elastic scattering data at a 8 He incident energy of 22 MeV [1], elastic scattering data were also obtained at 16 MeV and 6 He and 4 He yields at both energies. Figure 1(a) shows the events from all the strip detectors gated on 4 He at 22 MeV.…”

“…The procedure for establishing the detection angle of a given strip is given in Ref. [1] and relied on comparing a detailed simulation of the detection system with the elastic scattering in the region where it is dominated by Coulomb scattering.…”

“…Recently, precise data for the elastic scattering of 8 He from a 208 Pb target at an incident energy of 22 MeV, slightly above the Coulomb barrier, were presented and compared with existing data for 6 He + 208 Pb at the same incident energy [1]. A larger total reaction cross section was obtained for 8 He than for 6 He, suggesting an increased neutron stripping cross section for 8 He that more than compensates for an expected lower breakup cross section than 6 He, due to its higher breakup threshold and probable weaker dipole coupling to the continuum.…”