Halo-induced large enhancement of soft dipole excitation of 11 Li observed via proton inelastic scattering

Abstract

Proton inelastic scattering off a neutron halo nucleus, 11 Li, has been studied in inverse kinematics at the IRIS facility at TRIUMF. The aim was to establish a soft dipole resonance and to obtain its dipole strength. Using a high quality 66 MeV 11 Li beam, a strongly populated excited state in 11 Li was observed at E x =0.80 ± 0.02 MeV with a width of Γ = 1.15 ± 0.06 MeV. A DWBA (distorted-wave Born approximation) analysis of the measured differential cross section with isoscalar macroscopic form factors leads to conclude that this observed state is excited in an electric dipole (E1) transition. Under the assumption of isoscalar E1 transition, the strength is evaluated to be ex- * Corresponding author.

Low-energy dipole response of exotic nuclei

“…A low-lying E1 resonance in 11 Li has also been reported from a recent experiment performed at TRIUMF utilising a very different reaction, namely proton inelastic scattering [39]. The spectrum is shown in fig.…”

“…The extracted B(E1) distribution from the differential cross section for Coulomb dissociation of 6 He at 240 MeV/u has been analyzed in that way. From the integrated E1 strength up to 10 MeV of 1.2(2) e 2 fm 2 , a root-mean square distance r α,2n = 3.36 (39) fm between the α core and the two halo neutrons has been deduced in ref. [35], which is in good agreement with three-body models (see the compilation given in table 3 of ref.…”

Report on scipost_201911_00043v1

“…This study reported 10 Li energy spectrum up to 4.6 MeV, with the existence of p 1/2 resonance at 0.45±0.03 MeV along with other two high lying structures at 1.5 and 2.9 MeV [8]. Also the role of 10 Li resonances is investigated in the halo structure of 11 Li via 11 Li(p, d) 10 Li transfer reaction at TRIUMF [5] and at the same facility the first conclusive evidence of a dipole resonance in 11 Li having an isoscalar character has been reported [9,10]. In view of these new measurements and ambiguities over the experimental data, we aim to explore the sensitivity of the 9 Li + n potential with the configuration mixing in the ground state of of three-body system ( 9 Li + n + n).…”

“…The four valence neutron continuum orbits, i.e., p 1/2 , d 5/2 , s 1/2 and d 3/2 are considered in the present calculations for 10 Li. 10 Li is interesting in the sense that it shows inversion of s 1/2 and p 1/2 levels.…”

“…In order to understand the 11 Li structure, the information over low-lying spectrum of 10 Li is needed as a fundamental ingredient of three-body calculations. However, the 10 Li structure was studied by various techniques such as fragmentation [4], 11 Li(p, d) 10 Li transfer reaction at TRIUMF [5], multi-neutron transfer [6] and pion absorption reactions [7]. Maximum of these studies report the low-lying p 1/2 neutron resonance with peak lying in the range of 500-700 keV.…”