Investigation of the Li10 shell inversion by neutron continuum transfer reaction

Abstract

This Letter reports a study of the highly debated ^{10}Li structure through the d(^{9}Li,p)^{10}Li one-neutron transfer reaction at 100 MeV. The ^{10}Li energy spectrum is measured up to 4.6 MeV and angular distributions corresponding to different excitation energy regions are reported for the first time. The comparison between data and theoretical predictions, including pairing correlation effects, shows the existence of a p_{1/2} resonance at 0.45±0.03 MeV excitation energy, while no evidence for a significant s-wave contribution close to the threshold energy is observed. Moreover, two high-lying structures are populated at 1.5 and 2.9 MeV. The corresponding angular distributions suggest a significant s_{1/2} partial-wave contribution for the 1.5 MeV structure and a mixing of configurations at higher energy, with the d_{5/2} partial-wave contributing the most to the cross section.

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

“…tremely large amounting to 600∼2000 Weisskopf units, exhausting 4%∼14% of the isoscalar E1 energy-weighted sum rule (EWSR) value. The large observed strength originates from the halo and is consistent with the simple di-neutron model of 11 Li halo.…”

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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.

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“…Keywords: 11 Li, Neutron halo, Soft-dipole resonance, Proton inelastic scattering, Isoscalar E1 Understanding the 11 Li structure is a landmark in studies of the halo nuclei [1,2]. The two valence neutrons in 11 Li have a very low separation energy, forming a low-density halo.…”

“…Keywords: 11 Li, Neutron halo, Soft-dipole resonance, Proton inelastic scattering, Isoscalar E1 Understanding the 11 Li structure is a landmark in studies of the halo nuclei [1,2]. The two valence neutrons in 11 Li have a very low separation energy, forming a low-density halo. As a collective excitation of the two-neutron halo, the soft-dipole resonances in 11 Li are expected to appear at low excitation energies [3] and by nature of the excitation should have both isovector and isoscalar components.…”

Pygmy resonances: what’s in a name?

“…In e.g. 208 Pb and122 Sn although the vibrational amplitude of the PDR and the role of pairing are larger than in the case of the GDR, the PDR is still a small amplitude mode.On the other hand pairing, at the level of single Cooper pair, plays an important role in the case of the low-energy dipole resonance of11 Li, being this mode a large amplitude vibration.…”