Near-threshold dipole strength in {^{10}}Be with isoscalar character

TL;DR

This paper reports the observation of a near-threshold isoscalar dipole resonance in 10Be, indicating pronounced alpha cluster structures and emphasizing the importance of four-body cluster calculations for understanding these excitations.

Contribution

It provides experimental evidence of a near-threshold 1^- resonance with isoscalar character in 10Be and demonstrates the significance of four-body cluster models in describing these states.

Findings

The 1^- resonance exhausts 5-15% of the isoscalar dipole sum rule.

Coupled channel calculations support the cluster structure interpretation.

Four-body calculations reproduce the observed dipole strength.

Abstract

Isoscalar dipole transitions are a distinctive fingerprint of cluster structures. A {1^-} resonance at 7.27(10) MeV, located just below the {\alpha}-emission threshold, has been observed in the deuteron inelastic scattering reactions off 10Be. The deformation lengths of the excited states in 10Be below 9 MeV have been inferred from the differential cross sections using coupled channel calculations. This observed {1^-} resonance has isoscalar characteristics and exhausts approximately 5{\%}-15{\%} of the isoscalar dipole energy-weighted sum rule, providing evidence for pronounced {\alpha} cluster structure in 10Be. The Gamow coupled channel approach supports this interpretation and suggests the near-threshold effect might be playing an important role in this excitation energy domain. The {\alpha}+{\alpha}+n+n four-body calculation reproduces the observed enhanced dipole strength, implying that the four-body cluster structure is essential to describe the {1^-} states in 10Be.