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.
Categories: nucl-ex nucl-th