Resonant α scattering of 6He: Limits of clustering in 10Be

The structure of 10Be was studied via resonant α-particle scattering of a neutron-rich 6He beam. A time projection chamber, PAT-TPC, was operated in an active-target mode to provide a gaseous 4He target and trace the beam and reaction products traversing its active tracking volume. This significantly lowered the detection threshold of reaction products at low energies. Elastic scattering, inelastic scattering to the 6He 2⁺ state, and the 6He(α, 2n)8Be reaction were measured below an energy of 6 MeV in the center-of-mass frame. Continuous spectra of excitation functions and angular distributions were obtained from unambiguously-identified recoiling α particles for the elastic and inelastic channels. While a resonance of the 4⁺ state at 10.15 MeV in 10Be previously reported was confirmed, no other resonances were identified in the elastic channel over the measured energy region. The results are in line with antisymmetric molecular dynamics calculations that predict the limits of α clustering in high-spin states due to a spin-orbit force.