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

The structure of Be-10 was studied via resonant alpha-particle scattering of a neutron-rich He-6 beam. A time projection chamber, PAT-TPC, was operated in an active-target mode to provide a gaseous He-4 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 He-6 2(+) state, and the He-6(alpha, 2n)Be-8 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 alpha particles for the elastic and inelastic channels. While a resonance of the 4(+) state at 10.15 MeV in Be-10 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 alpha clustering in high-spin states due to a spin-orbit force.