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

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