Determination of the cluster-decay branching ratio from a near-threshold molecular state in Be10

A puzzle has long existed for the alpha-cluster content in the near-threshold 7.54-MeV state of Be-10. A new measurement was conducted to measure the cluster-decay partial width of this state using the reaction Be-9(Be-9, Be-10* -> alpha + He-6) Be-8 at 45-MeV beam energy. Special measures were taken to reduce the strong near-threshold background. The neutron-decay strength was also obtained based on the threefold coincident measurement. A cluster-decay branching ratio of (4.04 +/- 1.26) x 10(-4) is obtained, resulting in a reasonably large alpha-cluster spectroscopic factor. The present Rapid Communication confirms the formation of the sigma-bond molecular rotational band headed by the 6.18-MeV state in Be-10.