Determination of the cluster-decay branching ratio from a near-threshold molecular state in ${}^{10}$Be

Abstract

A puzzle has long existed for the $\hat{I}\pm$-cluster content in the near-threshold 7.54 MeV state of ${}^{10}$Be. A new measurement was conducted to measure the cluster-decay partial width of this state, using the reaction ${}^9\mathrm{Be}({}^9\mathrm{Be},{{}^{10}\mathrm{Be}}^{\ast }\to \hat{\mathrm{I}}\pm +{}^6\mathrm{He}){}^8\mathrm{Be}$ 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 three-fold coincident measurement. A cluster-decay branching ratio of $(4.04\pm 1.26)\times 10^{-4}$ is obtained, resulting in a reasonably large $\hat{I}\pm$-cluster spectroscopic factor. The present work confirms the formation of the $\ddot{I}ƒ$-bond molecular rotational band headed by the 6.18 MeV state in ${}^{10}$Be.