Decay path measurements for the 2.429-MeV state in Be-9: Implications for the astrophysical alpha + alpha + n reaction

An experiment was performed at the Australian National University to study the $^{9}\mathrm{Be}$($^{6}\mathrm{Li}$,$^{6}\mathrm{Li}$)$^{9}\mathrm{Be}$${}^{*}\ensuremath{\rightarrow}\ensuremath{\alpha}+\ensuremath{\alpha}+n$ reaction. This experiment was designed to study the breakup of $^{9}\mathrm{Be}$, in an attempt to quantify the contribution played by the $^{5}\mathrm{He}+\ensuremath{\alpha}$ and ${}^{8}{\mathrm{Be}}^{{2}^{+}}+n$ channels for the low lying excited states. This information is required in order to resolve uncertainties in the $\ensuremath{\alpha}+\ensuremath{\alpha}+n\ensuremath{\rightarrow}$ $^{9}\mathrm{Be}$ reaction rate in high-energy and neutron-rich astrophysical environments such as supernovae. Angular correlation measurements have been used to deduce that the 2.429 MeV state breaks up almost exclusively via the ${}^{8}{\mathrm{Be}}^{{2}^{+}}$ channel. This method of identifying the break-up channel resolves the problem of distinguishing between the ${}^{8}{\mathrm{Be}}^{{2}^{+}}$ and ${}^{5}{\mathrm{He}}^{\text{g.s.}}$ channels which are kinetically identical at this excitation energy.