The reaction of triple radiative capture αα(n,γ)⁹Be studied in a β decay of ⁹Li

A new way of study the reaction of triple radiative capture αα(n,γ)⁹Be is demonstrated. At the GSI-ISOL facility, we have measured the γ decays of excited 1/2⁺, 5/2⁻ and 1/2⁻ states in ⁹Be, which are strongly populated in the β decay of ⁹Li. The respective partial γ-widths are of astrophysical interest in order to reliably estimate the αα(n,γ)⁹Be rates in SN type-II as a possible site of the synthesis of heavy elements in the Universe. The ⁹Li nuclei were implanted into a foil viewed by high-granularity arrays of β and γ detectors. The γ-ray spectra were measured in coincidence with the β-particles by selecting large β-γ angles in order to suppress the bremsstrahlung background. For the first time, the γ-rays from the 1/2⁺ and 5/2⁻ states in ⁹Be were observed in ⁹Li decay, with the 1/2⁺-state energy and width measured to be 1689(10) and 224(7) keV, respectively, while the latter transition provided a reference point. The upper limit of the 1/2⁻ partial γ-width is measured to be $7\cdot {10}^6\text{ MeV}$. An improved sensitivity experiment is feasible at facilities with the larger yield of ⁹Li.