Spectroscopy of ⁹B via high-resolution ejectile-tagged recoil break-up

An experiment has been carried out using the ⁹Be(³He, t) ⁹B^∗ reaction at a beam energy of 33 MeV. A large acceptance silicon-strip array was used to detect the ⁹B^∗ break-up in coincidence with the triton ejectiles in the high-resolution Munich-Q3D spectrograph. The excitation energy regime <3 MeV has been explored and the spectrum resulting from proton decaying states, isolated and characterized. Additional resonance strength is observed at 1.86 MeV ±70 keV(stat) ±35 keV(syst), in agreement with two other recent measurements at higher energies and different angles. The consequences for the “missing” ½⁺ first excited state are discussed. Additionally, the branching ratios for the 2.36 MeV 5/2⁻ state have been measured as Γ_α0/Γ = 0.98 ± 0.12 and Γ_p0/Γ = 0.016 ± 0.008, in close agreement with earlier work.