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Abstract

The β-decay of ⁹C (ti/2=126.5 ms) to the particle-unstable nucleus ⁹B has been studied at the TISOL facility at TRIUMF with an intent to measure the μ-decay scheme and to study the structure of ⁹B . A l l of the states in ⁹B populated by the β⁺ decay of ⁹C are unbound and decay ultimately into 2α+p. It is therefore necessary to measure the decay particles in coincidence in order to measure the excitation energy of ⁹B . Two coincidence experiments with different detector geometries were performed. In the first experiment, four ΔE - E particle telescopes arranged in face-to-face pairs measured singles and double coincidence particle spectra. For the second experiment, a pair of position sensitive Double-Sided Silicon Strip Detectors were used in conjunction with particle telescopes to record three-fold coincidence events. The coincidence measurements allowed us to kinematically identify events from ⁵L i +α and ⁸Be+p, the two major decay modes of the states of ⁹B . Several states in ⁹B have been observed and β-branching ratios to these states, and a and proton decay branches from these states have been measured. Because most of the ⁹B levels are broad, the state shapes fed by the β decay of ⁹C are distorted by the β-decay phase-space factor. In order to describe the states of ⁹B , and the secondary compound states such as ⁵Li into which the ⁹B states decay, a simplified one-level .R-matrix description of these states was used, and the spectra from both decay modes were fitted. β-decay branching ratios as well as Gamow-Teller strengths for the observed states of ⁹B were extracted from these fits. Four strongly populated states of ⁹B have been observed; the ground state (47±5) % and excited states at 2.34 (35±7) %, 2.8 (6.7±0.7) % and 12.16 (6.8±0.7)% MeV. The strong branch to the 12.16 M eV state corresponds to a large Gamow-Teller matrix element with BGT=2.5±0.25.