Beta delayed particle decay of C-9 and the A=9, T = 1/2 nuclear system: R-matrix fits, the A=9 nuclear system, and the stellar reaction rate of He-4 (alpha n, gamma) Be-9

The decay of ${}^{9}\mathrm{C}$ ${(T}_{1/2}=126.5$ ms) has been observed in two experiments at the TISOL facility at TRIUMF employing different detector configurations for each run. In the first of two papers [E. Gete et al., Phys. Rev. C 61, 064310 (2000)], the experimental technique and data analysis were described. Phenomenological branching ratios and Gamow-Teller strengths were then deduced. In this paper, the data are analyzed using a multichannel, multistate $R\ensuremath{-}\mathrm{m}\mathrm{a}\mathrm{t}\mathrm{r}\mathrm{i}\mathrm{x}$ approach which leads to a different interpretation of the spectra and therefore modified state energies, widths, branching ratios, and Gamow-Teller strengths. Difficulties in fitting the second excited state of ${}^{9}\mathrm{B}$ at 2.34 MeV and possible modifications to the penetrability are described. The existence of a ${J}^{\ensuremath{\pi}}{=1/2}^{\ensuremath{-}}$ state at about 5 MeV excitation energy is suggested from the fits, as well as a considerable decay strength from the ${}^{9}\mathrm{B}$ ground state at high energies. Consequences for the properties of the $A=9,$ $T=1/2$ nuclear system are then discussed; in particular, it is shown that the data agree qualitatively with shell model predictions without unusual Gamow-Teller strength present at high excitation energies. Finally, an estimate of the ${}^{4}\mathrm{He}(\ensuremath{\alpha}n,\ensuremath{\gamma}{)}^{9}\mathrm{Be}$ stellar reaction rate is given.