Figure 1

(a) The $Q$-value spectrum for three detected particles assumed to proceed from the ${}^9\mathrm{Be}$(${}^4\mathrm{He}$, ${}^4\mathrm{He}$ + ${}^4\mathrm{He}$ + ${}^4\mathrm{He}$) reaction. (b) The $Q$-value spectrum for three detected particles assumed to proceed from the ${}^{12}\mathrm{C}$(${}^4\mathrm{He}$, ${}^4\mathrm{He}$ + ${}^4\mathrm{He}$ + ${}^4\mathrm{He}$) reaction. (c) Relative energy spectrum for two $\alpha$ particles. The peak associated with the decay from the ${}^8\mathrm{Be}$ ground state is observed at 92 keV. The vertical lines indicate the expected energy of the three peaks. Discrepancies are due to uncertainties in the energy loss of the detected particles and the beam in the target.Reuse & Permissions

Figure 2

Dalitz plot for the ${}^9\mathrm{Be}$(${}^4\mathrm{He}$, ${}^4\mathrm{He}$ + ${}^4\mathrm{He}$ $+$${}^4\mathrm{He}$)$n$ reaction measured at a beam energy of 22 MeV. The reconstructed ${}^{12}\mathrm{C}$ excitation energy (horizontal axis) is plotted against the calculated ${}^9\mathrm{Be}$ excitation energy. States associated with the decay of ${}^5\mathrm{He}$ form diagonal loci.Reuse & Permissions

Figure 3

Carbon-12 excitation energy spectra. (a) Projection of the data in Fig. 2 onto the horizontal axis (blue solid line). The spectrum corresponding to measurements at 26 MeV is shown by the dots. The backgrounds obtained by gating above the ${}^8\mathrm{Be}$ peak (thick dashed line) and both above and below the $Q$-value peak (dot-dashed line) are both illustrated. (b) Fit to the 26-MeV data, given by the blue solid line. The polynomial background (red line) and line shape for the new peak (shaded area) is shown (see text for details). (c) Excitation energy spectrum for events not proceeding via the decay to the ${}^8\mathrm{Be}$ ground state.Reuse & Permissions

Figure 4

Dalitz plot for the ${}^{12}\mathrm{C}$(${}^4\mathrm{He}$, ${}^4\mathrm{He}$ + ${}^4\mathrm{He}$ + ${}^4\mathrm{He}$)${}^4\mathrm{He}$ reaction measured at a beam energy of 30 MeV. The ${}^{12}\mathrm{C}$ excitation energy reconstructed from the three detected $\alpha$ particles is plotted on the horizontal axis. The vertical axis corresponds to the ${}^{12}\mathrm{C}$ excitation energy calculated assuming that, in addition to the ${}^4\mathrm{He}$ nuclei detected from the ground state decay of ${}^8\mathrm{Be}$, the third detected $\alpha$ particle is the recoil in the above reaction. States associated with the decay of ${}^8\mathrm{Be}$ form diagonal loci. The dotted boxes show the region selected for the angular correlation measurements of the 13.3-MeV peak, which is shown in Fig. 7.Reuse & Permissions

Figure 5

Carbon-12 excitation energy spectra. (a) Projection of the data in Fig. 4 onto the vertical axis (dots). The fit to the data (blue line) is shown together with the polynomial background (red line) and the proposed peak (shaded region). The vertically displaced spectrum is extracted from the previously reported ${}^9\mathrm{Be}$(${}^4\mathrm{He}$,${}^{12}\mathrm{C}$) measurements (see Fig. 1 in Ref. [20]). (b) Projection of the data in Fig. 4 onto the horizontal axis (dots). The fit to the data (blue line) is shown together with the polynomial background (red line) and the proposed peak (shaded region). (c) Excitation energy spectrum for events not proceeding via the decay to the ${}^8\mathrm{Be}$ ground state.Reuse & Permissions

Figure 6

Angular correlation plots for states of known spin and parity. (a) 7.65 MeV, 0${}^{+}$, (b) 10.84 MeV, 1${}^{-}$, (c) 9.64 MeV, 3${}^{-}$, and (d) 14.08 MeV, 4${}^{+}$.Reuse & Permissions

Figure 7

Angular correlations projected onto the $\psi$ axis (dots) compared with $P_J[\cos (\psi )]{}^2$ functions. (a) 10.84 MeV, 1${}^{-}$; red line shows $P_1[\cos (\psi )]{}^2$. (b) 9.64 MeV, 3${}^{-}$; red line shows $P_3[\cos (\psi )]{}^2$). (c) 14.08 MeV, 4${}^{+}$; red line shows $P_4[\cos (\psi )]{}^2$. (d), (e), and (f) The corresponding data associated with the 13.3-MeV peak projected at the same angles as in (a), (b), and (c), respectively. The Legendre polynomials shown (red lines) are (d) $P_1[\cos (\psi )]{}^2$, (e) $P_3[\cos (\psi )]{}^2$, and (f) $P_4[\cos (\psi )]{}^2$. (g) and (h) The data for the 13.3-MeV peak projected at angles for states of spin 2 and 5, respectively; the red lines show (g) $P_2[\cos (\psi )]{}^2$ and (h) $P_5[\cos (\psi )]{}^2$.Reuse & Permissions