Cluster structure of ${}^{17}\mathrm{O}$

The transfer reaction ${}^{13}\mathrm{C}({}^{11}\mathrm{B},{}^7\mathrm{Li}){}^{17}\mathrm{O}$ leading to the ground and several excited states of ${}^{17}\mathrm{O}$ was investigated at an incident boron beam energy of 45 MeV. The experimental data were analyzed by means of coupled-channel Born approximation calculations and ${}^{17}\mathrm{O}=\alpha +{}^{13}\mathrm{C}$ spectroscopic factors were extracted from a comparison of the data and the calculations at forward angles. The largest spectroscopic factor obtained was that for the subthreshold 6.356 MeV $1/2^{+}$ state, important for the production of neutrons in the stellar environment, and the squared Coulomb modified asymptotic normalization coefficient, ${\tilde{C}}^2$, is consistent with previous determinations. A significant rise in the experimental data at backward scattering angles suggested the possibility of ${}^{17}\mathrm{O}={}^6\mathrm{Li}+{}^{11}\mathrm{B}$ clustering in some ${}^{17}\mathrm{O}$ states, including the ground state. However, explicit inclusion of ${}^6\mathrm{Li}$ transfer in the calculations could not explain the observed effect. Compound nucleus calculations suggested that while the backward angle rise could be explained by such processes for two of the populated ${}^{17}\mathrm{O}$ states other multistep direct processes must contribute significantly to the other two.

Figure 1

Angular distributions of the elastic and inelastic scattering leading to the first excited state of ${}^{11}\mathrm{B}$. The curves denote the results of coupled-channel calculations with the optical potentials listed in Table 1 (solid: potential B, dashed: potential A). The experimental data are from Ref. [4].

Figure 2

Angular distributions of the emitted ${}^7\mathrm{Li}$ and ${}^{17}\mathrm{O}$. The solid curves show the results of the CCBA $\alpha$ transfer calculations while the dashed curves (almost identical with the solid curves for these states) denote the sum of the $\alpha$ and ${}^6\mathrm{Li}$ transfer results with the $S_{{}^6\mathrm{Li}}$ from Table 2. The dotted curves denote the results of compound nucleus calculations with the code helga, see text for details.

Figure 3

As in Fig. 2 but for the 3.055 MeV and 3.843 MeV excited states of ${}^{17}\mathrm{O}$.

Figure 4

Comparison of the experimental and theoretical results for the 4.554 MeV and 6.356 MeV excited states of ${}^{17}\mathrm{O}$. All the curves show the results of CCBA $\alpha$ transfer calculations: solid, as in Figs. 2 and 3; dashed, with Potential A in the entrance channel; dotted, with the global OM potential of Ref. [10] in the exit channel.